Forge has plugin message chanell 'FML|HS' (about plugin message chanells), could you tell me where I can read about it?
sorry for my English

Im not really sure what your question is. The link you posted has all the details you need for the forge message. Fabric does not have anything like this currenly.

it's a vanilla thing. fabric can connect to any server/client without needing to send any packets, and if you.want to deal with packets we have networking api.