On 7/3/18 3:53 AM, Alex Balashov wrote:
No, it's not illegal to retry a call to the same gateway (in case of 6xx
response).
Nor is it illegal to reject it. :-)
My experience in an applied sense with SSTs (SIP Session Timers) is that they
are poorly supported, seemingly due to all the state-keeping involved. Many UAs
commit to a refresher role, for instance, but don't actually issue the
reinvites to refresh.
Instead, it is a more commonplace to approach to just use nullary-change
reinvites for signalling-level DPD (dead peer detection), without the baggage
of SSTs. So for instance, there are a lot of carriers out there whose equipment
will just send you a reinvite every 15 minutes to check if you're alive, quite
regardless of any SSTs, roles, support for SSTs, etc.
I think people forget that UAs have no need of session timers, since
they can do as you say, whenever they wonder about the status of the
session.
The real point of session timers is in support of proxies in the
signaling path. If they want to keep session state, then they have no
way to know when to clear that state if they see no signaling for a long
time. The session timers give them a way to ask the UAs to help them out.
More in another reply.
Thanks,
Paul
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