Subject: Re: [Sip] 200 UPDATE race condition

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 25 Sep 2002 02:53:30 -0400

Christer Holmberg wrote:
> Hi,

>>>1. UA_A (the caller) receives the 200 for the INVITE, sends ACK, and
>>>then sends UPDATE, but for whatever reason the UPDATE reaches UA_B
>>>before the ACK.
>>>
>>>2. UA_A sends the UPDATE at the same time as UA_B sends the 200 for the
>>>INVITE, ie we have a race condition.
>>
>>Why? There is no SDP in the 2xx to the INVITE, or in the ACK. Thus, the
>>relative ordering of the 2xx and the UPDATE are irrelevant. There is no
>>race condition.
> 
> 
> That is true for SDP, but let's assume it's a general message body (even if
> the offer/answer rules don't allow us to include an SDP in the 2xx, I assume
> we can include other kind of message bodies - ISUP MIMEs, for example...),
> then, where the CONTENT of the message body in the UPDATE would be different
> if generated before or after the 2xx. Yes, UA_A may always generate a new
> UPDATE when it has received the 2xx, but the first UPDATE may already have
> caused some "damage".

This has nothing to do with the UPDATE spec. Sending a request with a 
body whose interpretation depends on whether the other side has sent a 
specific message or not, is a bad idea. There is no way to know whether 
or not that other message has been sent.

Anyway, this sounds academic. Is there a real problem here?

-Jonathan R.

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

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