With SSL/TLS, the client connects and sends a ClientHello message first, and then the server responds; with SSH, the server will send a version string upon connection (and expects the client to do the same). With plain HTTP, the client sends the request first. The server can detect which one of these cases it is.

I'm still being not clear of what you mean by:

>with SSH, the server will send a version string upon connection (and expects the client to do the same).

Say for example if I do:

   ssh some.machine.com

I'm (being the client ) call the ssh port ( server ) running on the some.machine.com, right? If thats the case, client is who starting the conversation right?

Correct me if I'm wrong.

Establishing a connection isn't considered 'sending a message'.

Oh ok. Now I understood, thanks.