Session_id in SSH?

[Paul Hoffman / VPNC <paul.hoffman%vpnc.org@localhost>]

Greetings again. I'm trying to figure out the key exchange in SSH 
from reading secsh-transport-16 and have hit a roadblock. Section 5.2 
has you doing hashes over strings that include "session_id", but that 
is never defined in the document.

The text in the first paragraph of 5.2 says:
      The exchange hash H from the first key exchange is
      additionally used as the session identifier, which is a unique
      identifier for this connection.
It sounds like session_id and H are the same thing, but that makes no 
sense when looking at the contents of the hashed strings. Why would 
you include the contents of "H" twice?

Any help would be appreciated.

--Paul