Re: [Sip] 200 UPDATE race condition

[Christer Holmberg <christer.holmberg@lmf.ericsson.se>]

Hi,

Jonathan Rosenberg wrote:

> Christer Holmberg wrote:
> >
> > 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.
>
> 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".

Regards,

Christer Holmberg
Ericsson Finland





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