The relay part is the part responsible for information transmission. The simplest model is the gateway, the primary function of which is information transmission and translation. After the upgrade, it is the relay node to perform the information communication process. When this part has its own ledger and consensus, it will have higher security. It can be a part of protecting other chains. In Cosmos and Polkadot, the relay level part is very high. The relay nodes are part of the main network nodes, and the data synchronized by the full nodes is the chain general ledger. The nodes of the relay also include the nodes of the lower chain. That is, the ledgers of the lower chain and the relay chain are also synchronized. The consensus of the relay chain protects the security of the lower chain ledger, and the lower chain also participates in the consensus process of the relay chain.