Subject: [SIP] Inconsistency between SIP draft and FAQ ?

From: Nils Henrik Lorentzen <[email-masked]>
Date: Mon, 2 Apr 2001 17:21:03 +0200

Hi,

I have trouble understanding how to recognize when a request is
a retransmit.

From the FAQ:

----
header retransmitted   duplicate    matching response
From        same          same               same

 To         same          same    same, but tag may have been added

Call-ID     same          same               same

request URI same          same               n/a

CSeq        same          same               same

Via           -             -      must be local host; check for 
                                      branch parameter to identify which
---

So retransmits may be recognized by comparing
From, To, CallID, CSeq and Request-URI.

However, the sip draft says in section 11.5:

"2.   If the Call-ID exists, the request is for an existing call.
If the To, From, Call-ID, and CSeq values exactly match
(including tags) those of any requests received previously,
the request is a retransmission."

Here, the request-URI is not mentioned.

Reason why I ask:

If more than one of the forked requests of a forking proxy
ends up at the same UAS, how does the UAS
know that these are different callegs ?
From what I can see in the examples in the spec,
the forking proxy's downstream requests 
only differ in via branch and in request URL,
ie To, From, CallID and CSeq are the same.

So if the UAS uses just To, From, CallID and CSeq to identify
a transaction, all but the first request that resulted from the fork
will be ignored as retransmits.

Would someone please enlighten me on this ?

Nils Henrik

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