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@freenet.ag Organization: Freenet Cityline GmbH To: SIP sip@arcdiv.com References: b222g3dmntvc38gk3v2uq7vau6vmfcjem1@4ax.com 4701F388.7020109@freenet.ag 470217DF.9020607@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