diff --git a/substrate/core/consensus/aura/src/lib.rs b/substrate/core/consensus/aura/src/lib.rs
index e3a87e8ac9..3f8358d3a2 100644
--- a/substrate/core/consensus/aura/src/lib.rs
+++ b/substrate/core/consensus/aura/src/lib.rs
@@ -699,11 +699,12 @@ mod tests {
 	const TEST_ROUTING_INTERVAL: Duration = Duration::from_millis(50);
 
 	pub struct AuraTestNet {
-		peers: Vec<Arc<Peer<()>>>,
+		peers: Vec<Arc<Peer<(), DummySpecialization>>>,
 		started: bool,
 	}
 
 	impl TestNetFactory for AuraTestNet {
+		type Specialization = DummySpecialization;
 		type Verifier = AuraVerifier<PeersClient, NothingExtra>;
 		type PeerData = ();
 
@@ -734,15 +735,15 @@ mod tests {
 			})
 		}
 
-		fn peer(&self, i: usize) -> &Peer<Self::PeerData> {
+		fn peer(&self, i: usize) -> &Peer<Self::PeerData, DummySpecialization> {
 			&self.peers[i]
 		}
 
-		fn peers(&self) -> &Vec<Arc<Peer<Self::PeerData>>> {
+		fn peers(&self) -> &Vec<Arc<Peer<Self::PeerData, DummySpecialization>>> {
 			&self.peers
 		}
 
-		fn mut_peers<F: Fn(&mut Vec<Arc<Peer<Self::PeerData>>>)>(&mut self, closure: F) {
+		fn mut_peers<F: FnOnce(&mut Vec<Arc<Peer<Self::PeerData, DummySpecialization>>>)>(&mut self, closure: F) {
 			closure(&mut self.peers);
 		}
 
diff --git a/substrate/core/consensus/common/src/import_queue.rs b/substrate/core/consensus/common/src/import_queue.rs
index 89f3a563b5..38f7980435 100644
--- a/substrate/core/consensus/common/src/import_queue.rs
+++ b/substrate/core/consensus/common/src/import_queue.rs
@@ -27,12 +27,11 @@
 use crate::block_import::{ImportBlock, BlockImport, JustificationImport, ImportResult, BlockOrigin};
 use crossbeam_channel::{self as channel, Receiver, Sender};
 
-use std::collections::HashSet;
 use std::sync::Arc;
 use std::thread;
 
 use runtime_primitives::traits::{
-	AuthorityIdFor, Block as BlockT, Header as HeaderT, NumberFor, Zero,
+	AuthorityIdFor, Block as BlockT, Header as HeaderT, NumberFor
 };
 use runtime_primitives::Justification;
 
@@ -85,14 +84,8 @@ pub trait ImportQueue<B: BlockT>: Send + Sync + ImportQueueClone<B> {
 	fn start(&self, _link: Box<Link<B>>) -> Result<(), std::io::Error> {
 		Ok(())
 	}
-	/// Clear the queue when sync is restarting.
-	fn clear(&self);
 	/// Clears the import queue and stops importing.
 	fn stop(&self);
-	/// Get queue status.
-	fn status(&self) -> ImportQueueStatus<B>;
-	/// Is block with given hash currently in the queue.
-	fn is_importing(&self, hash: &B::Hash) -> bool;
 	/// Import bunch of blocks.
 	fn import_blocks(&self, origin: BlockOrigin, blocks: Vec<IncomingBlock<B>>);
 	/// Import a block justification.
@@ -109,15 +102,6 @@ impl<B: BlockT> Clone for Box<ImportQueue<B>> {
 	}
 }
 
-/// Import queue status. It isn't completely accurate.
-#[derive(Debug)]
-pub struct ImportQueueStatus<B: BlockT> {
-	/// Number of blocks that are currently in the queue.
-	pub importing_count: usize,
-	/// The number of the best block that was ever in the queue since start/last failure.
-	pub best_importing_number: NumberFor<B>,
-}
-
 /// Interface to a basic block import queue that is importing blocks sequentially in a separate thread,
 /// with pluggable verification.
 #[derive(Clone)]
@@ -165,18 +149,12 @@ impl<B: BlockT> BasicQueue<B> {
 
 impl<B: BlockT> ImportQueue<B> for BasicQueue<B> {
 	fn start(&self, link: Box<Link<B>>) -> Result<(), std::io::Error> {
+		let (sender, port) = channel::unbounded();
 		let _ = self
 			.sender
-			.send(BlockImportMsg::Start(link))
-			.expect("1. self is holding a sender to the Importer, 2. Importer should handle messages while there are senders around; qed");
-		Ok(())
-	}
-
-	fn clear(&self) {
-		let _ = self
-			.sender
-			.send(BlockImportMsg::Clear)
+			.send(BlockImportMsg::Start(link, sender))
 			.expect("1. self is holding a sender to the Importer, 2. Importer should handle messages while there are senders around; qed");
+		port.recv().expect("1. self is holding a sender to the Importer, 2. Importer should handle messages while there are senders around; qed")
 	}
 
 	fn stop(&self) {
@@ -186,24 +164,6 @@ impl<B: BlockT> ImportQueue<B> for BasicQueue<B> {
 			.expect("1. self is holding a sender to the Importer, 2. Importer should handle messages while there are senders around; qed");
 	}
 
-	fn status(&self) -> ImportQueueStatus<B> {
-		let (sender, port) = channel::unbounded();
-		let _ = self
-			.sender
-			.send(BlockImportMsg::Status(sender))
-			.expect("1. self is holding a sender to the Importer, 2. Importer should handle messages while there are senders around; qed");
-		port.recv().expect("1. self is holding a sender to the Importer, 2. Importer should handle messages while there are senders around; qed")
-	}
-
-	fn is_importing(&self, hash: &B::Hash) -> bool {
-		let (sender, port) = channel::unbounded();
-		let _ = self
-			.sender
-			.send(BlockImportMsg::IsImporting(hash.clone(), sender))
-			.expect("1. self is holding a sender to the Importer, 2. Importer should handle messages while there are senders around; qed");
-		port.recv().expect("1. self is holding a sender to the Importer, 2. Importer should handle messages while there are senders around; qed")
-	}
-
 	fn import_blocks(&self, origin: BlockOrigin, blocks: Vec<IncomingBlock<B>>) {
 		if blocks.is_empty() {
 			return;
@@ -224,11 +184,8 @@ impl<B: BlockT> ImportQueue<B> for BasicQueue<B> {
 
 pub enum BlockImportMsg<B: BlockT> {
 	ImportBlocks(BlockOrigin, Vec<IncomingBlock<B>>),
-	Clear,
-	Status(Sender<ImportQueueStatus<B>>),
-	IsImporting(B::Hash, Sender<bool>),
 	ImportJustification(Origin, B::Hash, NumberFor<B>, Justification),
-	Start(Box<Link<B>>),
+	Start(Box<Link<B>>, Sender<Result<(), std::io::Error>>),
 	Stop,
 }
 
@@ -251,8 +208,6 @@ struct BlockImporter<B: BlockT> {
 	port: Receiver<BlockImportMsg<B>>,
 	result_port: Receiver<BlockImportWorkerMsg<B>>,
 	worker_sender: Sender<BlockImportWorkerMsg<B>>,
-	queue_blocks: HashSet<B::Hash>,
-	best_importing_number: NumberFor<B>,
 	link: Option<Box<dyn Link<B>>>,
 	justification_import: Option<SharedJustificationImport<B>>,
 }
@@ -271,8 +226,6 @@ impl<B: BlockT> BlockImporter<B> {
 					port,
 					result_port,
 					worker_sender,
-					queue_blocks: HashSet::new(),
-					best_importing_number: Zero::zero(),
 					link: None,
 					justification_import,
 				};
@@ -310,25 +263,18 @@ impl<B: BlockT> BlockImporter<B> {
 		match msg {
 			BlockImportMsg::ImportBlocks(origin, incoming_blocks) => {
 				self.handle_import_blocks(origin, incoming_blocks)
-			}
-			BlockImportMsg::Clear => self.handle_clear(),
-			BlockImportMsg::Status(reply_sender) => self.handle_status(reply_sender),
-			BlockImportMsg::IsImporting(hash, reply_sender) => {
-				self.handle_is_importing(hash, reply_sender)
-			}
+			},
 			BlockImportMsg::ImportJustification(who, hash, number, justification) => {
 				self.handle_import_justification(who, hash, number, justification)
-			}
-			BlockImportMsg::Start(link) => {
+			},
+			BlockImportMsg::Start(link, sender) => {
 				if let Some(justification_import) = self.justification_import.as_ref() {
 					justification_import.on_start(&*link);
 				}
 				self.link = Some(link);
-			}
-			BlockImportMsg::Stop => {
-				self.handle_clear();
-				return false;
-			}
+				let _ = sender.send(Ok(()));
+			},
+			BlockImportMsg::Stop => return false,
 		}
 		true
 	}
@@ -339,15 +285,15 @@ impl<B: BlockT> BlockImporter<B> {
 			_ => unreachable!("Import Worker does not send ImportBlocks message; qed"),
 		};
 		let mut has_error = false;
+		let mut hashes = vec![];
 		for (result, hash) in results {
-			self.queue_blocks.remove(&hash);
+			hashes.push(hash);
 
 			if has_error {
 				continue;
 			}
 
 			if result.is_err() {
-				self.best_importing_number = Zero::zero();
 				has_error = true;
 			}
 
@@ -389,28 +335,11 @@ impl<B: BlockT> BlockImporter<B> {
 			};
 		}
 		if let Some(link) = self.link.as_ref() {
-			link.maintain_sync();
+			link.blocks_processed(hashes, has_error);
 		}
 		true
 	}
 
-	fn handle_clear(&mut self) {
-		self.queue_blocks.clear();
-		self.best_importing_number = Zero::zero();
-	}
-
-	fn handle_status(&self, reply_sender: Sender<ImportQueueStatus<B>>) {
-		let status = ImportQueueStatus {
-			importing_count: self.queue_blocks.len(),
-			best_importing_number: self.best_importing_number,
-		};
-		let _ = reply_sender.send(status);
-	}
-
-	fn handle_is_importing(&self, hash: B::Hash, reply_sender: Sender<bool>) {
-		let _ = reply_sender.send(self.queue_blocks.contains(&hash));
-	}
-
 	fn handle_import_justification(&self, who: Origin, hash: B::Hash, number: NumberFor<B>, justification: Justification) {
 		let success = self.justification_import.as_ref().map(|justification_import| {
 			justification_import.import_justification(hash, number, justification)
@@ -426,16 +355,6 @@ impl<B: BlockT> BlockImporter<B> {
 
 	fn handle_import_blocks(&mut self, origin: BlockOrigin, blocks: Vec<IncomingBlock<B>>) {
 		trace!(target:"sync", "Scheduling {} blocks for import", blocks.len());
-
-		let new_best_importing_number = blocks
-			.last()
-			.and_then(|b| b.header.as_ref().map(|h| h.number().clone()))
-			.unwrap_or_else(|| Zero::zero());
-		self.queue_blocks
-			.extend(blocks.iter().map(|b| b.hash.clone()));
-		if new_best_importing_number > self.best_importing_number {
-			self.best_importing_number = new_best_importing_number;
-		}
 		self.worker_sender
 			.send(BlockImportWorkerMsg::ImportBlocks(origin, blocks))
 			.expect("1. This is holding a sender to the worker, 2. the worker should not quit while a sender is still held; qed");
@@ -530,12 +449,12 @@ impl<B: BlockT, V: 'static + Verifier<B>> BlockImportWorker<B, V> {
 pub trait Link<B: BlockT>: Send {
 	/// Block imported.
 	fn block_imported(&self, _hash: &B::Hash, _number: NumberFor<B>) { }
+	/// Batch of blocks imported, with or without error.
+	fn blocks_processed(&self, _processed_blocks: Vec<B::Hash>, _has_error: bool) {}
 	/// Justification import result.
 	fn justification_imported(&self, _who: Origin, _hash: &B::Hash, _number: NumberFor<B>, _success: bool) { }
 	/// Request a justification for the given block.
 	fn request_justification(&self, _hash: &B::Hash, _number: NumberFor<B>) { }
-	/// Maintain sync.
-	fn maintain_sync(&self) {}
 	/// Disconnect from peer.
 	fn useless_peer(&self, _who: Origin, _reason: &str) {}
 	/// Disconnect from peer and restart sync.
@@ -674,8 +593,6 @@ mod tests {
 		fn block_imported(&self, _hash: &Hash, _number: NumberFor<Block>) {
 			let _ = self.sender.send(LinkMsg::BlockImported);
 		}
-		fn maintain_sync(&self) {
-		}
 		fn useless_peer(&self, _: Origin, _: &str) {
 			let _ = self.sender.send(LinkMsg::Disconnected);
 		}
@@ -695,12 +612,11 @@ mod tests {
 		let (link_sender, link_port) = channel::unbounded();
 		let importer_sender = BlockImporter::<Block>::new(result_port, worker_sender, None);
 		let link = TestLink::new(link_sender);
-		let _ = importer_sender.send(BlockImportMsg::Start(Box::new(link.clone())));
+		let (ack_sender, start_ack_port) = channel::bounded(4);
+		let _ = importer_sender.send(BlockImportMsg::Start(Box::new(link.clone()), ack_sender));
 
 		// Ensure the importer handles Start before any result messages.
-		let (ack_sender, ack_port) = channel::unbounded();
-		let _ = importer_sender.send(BlockImportMsg::Status(ack_sender));
-		let _ = ack_port.recv();
+		let _ = start_ack_port.recv();
 
 		// Send a known
 		let results = vec![(Ok(BlockImportResult::ImportedKnown(Default::default())), Default::default())];
diff --git a/substrate/core/finality-grandpa/src/tests.rs b/substrate/core/finality-grandpa/src/tests.rs
index 029e517943..733421c4df 100644
--- a/substrate/core/finality-grandpa/src/tests.rs
+++ b/substrate/core/finality-grandpa/src/tests.rs
@@ -17,7 +17,7 @@
 //! Tests and test helpers for GRANDPA.
 
 use super::*;
-use network::test::{Block, Hash, TestNetFactory, Peer, PeersClient};
+use network::test::{Block, DummySpecialization, Hash, TestNetFactory, Peer, PeersClient};
 use network::test::{PassThroughVerifier};
 use network::config::{ProtocolConfig, Roles};
 use parking_lot::Mutex;
@@ -52,12 +52,12 @@ type PeerData =
 			>
 		>
 	>;
-type GrandpaPeer = Peer<PeerData>;
+type GrandpaPeer = Peer<PeerData, DummySpecialization>;
 
 struct GrandpaTestNet {
 	peers: Vec<Arc<GrandpaPeer>>,
 	test_config: TestApi,
-	started: bool
+	started: bool,
 }
 
 impl GrandpaTestNet {
@@ -68,16 +68,15 @@ impl GrandpaTestNet {
 			test_config,
 		};
 		let config = Self::default_config();
-
 		for _ in 0..n_peers {
 			net.add_peer(&config);
 		}
-
 		net
 	}
 }
 
 impl TestNetFactory for GrandpaTestNet {
+	type Specialization = DummySpecialization;
 	type Verifier = PassThroughVerifier;
 	type PeerData = PeerData;
 
@@ -86,7 +85,7 @@ impl TestNetFactory for GrandpaTestNet {
 		GrandpaTestNet {
 			peers: Vec::new(),
 			test_config: Default::default(),
-			started: false
+			started: false,
 		}
 	}
 
@@ -122,7 +121,7 @@ impl TestNetFactory for GrandpaTestNet {
 		&self.peers
 	}
 
-	fn mut_peers<F: Fn(&mut Vec<Arc<GrandpaPeer>>)>(&mut self, closure: F) {
+	fn mut_peers<F: FnOnce(&mut Vec<Arc<GrandpaPeer>>)>(&mut self, closure: F) {
 		closure(&mut self.peers);
 	}
 
diff --git a/substrate/core/network/src/protocol.rs b/substrate/core/network/src/protocol.rs
index 65c02a39aa..47bfde1bfb 100644
--- a/substrate/core/network/src/protocol.rs
+++ b/substrate/core/network/src/protocol.rs
@@ -206,8 +206,8 @@ impl<B: BlockT, F: FnOnce(&mut ConsensusGossip<B>, &mut Context<B>)> GossipTask<
 
 /// Messages sent to Protocol from elsewhere inside the system.
 pub enum ProtocolMsg<B: BlockT, S: NetworkSpecialization<B>> {
-	/// Tell protocol to maintain sync.
-	MaintainSync,
+	/// A batch of blocks has been processed, with or without errors.
+	BlocksProcessed(Vec<B::Hash>, bool),
 	/// Tell protocol to restart sync.
 	RestartSync,
 	/// Ask the protocol for its status.
@@ -367,11 +367,12 @@ impl<B: BlockT, S: NetworkSpecialization<B>, H: ExHashT> Protocol<B, S, H> {
 			ProtocolMsg::GossipConsensusMessage(topic, engine_id, message) => {
 				self.gossip_consensus_message(topic, engine_id, message)
 			}
-			ProtocolMsg::MaintainSync => {
+			ProtocolMsg::BlocksProcessed(hashes, has_error) => {
+				self.sync.blocks_processed(hashes, has_error);
 				let mut context =
 					ProtocolContext::new(&mut self.context_data, &self.network_chan);
 				self.sync.maintain_sync(&mut context);
-			}
+			},
 			ProtocolMsg::RestartSync => {
 				let mut context =
 					ProtocolContext::new(&mut self.context_data, &self.network_chan);
@@ -624,16 +625,7 @@ impl<B: BlockT, S: NetworkSpecialization<B>, H: ExHashT> Protocol<B, S, H> {
 				response,
 			);
 		} else {
-			// import_queue.import_blocks also acquires sync.write();
-			// Break the cycle by doing these separately from the outside;
-			let new_blocks = {
-				self.sync.on_block_data(&mut ProtocolContext::new(&mut self.context_data, &self.network_chan), peer, request, response)
-			};
-
-			if let Some((origin, new_blocks)) = new_blocks {
-				let import_queue = self.sync.import_queue();
-				import_queue.import_blocks(origin, new_blocks);
-			}
+			self.sync.on_block_data(&mut ProtocolContext::new(&mut self.context_data, &self.network_chan), peer, request, response);
 		}
 	}
 
diff --git a/substrate/core/network/src/service.rs b/substrate/core/network/src/service.rs
index 0741c9f1d9..3ccb9c1277 100644
--- a/substrate/core/network/src/service.rs
+++ b/substrate/core/network/src/service.rs
@@ -71,6 +71,7 @@ pub trait TransactionPool<H: ExHashT, B: BlockT>: Send + Sync {
 }
 
 /// A link implementation that connects to the network.
+#[derive(Clone)]
 pub struct NetworkLink<B: BlockT, S: NetworkSpecialization<B>> {
 	/// The protocol sender
 	pub(crate) protocol_sender: Sender<ProtocolMsg<B, S>>,
@@ -83,6 +84,10 @@ impl<B: BlockT, S: NetworkSpecialization<B>> Link<B> for NetworkLink<B, S> {
 		let _ = self.protocol_sender.send(ProtocolMsg::BlockImportedSync(hash.clone(), number));
 	}
 
+	fn blocks_processed(&self, processed_blocks: Vec<B::Hash>, has_error: bool) {
+		let _ = self.protocol_sender.send(ProtocolMsg::BlocksProcessed(processed_blocks, has_error));
+	}
+
 	fn justification_imported(&self, who: NodeIndex, hash: &B::Hash, number: NumberFor<B>, success: bool) {
 		let _ = self.protocol_sender.send(ProtocolMsg::JustificationImportResult(hash.clone(), number, success));
 		if !success {
@@ -95,10 +100,6 @@ impl<B: BlockT, S: NetworkSpecialization<B>> Link<B> for NetworkLink<B, S> {
 		let _ = self.protocol_sender.send(ProtocolMsg::RequestJustification(hash.clone(), number));
 	}
 
-	fn maintain_sync(&self) {
-		let _ = self.protocol_sender.send(ProtocolMsg::MaintainSync);
-	}
-
 	fn useless_peer(&self, who: NodeIndex, reason: &str) {
 		trace!(target:"sync", "Useless peer {}, {}", who, reason);
 		self.network_sender.send(NetworkMsg::ReportPeer(who, Severity::Useless(reason.to_string())));
diff --git a/substrate/core/network/src/sync.rs b/substrate/core/network/src/sync.rs
index 1cf639ee65..6ba6617d7a 100644
--- a/substrate/core/network/src/sync.rs
+++ b/substrate/core/network/src/sync.rs
@@ -14,6 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
+use std::cmp::max;
 use std::collections::{HashMap, VecDeque};
 use std::time::{Duration, Instant};
 use log::{debug, trace, warn};
@@ -26,10 +27,11 @@ use consensus::import_queue::{ImportQueue, IncomingBlock};
 use client::error::Error as ClientError;
 use crate::blocks::BlockCollection;
 use runtime_primitives::Justification;
-use runtime_primitives::traits::{Block as BlockT, Header as HeaderT, As, NumberFor};
+use runtime_primitives::traits::{Block as BlockT, Header as HeaderT, As, NumberFor, Zero};
 use runtime_primitives::generic::BlockId;
 use crate::message::{self, generic::Message as GenericMessage};
 use crate::config::Roles;
+use std::collections::HashSet;
 use std::sync::Arc;
 use std::sync::atomic::{AtomicBool, Ordering};
 
@@ -303,6 +305,8 @@ pub struct ChainSync<B: BlockT> {
 	required_block_attributes: message::BlockAttributes,
 	justifications: PendingJustifications<B>,
 	import_queue: Box<ImportQueue<B>>,
+	queue_blocks: HashSet<B::Hash>,
+	best_importing_number: NumberFor<B>,
 	is_stopping: AtomicBool,
 	is_offline: Arc<AtomicBool>,
 	is_major_syncing: Arc<AtomicBool>,
@@ -367,6 +371,8 @@ impl<B: BlockT> ChainSync<B> {
 			justifications: PendingJustifications::new(),
 			required_block_attributes,
 			import_queue,
+			queue_blocks: Default::default(),
+			best_importing_number: Zero::zero(),
 			is_stopping: Default::default(),
 			is_offline,
 			is_major_syncing,
@@ -377,11 +383,6 @@ impl<B: BlockT> ChainSync<B> {
 		self.peers.values().max_by_key(|p| p.best_number).map(|p| p.best_number)
 	}
 
-	/// Returns import queue reference.
-	pub(crate) fn import_queue(&self) -> Box<ImportQueue<B>> {
-		self.import_queue.clone()
-	}
-
 	fn state(&self, best_seen: &Option<NumberFor<B>>) -> SyncState {
 		match best_seen {
 			&Some(n) if n > self.best_queued_number && n - self.best_queued_number > As::sa(5) => SyncState::Downloading,
@@ -410,7 +411,7 @@ impl<B: BlockT> ChainSync<B> {
 		let previous_state = self.state(&previous_best_seen);
 
 		if let Some(info) = protocol.peer_info(who) {
-			match (block_status(&*protocol.client(), &*self.import_queue, info.best_hash), info.best_number) {
+			match (block_status(&*protocol.client(), &self.queue_blocks, info.best_hash), info.best_number) {
 				(Err(e), _) => {
 					debug!(target:"sync", "Error reading blockchain: {:?}", e);
 					let reason = format!("Error legimimately reading blockchain status: {:?}", e);
@@ -424,7 +425,7 @@ impl<B: BlockT> ChainSync<B> {
 					let reason = format!("New peer with unknown genesis hash {} ({}).", info.best_hash, info.best_number);
 					protocol.report_peer(who, Severity::Bad(reason));
 				},
-				(Ok(BlockStatus::Unknown), _) if self.import_queue.status().importing_count > MAJOR_SYNC_BLOCKS => {
+				(Ok(BlockStatus::Unknown), _) if self.queue_blocks.len() > MAJOR_SYNC_BLOCKS => {
 					// when actively syncing the common point moves too fast.
 					debug!(target:"sync", "New peer with unknown best hash {} ({}), assuming common block.", self.best_queued_hash, self.best_queued_number);
 					self.peers.insert(who, PeerSync {
@@ -498,7 +499,7 @@ impl<B: BlockT> ChainSync<B> {
 		who: NodeIndex,
 		request: message::BlockRequest<B>,
 		response: message::BlockResponse<B>
-	) -> Option<(BlockOrigin, Vec<IncomingBlock<B>>)> {
+	) {
 		let new_blocks: Vec<IncomingBlock<B>> = if let Some(ref mut peer) = self.peers.get_mut(&who) {
 			let mut blocks = response.blocks;
 			if request.direction == message::Direction::Descending {
@@ -553,24 +554,24 @@ impl<B: BlockT> ChainSync<B> {
 									let n = n - As::sa(1);
 									peer.state = PeerSyncState::AncestorSearch(n);
 									Self::request_ancestry(protocol, who, n);
-									return None;
+									return;
 								},
 								Ok(_) => { // genesis mismatch
 									trace!(target:"sync", "Ancestry search: genesis mismatch for peer {}", who);
 									protocol.report_peer(who, Severity::Bad("Ancestry search: genesis mismatch for peer".to_string()));
-									return None;
+									return;
 								},
 								Err(e) => {
 									let reason = format!("Error answering legitimate blockchain query: {:?}", e);
 									protocol.report_peer(who, Severity::Useless(reason));
-									return None;
+									return;
 								}
 							}
 						},
 						None => {
 							trace!(target:"sync", "Invalid response when searching for ancestor from {}", who);
 							protocol.report_peer(who, Severity::Bad("Invalid response when searching for ancestor".to_string()));
-							return None;
+							return;
 						}
 					}
 				},
@@ -593,7 +594,14 @@ impl<B: BlockT> ChainSync<B> {
 			self.block_queued(&hash, number);
 		}
 		self.maintain_sync(protocol);
-		Some((origin, new_blocks))
+		let new_best_importing_number = new_blocks
+			.last()
+			.and_then(|b| b.header.as_ref().map(|h| h.number().clone()))
+			.unwrap_or_else(|| Zero::zero());
+		self.queue_blocks
+			.extend(new_blocks.iter().map(|b| b.hash.clone()));
+		self.best_importing_number = max(new_best_importing_number, self.best_importing_number);
+		self.import_queue.import_blocks(origin, new_blocks);
 	}
 
 	/// Handle new justification data.
@@ -644,6 +652,16 @@ impl<B: BlockT> ChainSync<B> {
 		self.maintain_sync(protocol);
 	}
 
+	/// A batch of blocks have been processed, with or without errors.
+	pub fn blocks_processed(&mut self, processed_blocks: Vec<B::Hash>, has_error: bool) {
+		for hash in processed_blocks {
+			self.queue_blocks.remove(&hash);
+		}
+		if has_error {
+			self.best_importing_number = Zero::zero();
+		}
+	}
+
 	/// Maintain the sync process (download new blocks, fetch justifications).
 	pub fn maintain_sync(&mut self, protocol: &mut Context<B>) {
 		if self.is_stopping.load(Ordering::SeqCst) {
@@ -787,7 +805,7 @@ impl<B: BlockT> ChainSync<B> {
 	}
 
 	fn is_known(&self, protocol: &mut Context<B>, hash: &B::Hash) -> bool {
-		block_status(&*protocol.client(), &*self.import_queue, *hash).ok().map_or(false, |s| s != BlockStatus::Unknown)
+		block_status(&*protocol.client(), &self.queue_blocks, *hash).ok().map_or(false, |s| s != BlockStatus::Unknown)
 	}
 
 	/// Handle disconnected peer.
@@ -813,7 +831,8 @@ impl<B: BlockT> ChainSync<B> {
 
 	/// Restart the sync process.
 	pub(crate) fn restart(&mut self, protocol: &mut Context<B>) {
-		self.import_queue.clear();
+		self.queue_blocks.clear();
+		self.best_importing_number = Zero::zero();
 		self.blocks.clear();
 		match protocol.client().info() {
 			Ok(info) => {
@@ -884,9 +903,8 @@ impl<B: BlockT> ChainSync<B> {
 	// Issue a request for a peer to download new blocks, if any are available
 	fn download_new(&mut self, protocol: &mut Context<B>, who: NodeIndex) {
 		if let Some(ref mut peer) = self.peers.get_mut(&who) {
-			let import_status = self.import_queue.status();
 			// when there are too many blocks in the queue => do not try to download new blocks
-			if import_status.importing_count > MAX_IMPORTING_BLOCKS {
+			if self.queue_blocks.len() > MAX_IMPORTING_BLOCKS {
 				trace!(target: "sync", "Too many blocks in the queue.");
 				return;
 			}
@@ -931,10 +949,10 @@ impl<B: BlockT> ChainSync<B> {
 /// Get block status, taking into account import queue.
 fn block_status<B: BlockT>(
 	chain: &crate::chain::Client<B>,
-	queue: &ImportQueue<B>,
+	queue_blocks: &HashSet<B::Hash>,
 	hash: B::Hash) -> Result<BlockStatus, ClientError>
 {
-	if queue.is_importing(&hash) {
+	if queue_blocks.contains(&hash) {
 		return Ok(BlockStatus::Queued);
 	}
 
diff --git a/substrate/core/network/src/test/mod.rs b/substrate/core/network/src/test/mod.rs
index 1ff52c9916..47750080a6 100644
--- a/substrate/core/network/src/test/mod.rs
+++ b/substrate/core/network/src/test/mod.rs
@@ -93,7 +93,8 @@ pub struct NoopLink { }
 impl<B: BlockT> Link<B> for NoopLink { }
 
 /// The test specialization.
-pub struct DummySpecialization { }
+#[derive(Clone)]
+pub struct DummySpecialization;
 
 impl NetworkSpecialization<Block> for DummySpecialization {
 	fn status(&self) -> Vec<u8> {
@@ -117,23 +118,92 @@ impl NetworkSpecialization<Block> for DummySpecialization {
 
 pub type PeersClient = client::Client<test_client::Backend, test_client::Executor, Block, test_client::runtime::RuntimeApi>;
 
-pub struct Peer<D> {
+#[derive(Clone)]
+/// A Link that can wait for a block to have been imported.
+pub struct TestLink<S: NetworkSpecialization<Block> + Clone> {
+	import_done: Arc<AtomicBool>,
+	hash: Arc<Mutex<Hash>>,
+	link: NetworkLink<Block, S>,
+}
+
+impl<S: NetworkSpecialization<Block> + Clone> TestLink<S> {
+	fn new(
+		protocol_sender: Sender<ProtocolMsg<Block, S>>,
+		network_sender: NetworkChan<Block>
+	) -> TestLink<S> {
+		TestLink {
+			import_done: Arc::new(AtomicBool::new(false)),
+			hash: Arc::new(Mutex::new(Default::default())),
+			link: NetworkLink {
+				protocol_sender,
+				network_sender,
+			}
+		}
+	}
+
+	/// Set the hash which will be awaited for import.
+	fn with_hash(&self, hash: Hash) {
+		self.import_done.store(false, Ordering::SeqCst);
+		*self.hash.lock() = hash;
+	}
+
+	/// Simulate a synchronous import.
+	fn wait_for_import(&self) {
+		while !self.import_done.load(Ordering::SeqCst) {
+			thread::sleep(Duration::from_millis(20));
+		}
+	}
+}
+
+impl<S: NetworkSpecialization<Block> + Clone> Link<Block> for TestLink<S> {
+	fn block_imported(&self, hash: &Hash, number: NumberFor<Block>) {
+		if hash == &*self.hash.lock() {
+			self.import_done.store(true, Ordering::SeqCst);
+		}
+		self.link.block_imported(hash, number);
+	}
+
+	fn blocks_processed(&self, processed_blocks: Vec<Hash>, has_error: bool) {
+		self.link.blocks_processed(processed_blocks, has_error);
+	}
+
+	fn justification_imported(&self, who: NodeIndex, hash: &Hash, number:NumberFor<Block>, success: bool) {
+		self.link.justification_imported(who, hash, number, success);
+	}
+
+	fn request_justification(&self, hash: &Hash, number: NumberFor<Block>) {
+		self.link.request_justification(hash, number);
+	}
+
+	fn useless_peer(&self, who: NodeIndex, reason: &str) {
+		self.link.useless_peer(who, reason);
+	}
+
+	fn note_useless_and_restart_sync(&self, who: NodeIndex, reason: &str) {
+		self.link.note_useless_and_restart_sync(who, reason);
+	}
+
+	fn restart(&self) {
+		self.link.restart();
+	}
+}
+
+pub struct Peer<D, S: NetworkSpecialization<Block> + Clone> {
 	pub is_offline: Arc<AtomicBool>,
 	pub is_major_syncing: Arc<AtomicBool>,
 	pub peers: Arc<RwLock<HashMap<NodeIndex, ConnectedPeer<Block>>>>,
 	client: Arc<PeersClient>,
 	network_to_protocol_sender: Sender<FromNetworkMsg<Block>>,
-	pub protocol_sender: Sender<ProtocolMsg<Block, DummySpecialization>>,
-
-	network_port: Mutex<NetworkPort<Block>>,
+	pub protocol_sender: Sender<ProtocolMsg<Block, S>>,
+	network_link: TestLink<S>,
+	network_port: Arc<Mutex<NetworkPort<Block>>>,
 	pub import_queue: Box<ImportQueue<Block>>,
-	network_sender: NetworkChan<Block>,
 	pub data: D,
 	best_hash: Mutex<Option<H256>>,
 	finalized_hash: Mutex<Option<H256>>,
 }
 
-impl<D> Peer<D> {
+impl<D, S: NetworkSpecialization<Block> + Clone> Peer<D, S> {
 	fn new(
 		is_offline: Arc<AtomicBool>,
 		is_major_syncing: Arc<AtomicBool>,
@@ -141,12 +211,14 @@ impl<D> Peer<D> {
 		client: Arc<PeersClient>,
 		import_queue: Box<ImportQueue<Block>>,
 		network_to_protocol_sender: Sender<FromNetworkMsg<Block>>,
-		protocol_sender: Sender<ProtocolMsg<Block, DummySpecialization>>,
+		protocol_sender: Sender<ProtocolMsg<Block, S>>,
 		network_sender: NetworkChan<Block>,
 		network_port: NetworkPort<Block>,
 		data: D,
 	) -> Self {
-		let network_port = Mutex::new(network_port);
+		let network_port = Arc::new(Mutex::new(network_port));
+		let network_link = TestLink::new(protocol_sender.clone(), network_sender.clone());
+		import_queue.start(Box::new(network_link.clone())).expect("Test ImportQueue always starts");
 		Peer {
 			is_offline,
 			is_major_syncing,
@@ -155,7 +227,7 @@ impl<D> Peer<D> {
 			network_to_protocol_sender,
 			protocol_sender,
 			import_queue,
-			network_sender,
+			network_link,
 			network_port,
 			data,
 			best_hash: Mutex::new(None),
@@ -171,12 +243,6 @@ impl<D> Peer<D> {
 			.header(&BlockId::Hash(info.chain.best_hash))
 			.unwrap()
 			.unwrap();
-		let network_link = NetworkLink {
-			protocol_sender: self.protocol_sender.clone(),
-			network_sender: self.network_sender.clone(),
-		};
-
-		self.import_queue.start(Box::new(network_link)).expect("Test ImportQueue always starts");
 		let _ = self
 			.protocol_sender
 			.send(ProtocolMsg::BlockImported(info.chain.best_hash, header));
@@ -237,8 +303,7 @@ impl<D> Peer<D> {
 
 	/// Whether this peer is done syncing (has no messages to send).
 	fn is_done(&self) -> bool {
-		self.import_queue.status().importing_count == 0 &&
-			self.network_port.lock().receiver().is_empty()
+		self.network_port.lock().receiver().is_empty()
 	}
 
 	/// Execute a "sync step". This is called for each peer after it sends a packet.
@@ -362,7 +427,7 @@ impl<D> Peer<D> {
 			);
 			let header = block.header.clone();
 			at = hash;
-
+			self.network_link.with_hash(hash);
 			self.import_queue.import_blocks(
 				origin,
 				vec![IncomingBlock {
@@ -373,10 +438,8 @@ impl<D> Peer<D> {
 					justification: None,
 				}],
 			);
-			// Simulate a synchronous import.
-			while self.import_queue.status().importing_count > 0 {
-				thread::sleep(Duration::from_millis(20));
-			}
+			// Simulate a sync import.
+			self.network_link.wait_for_import();
 		}
 		at
 	}
@@ -436,7 +499,18 @@ impl TransactionPool<Hash, Block> for EmptyTransactionPool {
 	fn on_broadcasted(&self, _: HashMap<Hash, Vec<String>>) {}
 }
 
+pub trait SpecializationFactory {
+    fn create() -> Self;
+}
+
+impl SpecializationFactory for DummySpecialization {
+	fn create() -> DummySpecialization {
+		DummySpecialization
+	}
+}
+
 pub trait TestNetFactory: Sized {
+	type Specialization: NetworkSpecialization<Block> + Clone + SpecializationFactory;
 	type Verifier: 'static + Verifier<Block>;
 	type PeerData: Default;
 
@@ -445,9 +519,9 @@ pub trait TestNetFactory: Sized {
 	fn make_verifier(&self, client: Arc<PeersClient>, config: &ProtocolConfig) -> Arc<Self::Verifier>;
 
 	/// Get reference to peer.
-	fn peer(&self, i: usize) -> &Peer<Self::PeerData>;
-	fn peers(&self) -> &Vec<Arc<Peer<Self::PeerData>>>;
-	fn mut_peers<F: Fn(&mut Vec<Arc<Peer<Self::PeerData>>>)>(&mut self, closure: F);
+	fn peer(&self, i: usize) -> &Peer<Self::PeerData, Self::Specialization>;
+	fn peers(&self) -> &Vec<Arc<Peer<Self::PeerData, Self::Specialization>>>;
+	fn mut_peers<F: FnOnce(&mut Vec<Arc<Peer<Self::PeerData, Self::Specialization>>>)>(&mut self, closure: F);
 
 	fn started(&self) -> bool;
 	fn set_started(&mut self, now: bool);
@@ -483,9 +557,9 @@ pub trait TestNetFactory: Sized {
 		let (network_sender, network_port) = network_channel(ProtocolId::default());
 
 		let import_queue = Box::new(BasicQueue::new(verifier, block_import, justification_import));
-		let specialization = DummySpecialization {};
 		let is_offline = Arc::new(AtomicBool::new(true));
 		let is_major_syncing = Arc::new(AtomicBool::new(false));
+		let specialization = self::SpecializationFactory::create();
 		let peers: Arc<RwLock<HashMap<NodeIndex, ConnectedPeer<Block>>>> = Arc::new(Default::default());
 		let (protocol_sender, network_to_protocol_sender) = Protocol::new(
 			is_offline.clone(),
@@ -514,7 +588,7 @@ pub trait TestNetFactory: Sized {
 		));
 
 		self.mut_peers(|peers| {
-			peers.push(peer.clone())
+			peers.push(peer)
 		});
 	}
 
@@ -666,11 +740,12 @@ pub trait TestNetFactory: Sized {
 }
 
 pub struct TestNet {
-	peers: Vec<Arc<Peer<()>>>,
+	peers: Vec<Arc<Peer<(), DummySpecialization>>>,
 	started: bool,
 }
 
 impl TestNetFactory for TestNet {
+	type Specialization = DummySpecialization;
 	type Verifier = PassThroughVerifier;
 	type PeerData = ();
 
@@ -688,15 +763,15 @@ impl TestNetFactory for TestNet {
 		Arc::new(PassThroughVerifier(false))
 	}
 
-	fn peer(&self, i: usize) -> &Peer<()> {
+	fn peer(&self, i: usize) -> &Peer<(), Self::Specialization> {
 		&self.peers[i]
 	}
 
-	fn peers(&self) -> &Vec<Arc<Peer<()>>> {
+	fn peers(&self) -> &Vec<Arc<Peer<(), Self::Specialization>>> {
 		&self.peers
 	}
 
-	fn mut_peers<F: Fn(&mut Vec<Arc<Peer<()>>>)>(&mut self, closure: F) {
+	fn mut_peers<F: FnOnce(&mut Vec<Arc<Peer<(), Self::Specialization>>>)>(&mut self, closure: F) {
 		closure(&mut self.peers);
 	}
 
@@ -728,6 +803,7 @@ impl JustificationImport<Block> for ForceFinalized {
 pub struct JustificationTestNet(TestNet);
 
 impl TestNetFactory for JustificationTestNet {
+	type Specialization = DummySpecialization;
 	type Verifier = PassThroughVerifier;
 	type PeerData = ();
 
@@ -741,15 +817,15 @@ impl TestNetFactory for JustificationTestNet {
 		self.0.make_verifier(client, config)
 	}
 
-	fn peer(&self, i: usize) -> &Peer<Self::PeerData> {
+	fn peer(&self, i: usize) -> &Peer<Self::PeerData, Self::Specialization> {
 		self.0.peer(i)
 	}
 
-	fn peers(&self) -> &Vec<Arc<Peer<Self::PeerData>>> {
+	fn peers(&self) -> &Vec<Arc<Peer<Self::PeerData, Self::Specialization>>> {
 		self.0.peers()
 	}
 
-	fn mut_peers<F: Fn(&mut Vec<Arc<Peer<Self::PeerData>>>)>(&mut self, closure: F ) {
+	fn mut_peers<F: FnOnce(&mut Vec<Arc<Peer<Self::PeerData, Self::Specialization>>>)>(&mut self, closure: F ) {
 		self.0.mut_peers(closure)
 	}