# Parachains Finality Relay

Source Relay Chain is running GRANDPA Finality Gadget. Source Parachain is a parachain of the Source Relay Chain. Bridge GRANDPA finality pallet is deployed at Target Chain runtime and is "connected" to the Source Relay Chain. Bridge Parachains finality pallet is deployed at Target Chain and is configured to track the Source Parachain. GRANDPA Relayer is configured to relay Source Relay Chain finality to Target Chain. Parachains Relayer is configured to relay Source Parachain headers finality to Target Chain.

sequenceDiagram participant Source Parachain participant Source Relay Chain participant GRANDPA Relayer participant Parachains Relayer participant Target Chain Note left of Source Parachain: Best: 125 Note left of Source Relay Chain: Finalized: 500, Best Parachain at Finalized: 120 Note right of Target Chain: Best Relay: 480, Best Parachain: 110 Source Parachain ->> Source Parachain: Import Block 126 Source Parachain ->> Source Relay Chain: Receives the Parachain block 126 Source Relay Chain ->> Source Relay Chain: Import block 501 Source Relay Chain ->> Source Relay Chain: Finalize block 501 Note left of Source Relay Chain: Finalized: 501, Best Parachain at Finalized: 126 Source Relay Chain ->> Parachains Relayer: notes new Source Parachain Block 126 Note left of Parachains Relayer: can't relay Source Parachain Block 126, because it requires at least Source Relay Block 501 at Target Chain Source Relay Chain ->> Source Relay Chain: Import block 502 Source Relay Chain ->> Source Relay Chain: Finalize block 502 Source Relay Chain ->> GRANDPA Relayer: read GRANDPA Finality Proof of Block 502 GRANDPA Relayer ->> Target Chain: submit GRANDPA Finality Proof of Block 502 Note right of Target Chain: Best Relay: 502, Best Parachain: 110 Target Chain ->> Parachains Relayer: notes finalized Source Relay Block 502 at Target Chain Source Relay Chain ->> Parachains Relayer: read Parachain Finality Proof at Relay Block 502 Parachains Relayer ->> Target Chain: submit Parachain Finality Proof at Relay Block 502 Note right of Target Chain: Best Relay: 502, Best Parachain: 126