It seems I have to say this every few weeks...
*WHY* is the UAC requesting a session timer???
The real purpose of session timer is so that a record-routed proxy can
cause one of the UAs to send periodic messages - confirming for the
proxy that the session is still active. (A proxy isn't allowed to
originate messages itself to determine this.)
A UA has no need of this. At any time, if it gets to wondering if the
other end is still alive, it can send a message in the dialog. It
doesn't need to negotiate anything to do so.
So, while it is *legal* for a UAC to include the Session-Expires there
is no reason to do so. It can just include "Supported:timer" and then a
proxy that needs it will know it is available.
Paul
praveen dandin wrote:
> Hi all,
> I have a query regarding session timer functionality. UAC sends the INVITE
> message with Session-Expires header. The UAS does not support session timer
> fuctionality. Now possible behaviour of UAS are:
> 1) UAS copies the value of Session-Expires header value into 2xx and sends
> the response to UAC.
> This is as per section 9 statement of draft:
> draft-ietf-sip-session-timer-10.txt
> If the UAS wishes to accept the request, it copies the value of the
> Session-Expires header field from the request into the 2xx response.
> Here it is not mentioned that whether the UAS is supporting session timers
> or not.
> 2) The UAS MUST NOT send Session-Expires in 2xx response.
> Section 7.2 statement of draft :draft-ietf-sip-session-timer-10.txt gives
> some info regarding this.
> It is possible that the UAC requested session timer (and thus included a
> Session-Expires header field in the request), but there was no
> Require or Session-Expires header field in the 2xx response. This
> will happen when the UAS doesn't support the session timer extension,
> and only the UAC has asked for a session timer (no proxies have
> requested it).
> Please let me know the correct behaviour of UAS.
>
> Also the draft says that the session timer extension has the property that
> it works even when only one UA in a dialog supports it. So what should be
> the behaviour of UAC (which is supporting session timers) in case UAS does
> not support session timers?.
>
> Thanks,
> Praveen Dandin
>
>
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