Subject: [Sip] Questions about "Check response for forwarding"...

From: "Patrick Lam" <[email-masked]>
Date: Tue, 15 Apr 2003 10:00:17 +0800

Dear all:

On p.110 of RFC 3261, it states:

"After a final response has been sent on the server transaction, the
following responses MUST be forwarded immediately:
         -  Any 2xx response to an INVITE request"

I am just wondering why the proxy would still forward a 2xx after sending
another final response.  Does this mean that after sending, say a 4xx
response upstream, the proxy should still forward a 2xx response upstream?  

I think I am confused about the wording here.  Why the "final response" is
*sent*, while the "2xx response" is *forwarded*?  Also, isn't 2xx a final
response as well?

At a later paragraph, RFC 3261 states:

"This step, combined with the next, ensures that a stateful proxy will
forward exactly one final response to a non-INVITE         request, and
either exactly one non-2xx response or one or more 2xx responses to an
INVITE request."

I do not see how this conclusion can be drawn.  Nothing about "non-INVITE"
request has been mentioned in this section ('Check response for forwarding')
at all.  Can someone please spend a little time to explain to me how this
conclusion is drawn from the previous paragraphs?

Thanks very much in advance.

Patrick Lam