Harsha. R wrote:
> Hi,
> Consider the following scenario with regard to session-refresh
>
> INVITE[Min SE:900, (SE:900,refresher=uas),k:timer]
> UAC--------------------------------------------------------------------------------->UAS
>
> 183 SP,PRACK(183),200OK PRACK,180 Ringing, PRACK(180),200 OK PRACK follow
>
> 200 OK[(SE:1800,refresher=uas), k:timer]
> UAC<---------------------------------------------------------------------------------UAS
>
> Because the refresher is UAS, can UAS increase the value of
> Session-Expires value in 200 OK to the INVITE?
IMO No.
> My understanding of RFC 4028 is as follows.
>
> 1. In any negotiation of the session-refresh interval, MinSE is the
> lower bound and SE is the upper bound.
> 2. UAS MUST NOT increase the value of SE, however it can decrease it.
>
> The above points are also clearly documented in the RFC 4028, Section
> 9 and I quote
>
> " 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.
> The UAS response MAY reduce its value but MUST NOT set it to a
> duration lower than the value in the Min-SE header field in the
> request, if it is present; otherwise the UAS MAY reduce its value but
> MUST NOT set it to a duration lower than 90 seconds. The UAS MUST
> NOT increase the value of the Session-Expires header field."
>
>
> Now my question is, since UAC has clearly set the MinSE(900) and
> SE(900) values in the Session-Refresh request and chosen UAS as the
> refresher in the process, is UAS allowed the latitude to INCREASE the
> value of Session Expires header to 1800 in the response to
> Session-Refresh request?
The use case is bizarre. The UAC is doing something legal but stupid.
The UAS is doing something illegal.
The UAC ought not to be *deciding* the UAS will be the refresher. Doing
so will cause the call to fail if the UAS isn't willing to do so.
The UAC has also constrained the refresh interval to a single value,
which, while not illegal, is also likely to result in interop problems.
The UAS should:
1) note that it has been *told* that it must be the refresher
2) note that the the refresh interval is constrained to 900.
It should then decide if it can live with those limits. If not it should
reject the call. It isn't permitted to raise the limit above 900.
Paul
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