# Introduction
The RPC service is the link between the SDK and the nodes on the chain.
Currently, the official RPC service for testing and production environments is provided, and developers can choose which one to use when using the SDK.
TestNet:
Account Chain : test1.thinkiumrpc.net chainId: 60001
PoS Chain : test2.thinkiumrpc.net chainId: 60002
Business Chain : test103.thinkiumrpc.net chainId : 60103
Cross Chain: test.thinkiumrpc.net
MainNet:
Account Chain : proxy1.thinkiumrpc.net chainId: 70001
PoS Chain : proxy2.thinkiumrpc.net chainId: 70002
Business Chain : proxy103.thinkiumrpc.net chainId : 70103
Cross Chain: proxy.thinkiumrpc.net