Subject: [SIP] Retransmission detection and spirals

From: Bernie Hoeneisen <[email-masked]>
Date: Wed, 25 Apr 2001 17:25:30 +0300 (EET DST)

Hi!

1) In the current version of RFC2543bis-02, in section 11.5 it says:

   "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."

   On the other hand, according to section 6.47.6 visiting the same
   SIP proxy twice, but with different Request URIs is allowed,
   (called spiraling or legal loops).

   This leads to the situation, that when such a request is arriving the
   second time at the same SIP proxy (spiraling), is recognized as a
   retransmission according to section 11.5.

   Thus, we need to add in section 11.5.2 something, that also the Request
   URI is checked for retransimission detection.

   Or did I understand something wrongly?

2) Similar to this issue, I found something in the mailing archives:
   http://lists.bell-labs.com/pipermail/sip/2000q4/004567.html
   "The call leg is idenfitied with a tag, but the transaction is
   identified based on the To, From, Call-ID, CSeq, R-URI and top via.
   (the latter two being new since rfc2543, to handle spirals and request
   merging, respectively)."
   This statement of Jonathan seems to be not (yet?) reflected in the
   RFC2543bis-02 draft. Is this coming in the next version? Comments?

cheers,
 Bernie

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---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 25 Apr 2001 13:42:16 -0400

> -----Original Message-----
> From: Bernie Hoeneisen [mailto:[email-masked]]
> Sent: Wednesday, April 25, 2001 10:26 AM
> To: IETF SIP Mailinglist
> Subject: [SIP] Retransmission detection and spirals
> 
> 
> Hi!
> 

You are correct, although it may not matter in the context of this section. 

A request is mapped to a transaction through the combination of the Call-ID,
to, from, Call-ID, CSeq, R-URI and top via, as you point out below. Thus,
this text in section 11.5 is wrong, in that this is not sufficent to
identify a retransmission. 

However, section 11.5 deals with UA behavior. Spirals are not of importance
for a UA (although merged requests are, and those require attention be paid
to the top via). Really, this statement doesn't even belong in section 11.5,
since retransmissions should be handled at a transaction level, and thats
not specific to a UA.

So, this needs correcting by updating it and moving it somewhere else.

>    RFC2543bis-02 draft. Is this coming in the next version? Comments?

It has already been corrected in the text I have for the next revision of
the spec, due out very shortly. However, I still need to move it elsewhere.
That will probably be part of a more extensive editing task for -04.

-Jonathan R.

---
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
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