On 2/11/15 4:17 PM, rsw2111 wrote:
4028 is clear that the supported header in the initial INVITE indicates
whether or not refreshers are supported by the UAC. In this case, there is
no Supported header in the initial INVITE, so it can be assumed that the
A-side does not support refreshers. That being the case, is the B-side
allowed to sending the Session-Expires: 3700;refresher=uac and Min-SE: 600
in the re-invite?
Note that the scope (duration of applicability) of support indicated by
a Supported header is not well defined. You cannot assume that it is a
permanent statement of fact for a device, or even that it applies for
the duration of a dialog. These things can change midway through a
dialog. It is certainly applicable for the duration of the request or
response carrying it, and *probably* applicable for the duration of
corresponding transaction. Beyond that you can only consider it a hint.
In any case, even if the lack of the Supported:timer did mean that A
doesn't support it, then B is still permitted to make the request in the
reINVITE. Assuming the reINVITE did *not* contain Require:timer, then A
should have simply ignored the Session-Expires and Max-SE headers. If it
is getting upset by the presence of those particular headers then it
means it understands them, which implies that it *does* "support"
session timer. If it is returning 480 because it received a request with
headers that it doesn't understand at all then it is a very broken SIP
implementation.
Thanks,
Paul
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