Subject: [Sip] 200 UPDATE race condition

From: Christer Holmberg <[email-masked]>
Date: Sat, 09 Mar 2002 10:52:15 +0200

Hi,

Another race condition...

Assume UA_B sends a 200 to an INVITE, without SDP (it has been sent
earlier in a reliable 18x).

Then it receives an UPDATE, with a new offer.

Now, there are two possible scenarios:

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.

Now, UA_B doesn't know which case is true.

Now, one could argue that UA_B doesn't have to care. It receives an
UPDATE, accepts it, and that's it. Also, UA_B will receive the 200 for
the INVITE first, but it will wait for the UPDATE response. So, IF both
UA_A and UA_B handle the situation this way I guess things could work.

However, UA_B may want to send 491 for the UPDATE, since it hasn't
received ACK for the INVITE. Is it allowed to do so - EVEN if there is
no answer/offer conflict in this case (since the 200 didn't contain
SDP)?

Regards,

Christer Holmberg
Ericsson Finland

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---

From: Jonathan Rosenberg <[email-masked]>
Date: Sun, 17 Mar 2002 22:57:04 -0500

> 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.

-Jonathan R.
-- 
Jonathan D. Rosenberg, Ph.D.            72 Eagle Rock Avenue
Chief Scientist                         First Floor
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From: Christer Holmberg <[email-masked]>
Date: Mon, 18 Mar 2002 13:27:50 +0200

Hi,

> relative ordering of the 2xx and the UPDATE are irrelevant. There is no

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".

Regards,

Christer Holmberg
Ericsson Finland