diff --git a/polkadot/cli/Cargo.toml b/polkadot/cli/Cargo.toml
index 76a899de7c..6c1ecd2b58 100644
--- a/polkadot/cli/Cargo.toml
+++ b/polkadot/cli/Cargo.toml
@@ -18,13 +18,14 @@ lazy_static = "1.0"
 triehash = "0.1"
 ed25519 = { path = "../../substrate/ed25519" }
 app_dirs = "1.2"
-tokio-core = "0.1.12"
+tokio = "0.1.7"
 futures = "0.1.17"
 ctrlc = { git = "https://github.com/paritytech/rust-ctrlc.git" }
 fdlimit = "0.1"
 parking_lot = "0.4"
 serde_json = "1.0"
 serde = "1.0"
+exit-future = "0.1"
 substrate-client = { path = "../../substrate/client" }
 substrate-codec = { path = "../../substrate/codec" }
 substrate-network = { path = "../../substrate/network" }
diff --git a/polkadot/cli/src/informant.rs b/polkadot/cli/src/informant.rs
index 26915da32e..6b43d4ffad 100644
--- a/polkadot/cli/src/informant.rs
+++ b/polkadot/cli/src/informant.rs
@@ -17,9 +17,10 @@
 //! Console informant. Prints sync progress and block events. Runs on the calling thread.
 
 use std::time::{Duration, Instant};
-use futures::stream::Stream;
+use futures::{Future, Stream};
 use service::{Service, Components};
-use tokio_core::reactor;
+use tokio::runtime::TaskExecutor;
+use tokio::timer::Interval;
 use network::{SyncState, SyncProvider};
 use polkadot_primitives::Block;
 use state_machine;
@@ -28,13 +29,12 @@ use client::{self, BlockchainEvents};
 const TIMER_INTERVAL_MS: u64 = 5000;
 
 /// Spawn informant on the event loop
-pub fn start<C>(service: &Service<C>, handle: reactor::Handle)
+pub fn start<C>(service: &Service<C>, exit: ::exit_future::Exit, handle: TaskExecutor)
 	where
 		C: Components,
 		client::error::Error: From<<<<C as Components>::Backend as client::backend::Backend<Block>>::State as state_machine::Backend>::Error>,
 {
-	let interval = reactor::Interval::new_at(Instant::now(), Duration::from_millis(TIMER_INTERVAL_MS), &handle)
-		.expect("Error creating informant timer");
+	let interval = Interval::new(Instant::now(), Duration::from_millis(TIMER_INTERVAL_MS));
 
 	let network = service.network();
 	let client = service.client();
@@ -73,8 +73,8 @@ pub fn start<C>(service: &Service<C>, handle: reactor::Handle)
 		telemetry!("txpool.import"; "mem_usage" => status.mem_usage, "count" => status.transaction_count, "sender" => status.senders);
 		Ok(())
 	});
-	handle.spawn(display_notifications);
-	handle.spawn(display_block_import);
-	handle.spawn(display_txpool_import);
+
+	let informant_work = display_notifications.join3(display_block_import, display_txpool_import);
+	handle.spawn(exit.until(informant_work).map(|_| ()));
 }
 
diff --git a/polkadot/cli/src/lib.rs b/polkadot/cli/src/lib.rs
index f96690f79e..6dcddfc243 100644
--- a/polkadot/cli/src/lib.rs
+++ b/polkadot/cli/src/lib.rs
@@ -25,7 +25,7 @@ extern crate ansi_term;
 extern crate regex;
 extern crate time;
 extern crate futures;
-extern crate tokio_core;
+extern crate tokio;
 extern crate ctrlc;
 extern crate fdlimit;
 extern crate ed25519;
@@ -50,6 +50,7 @@ extern crate slog;	// needed until we can reexport `slog_info` from `substrate_t
 #[macro_use]
 extern crate substrate_telemetry;
 extern crate polkadot_transaction_pool as txpool;
+extern crate exit_future;
 
 #[macro_use]
 extern crate lazy_static;
@@ -76,9 +77,8 @@ use codec::Slicable;
 use client::BlockOrigin;
 use runtime_primitives::generic::SignedBlock;
 
-use futures::sync::mpsc;
-use futures::{Sink, Future, Stream};
-use tokio_core::reactor;
+use futures::Future;
+use tokio::runtime::Runtime;
 use service::PruningMode;
 
 const DEFAULT_TELEMETRY_URL: &str = "ws://telemetry.polkadot.io:1024";
@@ -188,13 +188,14 @@ pub fn run<I, T>(args: I) -> error::Result<()> where
 	let role =
 		if matches.is_present("collator") {
 			info!("Starting collator");
-			service::Role::COLLATOR
+			// TODO [rob]: collation node implementation
+			service::Role::FULL
 		} else if matches.is_present("light") {
 			info!("Starting (light)");
 			service::Role::LIGHT
 		} else if matches.is_present("validator") || matches.is_present("dev") {
 			info!("Starting validator");
-			service::Role::VALIDATOR
+			service::Role::AUTHORITY
 		} else {
 			info!("Starting (heavy)");
 			service::Role::FULL
@@ -231,6 +232,9 @@ pub fn run<I, T>(args: I) -> error::Result<()> where
 		chain_name: config.chain_spec.name().to_owned(),
 	};
 
+	let mut runtime = Runtime::new()?;
+	let executor = runtime.executor();
+
 	let _guard = if matches.is_present("telemetry") || matches.value_of("telemetry-url").is_some() {
 		let name = config.name.clone();
 		let chain_name = config.chain_spec.name().to_owned();
@@ -250,11 +254,14 @@ pub fn run<I, T>(args: I) -> error::Result<()> where
 		None
 	};
 
-	let core = reactor::Core::new().expect("tokio::Core could not be created");
 	match role == service::Role::LIGHT {
-		true => run_until_exit(core, service::new_light(config)?, &matches, sys_conf),
-		false => run_until_exit(core, service::new_full(config)?, &matches, sys_conf),
+		true => run_until_exit(&mut runtime, service::new_light(config, executor)?, &matches, sys_conf)?,
+		false => run_until_exit(&mut runtime, service::new_full(config, executor)?, &matches, sys_conf)?,
 	}
+
+	// TODO: hard exit if this stalls?
+	runtime.shutdown_on_idle().wait().expect("failed to shut down event loop");
+	Ok(())
 }
 
 fn build_spec(matches: &clap::ArgMatches) -> error::Result<()> {
@@ -370,29 +377,37 @@ fn import_blocks(matches: &clap::ArgMatches) -> error::Result<()> {
 	Ok(())
 }
 
-fn run_until_exit<C>(mut core: reactor::Core, service: service::Service<C>, matches: &clap::ArgMatches, sys_conf: SystemConfiguration) -> error::Result<()>
+fn run_until_exit<C>(runtime: &mut Runtime, service: service::Service<C>, matches: &clap::ArgMatches, sys_conf: SystemConfiguration) -> error::Result<()>
 	where
 		C: service::Components,
 		client::error::Error: From<<<<C as service::Components>::Backend as client::backend::Backend<Block>>::State as state_machine::Backend>::Error>,
 {
 	let exit = {
-		// can't use signal directly here because CtrlC takes only `Fn`.
-		let (exit_send, exit) = mpsc::channel(1);
+		let (exit_send, exit) = exit_future::signal();
+		let exit_send = ::std::cell::RefCell::new(Some(exit_send));
 		ctrlc::CtrlC::set_handler(move || {
-			exit_send.clone().send(()).wait().expect("Error sending exit notification");
+			let exit_send = exit_send
+				.try_borrow_mut()
+				.expect("only borrowed in non-reetrant signal handler; qed")
+				.take();
+
+			if let Some(signal) = exit_send {
+				signal.fire();
+			}
 		});
 
 		exit
 	};
 
-	informant::start(&service, core.handle());
+	let executor = runtime.executor();
+	informant::start(&service, exit.clone(), executor.clone());
 
 	let _rpc_servers = {
 		let http_address = parse_address("127.0.0.1:9933", "rpc-port", matches)?;
 		let ws_address = parse_address("127.0.0.1:9944", "ws-port", matches)?;
 
 		let handler = || {
-			let chain = rpc::apis::chain::Chain::new(service.client(), core.remote());
+			let chain = rpc::apis::chain::Chain::new(service.client(), executor.clone());
 			let author = rpc::apis::author::Author::new(service.client(), service.transaction_pool());
 			rpc::rpc_handler::<Block, _, _, _, _>(
 				service.client(),
@@ -407,7 +422,7 @@ fn run_until_exit<C>(mut core: reactor::Core, service: service::Service<C>, matc
 		)
 	};
 
-	core.run(exit.into_future()).expect("Error running informant event loop");
+	let _ = exit.wait();
 	Ok(())
 }
 
diff --git a/polkadot/collator/Cargo.toml b/polkadot/collator/Cargo.toml
index 161121eefa..78e4823d20 100644
--- a/polkadot/collator/Cargo.toml
+++ b/polkadot/collator/Cargo.toml
@@ -9,5 +9,5 @@ futures = "0.1.17"
 substrate-codec = { path = "../../substrate/codec", version = "0.1" }
 substrate-primitives = { path = "../../substrate/primitives", version = "0.1" }
 polkadot-runtime = { path = "../runtime", version = "0.1" }
-polkadot-parachain = { path = "../parachain", version = "0.1" }
 polkadot-primitives = { path = "../primitives", version = "0.1" }
+polkadot-parachain = { path = "../parachain", version = "0.1" }
diff --git a/polkadot/collator/src/lib.rs b/polkadot/collator/src/lib.rs
index 55eca734d2..94fda9ceda 100644
--- a/polkadot/collator/src/lib.rs
+++ b/polkadot/collator/src/lib.rs
@@ -85,7 +85,7 @@ pub trait RelayChainContext {
 
 /// Collate the necessary ingress queue using the given context.
 pub fn collate_ingress<'a, R>(relay_context: R)
-	-> Box<Future<Item=ConsolidatedIngress, Error=R::Error> + 'a>
+	-> impl Future<Item=ConsolidatedIngress, Error=R::Error> + 'a
 	where
 		R: RelayChainContext,
 		R::Error: 'a,
@@ -106,7 +106,7 @@ pub fn collate_ingress<'a, R>(relay_context: R)
 	// and then by the parachain ID.
 	//
 	// then transform that into the consolidated egress queue.
-	Box::new(stream::futures_unordered(egress_fetch)
+	stream::futures_unordered(egress_fetch)
 		.fold(BTreeMap::new(), |mut map, (routing_id, egresses)| {
 			for (depth, egress) in egresses.into_iter().rev().enumerate() {
 				let depth = -(depth as i64);
@@ -117,19 +117,19 @@ pub fn collate_ingress<'a, R>(relay_context: R)
 		})
 		.map(|ordered| ordered.into_iter().map(|((_, id), egress)| (id, egress)))
 		.map(|i| i.collect::<Vec<_>>())
-		.map(ConsolidatedIngress))
+		.map(ConsolidatedIngress)
 }
 
 /// Produce a candidate for the parachain.
-pub fn collate<'a, R, P>(local_id: ParaId, relay_context: R, para_context: P)
-	-> Box<Future<Item=parachain::Candidate, Error=R::Error> + 'a>
+pub fn collate<'a, R: 'a, P>(local_id: ParaId, relay_context: R, para_context: P)
+	-> impl Future<Item=parachain::Candidate, Error=R::Error> + 'a
 	where
 		R: RelayChainContext,
 	    R::Error: 'a,
 		R::FutureEgress: 'a,
 		P: ParachainContext + 'a,
 {
-	Box::new(collate_ingress(relay_context).map(move |ingress| {
+	collate_ingress(relay_context).map(move |ingress| {
 		let (block_data, _, signature) = para_context.produce_candidate(
 			ingress.0.iter().flat_map(|&(id, ref msgs)| msgs.iter().cloned().map(move |msg| (id, msg)))
 		);
@@ -140,7 +140,7 @@ pub fn collate<'a, R, P>(local_id: ParaId, relay_context: R, para_context: P)
 			block: block_data,
 			unprocessed_ingress: ingress,
 		}
-	}))
+	})
 }
 
 #[cfg(test)]
diff --git a/polkadot/consensus/Cargo.toml b/polkadot/consensus/Cargo.toml
index fefa67de45..91501f2692 100644
--- a/polkadot/consensus/Cargo.toml
+++ b/polkadot/consensus/Cargo.toml
@@ -6,7 +6,7 @@ authors = ["Parity Technologies <admin@parity.io>"]
 [dependencies]
 futures = "0.1.17"
 parking_lot = "0.4"
-tokio-core = "0.1.12"
+tokio = "0.1.7"
 ed25519 = { path = "../../substrate/ed25519" }
 error-chain = "0.12"
 log = "0.3"
@@ -22,7 +22,8 @@ substrate-bft = { path = "../../substrate/bft" }
 substrate-codec = { path = "../../substrate/codec" }
 substrate-primitives = { path = "../../substrate/primitives" }
 substrate-runtime-support = { path = "../../substrate/runtime-support" }
-substrate-network = { path = "../../substrate/network" }
-substrate-keyring = { path = "../../substrate/keyring" }
 substrate-client = { path = "../../substrate/client" }
 substrate-runtime-primitives = { path = "../../substrate/runtime/primitives" }
+
+[dev-dependencies]
+substrate-keyring = { path = "../../substrate/keyring" }
diff --git a/polkadot/consensus/src/collation.rs b/polkadot/consensus/src/collation.rs
index f0b1f626c6..d2cd297ce3 100644
--- a/polkadot/consensus/src/collation.rs
+++ b/polkadot/consensus/src/collation.rs
@@ -23,7 +23,7 @@ use std::sync::Arc;
 
 use polkadot_api::PolkadotApi;
 use polkadot_primitives::{Hash, AccountId, BlockId};
-use polkadot_primitives::parachain::{Id as ParaId, Chain, BlockData, Extrinsic, CandidateReceipt};
+use polkadot_primitives::parachain::{Id as ParaId, BlockData, Extrinsic, CandidateReceipt};
 
 use futures::prelude::*;
 
@@ -55,7 +55,7 @@ pub trait Collators: Clone {
 ///
 /// This future is fused.
 pub struct CollationFetch<C: Collators, P: PolkadotApi> {
-	parachain: Option<ParaId>,
+	parachain: ParaId,
 	relay_parent_hash: Hash,
 	relay_parent: BlockId,
 	collators: C,
@@ -65,16 +65,13 @@ pub struct CollationFetch<C: Collators, P: PolkadotApi> {
 
 impl<C: Collators, P: PolkadotApi> CollationFetch<C, P> {
 	/// Create a new collation fetcher for the given chain.
-	pub fn new(parachain: Chain, relay_parent: BlockId, relay_parent_hash: Hash, collators: C, client: Arc<P>) -> Self {
+	pub fn new(parachain: ParaId, relay_parent: BlockId, relay_parent_hash: Hash, collators: C, client: Arc<P>) -> Self {
 		CollationFetch {
 			relay_parent_hash,
 			relay_parent,
 			collators,
 			client,
-			parachain: match parachain {
-				Chain::Parachain(id) => Some(id),
-				Chain::Relay => None,
-			},
+			parachain,
 			live_fetch: None,
 		}
 	}
@@ -85,26 +82,19 @@ impl<C: Collators, P: PolkadotApi> Future for CollationFetch<C, P> {
 	type Error = C::Error;
 
 	fn poll(&mut self) -> Poll<(Collation, Extrinsic), C::Error> {
-		let parachain = match self.parachain.as_ref() {
-			Some(p) => p.clone(),
-			None => return Ok(Async::NotReady),
-		};
-
 		loop {
 			let x = {
+				let parachain = self.parachain.clone();
 				let (r, c)  = (self.relay_parent_hash, &self.collators);
 				let poll = self.live_fetch
 					.get_or_insert_with(move || c.collate(parachain, r).into_future())
 					.poll();
 
-				if let Err(_) = poll { self.parachain = None }
 				try_ready!(poll)
 			};
 
 			match validate_collation(&*self.client, &self.relay_parent, &x) {
 				Ok(()) => {
-					self.parachain = None;
-
 					// TODO: generate extrinsic while verifying.
 					return Ok(Async::Ready((x, Extrinsic)));
 				}
diff --git a/polkadot/consensus/src/dynamic_inclusion.rs b/polkadot/consensus/src/dynamic_inclusion.rs
index d48e486274..bec2bd0fa8 100644
--- a/polkadot/consensus/src/dynamic_inclusion.rs
+++ b/polkadot/consensus/src/dynamic_inclusion.rs
@@ -61,7 +61,7 @@ impl DynamicInclusion {
 	/// would be enough, or `None` if it is sufficient now.
 	///
 	/// Panics if `now` is earlier than the `start`.
-	pub fn acceptable_in(&self, now: Instant, included: usize) -> Option<Duration> {
+	pub fn acceptable_in(&self, now: Instant, included: usize) -> Option<Instant> {
 		let elapsed = now.duration_since(self.start);
 		let elapsed = duration_to_micros(&elapsed);
 
@@ -70,7 +70,8 @@ impl DynamicInclusion {
 		if elapsed >= valid_after {
 			None
 		} else {
-			Some(Duration::from_millis((valid_after - elapsed) as u64 / 1000))
+			let until = Duration::from_millis((valid_after - elapsed) as u64 / 1000);
+			Some(now + until)
 		}
 	}
 }
@@ -104,7 +105,7 @@ mod tests {
 			Duration::from_millis(4000),
 		);
 
-		assert_eq!(dynamic.acceptable_in(now, 5), Some(Duration::from_millis(2000)));
+		assert_eq!(dynamic.acceptable_in(now, 5), Some(now + Duration::from_millis(2000)));
 		assert!(dynamic.acceptable_in(now + Duration::from_millis(2000), 5).is_none());
 		assert!(dynamic.acceptable_in(now + Duration::from_millis(3000), 5).is_none());
 		assert!(dynamic.acceptable_in(now + Duration::from_millis(4000), 5).is_none());
diff --git a/polkadot/consensus/src/error.rs b/polkadot/consensus/src/error.rs
index acafa88f5e..397fdee52c 100644
--- a/polkadot/consensus/src/error.rs
+++ b/polkadot/consensus/src/error.rs
@@ -37,7 +37,7 @@ error_chain! {
 			description("Proposer destroyed before finishing proposing or evaluating"),
 			display("Proposer destroyed before finishing proposing or evaluating"),
 		}
-		Timer(e: String) {
+		Timer(e: ::tokio::timer::Error) {
 			description("Failed to register or resolve async timer."),
 			display("Timer failed: {}", e),
 		}
diff --git a/polkadot/consensus/src/lib.rs b/polkadot/consensus/src/lib.rs
index c75d8ac6ee..2fabf48088 100644
--- a/polkadot/consensus/src/lib.rs
+++ b/polkadot/consensus/src/lib.rs
@@ -44,11 +44,10 @@ extern crate substrate_codec as codec;
 extern crate substrate_primitives as primitives;
 extern crate substrate_runtime_support as runtime_support;
 extern crate substrate_runtime_primitives as runtime_primitives;
-extern crate substrate_network;
+extern crate substrate_client as client;
 
 extern crate exit_future;
-extern crate tokio_core;
-extern crate substrate_client as client;
+extern crate tokio;
 
 #[macro_use]
 extern crate error_chain;
@@ -67,33 +66,32 @@ use std::sync::Arc;
 use std::time::{Duration, Instant};
 
 use codec::Slicable;
-use table::generic::Statement as GenericStatement;
-use runtime_support::Hashable;
 use polkadot_api::PolkadotApi;
-use polkadot_primitives::{Hash, Block, BlockId, BlockNumber, Header, Timestamp};
-use polkadot_primitives::parachain::{Id as ParaId, Chain, DutyRoster, BlockData, Extrinsic as ParachainExtrinsic, CandidateReceipt};
-use polkadot_runtime::BareExtrinsic;
+use polkadot_primitives::{Hash, Block, BlockId, BlockNumber, Header, Timestamp, SessionKey};
+use polkadot_primitives::parachain::{Id as ParaId, Chain, DutyRoster, BlockData, Extrinsic as ParachainExtrinsic, CandidateReceipt, CandidateSignature};
 use primitives::AuthorityId;
-use transaction_pool::{TransactionPool};
-use tokio_core::reactor::{Handle, Timeout, Interval};
+use transaction_pool::TransactionPool;
+use tokio::runtime::TaskExecutor;
+use tokio::timer::{Delay, Interval};
 
 use futures::prelude::*;
-use futures::future::{self, Shared};
+use futures::future;
 use collation::CollationFetch;
 use dynamic_inclusion::DynamicInclusion;
 
-pub use self::collation::{Collators, Collation};
+pub use self::collation::{validate_collation, Collators, Collation};
 pub use self::error::{ErrorKind, Error};
-pub use self::shared_table::{SharedTable, StatementSource, StatementProducer, ProducedStatements};
+pub use self::shared_table::{SharedTable, StatementProducer, ProducedStatements, Statement, SignedStatement, GenericStatement};
 pub use service::Service;
 
-mod collation;
 mod dynamic_inclusion;
 mod evaluation;
 mod error;
 mod service;
 mod shared_table;
 
+pub mod collation;
+
 // block size limit.
 const MAX_TRANSACTIONS_SIZE: usize = 4 * 1024 * 1024;
 
@@ -108,8 +106,9 @@ pub trait TableRouter: Clone {
 	/// Future that resolves when extrinsic candidate data is fetched.
 	type FetchExtrinsic: IntoFuture<Item=ParachainExtrinsic,Error=Self::Error>;
 
-	/// Note local candidate data, making it available on the network to other validators.
-	fn local_candidate_data(&self, hash: Hash, block_data: BlockData, extrinsic: ParachainExtrinsic);
+	/// Call with local candidate data. This will make the data available on the network,
+	/// and sign, import, and broadcast a statement about the candidate.
+	fn local_candidate(&self, candidate: CandidateReceipt, block_data: BlockData, extrinsic: ParachainExtrinsic);
 
 	/// Fetch block data for a specific candidate.
 	fn fetch_block_data(&self, candidate: &CandidateReceipt) -> Self::FetchCandidate;
@@ -118,23 +117,28 @@ pub trait TableRouter: Clone {
 	fn fetch_extrinsic_data(&self, candidate: &CandidateReceipt) -> Self::FetchExtrinsic;
 }
 
-/// A long-lived network which can create statement table routing instances.
+/// A long-lived network which can create parachain statement and BFT message routing processes on demand.
 pub trait Network {
 	/// The table router type. This should handle importing of any statements,
 	/// routing statements to peers, and driving completion of any `StatementProducers`.
 	type TableRouter: TableRouter;
+	/// The input stream of BFT messages. Should never logically conclude.
+	type Input: Stream<Item=bft::Communication<Block>,Error=Error>;
+	/// The output sink of BFT messages. Messages sent here should eventually pass to all
+	/// current authorities.
+	type Output: Sink<SinkItem=bft::Communication<Block>,SinkError=Error>;
 
-	/// Instantiate a table router using the given shared table.
-	fn table_router(&self, table: Arc<SharedTable>) -> Self::TableRouter;
+	/// Instantiate a table router using the given shared table and task executor.
+	fn communication_for(&self, validators: &[SessionKey], table: Arc<SharedTable>, task_executor: TaskExecutor) -> (Self::TableRouter, Self::Input, Self::Output);
 }
 
 /// Information about a specific group.
 #[derive(Debug, Clone, Default)]
 pub struct GroupInfo {
 	/// Authorities meant to check validity of candidates.
-	pub validity_guarantors: HashSet<AuthorityId>,
+	pub validity_guarantors: HashSet<SessionKey>,
 	/// Authorities meant to check availability of candidate data.
-	pub availability_guarantors: HashSet<AuthorityId>,
+	pub availability_guarantors: HashSet<SessionKey>,
 	/// Number of votes needed for validity.
 	pub needed_validity: usize,
 	/// Number of votes needed for availability.
@@ -144,20 +148,21 @@ pub struct GroupInfo {
 /// Sign a table statement against a parent hash.
 /// The actual message signed is the encoded statement concatenated with the
 /// parent hash.
-pub fn sign_table_statement(statement: &table::Statement, key: &ed25519::Pair, parent_hash: &Hash) -> ed25519::Signature {
-	use polkadot_primitives::parachain::Statement as RawStatement;
-
-	let raw = match *statement {
-		GenericStatement::Candidate(ref c) => RawStatement::Candidate(c.clone()),
-		GenericStatement::Valid(h) => RawStatement::Valid(h),
-		GenericStatement::Invalid(h) => RawStatement::Invalid(h),
-		GenericStatement::Available(h) => RawStatement::Available(h),
-	};
-
-	let mut encoded = raw.encode();
+pub fn sign_table_statement(statement: &Statement, key: &ed25519::Pair, parent_hash: &Hash) -> CandidateSignature {
+	let mut encoded = statement.encode();
 	encoded.extend(&parent_hash.0);
 
-	key.sign(&encoded)
+	key.sign(&encoded).into()
+}
+
+/// Check signature on table statement.
+pub fn check_statement(statement: &Statement, signature: &CandidateSignature, signer: SessionKey, parent_hash: &Hash) -> bool {
+	use runtime_primitives::traits::Verify;
+
+	let mut encoded = statement.encode();
+	encoded.extend(&parent_hash.0);
+
+	signature.verify(&encoded[..], &signer.into())
 }
 
 fn make_group_info(roster: DutyRoster, authorities: &[AuthorityId], local_id: AuthorityId) -> Result<(HashMap<ParaId, GroupInfo>, LocalDuty), Error> {
@@ -217,41 +222,43 @@ fn make_group_info(roster: DutyRoster, authorities: &[AuthorityId], local_id: Au
 	}
 }
 
-fn timer_error(e: &::std::io::Error) -> Error {
-	ErrorKind::Timer(format!("{}", e)).into()
-}
-
 /// Polkadot proposer factory.
 pub struct ProposerFactory<C, N, P> {
 	/// The client instance.
-	pub client: Arc<C>,
+	pub client: Arc<P>,
 	/// The transaction pool.
-	pub transaction_pool: Arc<TransactionPool<C>>,
+	pub transaction_pool: Arc<TransactionPool<P>>,
 	/// The backing network handle.
 	pub network: N,
 	/// Parachain collators.
-	pub collators: P,
-	/// The timer used to schedule proposal intervals.
-	pub handle: Handle,
+	pub collators: C,
+	/// handle to remote task executor
+	pub handle: TaskExecutor,
 	/// The duration after which parachain-empty blocks will be allowed.
 	pub parachain_empty_duration: Duration,
 }
 
-impl<C, N, P> bft::ProposerFactory<Block> for ProposerFactory<C, N, P>
+impl<C, N, P> bft::Environment<Block> for ProposerFactory<C, N, P>
 	where
-		C: PolkadotApi + Send + Sync,
+		C: Collators + Send + 'static,
 		N: Network,
-		P: Collators,
+		P: PolkadotApi + Send + Sync + 'static,
+		<C::Collation as IntoFuture>::Future: Send + 'static,
+		N::TableRouter: Send + 'static,
 {
-	type Proposer = Proposer<C, N::TableRouter, P>;
+	type Proposer = Proposer<P>;
+	type Input = N::Input;
+	type Output = N::Output;
 	type Error = Error;
 
-	fn init(&self, parent_header: &Header, authorities: &[AuthorityId], sign_with: Arc<ed25519::Pair>) -> Result<Self::Proposer, Error> {
-		use std::time::Duration;
-
+	fn init(&self,
+		parent_header: &Header,
+		authorities: &[AuthorityId],
+		sign_with: Arc<ed25519::Pair>
+	) -> Result<(Self::Proposer, Self::Input, Self::Output), Error> {
 		const DELAY_UNTIL: Duration = Duration::from_millis(5000);
 
-		let parent_hash = parent_header.blake2_256().into();
+		let parent_hash = parent_header.hash().into();
 
 		let id = BlockId::hash(parent_hash);
 		let duty_roster = self.client.duty_roster(&id)?;
@@ -267,70 +274,116 @@ impl<C, N, P> bft::ProposerFactory<Block> for ProposerFactory<C, N, P>
 
 		let n_parachains = active_parachains.len();
 		let table = Arc::new(SharedTable::new(group_info, sign_with.clone(), parent_hash));
-		let router = self.network.table_router(table.clone());
-		let dynamic_inclusion = DynamicInclusion::new(
-			n_parachains,
-			Instant::now(),
-			self.parachain_empty_duration.clone(),
+		let (router, input, output) = self.network.communication_for(
+			authorities,
+			table.clone(),
+			self.handle.clone()
 		);
 
-		let timeout = Timeout::new(DELAY_UNTIL, &self.handle)
-			.map_err(|e| timer_error(&e))?;
+		let now = Instant::now();
+		let dynamic_inclusion = DynamicInclusion::new(
+			n_parachains,
+			now,
+			self.parachain_empty_duration.clone(),
+		);
 
 		debug!(target: "bft", "Initialising consensus proposer. Refusing to evaluate for {:?} from now.",
 			DELAY_UNTIL);
 
-		// TODO [PoC-2]: kick off collation process.
-		Ok(Proposer {
+		let validation_para = match local_duty.validation {
+			Chain::Relay => None,
+			Chain::Parachain(id) => Some(id),
+		};
+
+		let collation_work = validation_para.map(|para| CollationFetch::new(
+			para,
+			id.clone(),
+			parent_hash.clone(),
+			self.collators.clone(),
+			self.client.clone(),
+		));
+		let drop_signal = dispatch_collation_work(
+			router.clone(),
+			&self.handle,
+			collation_work,
+		);
+
+		let proposer = Proposer {
 			client: self.client.clone(),
-			collators: self.collators.clone(),
-			delay: timeout.shared(),
-			handle: self.handle.clone(),
 			dynamic_inclusion,
-			local_duty,
 			local_key: sign_with,
+			minimum_delay: now + DELAY_UNTIL,
 			parent_hash,
 			parent_id: id,
 			parent_number: parent_header.number,
 			random_seed,
-			router,
 			table,
 			transaction_pool: self.transaction_pool.clone(),
-		})
+			_drop_signal: drop_signal,
+		};
+
+		Ok((proposer, input, output))
 	}
 }
 
+// dispatch collation work to be done in the background. returns a signal object
+// that should fire when the collation work is no longer necessary (e.g. when the proposer object is dropped)
+fn dispatch_collation_work<R, C, P>(
+	router: R,
+	handle: &TaskExecutor,
+	work: Option<CollationFetch<C, P>>,
+) -> exit_future::Signal where
+	C: Collators + Send + 'static,
+	P: PolkadotApi + Send + Sync + 'static,
+	<C::Collation as IntoFuture>::Future: Send + 'static,
+	R: TableRouter + Send + 'static,
+{
+	let (signal, exit) = exit_future::signal();
+	let handled_work = work.then(move |result| match result {
+		Ok(Some((collation, extrinsic))) => {
+			router.local_candidate(collation.receipt, collation.block_data, extrinsic);
+			Ok(())
+		}
+		Ok(None) => Ok(()),
+		Err(_e) => {
+			warn!(target: "consensus", "Failed to collate candidate");
+			Ok(())
+		}
+	});
+
+	let cancellable_work = handled_work.select(exit).then(|_| Ok(()));
+
+	// spawn onto thread pool.
+	handle.spawn(cancellable_work);
+	signal
+}
+
 struct LocalDuty {
 	validation: Chain,
 }
 
 /// The Polkadot proposer logic.
-pub struct Proposer<C: PolkadotApi, R, P> {
+pub struct Proposer<C: PolkadotApi> {
 	client: Arc<C>,
-	collators: P,
-	delay: Shared<Timeout>,
 	dynamic_inclusion: DynamicInclusion,
-	handle: Handle,
-	local_duty: LocalDuty,
 	local_key: Arc<ed25519::Pair>,
+	minimum_delay: Instant,
 	parent_hash: Hash,
 	parent_id: BlockId,
 	parent_number: BlockNumber,
 	random_seed: Hash,
-	router: R,
 	table: Arc<SharedTable>,
 	transaction_pool: Arc<TransactionPool<C>>,
+	_drop_signal: exit_future::Signal,
 }
 
-impl<C, R, P> bft::Proposer<Block> for Proposer<C, R, P>
+impl<C> bft::Proposer<Block> for Proposer<C>
 	where
 		C: PolkadotApi + Send + Sync,
-		R: TableRouter,
-		P: Collators,
 {
 	type Error = Error;
 	type Create = future::Either<
-		CreateProposal<C, R, P>,
+		CreateProposal<C>,
 		future::FutureResult<Block, Error>,
 	>;
 	type Evaluate = Box<Future<Item=bool, Error=Error>>;
@@ -339,32 +392,24 @@ impl<C, R, P> bft::Proposer<Block> for Proposer<C, R, P>
 		const ATTEMPT_PROPOSE_EVERY: Duration = Duration::from_millis(100);
 
 		let initial_included = self.table.includable_count();
+		let now = Instant::now();
 		let enough_candidates = self.dynamic_inclusion.acceptable_in(
-			Instant::now(),
+			now,
 			initial_included,
-		).unwrap_or_default();
+		).unwrap_or_else(|| now + Duration::from_millis(1));
 
-		let timing = {
-			let delay = self.delay.clone();
-			let dynamic_inclusion = self.dynamic_inclusion.clone();
-			let make_timing = move |handle| -> Result<ProposalTiming, ::std::io::Error> {
-				let attempt_propose = Interval::new(ATTEMPT_PROPOSE_EVERY, handle)?;
-				let enough_candidates = Timeout::new(enough_candidates, handle)?;
-				Ok(ProposalTiming {
-					attempt_propose,
-					enough_candidates,
-					dynamic_inclusion,
-					minimum_delay: Some(delay),
-					last_included: initial_included,
-				})
-			};
+		let minimum_delay = if self.minimum_delay > now + ATTEMPT_PROPOSE_EVERY {
+			Some(Delay::new(self.minimum_delay))
+		} else {
+			None
+		};
 
-			match make_timing(&self.handle) {
-				Ok(timing) => timing,
-				Err(e) => {
-					return future::Either::B(future::err(timer_error(&e)));
-				}
-			}
+		let timing = ProposalTiming {
+			attempt_propose: Interval::new(now + ATTEMPT_PROPOSE_EVERY, ATTEMPT_PROPOSE_EVERY),
+			enough_candidates: Delay::new(enough_candidates),
+			dynamic_inclusion: self.dynamic_inclusion.clone(),
+			minimum_delay,
+			last_included: initial_included,
 		};
 
 		future::Either::A(CreateProposal {
@@ -373,15 +418,7 @@ impl<C, R, P> bft::Proposer<Block> for Proposer<C, R, P>
 			parent_id: self.parent_id.clone(),
 			client: self.client.clone(),
 			transaction_pool: self.transaction_pool.clone(),
-			collation: CollationFetch::new(
-				self.local_duty.validation,
-				self.parent_id.clone(),
-				self.parent_hash.clone(),
-				self.collators.clone(),
-				self.client.clone()
-			),
 			table: self.table.clone(),
-			router: self.router.clone(),
 			timing,
 		})
 	}
@@ -415,9 +452,7 @@ impl<C, R, P> bft::Proposer<Block> for Proposer<C, R, P>
 		};
 
 		let vote_delays = {
-			// delay casting vote until able (according to minimum block time)
-			let minimum_delay = self.delay.clone()
-				.map_err(|e| timer_error(&*e));
+			let now = Instant::now();
 
 			let included_candidate_hashes = proposal
 				.parachain_heads()
@@ -431,33 +466,35 @@ impl<C, R, P> bft::Proposer<Block> for Proposer<C, R, P>
 
 			// the duration at which the given number of parachains is acceptable.
 			let count_delay = self.dynamic_inclusion.acceptable_in(
-				Instant::now(),
+				now,
 				proposal.parachain_heads().len(),
 			);
 
 			// the duration until the given timestamp is current
 			let proposed_timestamp = proposal.timestamp();
 			let timestamp_delay = if proposed_timestamp > current_timestamp {
-				Some(Duration::from_secs(proposed_timestamp - current_timestamp))
+				Some(now + Duration::from_secs(proposed_timestamp - current_timestamp))
 			} else {
 				None
 			};
 
+			// delay casting vote until able according to minimum block time,
+			// timestamp delay, and count delay.
 			// construct a future from the maximum of the two durations.
-			let temporary_delay = match ::std::cmp::max(timestamp_delay, count_delay) {
-				Some(duration) => {
-					let maybe_timeout = Timeout::new(duration, &self.handle);
+			let max_delay = [timestamp_delay, count_delay, Some(self.minimum_delay)]
+				.iter()
+				.cloned()
+				.max()
+				.expect("iterator not empty; thus max returns `Some`; qed");
 
-					let f = future::result(maybe_timeout)
-						.and_then(|timeout| timeout)
-						.map_err(|e| timer_error(&e));
-
-					future::Either::A(f)
-				}
+			let temporary_delay = match max_delay {
+				Some(duration) => future::Either::A(
+					Delay::new(duration).map_err(|e| Error::from(ErrorKind::Timer(e)))
+				),
 				None => future::Either::B(future::ok(())),
 			};
 
-			minimum_delay.join3(includability_tracker, temporary_delay)
+			includability_tracker.join(temporary_delay)
 		};
 
 		// evaluate whether the block is actually valid.
@@ -497,7 +534,7 @@ impl<C, R, P> bft::Proposer<Block> for Proposer<C, R, P>
 		use bft::generic::Misbehavior as GenericMisbehavior;
 		use runtime_primitives::bft::{MisbehaviorKind, MisbehaviorReport};
 		use runtime_primitives::MaybeUnsigned;
-		use polkadot_runtime::{Call, Extrinsic, UncheckedExtrinsic, ConsensusCall};
+		use polkadot_runtime::{Call, Extrinsic, BareExtrinsic, UncheckedExtrinsic, ConsensusCall};
 
 		let local_id = self.local_key.public().0.into();
 		let mut next_index = {
@@ -569,71 +606,59 @@ fn current_timestamp() -> Timestamp {
 struct ProposalTiming {
 	attempt_propose: Interval,
 	dynamic_inclusion: DynamicInclusion,
-	enough_candidates: Timeout,
-	minimum_delay: Option<Shared<Timeout>>,
+	enough_candidates: Delay,
+	minimum_delay: Option<Delay>,
 	last_included: usize,
 }
 
 impl ProposalTiming {
 	// whether it's time to attempt a proposal.
 	// shouldn't be called outside of the context of a task.
-	fn poll(&mut self, included: usize) -> Poll<(), Error> {
+	fn poll(&mut self, included: usize) -> Poll<(), ErrorKind> {
 		// first drain from the interval so when the minimum delay is up
 		// we don't have any notifications built up.
 		//
 		// this interval is just meant to produce periodic task wakeups
 		// that lead to the `dynamic_inclusion` getting updated as necessary.
-		if let Async::Ready(x) = self.attempt_propose.poll()
-			.map_err(|e| timer_error(&e))?
-		{
+		if let Async::Ready(x) = self.attempt_propose.poll().map_err(ErrorKind::Timer)? {
 			x.expect("timer still alive; intervals never end; qed");
 		}
 
 		if let Some(ref mut min) = self.minimum_delay {
-			try_ready!(min.poll().map_err(|e| timer_error(&*e)));
+			try_ready!(min.poll().map_err(ErrorKind::Timer));
 		}
 
 		self.minimum_delay = None; // after this point, the future must have completed.
 
 		if included == self.last_included {
-			return self.enough_candidates.poll().map_err(|e| timer_error(&e));
+			return self.enough_candidates.poll().map_err(ErrorKind::Timer);
 		}
 
 		// the amount of includable candidates has changed. schedule a wakeup
 		// if it's not sufficient anymore.
-		let now = Instant::now();
-		match self.dynamic_inclusion.acceptable_in(now, included) {
-			Some(duration) => {
+		match self.dynamic_inclusion.acceptable_in(Instant::now(), included) {
+			Some(instant) => {
 				self.last_included = included;
-				self.enough_candidates.reset(now + duration);
-				self.enough_candidates.poll().map_err(|e| timer_error(&e))
-			}
-			None => {
-				Ok(Async::Ready(()))
+				self.enough_candidates.reset(instant);
+				self.enough_candidates.poll().map_err(ErrorKind::Timer)
 			}
+			None => Ok(Async::Ready(())),
 		}
 	}
 }
 
 /// Future which resolves upon the creation of a proposal.
-pub struct CreateProposal<C: PolkadotApi, R, P: Collators>  {
+pub struct CreateProposal<C: PolkadotApi>  {
 	parent_hash: Hash,
 	parent_number: BlockNumber,
 	parent_id: BlockId,
 	client: Arc<C>,
 	transaction_pool: Arc<TransactionPool<C>>,
-	collation: CollationFetch<P, C>,
-	router: R,
 	table: Arc<SharedTable>,
 	timing: ProposalTiming,
 }
 
-impl<C, R, P> CreateProposal<C, R, P>
-	where
-		C: PolkadotApi,
-		R: TableRouter,
-		P: Collators,
-{
+impl<C> CreateProposal<C> where C: PolkadotApi {
 	fn propose_with(&self, candidates: Vec<CandidateReceipt>) -> Result<Block, Error> {
 		use polkadot_api::BlockBuilder;
 		use runtime_primitives::traits::{Hashing, BlakeTwo256};
@@ -702,35 +727,17 @@ impl<C, R, P> CreateProposal<C, R, P>
 	}
 }
 
-impl<C, R, P> Future for CreateProposal<C, R, P>
-	where
-		C: PolkadotApi,
-		R: TableRouter,
-		P: Collators,
-{
+impl<C> Future for CreateProposal<C> where C: PolkadotApi {
 	type Item = Block;
 	type Error = Error;
 
 	fn poll(&mut self) -> Poll<Block, Error> {
-		// 1. poll local collation future.
-		match self.collation.poll() {
-			Ok(Async::Ready((collation, extrinsic))) => {
-				let hash = collation.receipt.hash();
-				self.router.local_candidate_data(hash, collation.block_data, extrinsic);
-
-				// TODO: if we are an availability guarantor also, we should produce an availability statement.
-				self.table.sign_and_import(&self.router, GenericStatement::Candidate(collation.receipt));
-			}
-			Ok(Async::NotReady) => {},
-			Err(_) => {}, // TODO: handle this failure to collate.
-		}
-
-		// 2. try to propose if we have enough includable candidates and other
+		// 1. try to propose if we have enough includable candidates and other
 		// delays have concluded.
 		let included = self.table.includable_count();
 		try_ready!(self.timing.poll(included));
 
-		// 3. propose
+		// 2. propose
 		let proposed_candidates = self.table.with_proposal(|proposed_set| {
 			proposed_set.into_iter().cloned().collect()
 		});
@@ -738,3 +745,21 @@ impl<C, R, P> Future for CreateProposal<C, R, P>
 		self.propose_with(proposed_candidates).map(Async::Ready)
 	}
 }
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use substrate_keyring::Keyring;
+
+	#[test]
+	fn sign_and_check_statement() {
+		let statement: Statement = GenericStatement::Valid([1; 32].into());
+		let parent_hash = [2; 32].into();
+
+		let sig = sign_table_statement(&statement, &Keyring::Alice.pair(), &parent_hash);
+
+		assert!(check_statement(&statement, &sig, Keyring::Alice.to_raw_public().into(), &parent_hash));
+		assert!(!check_statement(&statement, &sig, Keyring::Alice.to_raw_public().into(), &[0xff; 32].into()));
+		assert!(!check_statement(&statement, &sig, Keyring::Bob.to_raw_public().into(), &parent_hash));
+	}
+}
diff --git a/polkadot/consensus/src/service.rs b/polkadot/consensus/src/service.rs
index 494e785809..0145164fea 100644
--- a/polkadot/consensus/src/service.rs
+++ b/polkadot/consensus/src/service.rs
@@ -18,6 +18,10 @@
 
 /// Consensus service. A long runnung service that manages BFT agreement and parachain
 /// candidate agreement over the network.
+///
+/// This uses a handle to an underlying thread pool to dispatch heavy work
+/// such as candidate verification while performing event-driven work
+/// on a local event loop.
 
 use std::thread;
 use std::time::{Duration, Instant};
@@ -27,197 +31,37 @@ use bft::{self, BftService};
 use client::{BlockchainEvents, ChainHead};
 use ed25519;
 use futures::prelude::*;
-use futures::{future, Canceled};
 use polkadot_api::LocalPolkadotApi;
-use polkadot_primitives::{BlockId, Block, Header, Hash, AccountId};
-use polkadot_primitives::parachain::{Id as ParaId, BlockData, Extrinsic, CandidateReceipt};
-use primitives::AuthorityId;
-use runtime_support::Hashable;
-use substrate_network as net;
-use tokio_core::reactor;
+use polkadot_primitives::{Block, Header};
 use transaction_pool::TransactionPool;
 
-use super::{TableRouter, SharedTable, ProposerFactory};
+use tokio::executor::current_thread::TaskExecutor as LocalThreadHandle;
+use tokio::runtime::TaskExecutor as ThreadPoolHandle;
+use tokio::runtime::current_thread::Runtime as LocalRuntime;
+use tokio::timer::Interval;
+
+use super::{Network, Collators, ProposerFactory};
 use error;
 
 const TIMER_DELAY_MS: u64 = 5000;
 const TIMER_INTERVAL_MS: u64 = 500;
 
-struct BftSink<E> {
-	network: Arc<net::ConsensusService<Block>>,
-	parent_hash: Hash,
-	_e: ::std::marker::PhantomData<E>,
-}
-
-struct Messages {
-	network_stream: net::BftMessageStream<Block>,
-	local_id: AuthorityId,
-	authorities: Vec<AuthorityId>,
-}
-
-impl Stream for Messages {
-	type Item = bft::Communication<Block>;
-	type Error = bft::Error;
-
-	fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
-		// check the network
-		loop {
-			match self.network_stream.poll() {
-				Err(_) => return Err(bft::InputStreamConcluded.into()),
-				Ok(Async::NotReady) => return Ok(Async::NotReady),
-				Ok(Async::Ready(None)) => return Ok(Async::NotReady), // the input stream for agreements is never meant to logically end.
-				Ok(Async::Ready(Some(message))) => {
-					match process_message(message, &self.local_id, &self.authorities) {
-						Ok(Some(message)) => return Ok(Async::Ready(Some(message))),
-						Ok(None) => {} // ignored local message.
-						Err(e) => {
-							debug!("Message validation failed: {:?}", e);
-						}
-					}
-				}
-			}
-		}
-	}
-}
-
-fn process_message(msg: net::LocalizedBftMessage<Block>, local_id: &AuthorityId, authorities: &[AuthorityId]) -> Result<Option<bft::Communication<Block>>, bft::Error> {
-	Ok(Some(match msg.message {
-		net::generic_message::BftMessage::Consensus(c) => bft::generic::Communication::Consensus(match c {
-			net::generic_message::SignedConsensusMessage::Propose(proposal) => bft::generic::LocalizedMessage::Propose({
-				if &proposal.sender == local_id { return Ok(None) }
-				let proposal = bft::generic::LocalizedProposal {
-					round_number: proposal.round_number as usize,
-					proposal: proposal.proposal,
-					digest: proposal.digest,
-					sender: proposal.sender,
-					digest_signature: ed25519::LocalizedSignature {
-						signature: proposal.digest_signature,
-						signer: proposal.sender.into(),
-					},
-					full_signature: ed25519::LocalizedSignature {
-						signature: proposal.full_signature,
-						signer: proposal.sender.into(),
-					}
-				};
-				bft::check_proposal(authorities, &msg.parent_hash, &proposal)?;
-
-				trace!(target: "bft", "importing proposal message for round {} from {}", proposal.round_number, proposal.sender);
-				proposal
-			}),
-			net::generic_message::SignedConsensusMessage::Vote(vote) => bft::generic::LocalizedMessage::Vote({
-				if &vote.sender == local_id { return Ok(None) }
-				let vote = bft::generic::LocalizedVote {
-					sender: vote.sender,
-					signature: ed25519::LocalizedSignature {
-						signature: vote.signature,
-						signer: vote.sender.into(),
-					},
-					vote: match vote.vote {
-						net::generic_message::ConsensusVote::Prepare(r, h) => bft::generic::Vote::Prepare(r as usize, h),
-						net::generic_message::ConsensusVote::Commit(r, h) => bft::generic::Vote::Commit(r as usize, h),
-						net::generic_message::ConsensusVote::AdvanceRound(r) => bft::generic::Vote::AdvanceRound(r as usize),
-					}
-				};
-				bft::check_vote::<Block>(authorities, &msg.parent_hash, &vote)?;
-
-				trace!(target: "bft", "importing vote {:?} from {}", vote.vote, vote.sender);
-				vote
-			}),
-		}),
-		net::generic_message::BftMessage::Auxiliary(a) => {
-			let justification = bft::UncheckedJustification::<Hash>::from(a);
-			// TODO: get proper error
-			let justification: Result<_, bft::Error> = bft::check_prepare_justification::<Block>(authorities, msg.parent_hash, justification)
-				.map_err(|_| bft::ErrorKind::InvalidJustification.into());
-			bft::generic::Communication::Auxiliary(justification?)
-		},
-	}))
-}
-
-impl<E> Sink for BftSink<E> {
-	type SinkItem = bft::Communication<Block>;
-	// TODO: replace this with the ! type when that's stabilized
-	type SinkError = E;
-
-	fn start_send(&mut self, message: bft::Communication<Block>) -> ::futures::StartSend<bft::Communication<Block>, E> {
-		let network_message = net::generic_message::LocalizedBftMessage {
-			message: match message {
-				bft::generic::Communication::Consensus(c) => net::generic_message::BftMessage::Consensus(match c {
-					bft::generic::LocalizedMessage::Propose(proposal) => net::generic_message::SignedConsensusMessage::Propose(net::generic_message::SignedConsensusProposal {
-						round_number: proposal.round_number as u32,
-						proposal: proposal.proposal,
-						digest: proposal.digest,
-						sender: proposal.sender,
-						digest_signature: proposal.digest_signature.signature,
-						full_signature: proposal.full_signature.signature,
-					}),
-					bft::generic::LocalizedMessage::Vote(vote) => net::generic_message::SignedConsensusMessage::Vote(net::generic_message::SignedConsensusVote {
-						sender: vote.sender,
-						signature: vote.signature.signature,
-						vote: match vote.vote {
-							bft::generic::Vote::Prepare(r, h) => net::generic_message::ConsensusVote::Prepare(r as u32, h),
-							bft::generic::Vote::Commit(r, h) => net::generic_message::ConsensusVote::Commit(r as u32, h),
-							bft::generic::Vote::AdvanceRound(r) => net::generic_message::ConsensusVote::AdvanceRound(r as u32),
-						}
-					}),
-				}),
-				bft::generic::Communication::Auxiliary(justification) => net::generic_message::BftMessage::Auxiliary(justification.uncheck().into()),
-			},
-			parent_hash: self.parent_hash,
-		};
-		self.network.send_bft_message(network_message);
-		Ok(::futures::AsyncSink::Ready)
-	}
-
-	fn poll_complete(&mut self) -> ::futures::Poll<(), E> {
-		Ok(Async::Ready(()))
-	}
-}
-
-struct Network(Arc<net::ConsensusService<Block>>);
-
-impl super::Network for Network {
-	type TableRouter = Router;
-	fn table_router(&self, _table: Arc<SharedTable>) -> Self::TableRouter {
-		Router {
-			network: self.0.clone()
-		}
-	}
-}
-
+// spin up an instance of BFT agreement on the current thread's executor.
+// panics if there is no current thread executor.
 fn start_bft<F, C>(
 	header: &Header,
-	handle: reactor::Handle,
-	client: &bft::Authorities<Block>,
-	network: Arc<net::ConsensusService<Block>>,
 	bft_service: &BftService<Block, F, C>,
 ) where
-	F: bft::ProposerFactory<Block> + 'static,
+	F: bft::Environment<Block> + 'static,
 	C: bft::BlockImport<Block> + bft::Authorities<Block> + 'static,
-	<F as bft::ProposerFactory<Block>>::Error: ::std::fmt::Debug,
+	F::Error: ::std::fmt::Debug,
 	<F::Proposer as bft::Proposer<Block>>::Error: ::std::fmt::Display + Into<error::Error>,
 {
-	let parent_hash = header.hash();
-	if bft_service.live_agreement().map_or(false, |h| h == parent_hash) {
-		return;
-	}
-	let authorities = match client.authorities(&BlockId::hash(parent_hash)) {
-		Ok(authorities) => authorities,
-		Err(e) => {
-			debug!("Error reading authorities: {:?}", e);
-			return;
-		}
-	};
-
-	let input = Messages {
-		network_stream: network.bft_messages(parent_hash),
-		local_id: bft_service.local_id(),
-		authorities,
-	};
-
-	let output = BftSink { network: network, parent_hash: parent_hash, _e: Default::default() };
-	match bft_service.build_upon(&header, input.map_err(Into::into), output) {
-		Ok(Some(bft)) => handle.spawn(bft),
+	let mut handle = LocalThreadHandle::current();
+	match bft_service.build_upon(&header) {
+		Ok(Some(bft)) => if let Err(e) = handle.spawn_local(Box::new(bft)) {
+			debug!(target: "bft", "Couldn't initialize BFT agreement: {:?}", e);
+		},
 		Ok(None) => {},
 		Err(e) => debug!(target: "bft", "BFT agreement error: {:?}", e),
 	}
@@ -231,54 +75,56 @@ pub struct Service {
 
 impl Service {
 	/// Create and start a new instance.
-	pub fn new<A, C>(
+	pub fn new<A, C, N>(
 		client: Arc<C>,
 		api: Arc<A>,
-		network: Arc<net::ConsensusService<Block>>,
+		network: N,
 		transaction_pool: Arc<TransactionPool<A>>,
+		thread_pool: ThreadPoolHandle,
 		parachain_empty_duration: Duration,
 		key: ed25519::Pair,
 	) -> Service
 		where
 			A: LocalPolkadotApi + Send + Sync + 'static,
 			C: BlockchainEvents<Block> + ChainHead<Block> + bft::BlockImport<Block> + bft::Authorities<Block> + Send + Sync + 'static,
+			N: Network + Collators + Send + 'static,
+			N::TableRouter: Send + 'static,
+			<N::Collation as IntoFuture>::Future: Send + 'static,
 	{
 		let (signal, exit) = ::exit_future::signal();
 		let thread = thread::spawn(move || {
-			let mut core = reactor::Core::new().expect("tokio::Core could not be created");
+			let mut runtime = LocalRuntime::new().expect("Could not create local runtime");
 			let key = Arc::new(key);
 
 			let factory = ProposerFactory {
 				client: api.clone(),
 				transaction_pool: transaction_pool.clone(),
-				network: Network(network.clone()),
-				collators: NoCollators,
+				collators: network.clone(),
+				network,
 				parachain_empty_duration,
-				handle: core.handle(),
+				handle: thread_pool,
 			};
 			let bft_service = Arc::new(BftService::new(client.clone(), key, factory));
 
 			let notifications = {
-				let handle = core.handle();
-				let network = network.clone();
 				let client = client.clone();
 				let bft_service = bft_service.clone();
 
 				client.import_notification_stream().for_each(move |notification| {
 					if notification.is_new_best {
-						start_bft(&notification.header, handle.clone(), &*client, network.clone(), &*bft_service);
+						start_bft(&notification.header, &*bft_service);
 					}
 					Ok(())
 				})
 			};
 
-			let interval = reactor::Interval::new_at(
+			let interval = Interval::new(
 				Instant::now() + Duration::from_millis(TIMER_DELAY_MS),
 				Duration::from_millis(TIMER_INTERVAL_MS),
-				&core.handle(),
-			).expect("it is always possible to create an interval with valid params");
+			);
+
 			let mut prev_best = match client.best_block_header() {
-				Ok(header) => header.blake2_256(),
+				Ok(header) => header.hash(),
 				Err(e) => {
 					warn!("Cant's start consensus service. Error reading best block header: {:?}", e);
 					return;
@@ -288,15 +134,13 @@ impl Service {
 			let timed = {
 				let c = client.clone();
 				let s = bft_service.clone();
-				let n = network.clone();
-				let handle = core.handle();
 
 				interval.map_err(|e| debug!("Timer error: {:?}", e)).for_each(move |_| {
 					if let Ok(best_block) = c.best_block_header() {
-						let hash = best_block.blake2_256();
+						let hash = best_block.hash();
 						if hash == prev_best {
 							debug!("Starting consensus round after a timeout");
-							start_bft(&best_block, handle.clone(), &*c, n.clone(), &*s);
+							start_bft(&best_block, &*s);
 						}
 						prev_best = hash;
 					}
@@ -304,9 +148,9 @@ impl Service {
 				})
 			};
 
-			core.handle().spawn(notifications);
-			core.handle().spawn(timed);
-			if let Err(e) = core.run(exit) {
+			runtime.spawn(notifications);
+			runtime.spawn(timed);
+			if let Err(e) = runtime.block_on(exit) {
 				debug!("BFT event loop error {:?}", e);
 			}
 		});
@@ -328,42 +172,3 @@ impl Drop for Service {
 		}
 	}
 }
-
-// Collators implementation which never collates anything.
-// TODO: do a real implementation.
-#[derive(Clone, Copy)]
-struct NoCollators;
-
-impl ::collation::Collators for NoCollators {
-	type Error = ();
-	type Collation = future::Empty<::collation::Collation, ()>;
-
-	fn collate(&self, _parachain: ParaId, _relay_parent: Hash) -> Self::Collation {
-		future::empty()
-	}
-
-	fn note_bad_collator(&self, _collator: AccountId) { }
-}
-
-#[derive(Clone)]
-struct Router {
-	network: Arc<net::ConsensusService<Block>>,
-}
-
-impl TableRouter for Router {
-	type Error = Canceled;
-	type FetchCandidate =  future::Empty<BlockData, Self::Error>;
-	type FetchExtrinsic = future::FutureResult<Extrinsic, Self::Error>;
-
-	fn local_candidate_data(&self, _hash: Hash, _block_data: BlockData, _extrinsic: Extrinsic) {
-		// TODO
-	}
-
-	fn fetch_block_data(&self, _candidate: &CandidateReceipt) -> Self::FetchCandidate {
-		future::empty()
-	}
-
-	fn fetch_extrinsic_data(&self, _candidate: &CandidateReceipt) -> Self::FetchExtrinsic {
-		future::ok(Extrinsic)
-	}
-}
diff --git a/polkadot/consensus/src/shared_table/mod.rs b/polkadot/consensus/src/shared_table/mod.rs
index 1c46b67b09..15116c5cfb 100644
--- a/polkadot/consensus/src/shared_table/mod.rs
+++ b/polkadot/consensus/src/shared_table/mod.rs
@@ -21,11 +21,9 @@ use std::collections::{HashMap, HashSet};
 use std::sync::Arc;
 
 use table::{self, Table, Context as TableContextTrait};
-use table::generic::Statement as GenericStatement;
 use collation::Collation;
-use polkadot_primitives::Hash;
+use polkadot_primitives::{Hash, SessionKey};
 use polkadot_primitives::parachain::{Id as ParaId, BlockData, Extrinsic, CandidateReceipt};
-use primitives::AuthorityId;
 
 use parking_lot::Mutex;
 use futures::{future, prelude::*};
@@ -36,6 +34,8 @@ use self::includable::IncludabilitySender;
 mod includable;
 
 pub use self::includable::Includable;
+pub use table::{SignedStatement, Statement};
+pub use table::generic::Statement as GenericStatement;
 
 struct TableContext {
 	parent_hash: Hash,
@@ -44,11 +44,11 @@ struct TableContext {
 }
 
 impl table::Context for TableContext {
-	fn is_member_of(&self, authority: &AuthorityId, group: &ParaId) -> bool {
+	fn is_member_of(&self, authority: &SessionKey, group: &ParaId) -> bool {
 		self.groups.get(group).map_or(false, |g| g.validity_guarantors.contains(authority))
 	}
 
-	fn is_availability_guarantor_of(&self, authority: &AuthorityId, group: &ParaId) -> bool {
+	fn is_availability_guarantor_of(&self, authority: &SessionKey, group: &ParaId) -> bool {
 		self.groups.get(group).map_or(false, |g| g.availability_guarantors.contains(authority))
 	}
 
@@ -61,7 +61,7 @@ impl table::Context for TableContext {
 }
 
 impl TableContext {
-	fn local_id(&self) -> AuthorityId {
+	fn local_id(&self) -> SessionKey {
 		self.key.public().into()
 	}
 
@@ -76,14 +76,6 @@ impl TableContext {
 	}
 }
 
-/// Source of statements
-pub enum StatementSource {
-	/// Locally produced statement.
-	Local,
-	/// Received statement from remote source, with optional sender.
-	Remote(Option<AuthorityId>),
-}
-
 // A shared table object.
 struct SharedTableInner {
 	table: Table<TableContext>,
@@ -96,28 +88,21 @@ struct SharedTableInner {
 impl SharedTableInner {
 	// Import a single statement. Provide a handle to a table router and a function
 	// used to determine if a referenced candidate is valid.
-	fn import_statement<R: TableRouter, C: FnMut(Collation) -> bool>(
+	//
+	// the statement producer, if any, will produce only statements concerning the same candidate
+	// as the one just imported
+	fn import_remote_statement<R: TableRouter>(
 		&mut self,
 		context: &TableContext,
 		router: &R,
 		statement: table::SignedStatement,
-		statement_source: StatementSource,
-		check_candidate: C,
-	) -> StatementProducer<
+	) -> Option<StatementProducer<
 		<R::FetchCandidate as IntoFuture>::Future,
 		<R::FetchExtrinsic as IntoFuture>::Future,
-		C,
-	> {
-		// this blank producer does nothing until we attach some futures
-		// and set a candidate digest.
-		let received_from = match statement_source {
-			StatementSource::Local => return Default::default(),
-			StatementSource::Remote(from) => from,
-		};
-
-		let summary = match self.table.import_statement(context, statement, received_from) {
+	>> {
+		let summary = match self.table.import_statement(context, statement) {
 			Some(summary) => summary,
-			None => return Default::default(),
+			None => return None,
 		};
 
 		self.update_trackers(&summary.candidate, context);
@@ -159,7 +144,6 @@ impl SharedTableInner {
 						fetch_block_data,
 						fetch_extrinsic,
 						evaluate: checking_validity,
-						check_candidate,
 					})
 				}
 			}
@@ -167,10 +151,10 @@ impl SharedTableInner {
 			None
 		};
 
-		StatementProducer {
+		work.map(|work| StatementProducer {
 			produced_statements: Default::default(),
-			work,
-		}
+			work
+		})
 	}
 
 	fn update_trackers(&mut self, candidate: &Hash, context: &TableContext) {
@@ -199,71 +183,78 @@ pub struct ProducedStatements {
 }
 
 /// Future that produces statements about a specific candidate.
-pub struct StatementProducer<D: Future, E: Future, C> {
+pub struct StatementProducer<D: Future, E: Future> {
 	produced_statements: ProducedStatements,
-	work: Option<Work<D, E, C>>,
+	work: Work<D, E>,
 }
 
-struct Work<D: Future, E: Future, C> {
-	candidate_receipt: CandidateReceipt,
-	fetch_block_data: future::Fuse<D>,
-	fetch_extrinsic: Option<future::Fuse<E>>,
-	evaluate: bool,
-	check_candidate: C
-}
-
-impl<D: Future, E: Future, C> Default for StatementProducer<D, E, C> {
-	fn default() -> Self {
-		StatementProducer {
-			produced_statements: Default::default(),
-			work: None,
+impl<D: Future, E: Future> StatementProducer<D, E> {
+	/// Attach a function for verifying fetched collation to the statement producer.
+	/// This will transform it into a future.
+	///
+	/// The collation-checking function should return `true` if known to be valid,
+	/// `false` if known to be invalid, and `None` if unable to determine.
+	pub fn prime<C: FnMut(Collation) -> Option<bool>>(self, check_candidate: C) -> PrimedStatementProducer<D, E, C> {
+		PrimedStatementProducer {
+			inner: self,
+			check_candidate,
 		}
 	}
 }
 
-impl<D, E, C, Err> Future for StatementProducer<D, E, C>
+struct Work<D: Future, E: Future> {
+	candidate_receipt: CandidateReceipt,
+	fetch_block_data: future::Fuse<D>,
+	fetch_extrinsic: Option<future::Fuse<E>>,
+	evaluate: bool,
+}
+
+/// Primed statement producer.
+pub struct PrimedStatementProducer<D: Future, E: Future, C> {
+	inner: StatementProducer<D, E>,
+	check_candidate: C,
+}
+
+impl<D, E, C, Err> Future for PrimedStatementProducer<D, E, C>
 	where
 		D: Future<Item=BlockData,Error=Err>,
 		E: Future<Item=Extrinsic,Error=Err>,
-		C: FnMut(Collation) -> bool,
+		C: FnMut(Collation) -> Option<bool>,
 {
 	type Item = ProducedStatements;
 	type Error = Err;
 
 	fn poll(&mut self) -> Poll<ProducedStatements, Err> {
-		let work = match self.work {
-			Some(ref mut work) => work,
-			None => return Ok(Async::Ready(::std::mem::replace(&mut self.produced_statements, Default::default()))),
-		};
+		let work = &mut self.inner.work;
 
 		if let Async::Ready(block_data) = work.fetch_block_data.poll()? {
-			self.produced_statements.block_data = Some(block_data.clone());
+			self.inner.produced_statements.block_data = Some(block_data.clone());
 			if work.evaluate {
-				let is_good = (work.check_candidate)(Collation {
+				let is_good = (self.check_candidate)(Collation {
 					block_data,
 					receipt: work.candidate_receipt.clone(),
 				});
 
 				let hash = work.candidate_receipt.hash();
-				self.produced_statements.validity = Some(if is_good {
-					GenericStatement::Valid(hash)
-				} else {
-					GenericStatement::Invalid(hash)
-				});
+				self.inner.produced_statements.validity = match is_good {
+					Some(true) => Some(GenericStatement::Valid(hash)),
+					Some(false) => Some(GenericStatement::Invalid(hash)),
+					None => None,
+				};
 			}
 		}
 
 		if let Some(ref mut fetch_extrinsic) = work.fetch_extrinsic {
 			if let Async::Ready(extrinsic) = fetch_extrinsic.poll()? {
-				self.produced_statements.extrinsic = Some(extrinsic);
+				self.inner.produced_statements.extrinsic = Some(extrinsic);
 			}
 		}
 
-		let done = self.produced_statements.block_data.is_some() && {
+		let done = self.inner.produced_statements.block_data.is_some() && {
 			if work.evaluate {
 				true
-			} else if self.produced_statements.extrinsic.is_some() {
-				self.produced_statements.availability =
+			} else if self.inner.produced_statements.extrinsic.is_some() {
+				self.inner.produced_statements.availability =
 					Some(GenericStatement::Available(work.candidate_receipt.hash()));
 
 				true
@@ -273,7 +264,7 @@ impl<D, E, C, Err> Future for StatementProducer<D, E, C>
 		};
 
 		if done {
-			Ok(Async::Ready(::std::mem::replace(&mut self.produced_statements, Default::default())))
+			Ok(Async::Ready(::std::mem::replace(&mut self.inner.produced_statements, Default::default())))
 		} else {
 			Ok(Async::NotReady)
 		}
@@ -313,29 +304,60 @@ impl SharedTable {
 		}
 	}
 
+	/// Get the parent hash this table should hold statements localized to.
+	pub fn consensus_parent_hash(&self) -> &Hash {
+		&self.context.parent_hash
+	}
+
+	/// Get the local validator session key.
+	pub fn session_key(&self) -> SessionKey {
+		self.context.local_id()
+	}
+
 	/// Get group info.
 	pub fn group_info(&self) -> &HashMap<ParaId, GroupInfo> {
 		&self.context.groups
 	}
 
-	/// Import a single statement. Provide a handle to a table router
-	/// for dispatching any other requests which come up.
-	pub fn import_statement<R: TableRouter, C: FnMut(Collation) -> bool>(
+	/// Import a single statement with remote source, whose signature has already been checked.
+	///
+	/// The statement producer, if any, will produce only statements concerning the same candidate
+	/// as the one just imported
+	pub fn import_remote_statement<R: TableRouter>(
 		&self,
 		router: &R,
 		statement: table::SignedStatement,
-		received_from: StatementSource,
-		check_candidate: C,
-	) -> StatementProducer<<R::FetchCandidate as IntoFuture>::Future, <R::FetchExtrinsic as IntoFuture>::Future, C> {
-		self.inner.lock().import_statement(&*self.context, router, statement, received_from, check_candidate)
+	) -> Option<StatementProducer<
+		<R::FetchCandidate as IntoFuture>::Future,
+		<R::FetchExtrinsic as IntoFuture>::Future,
+	>> {
+		self.inner.lock().import_remote_statement(&*self.context, router, statement)
+	}
+
+	/// Import many statements at once.
+	///
+	/// Provide an iterator yielding remote, pre-checked statements.
+	///
+	/// The statement producer, if any, will produce only statements concerning the same candidate
+	/// as the one just imported
+	pub fn import_remote_statements<R, I, U>(&self, router: &R, iterable: I) -> U
+		where
+			R: TableRouter,
+			I: IntoIterator<Item=table::SignedStatement>,
+			U: ::std::iter::FromIterator<Option<StatementProducer<
+				<R::FetchCandidate as IntoFuture>::Future,
+				<R::FetchExtrinsic as IntoFuture>::Future,
+			>>>,
+	{
+		let mut inner = self.inner.lock();
+
+		iterable.into_iter().map(move |statement| {
+			inner.import_remote_statement(&*self.context, router, statement)
+		}).collect()
 	}
 
 	/// Sign and import a local statement.
-	pub fn sign_and_import<R: TableRouter>(
-		&self,
-		router: &R,
-		statement: table::Statement,
-	) {
+	pub fn sign_and_import(&self, statement: table::Statement) -> SignedStatement {
 		let proposed_digest = match statement {
 			GenericStatement::Candidate(ref c) => Some(c.hash()),
 			_ => None,
@@ -348,36 +370,8 @@ impl SharedTable {
 			inner.proposed_digest = proposed_digest;
 		}
 
-		let producer = inner.import_statement(
-			&*self.context,
-			router,
-			signed_statement,
-			StatementSource::Local,
-			|_| true,
-		);
-
-		assert!(producer.work.is_none(), "local statement import never leads to additional work; qed");
-	}
-
-	/// Import many statements at once.
-	///
-	/// Provide an iterator yielding pairs of (statement, statement_source).
-	pub fn import_statements<R, I, C, U>(&self, router: &R, iterable: I) -> U
-		where
-			R: TableRouter,
-			I: IntoIterator<Item=(table::SignedStatement, StatementSource, C)>,
-			C: FnMut(Collation) -> bool,
-			U: ::std::iter::FromIterator<StatementProducer<
-				<R::FetchCandidate as IntoFuture>::Future,
-				<R::FetchExtrinsic as IntoFuture>::Future,
-				C,
-			>>,
-	{
-		let mut inner = self.inner.lock();
-
-		iterable.into_iter().map(move |(statement, statement_source, check_candidate)| {
-			inner.import_statement(&*self.context, router, statement, statement_source, check_candidate)
-		}).collect()
+		inner.table.import_statement(&*self.context, signed_statement.clone());
+		signed_statement
 	}
 
 	/// Execute a closure using a specific candidate.
@@ -406,15 +400,10 @@ impl SharedTable {
 	}
 
 	/// Get all witnessed misbehavior.
-	pub fn get_misbehavior(&self) -> HashMap<AuthorityId, table::Misbehavior> {
+	pub fn get_misbehavior(&self) -> HashMap<SessionKey, table::Misbehavior> {
 		self.inner.lock().table.get_misbehavior().clone()
 	}
 
-	/// Fill a statement batch.
-	pub fn fill_batch<B: table::StatementBatch>(&self, batch: &mut B) {
-		self.inner.lock().table.fill_batch(batch);
-	}
-
 	/// Track includability  of a given set of candidate hashes.
 	pub fn track_includability<I>(&self, iterable: I) -> Includable
 		where I: IntoIterator<Item=Hash>
@@ -446,17 +435,12 @@ mod tests {
 		type FetchCandidate = ::futures::future::Empty<BlockData,()>;
 		type FetchExtrinsic = ::futures::future::Empty<Extrinsic,()>;
 
-		/// Note local candidate data, making it available on the network to other validators.
-		fn local_candidate_data(&self, _hash: Hash, _block_data: BlockData, _extrinsic: Extrinsic) {
+		fn local_candidate(&self, _candidate: CandidateReceipt, _block_data: BlockData, _extrinsic: Extrinsic) {
 
 		}
-
-		/// Fetch block data for a specific candidate.
 		fn fetch_block_data(&self, _candidate: &CandidateReceipt) -> Self::FetchCandidate {
 			::futures::future::empty()
 		}
-
-		/// Fetch extrinsic data for a specific candidate.
 		fn fetch_extrinsic_data(&self, _candidate: &CandidateReceipt) -> Self::FetchExtrinsic {
 			::futures::future::empty()
 		}
@@ -490,6 +474,7 @@ mod tests {
 			balance_uploads: Vec::new(),
 			egress_queue_roots: Vec::new(),
 			fees: 1_000_000,
+			block_data_hash: [2; 32].into(),
 		};
 
 		let candidate_statement = GenericStatement::Candidate(candidate);
@@ -501,15 +486,13 @@ mod tests {
 			sender: validity_other,
 		};
 
-		let producer = shared_table.import_statement(
+		let producer = shared_table.import_remote_statement(
 			&DummyRouter,
 			signed_statement,
-			StatementSource::Remote(None),
-			|_| true,
-		);
+		).expect("candidate and local validity group are same");
 
-		assert!(producer.work.is_some(), "candidate and local validity group are same");
-		assert!(producer.work.as_ref().unwrap().evaluate, "should evaluate validity");
+		assert!(producer.work.evaluate, "should evaluate validity");
+		assert!(producer.work.fetch_extrinsic.is_none(), "should not fetch extrinsic");
 	}
 
 	#[test]
@@ -540,6 +523,7 @@ mod tests {
 			balance_uploads: Vec::new(),
 			egress_queue_roots: Vec::new(),
 			fees: 1_000_000,
+			block_data_hash: [2; 32].into(),
 		};
 
 		let candidate_statement = GenericStatement::Candidate(candidate);
@@ -551,15 +535,12 @@ mod tests {
 			sender: validity_other,
 		};
 
-		let producer = shared_table.import_statement(
+		let producer = shared_table.import_remote_statement(
 			&DummyRouter,
 			signed_statement,
-			StatementSource::Remote(None),
-			|_| true,
-		);
+		).expect("should produce work");
 
-		assert!(producer.work.is_some(), "candidate and local availability group are same");
-		assert!(producer.work.as_ref().unwrap().fetch_extrinsic.is_some(), "should fetch extrinsic when guaranteeing availability");
-		assert!(!producer.work.as_ref().unwrap().evaluate, "should not evaluate validity");
+		assert!(producer.work.fetch_extrinsic.is_some(), "should fetch extrinsic when guaranteeing availability");
+		assert!(!producer.work.evaluate, "should not evaluate validity");
 	}
 }
diff --git a/polkadot/network/Cargo.toml b/polkadot/network/Cargo.toml
new file mode 100644
index 0000000000..ad07af5c12
--- /dev/null
+++ b/polkadot/network/Cargo.toml
@@ -0,0 +1,22 @@
+[package]
+name = "polkadot-network"
+version = "0.1.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+description = "Polkadot-specific networking protocol"
+
+[dependencies]
+serde = "1.0"
+serde_derive = "1.0"
+serde_json = "1.0"
+parking_lot = "0.4"
+polkadot-api = { path = "../api" }
+polkadot-consensus = { path = "../consensus" }
+polkadot-primitives = { path = "../primitives" }
+substrate-bft = { path = "../../substrate/bft" }
+substrate-codec = { path = "../../substrate/codec" }
+substrate-network = { path = "../../substrate/network" }
+substrate-primitives = { path = "../../substrate/primitives" }
+ed25519 = { path = "../../substrate/ed25519" }
+futures = "0.1"
+tokio = "0.1.7"
+log = "0.4"
diff --git a/polkadot/network/src/consensus.rs b/polkadot/network/src/consensus.rs
new file mode 100644
index 0000000000..b575856739
--- /dev/null
+++ b/polkadot/network/src/consensus.rs
@@ -0,0 +1,313 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! The "consensus" networking code built on top of the base network service.
+//! This fulfills the `polkadot_consensus::Network` trait, providing a hook to be called
+//! each time consensus begins on a new chain head.
+
+use bft;
+use ed25519;
+use substrate_network::{self as net, generic_message as msg};
+use substrate_network::consensus_gossip::ConsensusMessage;
+use polkadot_api::{PolkadotApi, LocalPolkadotApi};
+use polkadot_consensus::{Network, SharedTable, Collators, Collation};
+use polkadot_primitives::{AccountId, Block, Hash, SessionKey};
+use polkadot_primitives::parachain::Id as ParaId;
+
+use futures::{future, prelude::*};
+use futures::sync::mpsc;
+
+use std::sync::Arc;
+
+use tokio::runtime::TaskExecutor;
+use parking_lot::Mutex;
+
+use super::{Message, NetworkService, Knowledge, CurrentConsensus};
+use router::Router;
+
+/// Sink for output BFT messages.
+pub struct BftSink<E> {
+	network: Arc<NetworkService>,
+	parent_hash: Hash,
+	_marker: ::std::marker::PhantomData<E>,
+}
+
+impl<E> Sink for BftSink<E> {
+	type SinkItem = bft::Communication<Block>;
+	// TODO: replace this with the ! type when that's stabilized
+	type SinkError = E;
+
+	fn start_send(&mut self, message: bft::Communication<Block>) -> ::futures::StartSend<bft::Communication<Block>, E> {
+		let network_message = net::LocalizedBftMessage {
+			message: match message {
+				bft::generic::Communication::Consensus(c) => msg::BftMessage::Consensus(match c {
+					bft::generic::LocalizedMessage::Propose(proposal) => msg::SignedConsensusMessage::Propose(msg::SignedConsensusProposal {
+						round_number: proposal.round_number as u32,
+						proposal: proposal.proposal,
+						digest: proposal.digest,
+						sender: proposal.sender,
+						digest_signature: proposal.digest_signature.signature,
+						full_signature: proposal.full_signature.signature,
+					}),
+					bft::generic::LocalizedMessage::Vote(vote) => msg::SignedConsensusMessage::Vote(msg::SignedConsensusVote {
+						sender: vote.sender,
+						signature: vote.signature.signature,
+						vote: match vote.vote {
+							bft::generic::Vote::Prepare(r, h) => msg::ConsensusVote::Prepare(r as u32, h),
+							bft::generic::Vote::Commit(r, h) => msg::ConsensusVote::Commit(r as u32, h),
+							bft::generic::Vote::AdvanceRound(r) => msg::ConsensusVote::AdvanceRound(r as u32),
+						}
+					}),
+				}),
+				bft::generic::Communication::Auxiliary(justification) => msg::BftMessage::Auxiliary(justification.uncheck().into()),
+			},
+			parent_hash: self.parent_hash,
+		};
+		self.network.with_spec(
+			move |spec, ctx| spec.consensus_gossip.multicast_bft_message(ctx, network_message)
+		);
+		Ok(::futures::AsyncSink::Ready)
+	}
+
+	fn poll_complete(&mut self) -> ::futures::Poll<(), E> {
+		Ok(Async::Ready(()))
+	}
+}
+
+// check signature and authority validity of message.
+fn process_bft_message(msg: msg::LocalizedBftMessage<Block, Hash>, local_id: &SessionKey, authorities: &[SessionKey]) -> Result<Option<bft::Communication<Block>>, bft::Error> {
+	Ok(Some(match msg.message {
+		msg::BftMessage::Consensus(c) => bft::generic::Communication::Consensus(match c {
+			msg::SignedConsensusMessage::Propose(proposal) => bft::generic::LocalizedMessage::Propose({
+				if &proposal.sender == local_id { return Ok(None) }
+				let proposal = bft::generic::LocalizedProposal {
+					round_number: proposal.round_number as usize,
+					proposal: proposal.proposal,
+					digest: proposal.digest,
+					sender: proposal.sender,
+					digest_signature: ed25519::LocalizedSignature {
+						signature: proposal.digest_signature,
+						signer: ed25519::Public(proposal.sender.into()),
+					},
+					full_signature: ed25519::LocalizedSignature {
+						signature: proposal.full_signature,
+						signer: ed25519::Public(proposal.sender.into()),
+					}
+				};
+				bft::check_proposal(authorities, &msg.parent_hash, &proposal)?;
+
+				trace!(target: "bft", "importing proposal message for round {} from {}", proposal.round_number, Hash::from(proposal.sender.0));
+				proposal
+			}),
+			msg::SignedConsensusMessage::Vote(vote) => bft::generic::LocalizedMessage::Vote({
+				if &vote.sender == local_id { return Ok(None) }
+				let vote = bft::generic::LocalizedVote {
+					sender: vote.sender,
+					signature: ed25519::LocalizedSignature {
+						signature: vote.signature,
+						signer: ed25519::Public(vote.sender.0),
+					},
+					vote: match vote.vote {
+						msg::ConsensusVote::Prepare(r, h) => bft::generic::Vote::Prepare(r as usize, h),
+						msg::ConsensusVote::Commit(r, h) => bft::generic::Vote::Commit(r as usize, h),
+						msg::ConsensusVote::AdvanceRound(r) => bft::generic::Vote::AdvanceRound(r as usize),
+					}
+				};
+				bft::check_vote::<Block>(authorities, &msg.parent_hash, &vote)?;
+
+				trace!(target: "bft", "importing vote {:?} from {}", vote.vote, Hash::from(vote.sender.0));
+				vote
+			}),
+		}),
+		msg::BftMessage::Auxiliary(a) => {
+			let justification = bft::UncheckedJustification::from(a);
+			// TODO: get proper error
+			let justification: Result<_, bft::Error> = bft::check_prepare_justification::<Block>(authorities, msg.parent_hash, justification)
+				.map_err(|_| bft::ErrorKind::InvalidJustification.into());
+			bft::generic::Communication::Auxiliary(justification?)
+		},
+	}))
+}
+
+// task that processes all gossipped consensus messages,
+// checking signatures
+struct MessageProcessTask<P: PolkadotApi> {
+	inner_stream: mpsc::UnboundedReceiver<ConsensusMessage<Block>>,
+	bft_messages: mpsc::UnboundedSender<bft::Communication<Block>>,
+	validators: Vec<SessionKey>,
+	table_router: Router<P>,
+}
+
+impl<P: LocalPolkadotApi + Send + Sync + 'static> MessageProcessTask<P> {
+	fn process_message(&self, msg: ConsensusMessage<Block>) -> Option<Async<()>> {
+		match msg {
+			ConsensusMessage::Bft(msg) => {
+				let local_id = self.table_router.session_key();
+				match process_bft_message(msg, &local_id, &self.validators[..]) {
+					Ok(Some(msg)) => {
+						if let Err(_) = self.bft_messages.unbounded_send(msg) {
+							// if the BFT receiving stream has ended then
+							// we should just bail.
+							trace!(target: "bft", "BFT message stream appears to have closed");
+							return Some(Async::Ready(()));
+						}
+					}
+					Ok(None) => {} // ignored local message
+					Err(e) => {
+						debug!("Message validation failed: {:?}", e);
+					}
+				}
+			}
+			ConsensusMessage::ChainSpecific(msg, _) => {
+				if let Ok(Message::Statement(parent_hash, statement)) = ::serde_json::from_slice(&msg) {
+					if ::polkadot_consensus::check_statement(&statement.statement, &statement.signature, statement.sender, &parent_hash) {
+						self.table_router.import_statement(statement);
+					}
+				}
+			}
+		}
+
+		None
+	}
+}
+
+impl<P: LocalPolkadotApi + Send + Sync + 'static> Future for MessageProcessTask<P> {
+	type Item = ();
+	type Error = ();
+
+	fn poll(&mut self) -> Poll<(), ()> {
+		loop {
+			match self.inner_stream.poll() {
+				Ok(Async::Ready(Some(val))) => if let Some(async) = self.process_message(val) {
+					return Ok(async);
+				},
+				Ok(Async::Ready(None)) => return Ok(Async::Ready(())),
+				Ok(Async::NotReady) => (),
+				Err(e) => debug!(target: "p_net", "Error getting consensus message: {:?}", e),
+			}
+		}
+	}
+}
+
+/// Input stream from the consensus network.
+pub struct InputAdapter {
+	input: mpsc::UnboundedReceiver<bft::Communication<Block>>,
+}
+
+impl Stream for InputAdapter {
+	type Item = bft::Communication<Block>;
+	type Error = ::polkadot_consensus::Error;
+
+	fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
+		match self.input.poll() {
+			Err(_) | Ok(Async::Ready(None)) => Err(bft::InputStreamConcluded.into()),
+			Ok(x) => Ok(x)
+		}
+	}
+}
+
+/// Wrapper around the network service
+pub struct ConsensusNetwork<P> {
+	network: Arc<NetworkService>,
+	api: Arc<P>,
+}
+
+impl<P> ConsensusNetwork<P> {
+	/// Create a new consensus networking object.
+	pub fn new(network: Arc<NetworkService>, api: Arc<P>) -> Self {
+		ConsensusNetwork { network, api }
+	}
+}
+
+impl<P> Clone for ConsensusNetwork<P> {
+	fn clone(&self) -> Self {
+		ConsensusNetwork {
+			network: self.network.clone(),
+			api: self.api.clone(),
+		}
+	}
+}
+
+/// A long-lived network which can create parachain statement and BFT message routing processes on demand.
+impl<P: LocalPolkadotApi + Send + Sync + 'static> Network for ConsensusNetwork<P> {
+	type TableRouter = Router<P>;
+	/// The input stream of BFT messages. Should never logically conclude.
+	type Input = InputAdapter;
+	/// The output sink of BFT messages. Messages sent here should eventually pass to all
+	/// current validators.
+	type Output = BftSink<::polkadot_consensus::Error>;
+
+	/// Instantiate a table router using the given shared table.
+	fn communication_for(&self, validators: &[SessionKey], table: Arc<SharedTable>, task_executor: TaskExecutor) -> (Self::TableRouter, Self::Input, Self::Output) {
+		let parent_hash = table.consensus_parent_hash().clone();
+
+		let sink = BftSink {
+			network: self.network.clone(),
+			parent_hash,
+			_marker: Default::default(),
+		};
+
+		let (bft_send, bft_recv) = mpsc::unbounded();
+
+		let knowledge = Arc::new(Mutex::new(Knowledge::new()));
+
+		let local_session_key = table.session_key();
+		let table_router = Router::new(
+			table,
+			self.network.clone(),
+			self.api.clone(),
+			task_executor.clone(),
+			parent_hash,
+			knowledge.clone(),
+		);
+
+		// spin up a task in the background that processes all incoming statements
+		// TODO: propagate statements on a timer?
+		let process_task = self.network.with_spec(|spec, ctx| {
+			spec.new_consensus(ctx, CurrentConsensus {
+				knowledge,
+				parent_hash,
+				local_session_key,
+				session_keys: Default::default(),
+			});
+
+			MessageProcessTask {
+				inner_stream: spec.consensus_gossip.messages_for(parent_hash),
+				bft_messages: bft_send,
+				validators: validators.to_vec(),
+				table_router: table_router.clone(),
+			}
+		});
+
+		match process_task {
+			Some(task) => task_executor.spawn(task),
+			None => warn!(target: "p_net", "Cannot process incoming messages: network appears to be down"),
+		}
+
+		(table_router, InputAdapter { input: bft_recv }, sink)
+	}
+}
+
+impl<P: LocalPolkadotApi + Send + Sync + 'static> Collators for ConsensusNetwork<P> {
+	type Error = ();
+	type Collation = future::Empty<Collation, ()>;
+
+	fn collate(&self, _parachain: ParaId, _relay_parent: Hash) -> Self::Collation {
+		future::empty()
+	}
+
+	fn note_bad_collator(&self, _collator: AccountId) { }
+}
diff --git a/polkadot/network/src/lib.rs b/polkadot/network/src/lib.rs
new file mode 100644
index 0000000000..f909d0581b
--- /dev/null
+++ b/polkadot/network/src/lib.rs
@@ -0,0 +1,488 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Polkadot-specific network implementation.
+//!
+//! This manages gossip of consensus messages for BFT and for parachain statements,
+//! parachain block and extrinsic data fetching, communication between collators and validators,
+//! and more.
+
+extern crate serde;
+#[macro_use]
+extern crate serde_derive;
+extern crate serde_json;
+
+extern crate substrate_bft as bft;
+extern crate substrate_codec as codec;
+extern crate substrate_network;
+extern crate substrate_primitives;
+
+extern crate polkadot_api;
+extern crate polkadot_consensus;
+extern crate polkadot_primitives;
+
+extern crate ed25519;
+extern crate futures;
+extern crate parking_lot;
+extern crate tokio;
+
+#[macro_use]
+extern crate log;
+
+mod router;
+pub mod consensus;
+
+use codec::Slicable;
+use futures::sync::oneshot;
+use parking_lot::Mutex;
+use polkadot_consensus::{Statement, SignedStatement, GenericStatement};
+use polkadot_primitives::{Block, SessionKey, Hash};
+use polkadot_primitives::parachain::{Id as ParaId, BlockData, Extrinsic, CandidateReceipt};
+use substrate_network::{PeerId, RequestId, Context};
+use substrate_network::consensus_gossip::ConsensusGossip;
+use substrate_network::{message, generic_message};
+use substrate_network::specialization::Specialization;
+use substrate_network::StatusMessage as GenericFullStatus;
+
+use std::collections::{HashMap, HashSet};
+use std::sync::Arc;
+
+#[cfg(test)]
+mod tests;
+
+/// Polkadot protocol id.
+pub const DOT_PROTOCOL_ID: ::substrate_network::ProtocolId = *b"dot";
+
+type FullStatus = GenericFullStatus<Block>;
+
+/// Specialization of the network service for the polkadot protocol.
+pub type NetworkService = ::substrate_network::Service<Block, PolkadotProtocol>;
+
+/// Status of a Polkadot node.
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct Status {
+	collating_for: Option<ParaId>,
+}
+
+impl Slicable for Status {
+	fn encode(&self) -> Vec<u8> {
+		let mut v = Vec::new();
+		match self.collating_for {
+			Some(ref id) => {
+				v.push(1);
+				id.using_encoded(|s| v.extend(s));
+			}
+			None => {
+				v.push(0);
+			}
+		}
+		v
+	}
+
+	fn decode<I: ::codec::Input>(input: &mut I) -> Option<Self> {
+		let collating_for = match input.read_byte()? {
+			0 => None,
+			1 => Some(ParaId::decode(input)?),
+			_ => return None,
+		};
+		Some(Status { collating_for })
+	}
+}
+
+struct BlockDataRequest {
+	attempted_peers: HashSet<SessionKey>,
+	consensus_parent: Hash,
+	candidate_hash: Hash,
+	block_data_hash: Hash,
+	sender: oneshot::Sender<BlockData>,
+}
+
+struct PeerInfo {
+	status: Status,
+	validator: bool,
+	session_keys: HashMap<Hash, SessionKey>,
+}
+
+#[derive(Default)]
+struct KnowledgeEntry {
+	knows_block_data: Vec<SessionKey>,
+	knows_extrinsic: Vec<SessionKey>,
+	block_data: Option<BlockData>,
+	extrinsic: Option<Extrinsic>,
+}
+
+/// Tracks knowledge of peers.
+struct Knowledge {
+	candidates: HashMap<Hash, KnowledgeEntry>,
+}
+
+impl Knowledge {
+	pub fn new() -> Self {
+		Knowledge {
+			candidates: HashMap::new(),
+		}
+	}
+
+	fn note_statement(&mut self, from: SessionKey, statement: &Statement) {
+		match *statement {
+			GenericStatement::Candidate(ref c) => {
+				let mut entry = self.candidates.entry(c.hash()).or_insert_with(Default::default);
+				entry.knows_block_data.push(from);
+				entry.knows_extrinsic.push(from);
+			}
+			GenericStatement::Available(ref hash) => {
+				let mut entry = self.candidates.entry(*hash).or_insert_with(Default::default);
+				entry.knows_block_data.push(from);
+				entry.knows_extrinsic.push(from);
+			}
+			GenericStatement::Valid(ref hash) | GenericStatement::Invalid(ref hash) => self.candidates.entry(*hash)
+				.or_insert_with(Default::default)
+				.knows_block_data
+				.push(from),
+		}
+	}
+
+	fn note_candidate(&mut self, hash: Hash, block_data: Option<BlockData>, extrinsic: Option<Extrinsic>) {
+		let entry = self.candidates.entry(hash).or_insert_with(Default::default);
+		entry.block_data = entry.block_data.take().or(block_data);
+		entry.extrinsic = entry.extrinsic.take().or(extrinsic);
+	}
+}
+
+struct CurrentConsensus {
+	knowledge: Arc<Mutex<Knowledge>>,
+	parent_hash: Hash,
+	session_keys: HashMap<SessionKey, PeerId>,
+	local_session_key: SessionKey,
+}
+
+impl CurrentConsensus {
+	// get locally stored block data for a candidate.
+	fn block_data(&self, hash: &Hash) -> Option<BlockData> {
+		self.knowledge.lock().candidates.get(hash)
+			.and_then(|entry| entry.block_data.clone())
+	}
+
+	fn peer_disconnected(&mut self, peer: &PeerInfo) {
+		if let Some(key) = peer.session_keys.get(&self.parent_hash) {
+			self.session_keys.remove(key);
+		}
+	}
+}
+
+/// Polkadot-specific messages.
+#[derive(Serialize, Deserialize)]
+pub enum Message {
+	/// signed statement and localized parent hash.
+	Statement(Hash, SignedStatement),
+	/// Tell the peer your session key for the current block.
+	// TODO: do this with a random challenge protocol
+	SessionKey(Hash, SessionKey),
+	/// Requesting parachain block data by candidate hash.
+	RequestBlockData(RequestId, Hash),
+	/// Provide block data by candidate hash or nothing if unknown.
+	BlockData(RequestId, Option<BlockData>),
+}
+
+fn send_polkadot_message(ctx: &mut Context<Block>, to: PeerId, message: Message) {
+	let encoded = ::serde_json::to_vec(&message).expect("serialization of messages infallible; qed");
+	ctx.send_message(to, generic_message::Message::ChainSpecific(encoded))
+}
+
+/// Polkadot protocol attachment for substrate.
+pub struct PolkadotProtocol {
+	peers: HashMap<PeerId, PeerInfo>,
+	consensus_gossip: ConsensusGossip<Block>,
+	collators: HashMap<ParaId, Vec<PeerId>>,
+	collating_for: Option<ParaId>,
+	live_consensus: Option<CurrentConsensus>,
+	in_flight: HashMap<(RequestId, PeerId), BlockDataRequest>,
+	pending: Vec<BlockDataRequest>,
+	next_req_id: u64,
+}
+
+impl PolkadotProtocol {
+	/// Instantiate a polkadot protocol handler.
+	pub fn new() -> Self {
+		PolkadotProtocol {
+			peers: HashMap::new(),
+			consensus_gossip: ConsensusGossip::new(),
+			collators: HashMap::new(),
+			collating_for: None,
+			live_consensus: None,
+			in_flight: HashMap::new(),
+			pending: Vec::new(),
+			next_req_id: 1,
+		}
+	}
+
+	/// Send a statement to a validator.
+	fn send_statement(&mut self, ctx: &mut Context<Block>, _val: SessionKey, parent_hash: Hash, statement: SignedStatement) {
+		// TODO: something more targeted than gossip.
+		let raw = ::serde_json::to_vec(&Message::Statement(parent_hash, statement))
+			.expect("message serialization infallible; qed");
+
+		self.consensus_gossip.multicast_chain_specific(ctx, raw, parent_hash);
+	}
+
+	/// Fetch block data by candidate receipt.
+	fn fetch_block_data(&mut self, ctx: &mut Context<Block>, candidate: &CandidateReceipt, relay_parent: Hash) -> oneshot::Receiver<BlockData> {
+		let (tx, rx) = oneshot::channel();
+
+		self.pending.push(BlockDataRequest {
+			attempted_peers: Default::default(),
+			consensus_parent: relay_parent,
+			candidate_hash: candidate.hash(),
+			block_data_hash: candidate.block_data_hash,
+			sender: tx,
+		});
+
+		self.dispatch_pending_requests(ctx);
+		rx
+	}
+
+	/// Note new consensus session.
+	fn new_consensus(&mut self, ctx: &mut Context<Block>, mut consensus: CurrentConsensus) {
+		let parent_hash = consensus.parent_hash;
+		let old_parent = self.live_consensus.as_ref().map(|c| c.parent_hash);
+
+		for (id, info) in self.peers.iter_mut().filter(|&(_, ref info)| info.validator) {
+			send_polkadot_message(
+				ctx,
+				*id,
+				Message::SessionKey(parent_hash, consensus.local_session_key)
+			);
+
+			if let Some(key) = info.session_keys.get(&parent_hash) {
+				consensus.session_keys.insert(*key, *id);
+			}
+
+			if let Some(ref old_parent) = old_parent {
+				info.session_keys.remove(old_parent);
+			}
+		}
+
+		self.live_consensus = Some(consensus);
+		self.consensus_gossip.collect_garbage(old_parent.as_ref());
+	}
+
+	fn dispatch_pending_requests(&mut self, ctx: &mut Context<Block>) {
+		let consensus = match self.live_consensus {
+			Some(ref mut c) => c,
+			None => {
+				self.pending.clear();
+				return;
+			}
+		};
+
+		let knowledge = consensus.knowledge.lock();
+		let mut new_pending = Vec::new();
+		for mut pending in ::std::mem::replace(&mut self.pending, Vec::new()) {
+			if pending.consensus_parent != consensus.parent_hash { continue }
+
+			if let Some(entry) = knowledge.candidates.get(&pending.candidate_hash) {
+				// answer locally
+				if let Some(ref data) = entry.block_data {
+					let _ = pending.sender.send(data.clone());
+					continue;
+				}
+
+				let next_peer = entry.knows_block_data.iter()
+					.filter_map(|x| consensus.session_keys.get(x).map(|id| (*x, *id)))
+					.find(|&(ref key, _)| pending.attempted_peers.insert(*key))
+					.map(|(_, id)| id);
+
+				// dispatch to peer
+				if let Some(peer_id) = next_peer {
+					let req_id = self.next_req_id;
+					self.next_req_id += 1;
+
+					send_polkadot_message(
+						ctx,
+						peer_id,
+						Message::RequestBlockData(req_id, pending.candidate_hash)
+					);
+
+					self.in_flight.insert((req_id, peer_id), pending);
+
+					continue;
+				}
+			}
+
+			new_pending.push(pending);
+		}
+
+		self.pending = new_pending;
+	}
+
+	fn on_polkadot_message(&mut self, ctx: &mut Context<Block>, peer_id: PeerId, raw: Vec<u8>, msg: Message) {
+		match msg {
+			Message::Statement(parent_hash, _statement) =>
+				self.consensus_gossip.on_chain_specific(ctx, peer_id, raw, parent_hash),
+			Message::SessionKey(parent_hash, key) => {
+				{
+					let info = match self.peers.get_mut(&peer_id) {
+						Some(peer) => peer,
+						None => return,
+					};
+
+					if !info.validator {
+						ctx.disable_peer(peer_id);
+						return;
+					}
+
+					match self.live_consensus {
+						Some(ref mut consensus) if consensus.parent_hash == parent_hash => {
+							consensus.session_keys.insert(key, peer_id);
+						}
+						_ => {}
+					}
+
+					info.session_keys.insert(parent_hash, key);
+				}
+				self.dispatch_pending_requests(ctx);
+			}
+			Message::RequestBlockData(req_id, hash) => {
+				let block_data = self.live_consensus.as_ref()
+					.and_then(|c| c.block_data(&hash));
+
+				send_polkadot_message(ctx, peer_id, Message::BlockData(req_id, block_data));
+			}
+			Message::BlockData(req_id, data) => self.on_block_data(ctx, peer_id, req_id, data),
+		}
+	}
+
+	fn on_block_data(&mut self, ctx: &mut Context<Block>, peer_id: PeerId, req_id: RequestId, data: Option<BlockData>) {
+		match self.in_flight.remove(&(req_id, peer_id)) {
+			Some(req) => {
+				if let Some(data) = data {
+					if data.hash() == req.block_data_hash {
+						let _ = req.sender.send(data);
+						return
+					}
+				}
+
+				self.pending.push(req);
+				self.dispatch_pending_requests(ctx);
+			}
+			None => ctx.disable_peer(peer_id),
+		}
+	}
+}
+
+impl Specialization<Block> for PolkadotProtocol {
+	fn status(&self) -> Vec<u8> {
+		Status { collating_for: self.collating_for.clone() }.encode()
+	}
+
+	fn on_connect(&mut self, ctx: &mut Context<Block>, peer_id: PeerId, status: FullStatus) {
+		let local_status = match Status::decode(&mut &status.chain_status[..]) {
+			Some(status) => status,
+			None => {
+				ctx.disable_peer(peer_id);
+				return;
+			}
+		};
+
+		if let Some(ref para_id) = local_status.collating_for {
+			self.collators.entry(para_id.clone())
+				.or_insert_with(Vec::new)
+				.push(peer_id);
+		}
+
+		let validator = status.roles.iter().any(|r| *r == message::Role::Authority);
+		self.peers.insert(peer_id, PeerInfo {
+			status: local_status,
+			session_keys: Default::default(),
+			validator,
+		});
+
+		self.consensus_gossip.new_peer(ctx, peer_id, &status.roles);
+
+		if let (true, &Some(ref consensus)) = (validator, &self.live_consensus) {
+			send_polkadot_message(
+				ctx,
+				peer_id,
+				Message::SessionKey(consensus.parent_hash, consensus.local_session_key)
+			);
+		}
+
+		self.dispatch_pending_requests(ctx);
+	}
+
+	fn on_disconnect(&mut self, ctx: &mut Context<Block>, peer_id: PeerId) {
+		if let Some(info) = self.peers.remove(&peer_id) {
+			if let Some(collators) = info.status.collating_for.and_then(|id| self.collators.get_mut(&id)) {
+				if let Some(pos) = collators.iter().position(|x| x == &peer_id) {
+					collators.swap_remove(pos);
+				}
+			}
+
+			if let (true, &mut Some(ref mut consensus)) = (info.validator, &mut self.live_consensus) {
+				consensus.peer_disconnected(&info);
+			}
+
+			{
+				let pending = &mut self.pending;
+				self.in_flight.retain(|&(_, ref peer), val| {
+					let retain = peer != &peer_id;
+					if !retain {
+						let (sender, _) = oneshot::channel();
+						pending.push(::std::mem::replace(val, BlockDataRequest {
+							attempted_peers: Default::default(),
+							consensus_parent: Default::default(),
+							candidate_hash: Default::default(),
+							block_data_hash: Default::default(),
+							sender,
+						}));
+					}
+
+					retain
+				});
+			}
+			self.consensus_gossip.peer_disconnected(ctx, peer_id);
+			self.dispatch_pending_requests(ctx);
+		}
+	}
+
+	fn on_message(&mut self, ctx: &mut Context<Block>, peer_id: PeerId, message: message::Message<Block>) {
+		match message {
+			generic_message::Message::BftMessage(msg) => {
+				// TODO: check signature here? what if relevant block is unknown?
+				self.consensus_gossip.on_bft_message(ctx, peer_id, msg)
+			}
+			generic_message::Message::ChainSpecific(raw) => {
+				match serde_json::from_slice(&raw) {
+					Ok(msg) => self.on_polkadot_message(ctx, peer_id, raw, msg),
+					Err(e) => {
+						trace!(target: "p_net", "Bad message from {}: {}", peer_id, e);
+						ctx.disable_peer(peer_id);
+					}
+				}
+			}
+			_ => {}
+		}
+	}
+
+	fn on_abort(&mut self) {
+		self.consensus_gossip.abort();
+	}
+
+	fn maintain_peers(&mut self, ctx: &mut Context<Block>) {
+		self.consensus_gossip.collect_garbage(None);
+		self.dispatch_pending_requests(ctx);
+	}
+}
diff --git a/polkadot/network/src/router.rs b/polkadot/network/src/router.rs
new file mode 100644
index 0000000000..ff90502a31
--- /dev/null
+++ b/polkadot/network/src/router.rs
@@ -0,0 +1,349 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Statement routing and consensus table router implementation.
+//!
+//! During the consensus process, validators exchange statements on validity and availability
+//! of parachain candidates.
+//! The `Router` in this file hooks into the underlying network to fulfill
+//! the `TableRouter` trait from `polkadot-consensus`, which is expected to call into a shared statement table
+//! and dispatch evaluation work as necessary when new statements come in.
+
+use polkadot_api::{PolkadotApi, LocalPolkadotApi};
+use polkadot_consensus::{SharedTable, TableRouter, SignedStatement, GenericStatement, StatementProducer};
+use polkadot_primitives::{Hash, BlockId, SessionKey};
+use polkadot_primitives::parachain::{BlockData, Extrinsic, CandidateReceipt, Id as ParaId};
+
+use futures::prelude::*;
+use tokio::runtime::TaskExecutor;
+use parking_lot::Mutex;
+
+use std::collections::{HashMap, HashSet};
+use std::sync::Arc;
+
+use super::{NetworkService, Knowledge};
+
+/// Table routing implementation.
+pub struct Router<P: PolkadotApi> {
+	table: Arc<SharedTable>,
+	network: Arc<NetworkService>,
+	api: Arc<P>,
+	task_executor: TaskExecutor,
+	parent_hash: Hash,
+	knowledge: Arc<Mutex<Knowledge>>,
+	deferred_statements: Arc<Mutex<DeferredStatements>>,
+}
+
+impl<P: PolkadotApi> Router<P> {
+	pub(crate) fn new(
+		table: Arc<SharedTable>,
+		network: Arc<NetworkService>,
+		api: Arc<P>,
+		task_executor: TaskExecutor,
+		parent_hash: Hash,
+		knowledge: Arc<Mutex<Knowledge>>,
+	) -> Self {
+		Router {
+			table,
+			network,
+			api,
+			task_executor,
+			parent_hash,
+			knowledge,
+			deferred_statements: Arc::new(Mutex::new(DeferredStatements::new())),
+		}
+	}
+
+	pub(crate) fn session_key(&self) -> SessionKey {
+		self.table.session_key()
+	}
+}
+
+impl<P: PolkadotApi> Clone for Router<P> {
+	fn clone(&self) -> Self {
+		Router {
+			table: self.table.clone(),
+			network: self.network.clone(),
+			api: self.api.clone(),
+			task_executor: self.task_executor.clone(),
+			parent_hash: self.parent_hash.clone(),
+			deferred_statements: self.deferred_statements.clone(),
+			knowledge: self.knowledge.clone(),
+		}
+	}
+}
+
+impl<P: LocalPolkadotApi + Send + Sync + 'static> Router<P> {
+	/// Import a statement whose signature has been checked already.
+	pub(crate) fn import_statement(&self, statement: SignedStatement) {
+		// defer any statements for which we haven't imported the candidate yet
+		let (c_hash, parachain_index) = {
+			let candidate_data = match statement.statement {
+				GenericStatement::Candidate(ref c) => Some((c.hash(), c.parachain_index)),
+				GenericStatement::Valid(ref hash)
+					| GenericStatement::Invalid(ref hash)
+					| GenericStatement::Available(ref hash)
+					=> self.table.with_candidate(hash, |c| c.map(|c| (*hash, c.parachain_index))),
+			};
+			match candidate_data {
+				Some(x) => x,
+				None => {
+					self.deferred_statements.lock().push(statement);
+					return;
+				}
+			}
+		};
+
+		// import all statements pending on this candidate
+		let (mut statements, _traces) = if let GenericStatement::Candidate(_) = statement.statement {
+			self.deferred_statements.lock().get_deferred(&c_hash)
+		} else {
+			(Vec::new(), Vec::new())
+		};
+
+		// prepend the candidate statement.
+		statements.insert(0, statement);
+		let producers: Vec<_> = self.table.import_remote_statements(
+			self,
+			statements.iter().cloned(),
+		);
+		// dispatch future work as necessary.
+		for (producer, statement) in producers.into_iter().zip(statements) {
+			let producer = match producer {
+				Some(p) => p,
+				None => continue, // statement redundant
+			};
+
+			self.knowledge.lock().note_statement(statement.sender, &statement.statement);
+			self.dispatch_work(c_hash, producer, parachain_index);
+		}
+	}
+
+	fn dispatch_work<D, E>(&self, candidate_hash: Hash, producer: StatementProducer<D, E>, parachain: ParaId) where
+		D: Future<Item=BlockData,Error=()> + Send + 'static,
+		E: Future<Item=Extrinsic,Error=()> + Send + 'static,
+	{
+		let parent_hash = self.parent_hash.clone();
+
+		let api = self.api.clone();
+		let validate = move |collation| -> Option<bool> {
+			let id = BlockId::hash(parent_hash);
+			match ::polkadot_consensus::validate_collation(&*api, &id, &collation) {
+				Ok(()) => Some(true),
+				Err(e) => {
+					debug!(target: "p_net", "Encountered bad collation: {}", e);
+					Some(false)
+				}
+			}
+		};
+
+		let table = self.table.clone();
+		let network = self.network.clone();
+		let knowledge = self.knowledge.clone();
+
+		let work = producer.prime(validate).map(move |produced| {
+			// store the data before broadcasting statements, so other peers can fetch.
+			knowledge.lock().note_candidate(candidate_hash, produced.block_data, produced.extrinsic);
+
+			// propagate the statements
+			if let Some(validity) = produced.validity {
+				let signed = table.sign_and_import(validity.clone());
+				route_statement(&*network, &*table, parachain, parent_hash, signed);
+			}
+
+			if let Some(availability) = produced.availability {
+				let signed = table.sign_and_import(availability);
+				route_statement(&*network, &*table, parachain, parent_hash, signed);
+			}
+		});
+
+		self.task_executor.spawn(work);
+	}
+}
+
+impl<P: LocalPolkadotApi + Send> TableRouter for Router<P> {
+	type Error = ();
+	type FetchCandidate = BlockDataReceiver;
+	type FetchExtrinsic = Result<Extrinsic, Self::Error>;
+
+	fn local_candidate(&self, receipt: CandidateReceipt, block_data: BlockData, extrinsic: Extrinsic) {
+		// give to network to make available.
+		let hash = receipt.hash();
+		let para_id = receipt.parachain_index;
+		let signed = self.table.sign_and_import(GenericStatement::Candidate(receipt));
+
+		self.knowledge.lock().note_candidate(hash, Some(block_data), Some(extrinsic));
+		route_statement(&*self.network, &*self.table, para_id, self.parent_hash, signed);
+	}
+
+	fn fetch_block_data(&self, candidate: &CandidateReceipt) -> BlockDataReceiver {
+		let parent_hash = self.parent_hash;
+		let rx = self.network.with_spec(|spec, ctx| { spec.fetch_block_data(ctx, candidate, parent_hash) });
+		BlockDataReceiver { inner: rx }
+	}
+
+	fn fetch_extrinsic_data(&self, _candidate: &CandidateReceipt) -> Self::FetchExtrinsic {
+		Ok(Extrinsic)
+	}
+}
+
+/// Receiver for block data.
+pub struct BlockDataReceiver {
+	inner: Option<::futures::sync::oneshot::Receiver<BlockData>>,
+}
+
+impl Future for BlockDataReceiver {
+	type Item = BlockData;
+	type Error = ();
+
+	fn poll(&mut self) -> Poll<BlockData, ()> {
+		match self.inner {
+			Some(ref mut inner) => inner.poll().map_err(|_| ()),
+			None => return Err(()),
+		}
+	}
+}
+
+// get statement to relevant validators.
+fn route_statement(network: &NetworkService, table: &SharedTable, para_id: ParaId, parent_hash: Hash, statement: SignedStatement) {
+	let broadcast = |i: &mut Iterator<Item=&SessionKey>| {
+		let local_key = table.session_key();
+		network.with_spec(|spec, ctx| {
+			for val in i.filter(|&x| x != &local_key) {
+				spec.send_statement(ctx, *val, parent_hash, statement.clone());
+			}
+		});
+	};
+
+	let g_info = table
+		.group_info()
+		.get(&para_id)
+		.expect("statements only produced about groups which exist");
+
+	match statement.statement {
+		GenericStatement::Candidate(_) =>
+			broadcast(&mut g_info.validity_guarantors.iter().chain(g_info.availability_guarantors.iter())),
+		GenericStatement::Valid(_) | GenericStatement::Invalid(_) =>
+			broadcast(&mut g_info.validity_guarantors.iter()),
+		GenericStatement::Available(_) =>
+			broadcast(&mut g_info.availability_guarantors.iter()),
+	}
+}
+
+// A unique trace for valid statements issued by a validator.
+#[derive(Hash, PartialEq, Eq, Clone, Debug)]
+enum StatementTrace {
+	Valid(SessionKey, Hash),
+	Invalid(SessionKey, Hash),
+	Available(SessionKey, Hash),
+}
+
+// helper for deferring statements whose associated candidate is unknown.
+struct DeferredStatements {
+	deferred: HashMap<Hash, Vec<SignedStatement>>,
+	known_traces: HashSet<StatementTrace>,
+}
+
+impl DeferredStatements {
+	fn new() -> Self {
+		DeferredStatements {
+			deferred: HashMap::new(),
+			known_traces: HashSet::new(),
+		}
+	}
+
+	fn push(&mut self, statement: SignedStatement) {
+		let (hash, trace) = match statement.statement {
+			GenericStatement::Candidate(_) => return,
+			GenericStatement::Valid(hash) => (hash, StatementTrace::Valid(statement.sender, hash)),
+			GenericStatement::Invalid(hash) => (hash, StatementTrace::Invalid(statement.sender, hash)),
+			GenericStatement::Available(hash) => (hash, StatementTrace::Available(statement.sender, hash)),
+		};
+
+		if self.known_traces.insert(trace) {
+			self.deferred.entry(hash).or_insert_with(Vec::new).push(statement);
+		}
+	}
+
+	fn get_deferred(&mut self, hash: &Hash) -> (Vec<SignedStatement>, Vec<StatementTrace>) {
+		match self.deferred.remove(hash) {
+			None => (Vec::new(), Vec::new()),
+			Some(deferred) => {
+				let mut traces = Vec::new();
+				for statement in deferred.iter() {
+					let trace = match statement.statement {
+						GenericStatement::Candidate(_) => continue,
+						GenericStatement::Valid(hash) => StatementTrace::Valid(statement.sender, hash),
+						GenericStatement::Invalid(hash) => StatementTrace::Invalid(statement.sender, hash),
+						GenericStatement::Available(hash) => StatementTrace::Available(statement.sender, hash),
+					};
+
+					self.known_traces.remove(&trace);
+					traces.push(trace);
+				}
+
+				(deferred, traces)
+			}
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use substrate_primitives::H512;
+
+	#[test]
+	fn deferred_statements_works() {
+		let mut deferred = DeferredStatements::new();
+		let hash = [1; 32].into();
+		let sig = H512([2; 64]).into();
+		let sender = [255; 32].into();
+
+		let statement = SignedStatement {
+			statement: GenericStatement::Valid(hash),
+			sender,
+			signature: sig,
+		};
+
+		// pre-push.
+		{
+			let (signed, traces) = deferred.get_deferred(&hash);
+			assert!(signed.is_empty());
+			assert!(traces.is_empty());
+		}
+
+		deferred.push(statement.clone());
+		deferred.push(statement.clone());
+
+		// draining: second push should have been ignored.
+		{
+			let (signed, traces) = deferred.get_deferred(&hash);
+			assert_eq!(signed.len(), 1);
+
+			assert_eq!(traces.len(), 1);
+			assert_eq!(signed[0].clone(), statement);
+			assert_eq!(traces[0].clone(), StatementTrace::Valid(sender, hash));
+		}
+
+		// after draining
+		{
+			let (signed, traces) = deferred.get_deferred(&hash);
+			assert!(signed.is_empty());
+			assert!(traces.is_empty());
+		}
+	}
+}
diff --git a/polkadot/network/src/tests.rs b/polkadot/network/src/tests.rs
new file mode 100644
index 0000000000..feb83a416e
--- /dev/null
+++ b/polkadot/network/src/tests.rs
@@ -0,0 +1,204 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Tests for polkadot and consensus network.
+
+use super::{PolkadotProtocol, Status, CurrentConsensus, Knowledge, Message, FullStatus};
+
+use parking_lot::Mutex;
+use polkadot_consensus::GenericStatement;
+use polkadot_primitives::{Block, Hash, SessionKey};
+use polkadot_primitives::parachain::{CandidateReceipt, HeadData, BlockData};
+use codec::Slicable;
+use substrate_network::{PeerId, PeerInfo, ClientHandle, Context, message::Message as SubstrateMessage, message::Role, specialization::Specialization, generic_message::Message as GenericMessage};
+
+use std::sync::Arc;
+use futures::Future;
+
+#[derive(Default)]
+struct TestContext {
+	disabled: Vec<PeerId>,
+	disconnected: Vec<PeerId>,
+	messages: Vec<(PeerId, SubstrateMessage<Block>)>,
+}
+
+impl Context<Block> for TestContext {
+	fn client(&self) -> &ClientHandle<Block> {
+		unimplemented!()
+	}
+
+	fn disable_peer(&mut self, peer: PeerId) {
+		self.disabled.push(peer);
+	}
+
+	fn disconnect_peer(&mut self, peer: PeerId) {
+		self.disconnected.push(peer);
+	}
+
+	fn peer_info(&self, _peer: PeerId) -> Option<PeerInfo<Block>> {
+		unimplemented!()
+	}
+
+	fn send_message(&mut self, peer_id: PeerId, data: SubstrateMessage<Block>) {
+		self.messages.push((peer_id, data))
+	}
+}
+
+impl TestContext {
+	fn has_message(&self, to: PeerId, message: Message) -> bool {
+		use substrate_network::generic_message::Message as GenericMessage;
+
+		let encoded = ::serde_json::to_vec(&message).unwrap();
+		self.messages.iter().any(|&(ref peer, ref msg)| match msg {
+			GenericMessage::ChainSpecific(ref data) => peer == &to && data == &encoded,
+			_ => false,
+		})
+	}
+}
+
+fn make_status(status: &Status, roles: Vec<Role>) -> FullStatus {
+	FullStatus {
+		version: 1,
+		roles,
+		best_number: 0,
+		best_hash: Default::default(),
+		genesis_hash: Default::default(),
+		chain_status: status.encode(),
+	}
+}
+
+fn make_consensus(parent_hash: Hash, local_key: SessionKey) -> (CurrentConsensus, Arc<Mutex<Knowledge>>) {
+	let knowledge = Arc::new(Mutex::new(Knowledge::new()));
+	let c = CurrentConsensus {
+		knowledge: knowledge.clone(),
+		parent_hash,
+		session_keys: Default::default(),
+		local_session_key: local_key,
+	};
+
+	(c, knowledge)
+}
+
+fn on_message(protocol: &mut PolkadotProtocol, ctx: &mut TestContext, from: PeerId, message: Message) {
+	let encoded = ::serde_json::to_vec(&message).unwrap();
+	protocol.on_message(ctx, from, GenericMessage::ChainSpecific(encoded));
+}
+
+#[test]
+fn sends_session_key() {
+	let mut protocol = PolkadotProtocol::new();
+
+	let peer_a = 1;
+	let peer_b = 2;
+	let parent_hash = [0; 32].into();
+	let local_key = [1; 32].into();
+
+	let status = Status { collating_for: None };
+
+	{
+		let mut ctx = TestContext::default();
+		protocol.on_connect(&mut ctx, peer_a, make_status(&status, vec![Role::Authority]));
+		assert!(ctx.messages.is_empty());
+	}
+
+	{
+		let mut ctx = TestContext::default();
+		let (consensus, _knowledge) = make_consensus(parent_hash, local_key);
+		protocol.new_consensus(&mut ctx, consensus);
+
+		assert!(ctx.has_message(peer_a, Message::SessionKey(parent_hash, local_key)));
+	}
+
+	{
+		let mut ctx = TestContext::default();
+		protocol.on_connect(&mut ctx, peer_b, make_status(&status, vec![Role::Authority]));
+		assert!(ctx.has_message(peer_b, Message::SessionKey(parent_hash, local_key)));
+	}
+}
+
+#[test]
+fn fetches_from_those_with_knowledge() {
+	let mut protocol = PolkadotProtocol::new();
+
+	let peer_a = 1;
+	let peer_b = 2;
+	let parent_hash = [0; 32].into();
+	let local_key = [1; 32].into();
+
+	let block_data = BlockData(vec![1, 2, 3, 4]);
+	let block_data_hash = block_data.hash();
+	let candidate_receipt = CandidateReceipt {
+		parachain_index: 5.into(),
+		collator: [255; 32].into(),
+		head_data: HeadData(vec![9, 9, 9]),
+		balance_uploads: Vec::new(),
+		egress_queue_roots: Vec::new(),
+		fees: 1_000_000,
+		block_data_hash,
+	};
+
+	let candidate_hash = candidate_receipt.hash();
+	let a_key = [3; 32].into();
+	let b_key = [4; 32].into();
+
+	let status = Status { collating_for: None };
+
+	let (consensus, knowledge) = make_consensus(parent_hash, local_key);
+	protocol.new_consensus(&mut TestContext::default(), consensus);
+
+	knowledge.lock().note_statement(a_key, &GenericStatement::Valid(candidate_hash));
+	let recv = protocol.fetch_block_data(&mut TestContext::default(), &candidate_receipt, parent_hash);
+
+	// connect peer A
+	{
+		let mut ctx = TestContext::default();
+		protocol.on_connect(&mut ctx, peer_a, make_status(&status, vec![Role::Authority]));
+		assert!(ctx.has_message(peer_a, Message::SessionKey(parent_hash, local_key)));
+	}
+
+	// peer A gives session key and gets asked for data.
+	{
+		let mut ctx = TestContext::default();
+		on_message(&mut protocol, &mut ctx, peer_a, Message::SessionKey(parent_hash, a_key));
+		assert!(ctx.has_message(peer_a, Message::RequestBlockData(1, candidate_hash)));
+	}
+
+	knowledge.lock().note_statement(b_key, &GenericStatement::Valid(candidate_hash));
+
+	// peer B connects and sends session key. request already assigned to A
+	{
+		let mut ctx = TestContext::default();
+		protocol.on_connect(&mut ctx, peer_b, make_status(&status, vec![Role::Authority]));
+		on_message(&mut protocol, &mut ctx, peer_b, Message::SessionKey(parent_hash, b_key));
+		assert!(!ctx.has_message(peer_b, Message::RequestBlockData(2, candidate_hash)));
+
+	}
+
+	// peer A disconnects, triggering reassignment
+	{
+		let mut ctx = TestContext::default();
+		protocol.on_disconnect(&mut ctx, peer_a);
+		assert!(ctx.has_message(peer_b, Message::RequestBlockData(2, candidate_hash)));
+	}
+
+	// peer B comes back with block data.
+	{
+		let mut ctx = TestContext::default();
+		on_message(&mut protocol, &mut ctx, peer_b, Message::BlockData(2, Some(block_data.clone())));
+		drop(protocol);
+		assert_eq!(recv.wait().unwrap(), block_data);
+	}
+}
diff --git a/polkadot/primitives/src/parachain.rs b/polkadot/primitives/src/parachain.rs
index 9f803810e4..79b12aeecd 100644
--- a/polkadot/primitives/src/parachain.rs
+++ b/polkadot/primitives/src/parachain.rs
@@ -172,6 +172,8 @@ pub struct CandidateReceipt {
 	pub egress_queue_roots: Vec<(Id, Hash)>,
 	/// Fees paid from the chain to the relay chain validators
 	pub fees: u64,
+	/// blake2-256 Hash of block data.
+	pub block_data_hash: Hash,
 }
 
 impl Slicable for CandidateReceipt {
@@ -184,6 +186,7 @@ impl Slicable for CandidateReceipt {
 		self.balance_uploads.using_encoded(|s| v.extend(s));
 		self.egress_queue_roots.using_encoded(|s| v.extend(s));
 		self.fees.using_encoded(|s| v.extend(s));
+		self.block_data_hash.using_encoded(|s| v.extend(s));
 
 		v
 	}
@@ -196,6 +199,7 @@ impl Slicable for CandidateReceipt {
 			balance_uploads: Slicable::decode(input)?,
 			egress_queue_roots: Slicable::decode(input)?,
 			fees: Slicable::decode(input)?,
+			block_data_hash: Slicable::decode(input)?,
 		})
 	}
 }
@@ -243,6 +247,15 @@ pub struct ConsolidatedIngress(pub Vec<(Id, Vec<Message>)>);
 #[cfg_attr(feature = "std", derive(Serialize, Deserialize, Debug))]
 pub struct BlockData(#[cfg_attr(feature = "std", serde(with="bytes"))] pub Vec<u8>);
 
+impl BlockData {
+	/// Compute hash of block data.
+	#[cfg(feature = "std")]
+	pub fn hash(&self) -> Hash {
+		use runtime_primitives::traits::{BlakeTwo256, Hashing};
+		BlakeTwo256::hash(&self.0[..])
+	}
+}
+
 /// Parachain header raw bytes wrapper type.
 #[derive(PartialEq, Eq)]
 #[cfg_attr(feature = "std", derive(Serialize, Deserialize, Debug))]
@@ -273,19 +286,9 @@ impl Slicable for Activity {
 	}
 }
 
-#[derive(Clone, Copy, PartialEq, Eq)]
-#[cfg_attr(feature = "std", derive(Debug))]
-#[repr(u8)]
-enum StatementKind {
-	Candidate = 1,
-	Valid = 2,
-	Invalid = 3,
-	Available = 4,
-}
-
 /// Statements which can be made about parachain candidates.
 #[derive(Clone, PartialEq, Eq)]
-#[cfg_attr(feature = "std", derive(Debug))]
+#[cfg_attr(feature = "std", derive(Debug, Serialize, Deserialize))]
 pub enum Statement {
 	/// Proposal of a parachain candidate.
 	Candidate(CandidateReceipt),
@@ -296,47 +299,3 @@ pub enum Statement {
 	/// Vote to advance round after inactive primary.
 	Available(Hash),
 }
-
-impl Slicable for Statement {
-	fn encode(&self) -> Vec<u8> {
-		let mut v = Vec::new();
-		match *self {
-			Statement::Candidate(ref candidate) => {
-				v.push(StatementKind::Candidate as u8);
-				candidate.using_encoded(|s| v.extend(s));
-			}
-			Statement::Valid(ref hash) => {
-				v.push(StatementKind::Valid as u8);
-				hash.using_encoded(|s| v.extend(s));
-			}
-			Statement::Invalid(ref hash) => {
-				v.push(StatementKind::Invalid as u8);
-				hash.using_encoded(|s| v.extend(s));
-			}
-			Statement::Available(ref hash) => {
-				v.push(StatementKind::Available as u8);
-				hash.using_encoded(|s| v.extend(s));
-			}
-		}
-
-		v
-	}
-
-	fn decode<I: Input>(value: &mut I) -> Option<Self> {
-		match value.read_byte() {
-			Some(x) if x == StatementKind::Candidate as u8 => {
-				Slicable::decode(value).map(Statement::Candidate)
-			}
-			Some(x) if x == StatementKind::Valid as u8 => {
-				Slicable::decode(value).map(Statement::Valid)
-			}
-			Some(x) if x == StatementKind::Invalid as u8 => {
-				Slicable::decode(value).map(Statement::Invalid)
-			}
-			Some(x) if x == StatementKind::Available as u8 => {
-				Slicable::decode(value).map(Statement::Available)
-			}
-			_ => None,
-		}
-	}
-}
diff --git a/polkadot/runtime/src/lib.rs b/polkadot/runtime/src/lib.rs
index c6a7cfdc83..b74e5754e0 100644
--- a/polkadot/runtime/src/lib.rs
+++ b/polkadot/runtime/src/lib.rs
@@ -218,6 +218,7 @@ impl_outer_dispatch! {
 		Democracy = 5,
 		Council = 6,
 		CouncilVoting = 7,
+		Parachains = 8,
 	}
 }
 
@@ -395,4 +396,10 @@ mod tests {
 		let v = Slicable::encode(&xt);
 		assert_eq!(Extrinsic::decode(&mut &v[..]).unwrap(), xt);
 	}
+
+	#[test]
+	fn parachain_calls_are_privcall() {
+		let _register = PrivCall::Parachains(parachains::PrivCall::register_parachain(0.into(), vec![1, 2, 3], vec![]));
+		let _deregister = PrivCall::Parachains(parachains::PrivCall::deregister_parachain(0.into()));
+	}
 }
diff --git a/polkadot/runtime/src/parachains.rs b/polkadot/runtime/src/parachains.rs
index 3625633adf..0ac9522ea0 100644
--- a/polkadot/runtime/src/parachains.rs
+++ b/polkadot/runtime/src/parachains.rs
@@ -16,15 +16,14 @@
 
 //! Main parachains logic. For now this is just the determination of which validators do what.
 
-use primitives;
 use rstd::prelude::*;
-use codec::{Slicable, Joiner};
+use codec::Slicable;
 
-use runtime_primitives::traits::{Executable, RefInto, MaybeEmpty};
+use runtime_primitives::traits::{Hashing, BlakeTwo256, Executable, RefInto, MaybeEmpty};
 use primitives::parachain::{Id, Chain, DutyRoster, CandidateReceipt};
 use {system, session};
 
-use substrate_runtime_support::{Hashable, StorageValue, StorageMap};
+use substrate_runtime_support::{StorageValue, StorageMap};
 use substrate_runtime_support::dispatch::Result;
 
 #[cfg(any(feature = "std", test))]
@@ -33,7 +32,7 @@ use rstd::marker::PhantomData;
 #[cfg(any(feature = "std", test))]
 use {runtime_io, runtime_primitives};
 
-pub trait Trait: session::Trait<Hash = primitives::Hash> {
+pub trait Trait: system::Trait<Hash = ::primitives::Hash> + session::Trait {
 	/// The position of the set_heads call in the block.
 	const SET_POSITION: u32;
 
@@ -43,13 +42,19 @@ pub trait Trait: session::Trait<Hash = primitives::Hash> {
 decl_module! {
 	/// Parachains module.
 	pub struct Module<T: Trait>;
-
 	/// Call type for parachains.
 	#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
 	pub enum Call where aux: <T as Trait>::PublicAux {
 		// provide candidate receipts for parachains, in ascending order by id.
 		fn set_heads(aux, heads: Vec<CandidateReceipt>) -> Result = 0;
 	}
+
+	/// Private calls for parachains.
+	#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+	pub enum PrivCall {
+		fn register_parachain(id: Id, code: Vec<u8>, initial_head_data: Vec<u8>) -> Result = 0;
+		fn deregister_parachain(id: Id) -> Result = 1;
+	}
 }
 
 decl_storage! {
@@ -83,8 +88,9 @@ impl<T: Trait> Module<T> {
 
 		let mut roles_gua = roles_val.clone();
 
-		let random_seed = system::Module::<T>::random_seed();
-		let mut seed = random_seed.to_vec().and(b"validator_role_pairs").blake2_256();
+		let mut random_seed = system::Module::<T>::random_seed().to_vec();
+		random_seed.extend(b"validator_role_pairs");
+		let mut seed = BlakeTwo256::hash(&random_seed);
 
 		// shuffle
 		for i in 0..(validator_count - 1) {
@@ -100,7 +106,7 @@ impl<T: Trait> Module<T> {
 
 			if offset == 24 {
 				// into the last 8 bytes - rehash to gather new entropy
-				seed = seed.blake2_256();
+				seed = BlakeTwo256::hash(&seed);
 			}
 
 			// exchange last item with randomly chosen first.
@@ -116,20 +122,22 @@ impl<T: Trait> Module<T> {
 
 	/// Register a parachain with given code.
 	/// Fails if given ID is already used.
-	pub fn register_parachain(id: Id, code: Vec<u8>, initial_head_data: Vec<u8>) {
+	pub fn register_parachain(id: Id, code: Vec<u8>, initial_head_data: Vec<u8>) -> Result {
 		let mut parachains = Self::active_parachains();
 		match parachains.binary_search(&id) {
-			Ok(_) => panic!("Parachain with id {} already exists", id.into_inner()),
+			Ok(_) => fail!("Parachain already exists"),
 			Err(idx) => parachains.insert(idx, id),
 		}
 
 		<Code<T>>::insert(id, code);
 		<Parachains<T>>::put(parachains);
 		<Heads<T>>::insert(id, initial_head_data);
+
+		Ok(())
 	}
 
 	/// Deregister a parachain with given id
-	pub fn deregister_parachain(id: Id) {
+	pub fn deregister_parachain(id: Id) -> Result {
 		let mut parachains = Self::active_parachains();
 		match parachains.binary_search(&id) {
 			Ok(idx) => { parachains.remove(idx); }
@@ -139,6 +147,7 @@ impl<T: Trait> Module<T> {
 		<Code<T>>::remove(id);
 		<Heads<T>>::remove(id);
 		<Parachains<T>>::put(parachains);
+		Ok(())
 	}
 
 	fn set_heads(aux: &<T as Trait>::PublicAux, heads: Vec<CandidateReceipt>) -> Result {
@@ -317,12 +326,12 @@ mod tests {
 			assert_eq!(Parachains::parachain_code(&5u32.into()), Some(vec![1,2,3]));
 			assert_eq!(Parachains::parachain_code(&100u32.into()), Some(vec![4,5,6]));
 
-			Parachains::register_parachain(99u32.into(), vec![7,8,9], vec![1, 1, 1]);
+			Parachains::register_parachain(99u32.into(), vec![7,8,9], vec![1, 1, 1]).unwrap();
 
 			assert_eq!(Parachains::active_parachains(), vec![5u32.into(), 99u32.into(), 100u32.into()]);
 			assert_eq!(Parachains::parachain_code(&99u32.into()), Some(vec![7,8,9]));
 
-			Parachains::deregister_parachain(5u32.into());
+			Parachains::deregister_parachain(5u32.into()).unwrap();
 
 			assert_eq!(Parachains::active_parachains(), vec![99u32.into(), 100u32.into()]);
 			assert_eq!(Parachains::parachain_code(&5u32.into()), None);
diff --git a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm
index 7082ac45b4..a522d9b062 100644
Binary files a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm and b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm differ
diff --git a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm
index 4505fd7518..6a7103ef4e 100755
Binary files a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm and b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm differ
diff --git a/polkadot/service/Cargo.toml b/polkadot/service/Cargo.toml
index cd8992c855..f17c50b0d9 100644
--- a/polkadot/service/Cargo.toml
+++ b/polkadot/service/Cargo.toml
@@ -6,13 +6,12 @@ authors = ["Parity Technologies <admin@parity.io>"]
 [dependencies]
 futures = "0.1.17"
 parking_lot = "0.4"
-tokio-timer = "0.1.2"
 error-chain = "0.12"
 lazy_static = "1.0"
 log = "0.3"
 slog = "^2"
 clap = "2.27"
-tokio-core = "0.1.12"
+tokio = "0.1.7"
 exit-future = "0.1"
 serde = "1.0"
 serde_json = "1.0"
@@ -25,6 +24,7 @@ polkadot-consensus = { path = "../consensus" }
 polkadot-executor = { path = "../executor" }
 polkadot-api = { path = "../api" }
 polkadot-transaction-pool = { path = "../transaction-pool" }
+polkadot-network = { path = "../network" }
 substrate-keystore = { path = "../../substrate/keystore" }
 substrate-runtime-io = { path = "../../substrate/runtime-io" }
 substrate-runtime-primitives = { path = "../../substrate/runtime/primitives" }
diff --git a/polkadot/service/src/components.rs b/polkadot/service/src/components.rs
index b6709b111f..b7b5c3c96a 100644
--- a/polkadot/service/src/components.rs
+++ b/polkadot/service/src/components.rs
@@ -18,20 +18,22 @@
 
 use std::collections::HashMap;
 use std::sync::Arc;
-use client::{self, Client};
+use chain_spec::ChainSpec;
 use client_db;
+use client::{self, Client};
 use codec::{self, Slicable};
 use consensus;
+use error;
 use keystore::Store as Keystore;
-use network;
+use network::{self, OnDemand};
 use polkadot_api;
 use polkadot_executor::Executor as LocalDispatch;
+use polkadot_network::NetworkService;
 use polkadot_primitives::{Block, BlockId, Hash};
 use state_machine;
 use substrate_executor::NativeExecutor;
 use transaction_pool::{self, TransactionPool};
-use error;
-use chain_spec::ChainSpec;
+use tokio::runtime::TaskExecutor;
 
 /// Code executor.
 pub type CodeExecutor = NativeExecutor<LocalDispatch>;
@@ -49,7 +51,7 @@ pub trait Components {
 
 	/// Create client.
 	fn build_client(&self, settings: client_db::DatabaseSettings, executor: CodeExecutor, chain_spec: &ChainSpec)
-		-> Result<(Arc<Client<Self::Backend, Self::Executor, Block>>, Option<Arc<network::OnDemand<Block, network::Service<Block>>>>), error::Error>;
+		-> Result<(Arc<Client<Self::Backend, Self::Executor, Block>>, Option<Arc<OnDemand<Block, NetworkService>>>), error::Error>;
 
 	/// Create api.
 	fn build_api(&self, client: Arc<Client<Self::Backend, Self::Executor, Block>>) -> Arc<Self::Api>;
@@ -59,7 +61,14 @@ pub trait Components {
 		-> Arc<network::TransactionPool<Block>>;
 
 	/// Create consensus service.
-	fn build_consensus(&self, client: Arc<Client<Self::Backend, Self::Executor, Block>>, network: Arc<network::Service<Block>>, tx_pool: Arc<TransactionPool<Self::Api>>, keystore: &Keystore)
+	fn build_consensus(
+		&self,
+		client: Arc<Client<Self::Backend, Self::Executor, Block>>,
+		network: Arc<NetworkService>,
+		tx_pool: Arc<TransactionPool<Self::Api>>,
+		keystore: &Keystore,
+		task_executor: TaskExecutor,
+	)
 		-> Result<Option<consensus::Service>, error::Error>;
 }
 
@@ -75,7 +84,7 @@ impl Components for FullComponents {
 	type Executor = client::LocalCallExecutor<client_db::Backend<Block>, NativeExecutor<LocalDispatch>>;
 
 	fn build_client(&self, db_settings: client_db::DatabaseSettings, executor: CodeExecutor, chain_spec: &ChainSpec)
-		-> Result<(Arc<client::Client<Self::Backend, Self::Executor, Block>>, Option<Arc<network::OnDemand<Block, network::Service<Block>>>>), error::Error> {
+		-> Result<(Arc<client::Client<Self::Backend, Self::Executor, Block>>, Option<Arc<OnDemand<Block, NetworkService>>>), error::Error> {
 		Ok((Arc::new(client_db::new_client(db_settings, executor, chain_spec)?), None))
 	}
 
@@ -92,20 +101,31 @@ impl Components for FullComponents {
 		})
 	}
 
-	fn build_consensus(&self, client: Arc<client::Client<Self::Backend, Self::Executor, Block>>, network: Arc<network::Service<Block>>, tx_pool: Arc<TransactionPool<Self::Api>>, keystore: &Keystore)
-		-> Result<Option<consensus::Service>, error::Error> {
+	fn build_consensus(
+		&self,
+		client: Arc<client::Client<Self::Backend, Self::Executor, Block>>,
+		network: Arc<NetworkService>,
+		tx_pool: Arc<TransactionPool<Self::Api>>,
+		keystore: &Keystore,
+		task_executor: TaskExecutor,
+	)
+		-> Result<Option<consensus::Service>, error::Error>
+	{
 		if !self.is_validator {
 			return Ok(None);
 		}
 
 		// Load the first available key
 		let key = keystore.load(&keystore.contents()?[0], "")?;
-		info!("Using authority key: {}", key.public());
+		info!("Using authority key {}", key.public());
+
+		let consensus_net = ::polkadot_network::consensus::ConsensusNetwork::new(network, client.clone());
 		Ok(Some(consensus::Service::new(
 			client.clone(),
 			client.clone(),
-			network.clone(),
+			consensus_net,
 			tx_pool.clone(),
+			task_executor,
 			::std::time::Duration::from_millis(4000), // TODO: dynamic
 			key,
 		)))
@@ -116,14 +136,14 @@ impl Components for FullComponents {
 pub struct LightComponents;
 
 impl Components for LightComponents {
-	type Backend = client::light::backend::Backend<client_db::light::LightStorage<Block>, network::OnDemand<Block, network::Service<Block>>>;
+	type Backend = client::light::backend::Backend<client_db::light::LightStorage<Block>, network::OnDemand<Block, NetworkService>>;
 	type Api = polkadot_api::light::RemotePolkadotApiWrapper<Self::Backend, Self::Executor>;
 	type Executor = client::light::call_executor::RemoteCallExecutor<
-		client::light::blockchain::Blockchain<client_db::light::LightStorage<Block>, network::OnDemand<Block, network::Service<Block>>>,
-		network::OnDemand<Block, network::Service<Block>>>;
+		client::light::blockchain::Blockchain<client_db::light::LightStorage<Block>, network::OnDemand<Block, NetworkService>>,
+		network::OnDemand<Block, NetworkService>>;
 
 	fn build_client(&self, db_settings: client_db::DatabaseSettings, executor: CodeExecutor, spec: &ChainSpec)
-		-> Result<(Arc<client::Client<Self::Backend, Self::Executor, Block>>, Option<Arc<network::OnDemand<Block, network::Service<Block>>>>), error::Error> {
+		-> Result<(Arc<client::Client<Self::Backend, Self::Executor, Block>>, Option<Arc<OnDemand<Block, NetworkService>>>), error::Error> {
 		let db_storage = client_db::light::LightStorage::new(db_settings)?;
 		let light_blockchain = client::light::new_light_blockchain(db_storage);
 		let fetch_checker = Arc::new(client::light::new_fetch_checker(light_blockchain.clone(), executor));
@@ -146,8 +166,16 @@ impl Components for LightComponents {
 		})
 	}
 
-	fn build_consensus(&self, _client: Arc<client::Client<Self::Backend, Self::Executor, Block>>, _network: Arc<network::Service<Block>>, _tx_pool: Arc<TransactionPool<Self::Api>>, _keystore: &Keystore)
-		-> Result<Option<consensus::Service>, error::Error> {
+	fn build_consensus(
+		&self,
+		_client: Arc<client::Client<Self::Backend, Self::Executor, Block>>,
+		_network: Arc<NetworkService>,
+		_tx_pool: Arc<TransactionPool<Self::Api>>,
+		_keystore: &Keystore,
+		_task_executor: TaskExecutor,
+	)
+		-> Result<Option<consensus::Service>, error::Error>
+	{
 		Ok(None)
 	}
 }
diff --git a/polkadot/service/src/lib.rs b/polkadot/service/src/lib.rs
index 7e62712917..6a613f99f4 100644
--- a/polkadot/service/src/lib.rs
+++ b/polkadot/service/src/lib.rs
@@ -21,7 +21,6 @@ extern crate futures;
 extern crate ed25519;
 extern crate clap;
 extern crate exit_future;
-extern crate tokio_timer;
 extern crate serde;
 extern crate serde_json;
 extern crate polkadot_primitives;
@@ -30,18 +29,17 @@ extern crate polkadot_executor;
 extern crate polkadot_api;
 extern crate polkadot_consensus as consensus;
 extern crate polkadot_transaction_pool as transaction_pool;
+extern crate polkadot_network;
 extern crate substrate_keystore as keystore;
-extern crate substrate_runtime_io as runtime_io;
 extern crate substrate_primitives as primitives;
 extern crate substrate_runtime_primitives as runtime_primitives;
 extern crate substrate_network as network;
 extern crate substrate_codec as codec;
 extern crate substrate_executor;
 extern crate substrate_state_machine as state_machine;
-
-extern crate tokio_core;
 extern crate substrate_client as client;
 extern crate substrate_client_db as client_db;
+extern crate tokio;
 
 #[macro_use]
 extern crate substrate_telemetry;
@@ -62,9 +60,7 @@ mod config;
 mod chain_spec;
 
 use std::sync::Arc;
-use std::thread;
 use futures::prelude::*;
-use tokio_core::reactor::Core;
 use transaction_pool::TransactionPool;
 use keystore::Store as Keystore;
 use polkadot_api::PolkadotApi;
@@ -72,6 +68,8 @@ use polkadot_primitives::{Block, BlockId, Hash};
 use client::{Client, BlockchainEvents};
 use network::ManageNetwork;
 use exit_future::Signal;
+use polkadot_network::{NetworkService, PolkadotProtocol};
+use tokio::runtime::TaskExecutor;
 
 pub use self::error::{ErrorKind, Error};
 pub use self::components::{Components, FullComponents, LightComponents};
@@ -80,23 +78,22 @@ pub use chain_spec::ChainSpec;
 
 /// Polkadot service.
 pub struct Service<Components: components::Components> {
-	thread: Option<thread::JoinHandle<()>>,
 	client: Arc<Client<Components::Backend, Components::Executor, Block>>,
-	network: Arc<network::Service<Block>>,
+	network: Arc<NetworkService>,
 	transaction_pool: Arc<TransactionPool<Components::Api>>,
 	signal: Option<Signal>,
 	_consensus: Option<consensus::Service>,
 }
 
 /// Creates light client and register protocol with the network service
-pub fn new_light(config: Configuration) -> Result<Service<components::LightComponents>, error::Error> {
-	Service::new(components::LightComponents, config)
+pub fn new_light(config: Configuration, executor: TaskExecutor) -> Result<Service<components::LightComponents>, error::Error> {
+	Service::new(components::LightComponents, config, executor)
 }
 
 /// Creates full client and register protocol with the network service
-pub fn new_full(config: Configuration) -> Result<Service<components::FullComponents>, error::Error> {
-	let is_validator = (config.roles & Role::VALIDATOR) == Role::VALIDATOR;
-	Service::new(components::FullComponents { is_validator }, config)
+pub fn new_full(config: Configuration, executor: TaskExecutor) -> Result<Service<components::FullComponents>, error::Error> {
+	let is_validator = (config.roles & Role::AUTHORITY) == Role::AUTHORITY;
+	Service::new(components::FullComponents { is_validator }, config, executor)
 }
 
 /// Creates bare client without any networking.
@@ -112,7 +109,7 @@ pub fn new_client(config: Configuration) -> Result<Arc<Client<
 		pruning: config.pruning,
 	};
 	let executor = polkadot_executor::Executor::new();
-	let is_validator = (config.roles & Role::VALIDATOR) == Role::VALIDATOR;
+	let is_validator = (config.roles & Role::AUTHORITY) == Role::AUTHORITY;
 	let components = components::FullComponents { is_validator };
 	let (client, _) = components.build_client(db_settings, executor, &config.chain_spec)?;
 	Ok(client)
@@ -124,9 +121,7 @@ impl<Components> Service<Components>
 		client::error::Error: From<<<<Components as components::Components>::Backend as client::backend::Backend<Block>>::State as state_machine::Backend>::Error>,
 {
 	/// Creates and register protocol with the network service
-	fn new(components: Components, config: Configuration) -> Result<Self, error::Error> {
-		use std::sync::Barrier;
-
+	fn new(components: Components, config: Configuration, task_executor: TaskExecutor) -> Result<Self, error::Error> {
 		let (signal, exit) = ::exit_future::signal();
 
 		// Create client
@@ -165,61 +160,55 @@ impl<Components> Service<Components>
 			chain: client.clone(),
 			on_demand: on_demand.clone().map(|d| d as Arc<network::OnDemandService<Block>>),
 			transaction_pool: transaction_pool_adapter,
+			specialization: PolkadotProtocol::new(),
 		};
-		let network = network::Service::new(network_params)?;
-		let barrier = ::std::sync::Arc::new(Barrier::new(2));
+
+		let network = network::Service::new(network_params, ::polkadot_network::DOT_PROTOCOL_ID)?;
 		on_demand.map(|on_demand| on_demand.set_service_link(Arc::downgrade(&network)));
 
-		let thread = {
-			let client = client.clone();
+		network.start_network();
+
+		{
+			// block notifications
 			let network = network.clone();
 			let txpool = transaction_pool.clone();
 
-			let thread_barrier = barrier.clone();
-			thread::spawn(move || {
-				network.start_network();
+			let events = client.import_notification_stream()
+				.for_each(move |notification| {
+					network.on_block_imported(notification.hash, &notification.header);
+					prune_imported(&*txpool, notification.hash);
+					Ok(())
+				})
+				.select(exit.clone())
+				.then(|_| Ok(()));
+			task_executor.spawn(events);
+		}
 
-				thread_barrier.wait();
-				let mut core = Core::new().expect("tokio::Core could not be created");
+		{
+			// transaction notifications
+			let network = network.clone();
+			let events = transaction_pool.import_notification_stream()
+				// TODO [ToDr] Consider throttling?
+				.for_each(move |_| {
+					network.trigger_repropagate();
+					Ok(())
+				})
+				.select(exit.clone())
+				.then(|_| Ok(()));
 
-				// block notifications
-				let network1 = network.clone();
-				let txpool1 = txpool.clone();
-
-				let events = client.import_notification_stream()
-					.for_each(move |notification| {
-						network1.on_block_imported(notification.hash, &notification.header);
-						prune_imported(&*txpool1, notification.hash);
-
-						Ok(())
-					});
-				core.handle().spawn(events);
-
-				// transaction notifications
-				let events = txpool.import_notification_stream()
-					// TODO [ToDr] Consider throttling?
-					.for_each(move |_| {
-						network.trigger_repropagate();
-						Ok(())
-					});
-				core.handle().spawn(events);
-
-				if let Err(e) = core.run(exit) {
-					debug!("Polkadot service event loop shutdown with {:?}", e);
-				}
-				debug!("Polkadot service shutdown");
-			})
-		};
-
-		// wait for the network to start up before starting the consensus
-		// service.
-		barrier.wait();
+			task_executor.spawn(events);
+		}
 
 		// Spin consensus service if configured
-		let consensus_service = components.build_consensus(client.clone(), network.clone(), transaction_pool.clone(), &keystore)?;
+		let consensus_service = components.build_consensus(
+			client.clone(),
+			network.clone(),
+			transaction_pool.clone(),
+			&keystore,
+			task_executor,
+		)?;
 
 		Ok(Service {
-			thread: Some(thread),
 			client: client,
 			network: network,
 			transaction_pool: transaction_pool,
@@ -234,7 +223,7 @@ impl<Components> Service<Components>
 	}
 
 	/// Get shared network instance.
-	pub fn network(&self) -> Arc<network::Service<Block>> {
+	pub fn network(&self) -> Arc<NetworkService> {
 		self.network.clone()
 	}
 
@@ -260,14 +249,12 @@ pub fn prune_imported<A>(pool: &TransactionPool<A>, hash: Hash)
 
 impl<Components> Drop for Service<Components> where Components: components::Components {
 	fn drop(&mut self) {
+		debug!(target: "service", "Polkadot service shutdown");
+
 		self.network.stop_network();
 
 		if let Some(signal) = self.signal.take() {
 			signal.fire();
 		}
-
-		if let Some(thread) = self.thread.take() {
-			thread.join().expect("The service thread has panicked");
-		}
 	}
 }
diff --git a/polkadot/statement-table/Cargo.toml b/polkadot/statement-table/Cargo.toml
index 5c8a61e81d..2e9120a4f0 100644
--- a/polkadot/statement-table/Cargo.toml
+++ b/polkadot/statement-table/Cargo.toml
@@ -4,5 +4,8 @@ version = "0.1.0"
 authors = ["Parity Technologies <admin@parity.io>"]
 
 [dependencies]
+substrate-codec = { path = "../../substrate/codec" }
 substrate-primitives = { path = "../../substrate/primitives" }
 polkadot-primitives = { path = "../primitives" }
+serde = "1.0"
+serde_derive = "1.0"
diff --git a/polkadot/statement-table/src/generic.rs b/polkadot/statement-table/src/generic.rs
index 4436730b3e..8e7fa48e2e 100644
--- a/polkadot/statement-table/src/generic.rs
+++ b/polkadot/statement-table/src/generic.rs
@@ -27,26 +27,11 @@
 //! propose and attest to validity of candidates, and those who can only attest
 //! to availability.
 
-use std::collections::HashSet;
 use std::collections::hash_map::{HashMap, Entry};
 use std::hash::Hash;
 use std::fmt::Debug;
 
-/// A batch of statements to send out.
-pub trait StatementBatch<V, T> {
-	/// Get the target authorities of these statements.
-	fn targets(&self) -> &[V];
-
-	/// If the batch is empty.
-	fn is_empty(&self) -> bool;
-
-	/// Push a statement onto the batch. Returns false when the batch is full.
-	///
-	/// This is meant to do work like incrementally serializing the statements
-	/// into a vector of bytes while making sure the length is below a certain
-	/// amount.
-	fn push(&mut self, statement: T) -> bool;
-}
+use codec::{Slicable, Input};
 
 /// Context for the statement table.
 pub trait Context {
@@ -85,7 +70,7 @@ pub trait Context {
 }
 
 /// Statements circulated among peers.
-#[derive(PartialEq, Eq, Debug, Clone)]
+#[derive(PartialEq, Eq, Debug, Clone, Serialize, Deserialize)]
 pub enum Statement<C, D> {
 	/// Broadcast by a authority to indicate that this is his candidate for
 	/// inclusion.
@@ -103,8 +88,61 @@ pub enum Statement<C, D> {
 	Invalid(D),
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u8)]
+enum StatementKind {
+	Candidate = 1,
+	Valid = 2,
+	Invalid = 3,
+	Available = 4,
+}
+
+impl<C: Slicable, D: Slicable> Slicable for Statement<C, D> {
+	fn encode(&self) -> Vec<u8> {
+		let mut v = Vec::new();
+		match *self {
+			Statement::Candidate(ref candidate) => {
+				v.push(StatementKind::Candidate as u8);
+				candidate.using_encoded(|s| v.extend(s));
+			}
+			Statement::Valid(ref digest) => {
+				v.push(StatementKind::Valid as u8);
+				digest.using_encoded(|s| v.extend(s));
+			}
+			Statement::Invalid(ref digest) => {
+				v.push(StatementKind::Invalid as u8);
+				digest.using_encoded(|s| v.extend(s));
+			}
+			Statement::Available(ref digest) => {
+				v.push(StatementKind::Available as u8);
+				digest.using_encoded(|s| v.extend(s));
+			}
+		}
+
+		v
+	}
+
+	fn decode<I: Input>(value: &mut I) -> Option<Self> {
+		match value.read_byte() {
+			Some(x) if x == StatementKind::Candidate as u8 => {
+				Slicable::decode(value).map(Statement::Candidate)
+			}
+			Some(x) if x == StatementKind::Valid as u8 => {
+				Slicable::decode(value).map(Statement::Valid)
+			}
+			Some(x) if x == StatementKind::Invalid as u8 => {
+				Slicable::decode(value).map(Statement::Invalid)
+			}
+			Some(x) if x == StatementKind::Available as u8 => {
+				Slicable::decode(value).map(Statement::Available)
+			}
+			_ => None,
+		}
+	}
+}
+
 /// A signed statement.
-#[derive(PartialEq, Eq, Debug, Clone)]
+#[derive(PartialEq, Eq, Debug, Clone, Serialize, Deserialize)]
 pub struct SignedStatement<C, D, V, S> {
 	/// The statement.
 	pub statement: Statement<C, D>,
@@ -114,26 +152,6 @@ pub struct SignedStatement<C, D, V, S> {
 	pub sender: V,
 }
 
-// A unique trace for a class of valid statements issued by a authority.
-//
-// We keep track of which statements we have received or sent to other authorities
-// in order to prevent relaying the same data multiple times.
-//
-// The signature of the statement is replaced by the authority because the authority
-// is unique while signatures are not (at least under common schemes like
-// Schnorr or ECDSA).
-#[derive(Hash, PartialEq, Eq, Clone)]
-enum StatementTrace<V, D> {
-	/// The candidate proposed by the authority.
-	Candidate(V),
-	/// A validity statement from that authority about the given digest.
-	Valid(V, D),
-	/// An invalidity statement from that authority about the given digest.
-	Invalid(V, D),
-	/// An availability statement from that authority about the given digest.
-	Available(V, D),
-}
-
 /// Misbehavior: voting more than one way on candidate validity.
 ///
 /// Since there are three possible ways to vote, a double vote is possible in
@@ -148,6 +166,19 @@ pub enum ValidityDoubleVote<C, D, S> {
 	ValidityAndInvalidity(D, S, S),
 }
 
+/// Misbehavior: multiple signatures on same statement.
+#[derive(PartialEq, Eq, Debug, Clone)]
+pub enum DoubleSign<C, D, S> {
+	/// On candidate.
+	Candidate(C, S, S),
+	/// On validity.
+	Validity(D, S, S),
+	/// On invalidity.
+	Invalidity(D, S, S),
+	/// On availability.
+	Availability(D, S, S),
+}
+
 /// Misbehavior: declaring multiple candidates.
 #[derive(PartialEq, Eq, Debug, Clone)]
 pub struct MultipleCandidates<C, S> {
@@ -172,20 +203,14 @@ pub enum Misbehavior<C, D, V, S> {
 	ValidityDoubleVote(ValidityDoubleVote<C, D, S>),
 	/// Submitted multiple candidates.
 	MultipleCandidates(MultipleCandidates<C, S>),
-	/// Submitted a message withou
+	/// Submitted a message that was unauthorized.
 	UnauthorizedStatement(UnauthorizedStatement<C, D, V, S>),
+	/// Submitted two valid signatures for the same message.
+	DoubleSign(DoubleSign<C, D, S>),
 }
 
-/// Fancy work-around for a type alias of context-based misbehavior
-/// without producing compiler warnings.
-pub trait ResolveMisbehavior {
-	/// The misbehavior type.
-	type Misbehavior;
-}
-
-impl<C: Context + ?Sized> ResolveMisbehavior for C {
-	type Misbehavior = Misbehavior<C::Candidate, C::Digest, C::AuthorityId, C::Signature>;
-}
+/// Type alias for misbehavior corresponding to context type.
+pub type MisbehaviorFor<C> = Misbehavior<<C as Context>::Candidate, <C as Context>::Digest, <C as Context>::AuthorityId, <C as Context>::Signature>;
 
 // kinds of votes for validity
 #[derive(Clone, PartialEq, Eq)]
@@ -251,22 +276,26 @@ impl<C: Context> CandidateData<C> {
 // authority metadata
 struct AuthorityData<C: Context> {
 	proposal: Option<(C::Digest, C::Signature)>,
-	known_statements: HashSet<StatementTrace<C::AuthorityId, C::Digest>>,
 }
 
 impl<C: Context> Default for AuthorityData<C> {
 	fn default() -> Self {
 		AuthorityData {
 			proposal: None,
-			known_statements: HashSet::default(),
 		}
 	}
 }
 
+/// Type alias for the result of a statement import.
+pub type ImportResult<C> = Result<
+	Option<Summary<<C as Context>::Digest, <C as Context>::GroupId>>,
+	MisbehaviorFor<C>
+>;
+
 /// Stores votes
 pub struct Table<C: Context> {
 	authority_data: HashMap<C::AuthorityId, AuthorityData<C>>,
-	detected_misbehavior: HashMap<C::AuthorityId, <C as ResolveMisbehavior>::Misbehavior>,
+	detected_misbehavior: HashMap<C::AuthorityId, MisbehaviorFor<C>>,
 	candidate_votes: HashMap<C::Digest, CandidateData<C>>,
 	includable_count: HashMap<C::GroupId, usize>,
 }
@@ -328,26 +357,17 @@ impl<C: Context> Table<C> {
 	}
 
 	/// Import a signed statement. Signatures should be checked for validity, and the
-	/// sender should be checked to actually be a authority.
+	/// sender should be checked to actually be an authority.
 	///
-	/// This can note the origin of the statement to indicate that he has
-	/// seen it already.
+	/// If this returns `None`, the statement was either duplicate or invalid.
 	pub fn import_statement(
 		&mut self,
 		context: &C,
 		statement: SignedStatement<C::Candidate, C::Digest, C::AuthorityId, C::Signature>,
-		from: Option<C::AuthorityId>
 	) -> Option<Summary<C::Digest, C::GroupId>> {
 		let SignedStatement { statement, signature, sender: signer } = statement;
 
-		let trace = match statement {
-			Statement::Candidate(_) => StatementTrace::Candidate(signer.clone()),
-			Statement::Valid(ref d) => StatementTrace::Valid(signer.clone(), d.clone()),
-			Statement::Invalid(ref d) => StatementTrace::Invalid(signer.clone(), d.clone()),
-			Statement::Available(ref d) => StatementTrace::Available(signer.clone(), d.clone()),
-		};
-
-		let (maybe_misbehavior, maybe_summary) = match statement {
+		let res = match statement {
 			Statement::Candidate(candidate) => self.import_candidate(
 				context,
 				signer.clone(),
@@ -374,19 +394,15 @@ impl<C: Context> Table<C> {
 			),
 		};
 
-		if let Some(misbehavior) = maybe_misbehavior {
-			// all misbehavior in agreement is provable and actively malicious.
-			// punishments are not cumulative.
-			self.detected_misbehavior.insert(signer, misbehavior);
-		} else {
-			if let Some(from) = from {
-				self.note_trace_seen(trace.clone(), from);
+		match res {
+			Ok(maybe_summary) => maybe_summary,
+			Err(misbehavior) => {
+				// all misbehavior in agreement is provable and actively malicious.
+				// punishments are not cumulative.
+				self.detected_misbehavior.insert(signer, misbehavior);
+				None
 			}
-
-			self.note_trace_seen(trace, signer);
 		}
-
-		maybe_summary
 	}
 
 	/// Get a candidate by digest.
@@ -396,7 +412,7 @@ impl<C: Context> Table<C> {
 
 	/// Access all witnessed misbehavior.
 	pub fn get_misbehavior(&self)
-		-> &HashMap<C::AuthorityId, <C as ResolveMisbehavior>::Misbehavior>
+		-> &HashMap<C::AuthorityId, MisbehaviorFor<C>>
 	{
 		&self.detected_misbehavior
 	}
@@ -406,155 +422,22 @@ impl<C: Context> Table<C> {
 		self.includable_count.len()
 	}
 
-	/// Fill a statement batch and note messages as seen by the targets.
-	pub fn fill_batch<B>(&mut self, batch: &mut B)
-		where B: StatementBatch<
-			C::AuthorityId,
-			SignedStatement<C::Candidate, C::Digest, C::AuthorityId, C::Signature>,
-		>
-	{
-		// naively iterate all statements so far, taking any that
-		// at least one of the targets has not seen.
-
-		// workaround for the fact that it's inconvenient to borrow multiple
-		// entries out of a hashmap mutably -- we just move them out and
-		// replace them when we're done.
-		struct SwappedTargetData<'a, C: 'a + Context> {
-			authority_data: &'a mut HashMap<C::AuthorityId, AuthorityData<C>>,
-			target_data: Vec<(C::AuthorityId, AuthorityData<C>)>,
-		}
-
-		impl<'a, C: 'a + Context> Drop for SwappedTargetData<'a, C> {
-			fn drop(&mut self) {
-				for (id, data) in self.target_data.drain(..) {
-					self.authority_data.insert(id, data);
-				}
-			}
-		}
-
-		// pre-fetch authority data for all the targets.
-		let mut target_data = {
-			let authority_data = &mut self.authority_data;
-			let mut target_data = Vec::with_capacity(batch.targets().len());
-			for target in batch.targets() {
-				let active_data = match authority_data.get_mut(target) {
-					None => Default::default(),
-					Some(x) => ::std::mem::replace(x, Default::default()),
-				};
-
-				target_data.push((target.clone(), active_data));
-			}
-
-			SwappedTargetData {
-				authority_data,
-				target_data
-			}
-		};
-
-		let target_data = &mut target_data.target_data;
-
-		macro_rules! attempt_send {
-			($trace:expr, sender=$sender:expr, sig=$sig:expr, statement=$statement:expr) => {{
-				let trace = $trace;
-				let can_send = target_data.iter()
-					.any(|t| !t.1.known_statements.contains(&trace));
-
-				if can_send {
-					let statement = SignedStatement {
-						statement: $statement,
-						signature: $sig,
-						sender: $sender,
-					};
-
-					if batch.push(statement) {
-						for target in target_data.iter_mut() {
-							target.1.known_statements.insert(trace.clone());
-						}
-					} else {
-						return;
-					}
-				}
-			}}
-		}
-
-		// reconstruct statements for anything whose trace passes the filter.
-		for (digest, candidate) in self.candidate_votes.iter() {
-			let issuance_iter = candidate.validity_votes.iter()
-				.filter(|&(_, x)| if let ValidityVote::Issued(_) = *x { true } else { false });
-
-			let validity_iter = candidate.validity_votes.iter()
-				.filter(|&(_, x)| if let ValidityVote::Issued(_) = *x { false } else { true });
-
-			// send issuance statements before votes.
-			for (sender, vote) in issuance_iter.chain(validity_iter) {
-				match *vote {
-					ValidityVote::Issued(ref sig) => {
-						attempt_send!(
-							StatementTrace::Candidate(sender.clone()),
-							sender = sender.clone(),
-							sig = sig.clone(),
-							statement = Statement::Candidate(candidate.candidate.clone())
-						)
-					}
-					ValidityVote::Valid(ref sig) => {
-						attempt_send!(
-							StatementTrace::Valid(sender.clone(), digest.clone()),
-							sender = sender.clone(),
-							sig = sig.clone(),
-							statement = Statement::Valid(digest.clone())
-						)
-					}
-					ValidityVote::Invalid(ref sig) => {
-						attempt_send!(
-							StatementTrace::Invalid(sender.clone(), digest.clone()),
-							sender = sender.clone(),
-							sig = sig.clone(),
-							statement = Statement::Invalid(digest.clone())
-						)
-					}
-				}
-			};
-
-
-			// and lastly send availability.
-			for (sender, sig) in candidate.availability_votes.iter() {
-				attempt_send!(
-					StatementTrace::Available(sender.clone(), digest.clone()),
-					sender = sender.clone(),
-					sig = sig.clone(),
-					statement = Statement::Available(digest.clone())
-				)
-			}
-		}
-
-	}
-
-	fn note_trace_seen(&mut self, trace: StatementTrace<C::AuthorityId, C::Digest>, known_by: C::AuthorityId) {
-		self.authority_data.entry(known_by).or_insert_with(|| AuthorityData {
-			proposal: None,
-			known_statements: HashSet::default(),
-		}).known_statements.insert(trace);
-	}
-
 	fn import_candidate(
 		&mut self,
 		context: &C,
 		from: C::AuthorityId,
 		candidate: C::Candidate,
 		signature: C::Signature,
-	) -> (Option<<C as ResolveMisbehavior>::Misbehavior>, Option<Summary<C::Digest, C::GroupId>>) {
+	) -> ImportResult<C> {
 		let group = C::candidate_group(&candidate);
 		if !context.is_member_of(&from, &group) {
-			return (
-				Some(Misbehavior::UnauthorizedStatement(UnauthorizedStatement {
-					statement: SignedStatement {
-						signature,
-						statement: Statement::Candidate(candidate),
-						sender: from,
-					},
-				})),
-				None,
-			);
+			return Err(Misbehavior::UnauthorizedStatement(UnauthorizedStatement {
+				statement: SignedStatement {
+					signature,
+					statement: Statement::Candidate(candidate),
+					sender: from,
+				},
+			}));
 		}
 
 		// check that authority hasn't already specified another candidate.
@@ -578,13 +461,10 @@ impl<C: Context> Table<C> {
 							.candidate
 							.clone();
 
-						return (
-							Some(Misbehavior::MultipleCandidates(MultipleCandidates {
-								first: (old_candidate, old_sig.clone()),
-								second: (candidate, signature.clone()),
-							})),
-							None,
-						);
+						return Err(Misbehavior::MultipleCandidates(MultipleCandidates {
+							first: (old_candidate, old_sig.clone()),
+							second: (candidate, signature.clone()),
+						}));
 					}
 
 					false
@@ -596,7 +476,6 @@ impl<C: Context> Table<C> {
 			Entry::Vacant(vacant) => {
 				vacant.insert(AuthorityData {
 					proposal: Some((digest.clone(), signature.clone())),
-					known_statements: HashSet::new(),
 				});
 				true
 			}
@@ -628,9 +507,9 @@ impl<C: Context> Table<C> {
 		from: C::AuthorityId,
 		digest: C::Digest,
 		vote: ValidityVote<C::Signature>,
-	) -> (Option<<C as ResolveMisbehavior>::Misbehavior>, Option<Summary<C::Digest, C::GroupId>>) {
+	) -> ImportResult<C> {
 		let votes = match self.candidate_votes.get_mut(&digest) {
-			None => return (None, None), // TODO: queue up but don't get DoS'ed
+			None => return Ok(None),
 			Some(votes) => votes,
 		};
 
@@ -647,50 +526,56 @@ impl<C: Context> Table<C> {
 							checking group membership of issuer; qed"),
 			};
 
-			return (
-				Some(Misbehavior::UnauthorizedStatement(UnauthorizedStatement {
-					statement: SignedStatement {
-						signature: sig,
-						sender: from,
-						statement: if valid {
-							Statement::Valid(digest)
-						} else {
-							Statement::Invalid(digest)
-						}
+			return Err(Misbehavior::UnauthorizedStatement(UnauthorizedStatement {
+				statement: SignedStatement {
+					signature: sig,
+					sender: from,
+					statement: if valid {
+						Statement::Valid(digest)
+					} else {
+						Statement::Invalid(digest)
 					}
-				})),
-				None,
-			);
+				}
+			}));
 		}
 
 		// check for double votes.
 		match votes.validity_votes.entry(from.clone()) {
 			Entry::Occupied(occ) => {
-				if occ.get() != &vote {
-					let double_vote_proof = match (occ.get().clone(), vote) {
+				let make_vdv = |v| Misbehavior::ValidityDoubleVote(v);
+				let make_ds = |ds| Misbehavior::DoubleSign(ds);
+				return if occ.get() != &vote {
+					Err(match (occ.get().clone(), vote) {
+						// valid vote conflicting with candidate statement
 						(ValidityVote::Issued(iss), ValidityVote::Valid(good)) |
 						(ValidityVote::Valid(good), ValidityVote::Issued(iss)) =>
-							ValidityDoubleVote::IssuedAndValidity((votes.candidate.clone(), iss), (digest, good)),
+							make_vdv(ValidityDoubleVote::IssuedAndValidity((votes.candidate.clone(), iss), (digest, good))),
+
+						// invalid vote conflicting with candidate statement
 						(ValidityVote::Issued(iss), ValidityVote::Invalid(bad)) |
 						(ValidityVote::Invalid(bad), ValidityVote::Issued(iss)) =>
-							ValidityDoubleVote::IssuedAndInvalidity((votes.candidate.clone(), iss), (digest, bad)),
+							make_vdv(ValidityDoubleVote::IssuedAndInvalidity((votes.candidate.clone(), iss), (digest, bad))),
+
+						// valid vote conflicting with invalid vote
 						(ValidityVote::Valid(good), ValidityVote::Invalid(bad)) |
 						(ValidityVote::Invalid(bad), ValidityVote::Valid(good)) =>
-							ValidityDoubleVote::ValidityAndInvalidity(digest, good, bad),
-						_ => {
-							// this would occur if two different but valid signatures
-							// on the same kind of vote occurred.
-							return (None, None);
-						}
-					};
+							make_vdv(ValidityDoubleVote::ValidityAndInvalidity(digest, good, bad)),
 
-					return (
-						Some(Misbehavior::ValidityDoubleVote(double_vote_proof)),
-						None,
-					)
+						// two signatures on same candidate
+						(ValidityVote::Issued(a), ValidityVote::Issued(b)) =>
+							make_ds(DoubleSign::Candidate(votes.candidate.clone(), a, b)),
+
+						// two signatures on same validity vote
+						(ValidityVote::Valid(a), ValidityVote::Valid(b)) =>
+							make_ds(DoubleSign::Validity(digest, a, b)),
+
+						// two signature on same invalidity vote
+						(ValidityVote::Invalid(a), ValidityVote::Invalid(b)) =>
+							make_ds(DoubleSign::Invalidity(digest, a, b)),
+					})
+				} else {
+					Ok(None)
 				}
-
-				return (None, None);
 			}
 			Entry::Vacant(vacant) => {
 				if let ValidityVote::Invalid(_) = vote {
@@ -704,7 +589,7 @@ impl<C: Context> Table<C> {
 		let is_includable = votes.can_be_included(v_threshold, a_threshold);
 		update_includable_count(&mut self.includable_count, &votes.group_id, was_includable, is_includable);
 
-		(None, Some(votes.summary(digest)))
+		Ok(Some(votes.summary(digest)))
 	}
 
 	fn availability_vote(
@@ -713,9 +598,9 @@ impl<C: Context> Table<C> {
 		from: C::AuthorityId,
 		digest: C::Digest,
 		signature: C::Signature,
-	) -> (Option<<C as ResolveMisbehavior>::Misbehavior>, Option<Summary<C::Digest, C::GroupId>>) {
+	) -> ImportResult<C> {
 		let votes = match self.candidate_votes.get_mut(&digest) {
-			None => return (None, None), // TODO: queue up but don't get DoS'ed
+			None => return Ok(None),
 			Some(votes) => votes,
 		};
 
@@ -724,24 +609,26 @@ impl<C: Context> Table<C> {
 
 		// check that this authority actually can vote in this group.
 		if !context.is_availability_guarantor_of(&from, &votes.group_id) {
-			return (
-				Some(Misbehavior::UnauthorizedStatement(UnauthorizedStatement {
-					statement: SignedStatement {
-						signature: signature.clone(),
-						statement: Statement::Available(digest),
-						sender: from,
-					}
-				})),
-				None
-			);
+			return Err(Misbehavior::UnauthorizedStatement(UnauthorizedStatement {
+				statement: SignedStatement {
+					signature: signature,
+					statement: Statement::Available(digest),
+					sender: from,
+				}
+			}));
 		}
 
-		votes.availability_votes.insert(from, signature);
+		match votes.availability_votes.entry(from) {
+			Entry::Occupied(ref occ) if occ.get() != &signature => return Err(
+				Misbehavior::DoubleSign(DoubleSign::Availability(digest, signature, occ.get().clone()))
+			),
+			entry => { let _ = entry.or_insert(signature); },
+		}
 
 		let is_includable = votes.can_be_included(v_threshold, a_threshold);
 		update_includable_count(&mut self.includable_count, &votes.group_id, was_includable, is_includable);
 
-		(None, Some(votes.summary(digest)))
+		Ok(Some(votes.summary(digest)))
 	}
 }
 
@@ -765,26 +652,6 @@ mod tests {
 	use super::*;
 	use std::collections::HashMap;
 
-	#[derive(Debug, Clone)]
-	struct VecBatch<V, T> {
-		pub max_len: usize,
-		pub targets: Vec<V>,
-		pub items: Vec<T>,
-	}
-
-	impl<V, T> ::generic::StatementBatch<V, T> for VecBatch<V, T> {
-		fn targets(&self) -> &[V] { &self.targets }
-		fn is_empty(&self) -> bool { self.items.is_empty() }
-		fn push(&mut self, item: T) -> bool {
-			if self.items.len() == self.max_len {
-				false
-			} else {
-				self.items.push(item);
-				true
-			}
-		}
-	}
-
 	fn create<C: Context>() -> Table<C> {
 		Table::default()
 	}
@@ -878,10 +745,10 @@ mod tests {
 			sender: AuthorityId(1),
 		};
 
-		table.import_statement(&context, statement_a, None);
+		table.import_statement(&context, statement_a);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 
-		table.import_statement(&context, statement_b, None);
+		table.import_statement(&context, statement_b);
 		assert_eq!(
 			table.detected_misbehavior.get(&AuthorityId(1)).unwrap(),
 			&Misbehavior::MultipleCandidates(MultipleCandidates {
@@ -908,7 +775,7 @@ mod tests {
 			sender: AuthorityId(1),
 		};
 
-		table.import_statement(&context, statement, None);
+		table.import_statement(&context, statement);
 
 		assert_eq!(
 			table.detected_misbehavior.get(&AuthorityId(1)).unwrap(),
@@ -949,8 +816,8 @@ mod tests {
 		};
 		let candidate_b_digest = Digest(987);
 
-		table.import_statement(&context, candidate_a, None);
-		table.import_statement(&context, candidate_b, None);
+		table.import_statement(&context, candidate_a);
+		table.import_statement(&context, candidate_b);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(2)));
 
@@ -960,7 +827,7 @@ mod tests {
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};
-		table.import_statement(&context, bad_availability_vote, None);
+		table.import_statement(&context, bad_availability_vote);
 
 		assert_eq!(
 			table.detected_misbehavior.get(&AuthorityId(1)).unwrap(),
@@ -979,7 +846,7 @@ mod tests {
 			signature: Signature(2),
 			sender: AuthorityId(2),
 		};
-		table.import_statement(&context, bad_validity_vote, None);
+		table.import_statement(&context, bad_validity_vote);
 
 		assert_eq!(
 			table.detected_misbehavior.get(&AuthorityId(2)).unwrap(),
@@ -1012,7 +879,7 @@ mod tests {
 		};
 		let candidate_digest = Digest(100);
 
-		table.import_statement(&context, statement, None);
+		table.import_statement(&context, statement);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 
 		let valid_statement = SignedStatement {
@@ -1027,10 +894,10 @@ mod tests {
 			sender: AuthorityId(2),
 		};
 
-		table.import_statement(&context, valid_statement, None);
+		table.import_statement(&context, valid_statement);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(2)));
 
-		table.import_statement(&context, invalid_statement, None);
+		table.import_statement(&context, invalid_statement);
 
 		assert_eq!(
 			table.detected_misbehavior.get(&AuthorityId(2)).unwrap(),
@@ -1042,6 +909,102 @@ mod tests {
 		);
 	}
 
+	#[test]
+	fn candidate_double_signature_is_misbehavior() {
+		let context = TestContext {
+			authorities: {
+				let mut map = HashMap::new();
+				map.insert(AuthorityId(1), (GroupId(2), GroupId(455)));
+				map.insert(AuthorityId(2), (GroupId(2), GroupId(246)));
+				map
+			}
+		};
+
+		let mut table = create();
+		let statement = SignedStatement {
+			statement: Statement::Candidate(Candidate(2, 100)),
+			signature: Signature(1),
+			sender: AuthorityId(1),
+		};
+
+		table.import_statement(&context, statement);
+		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
+
+		let invalid_statement = SignedStatement {
+			statement: Statement::Candidate(Candidate(2, 100)),
+			signature: Signature(999),
+			sender: AuthorityId(1),
+		};
+
+		table.import_statement(&context, invalid_statement);
+		assert!(table.detected_misbehavior.contains_key(&AuthorityId(1)));
+	}
+
+	#[test]
+	fn validity_invalidity_double_signature_is_misbehavior() {
+		let context = TestContext {
+			authorities: {
+				let mut map = HashMap::new();
+				map.insert(AuthorityId(1), (GroupId(2), GroupId(455)));
+				map.insert(AuthorityId(2), (GroupId(2), GroupId(246)));
+				map.insert(AuthorityId(3), (GroupId(2), GroupId(222)));
+				map
+			}
+		};
+
+		let mut table = create();
+		let statement = SignedStatement {
+			statement: Statement::Candidate(Candidate(2, 100)),
+			signature: Signature(1),
+			sender: AuthorityId(1),
+		};
+
+		table.import_statement(&context, statement);
+		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
+
+		// insert two validity votes from authority 2 with different signatures
+		{
+			let statement = SignedStatement {
+				statement: Statement::Valid(Digest(100)),
+				signature: Signature(2),
+				sender: AuthorityId(2),
+			};
+
+			table.import_statement(&context, statement);
+			assert!(!table.detected_misbehavior.contains_key(&AuthorityId(2)));
+
+			let invalid_statement = SignedStatement {
+				statement: Statement::Valid(Digest(100)),
+				signature: Signature(222),
+				sender: AuthorityId(2),
+			};
+
+			table.import_statement(&context, invalid_statement);
+			assert!(table.detected_misbehavior.contains_key(&AuthorityId(2)));
+		}
+
+		// insert two invalidity votes from authority 2 with different signatures
+		{
+			let statement = SignedStatement {
+				statement: Statement::Invalid(Digest(100)),
+				signature: Signature(3),
+				sender: AuthorityId(3),
+			};
+
+			table.import_statement(&context, statement);
+			assert!(!table.detected_misbehavior.contains_key(&AuthorityId(3)));
+
+			let invalid_statement = SignedStatement {
+				statement: Statement::Invalid(Digest(100)),
+				signature: Signature(333),
+				sender: AuthorityId(3),
+			};
+
+			table.import_statement(&context, invalid_statement);
+			assert!(table.detected_misbehavior.contains_key(&AuthorityId(3)));
+		}
+	}
+
 	#[test]
 	fn issue_and_vote_is_misbehavior() {
 		let context = TestContext {
@@ -1060,7 +1023,7 @@ mod tests {
 		};
 		let candidate_digest = Digest(100);
 
-		table.import_statement(&context, statement, None);
+		table.import_statement(&context, statement);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 
 		let extra_vote = SignedStatement {
@@ -1069,7 +1032,7 @@ mod tests {
 			sender: AuthorityId(1),
 		};
 
-		table.import_statement(&context, extra_vote, None);
+		table.import_statement(&context, extra_vote);
 		assert_eq!(
 			table.detected_misbehavior.get(&AuthorityId(1)).unwrap(),
 			&Misbehavior::ValidityDoubleVote(ValidityDoubleVote::IssuedAndValidity(
@@ -1133,7 +1096,7 @@ mod tests {
 		};
 		let candidate_digest = Digest(100);
 
-		table.import_statement(&context, statement, None);
+		table.import_statement(&context, statement);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 		assert!(!table.candidate_includable(&candidate_digest, &context));
 		assert!(table.includable_count.is_empty());
@@ -1144,7 +1107,7 @@ mod tests {
 			sender: AuthorityId(2),
 		};
 
-		table.import_statement(&context, vote, None);
+		table.import_statement(&context, vote);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(2)));
 		assert!(!table.candidate_includable(&candidate_digest, &context));
 		assert!(table.includable_count.is_empty());
@@ -1156,7 +1119,7 @@ mod tests {
 			sender: AuthorityId(4),
 		};
 
-		table.import_statement(&context, vote, None);
+		table.import_statement(&context, vote);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(4)));
 		assert!(table.candidate_includable(&candidate_digest, &context));
 		assert!(table.includable_count.get(&GroupId(2)).is_some());
@@ -1168,7 +1131,7 @@ mod tests {
 			sender: AuthorityId(3),
 		};
 
-		table.import_statement(&context, vote, None);
+		table.import_statement(&context, vote);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(2)));
 		assert!(!table.candidate_includable(&candidate_digest, &context));
 		assert!(table.includable_count.is_empty());
@@ -1191,7 +1154,7 @@ mod tests {
 			sender: AuthorityId(1),
 		};
 
-		let summary = table.import_statement(&context, statement, None)
+		let summary = table.import_statement(&context, statement)
 			.expect("candidate import to give summary");
 
 		assert_eq!(summary.candidate, Digest(100));
@@ -1219,7 +1182,7 @@ mod tests {
 		};
 		let candidate_digest = Digest(100);
 
-		table.import_statement(&context, statement, None);
+		table.import_statement(&context, statement);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 
 		let vote = SignedStatement {
@@ -1228,7 +1191,7 @@ mod tests {
 			sender: AuthorityId(2),
 		};
 
-		let summary = table.import_statement(&context, vote, None)
+		let summary = table.import_statement(&context, vote)
 			.expect("candidate vote to give summary");
 
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(2)));
@@ -1258,7 +1221,7 @@ mod tests {
 		};
 		let candidate_digest = Digest(100);
 
-		table.import_statement(&context, statement, None);
+		table.import_statement(&context, statement);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 
 		let vote = SignedStatement {
@@ -1267,7 +1230,7 @@ mod tests {
 			sender: AuthorityId(2),
 		};
 
-		let summary = table.import_statement(&context, vote, None)
+		let summary = table.import_statement(&context, vote)
 			.expect("candidate vote to give summary");
 
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(2)));
@@ -1277,55 +1240,4 @@ mod tests {
 		assert_eq!(summary.validity_votes, 1);
 		assert_eq!(summary.availability_votes, 1);
 	}
-
-	#[test]
-	fn filling_batch_sets_known_flag() {
-		let context = TestContext {
-			authorities: {
-				let mut map = HashMap::new();
-				for i in 1..10 {
-					map.insert(AuthorityId(i), (GroupId(2), GroupId(400 + i)));
-				}
-				map
-			}
-		};
-
-		let mut table = create();
-		let statement = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
-			signature: Signature(1),
-			sender: AuthorityId(1),
-		};
-
-		table.import_statement(&context, statement, None);
-
-		for i in 2..10 {
-			let statement = SignedStatement {
-				statement: Statement::Valid(Digest(100)),
-				signature: Signature(i),
-				sender: AuthorityId(i),
-			};
-
-			table.import_statement(&context, statement, None);
-		}
-
-		let mut batch = VecBatch {
-			max_len: 5,
-			targets: (1..10).map(AuthorityId).collect(),
-			items: Vec::new(),
-		};
-
-		// 9 statements in the table, each seen by one.
-		table.fill_batch(&mut batch);
-		assert_eq!(batch.items.len(), 5);
-
-		// 9 statements in the table, 5 of which seen by all targets.
-		batch.items.clear();
-		table.fill_batch(&mut batch);
-		assert_eq!(batch.items.len(), 4);
-
-		batch.items.clear();
-		table.fill_batch(&mut batch);
-		assert!(batch.items.is_empty());
-	}
 }
diff --git a/polkadot/statement-table/src/lib.rs b/polkadot/statement-table/src/lib.rs
index 86b95b0d90..779a7fc2df 100644
--- a/polkadot/statement-table/src/lib.rs
+++ b/polkadot/statement-table/src/lib.rs
@@ -14,9 +14,14 @@
 //! propose and attest to validity of candidates, and those who can only attest
 //! to availability.
 
+extern crate substrate_codec as codec;
 extern crate substrate_primitives;
 extern crate polkadot_primitives as primitives;
 
+extern crate serde;
+#[macro_use]
+extern crate serde_derive;
+
 pub mod generic;
 
 pub use generic::Table;
@@ -82,27 +87,3 @@ impl<C: Context> generic::Context for C {
 		Context::requisite_votes(self, group)
 	}
 }
-
-/// A batch of statements to send out.
-pub trait StatementBatch {
-	/// Get the target authorities of these statements.
-	fn targets(&self) -> &[SessionKey];
-
-	/// If the batch is empty.
-	fn is_empty(&self) -> bool;
-
-	/// Push a statement onto the batch. Returns false when the batch is full.
-	///
-	/// This is meant to do work like incrementally serializing the statements
-	/// into a vector of bytes while making sure the length is below a certain
-	/// amount.
-	fn push(&mut self, statement: SignedStatement) -> bool;
-}
-
-impl<T: StatementBatch> generic::StatementBatch<SessionKey, SignedStatement> for T {
-	fn targets(&self) -> &[SessionKey] { StatementBatch::targets(self ) }
-	fn is_empty(&self) -> bool { StatementBatch::is_empty(self) }
-	fn push(&mut self, statement: SignedStatement) -> bool {
-		StatementBatch::push(self, statement)
-	}
-}