Subject: Re: Using branch in Via headers by a forking proxy

From: Sean Olson <[email-masked]>
Date: Tue, 14 Sep 1999 13:36:01 -0500 (CDT)

> 
> Can anyone shed some light as to why to do we use a branch field in the Via
> header ?
> 
> This has lots of things to remember.
> The response to the INVITE contain the branches in the Via field as well as the
> tag in the To header.
> So the proxy has to associate the endpoints using branches for sometime and then
> needs to use the tag field in future.
> 
> Would it not be easier if we said:
> 
> The tag in the "To" field is added by the forking proxy and not by the endpoint.
>

The Via: branch is from a different namespace than the To: tag. The Via: 
branch is also only used for a given transaction but a To: tag is intended
to be used for all subsequent requests/transactions within a call as well.
In general, it is not possible for the forking proxy to create a suitable
tag since it has meaning both for the forking proxy and for the User agent 
and must be unique within the User Agents' namespace.
 
> Thanks,
> Anoop

-----------------------------------------------------------------
Sean Olson            E-mail: [email-masked]
Ericsson Inc.         Voice: (972) 583-5472 
                      FAX: (972) 669-0154