Terry,
On 5/7/13 10:29 AM, Terry Song wrote:
> Hello Everybody,
>
> I have a question about the RFC4028 session timer of invite usage. The
> section 7.1 says:
>
> 7.1. Generating an Initial Session Refresh Request
>
> A UAC that supports the session timer extension defined here MUST
>
> include a Supported header field in each request (except ACK),
>
> listing the option tag 'timer' [2]. It MUST do so even if the UAC is
>
> not requesting usage of the session timer for this session.
>
> Does it mean all the requests created by the UAC must include the Supported
> header with tag ‘timer’? For example, the UPDATE request for SDP change also
> need include ‘timer’ tag in Supported header? And the BYE request also need
> include 'timer' tag?
SIP isn't specific about the duration of applicability of a Supported
header. At a minimum it applies for the duration of the request
transaction. In general you can't count on it applying longer, though it
some cases its clear that it must apply longer.
In the case of session timer, every INVITE or UPDATE resets or clears
any prior session timer. So you should include the Supported header in
every INVITE/UPDATE.
Including it in BYE is quite irrelevant, since after that there will no
dialog after that.
IMO Supported:timer in other messages within the dialog (e.g., INFO)
should be irrelevant. But in general the best policy is so signal
everything you support in every message, just to be sure.
Thanks,
Paul
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