Subject: [Sipping] draft-marjou-sipping-b2bua-00

From: Cullen Jennings <[email-masked]>
Date: Sat, 10 Mar 2007 15:37:00 -0800

The most important thing would be discussing handling of Supported  
and Required headers.

draft has
    The UAS SHOULD
    copy other header fields and body from the downstream response into
    this upstream response before sending it.

Let's say I sent a header than mean, all future messages will be  
compressed with gzip. If the UAS and UAC both supported this but the  
B2BUA in the middle did not, blindly coping this header would cause  
things to fail badly.

In section 4.2.3
    If the B2BUA receives forked SIP responses (i.e. responses with
    different to-tag for a previously forwarded request), it must  
forward
    upstream responses with different to-tag.

I think it is possible to build B2BUA that when there is forking on  
side B to N devices, the B2BUA end up simulating N UAs to side A.  
However, it is incredibly difficult to do right - think about  
handling INVITE w replaces for one example. You would likely need to  
say a lot more than just change the to-tag.

Cullen <with my individual hat on>

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