Everybody's behavior here seems a little odd.
While not illegal, it is probably bad form in general for the UAC to
specify that the UAS is to be the refresher. At best that only makes
sense in a restricted environment where the UAC has knowledge that the
UAS is willing and able to do so. (Apparently not the case here.)
What do you expect to happen if the UAS is unwilling to do this?
If the UAC is able to act as refresher, but would prefer the UAS to do
it, it should just remain silent about the refresher and let the UAS
volunteer, or not.
The UAS is doubly wrong here - not only is it not setting the refresher,
it is *increasing* the expiration time, which is not allowed. If it
finds 120 to be too small it should be returning a 422 response with a
Min-SE indicating the minimum value it will accept.
Because the UAS is acting in a non-compliant way, the UAC must make up
its own mind how to cope. The action most likely to work is to assume
that the UAS just doesn't support session timer, and act accordingly.
Paul
kavitha menneni wrote:
> Hi,
> I have a query regarding the Session Timer. Please find the call flow below
> and let me know what should be he UAC and UAS Behavior.
>
> INVITE( Session-Expires: 120;refresher=uas) |
>
> |--------------------------------------------------------------------------------->|
> | 100 Trying
> |
>
> |<---------------------------------------------------------------------------------|
> | 180
> |
>
> |<---------------------------------------------------------------------------------|
> | 200 (Session-Expires: 1800) |
>
> |<---------------------------------------------------------------------------------|
> | ACK
> |
>
> |-------------------------------------------------------------------------------->
> |
> .Here though the RFC says “The UAS MUST set the value of the refresher
> parameter in theSession-Expires header field in the 2xx response”. 200Ok is
> received with our refresher parameter but INVITE has set the refresher as uas.
>
> Can any one suggest what should the UAC should perform here -
> 1. Set the Refresher to Local i.e uac and perform the Refreshes.
> 2. Keep the refresher as uas itself and do not perform the refreshes and send
> the BYE after session expiry.
>
>
>
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