ADR 0018: Inter-Runtime Communication Protocol (IRCP)

[kostko]

No description provided.

[gw0]

It is a bit unclear how this would work on other nodes that do not run both runtimes (where do they get the packets from?). If packets are not written to the consensus layer or elsewhere, how do new nodes verify which packets were received in the past and in what way they affected the state?

[kostko]

This will be more clear once the protocol flow sections are written. But to answer briefly:

• Packets are transported via P2P, similar to transactions (see the Transport section), and are verified using Merkle proofs and light clients (see the Authentication section).
• All nodes sharing the consensus layer have a trusted view of consensus light headers. Since the consensus layer state stores all state roots of all runtimes, any node can obtain the state root at given height of any runtime.
• Verifiable packet batches (generated by the source runtime which does have access to the entire runtime state) contain Merkle proofs, rooted at the runtime's state root, proving a certain leaf is stored in source runtime's storage.
• Usually the leaf to be proven is the outgoing packet being stored in the source runtime's send queue.
• This proves (to the destination runtime) that the packet was indeed sent by the given runtime.
• Ordering is verified by tracking sequence numbers.