[Serusers] [Fwd: Re: How to change INVITE From field]

[Olaf Bergmann]

I should have Cc'd this to the list...

-------- Original Message --------
Subject: Re: [Serusers] How to change INVITE From field
Date: Tue, 02 Oct 2007 13:57:49 +0200
From: Olaf Bergmann <Olaf.Bergmann at freenet.ag>
Organization: Freenet Cityline GmbH
To: SIP <sip at arcdiv.com>
References: <b222g3dmntvc38gk3v2uq7vau6vmfcjem1 at 4ax.com>
<4701F388.7020109 at freenet.ag> <470217DF.9020607 at arcdiv.com>

SIP wrote:

[RFC 2543]

> The implication of this is that the ENTIRE From/To headers are not
> necessarily immutable, as the tag is used to identify them as unique.

Well, transaction matching in RFC 2543 has used the nameaddr part of
the From/To headers, therefore implementations were required not to
change these. Tags at that time have been introduced primarily for
dealing with forked requests.

In RFC 3261, this has been re-designed mainly for robustness of
transaction matching. Since there were many pre-3261
implementations, the requirement of immutable From and To headers is
still valid. (Nowadays, people start discussing if this is still
necessary.) To ensure interoperability, carriers typically use
dialog-stateful intermediaries (back-to-back user agents) to change
these headers.

> The question is, is there something elsewhere which contradicts this
> (and therefore enforced the rule of immutable From/To headers), or is
> this just a SER idiosyncrasy? If it's just a SER thing, might it not be
> different in other systems (something we might have to watch out for),
> or might it not be coded around within SER to allow modification of the
> From header?

IMHO it is a SER thing, and you could probably change the function
for branch creation (the problem is that you must find another way
for stateless generation of recognizable branch tags).

Regards,
Olaf