Hi,
>
> >Is the other scenario raised by Paul below?
> >
> > -> INVITE
> > <- 180rel
> > -> PRACK
> > <- 401
> >
> >And are there any other cases?IMO, only prack with new offer could
> cause this problem.
>
> A SIP request can be rejected e.g. because the UAS is overloaded.
>
> I don't we can assume that a PRACK will never be rejected, and as
> long as it may be rejected we need to know how to handle it.
If UAS is overloaded, the UAS may have difficult in proceeding all message
such as invite, 180, update ,prack...Then omitting the prack may be implemented
by the UAS.
Regards,
Eric
>
> >Also another question:
> >
> >Is the flows below valid according to recent arguments?
> >
> > UAC UAS
> > |----invite(SDP)--->|
> > |<--- 183(SDP)------|
> > |-----prack(SDP)--->|
> > |<--- 200(SDP)------|
> >
> > flow 1
>
> Assuming the 200 is the PRACK response, yes.
>
> >UAC UAS
> > |----invite-------->|
> > |<--- 183-----------|
> > |-----prack(SDP)--->|
> > |<--- 200(SDP)------|
> >
> > flow 2
>
> Not valid. If the INVITE does not contain SDP, a reliable answer
> must contain SDP. We are currently discussing whether the FIRST
> reliable response must contain SDP, or whether that rule can be
> related. But, that is a separate thread.
>
> Regards,
>
> Christer
>
>
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