Subject: Some problem with sip responses!!!

From: "Shary" <[email-masked]>
Date: Mon, 6 Sep 1999 16:07:43 +0200

Hello,
Let's suppose that A, B,C are 3 proxies connected in the following way:

UAC ---- A
 |       |
 C  ---- B
         |
        UAS

Moreover suppose that UAC send a sip request to UAS, request that passes in
the nodes A and B.  B finds the UAS.
All A, B  have added their "via" field in the request message.
Now, UAS has to send  the response upstream; making the additional
assumption that the path  B - A is down,
UAS has to find another one (for example C - UAC ).
Now, the problem is that ,normally, C would not examine this response
received with a topmost "via" without his addresses !!!!!
So, what about this response???? It will  never arrive to UAC or there are
other mechanisms to tell C to not drop this response?

Thanks in advance for your support..

---

From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 06 Sep 1999 16:52:33 -0400

> other mechanisms to tell C to not drop this response?

The response must take the reverse path from the request. This is needed
for proper transactional state maintenance in proxies. SIP has no
provision for routing responses along a different path. So, if B just
dies mid-transaction, pending transactions cannot complete along that
branch. A forking proxy would allow the transaction to complete along a
different branch. A smart server might see some ICMP errors and try a
different next hop server also.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
FAX: (732) 834-5379                         Rm. 4C-526
EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen