Subject: RE: [SIP] SIP proxies and CSeq numbers

From: [email-masked]
Date: Wed, 1 Nov 2000 17:25:31 +0530

Jean,
responses inline and prefixed by ARC>

Take this other scenario where the proxy is seating between a public net &
a
private trusted net and the proxy requires authentication on one leg only.
     A -> P: authentication is required, A is in the public net.  A
initiates an invite (F1), P challenges A (F2) but P also sends the request
to B (F3) while waiting for the credentials (proxies may act like this: the
proxy knows that A comes from a known but untrusted network and has
confidence the authentication should be ok so it sends the request F3
before
receiving F4).  Another justification for proxies to act this way may be
that to check the credentials on F4, the proxy has check with a remote
authentication server.
     P -> B: no authentication required

If the UA A behaves as you stated in this scenario and sends the ACK
directly to B, the CSeq=2 in the ACK: game over.

Any suggestions on how do we fix this?

ARC> Yes. The proxy should not forward the request (F3) to B in the first
place.
ARC> Since you say the proxy wants to challenge A, it should not go about
forwarding
ARC> the request to B. Let it wait for the challenge to be met. When agreed
upon
ARC> it should then forward the correct messge to B (in your case F4).

Jean-Francois Mule'

SIP UA: A                 Proxy                       SIP UA: B

 |                          |                          |
 |   F1 INVITE (Cseq=1)     |                          |
 |------------------------->|                          |
 |                          |                          |
 |   F2  407 Proxy auth. req|                          |
 |<-------------------------|   F3 INVITE  (Cseq=1)    |
 |                          |------------------------->|
 |   F4 INVITE (Cseq=2)     |                          |
 |------------------------->|                          |
 |                          |   F5  Trying (Cseq=1)    |
 |                          |<-------------------------|
 |   F6  Trying (Cseq=2)    |                          |
 |<-------------------------|                          |
 |                          |   F7  200 OK (Cseq=1)    |
 |                          |<-------------------------|
 |   F8  200 OK (Cseq=2)    |                          |
 |<-------------------------|                          |
 |                                                     |
 |                      F9  ACK (Cseq=2) !             |
 |---------------------------------------------------->|
 |                          |                          |

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]
> Sent: Monday, October 30, 2000 10:06 PM
> To: Jean-Francois Mule
> Cc: [email-masked]; [email-masked] '
> Subject: RE: [SIP] SIP proxies and CSeq numbers (was: SIP and T.38 fax

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---

From: Jean-Francois Mule <[email-masked]>
Date: Wed, 1 Nov 2000 10:18:38 -0800

Arjun:
Your suggestion would be the recommended way of handling this scenario and
this is how most of us are doing it.  But in any case, I do not think we can
enforce this at all.  Again, my proxy may want to buy some time when sending
F3 so that as soon as get F5, I have the F5 right in the queue and send the
F6 right away.

Jean-Francois.

---

From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 2 Nov 2000 00:44:58 -0500

> From: Jean-Francois Mule [mailto:[email-masked]]
> Sent: Wednesday, November 01, 2000 1:19 PM
> To: [email-masked]
> Cc: [email-masked] '
> Subject: RE: [SIP] SIP proxies and CSeq numbers
> 
> 
> Arjun:
> enforce this at all.

Well, we can't enforce people building elements compliant to the spec. The
behavior you are advocating is simply not compliant. It will not function
correctly with anyone elses equipment. It will result in bizarre, incorrect
behavior (things like the called party gets rung even though the credentials
fail, resulting in a dangling half call at the called party). 

-Jonathan R.

---
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (973) 952-5000
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