XCMP

XCMP, or Cross-Consensus Message Passing, is a protocol designed to enable cross-chain communication among parachains in Polkadot and Kusama networks. It provides a transport mechanism for messages and calls to be transmitted from one chain to another in a trust-minimized manner, using the relay chain as a routing and verification hub. Messages carried by XCMP are expressed using the Cross-Consensus Messaging (XCM) format and can represent actions such as function calls, asset transfers, or data queries, subject to the destination chain’s XCM rules.

Architecture and operation are based on the maintenance of outbound and inbound message queues on each parachain. When a parachain emits a message, it is included in a block and eventually relayed through the relay chain to the destination parachain. The destination chain validates and executes the XCM instructions in its runtime. XCMP is designed to be asynchronous and to preserve message ordering within a channel, with fees and weight reflecting resource usage to deter abuse.

Relation to XCM: XCMP is commonly described as the transport layer for XCM. XCM defines the semantics and interpretation of cross-chain messages, while XCMP provides the routing, delivery guarantees, and inter-chain transport that carries those messages between chains.

Status and usage: XCMP development is part of Polkadot’s interoperability program. Pilot implementations and testnets have demonstrated cross-chain message delivery and parachain interoperability, and ongoing upgrades continue to refine the protocol within the broader XCM framework.

Impact: By enabling direct cross-chain calls and asset transfers between parachains, XCMP reduces reliance on centralized bridges and supports more scalable multi-chain applications within the Polkadot ecosystem.