The current draft says:
4.2.3. Non Outbound Registrations
In an initial registration, a User Agent MUST NOT include a reg-id
header parameter in the Contact header field if the registering UA
is
not the same instance as the UA referred to by the target Contact
header field. (This practice is occasionally used to install
forwarding policy into registrars.)
A UAC also MUST NOT include an instance-id feature taf or reg-id
Contact header field parameter in a request to un-register all
Contacts (a single Contact header field value with the value of
"*").
This strikes me as odd in several ways.
The reg-id lets us know "which registration we are talking about". The
instance-id lets us know "which specific UA-appearance we are talking
about".
So for a 3rd-party registration, it might be useful to have reg-id or
instance-id values. Assume for example a voice-mail server that
registers a low q-value contact for an AOR, so that calls will
eventually reach it in a no-answer scenario. Withdrawing just those
specific registrations would seem to require a selection mechanism
from the set of registrations, and reg-id would appear to satisfy this
need.
In a different use case, assume a 3rd party registration is used to
install forwarding policy. The use of an instance-id in such a
registration would seem to allow the forwarding policy to target one
specific instance of the set of contacts registered to the target. In
other words, not "forward the call to sip:[EMAIL PROTECTED]", but
"forward the call to sip:[EMAIL PROTECTED]'s cell phone".
Now it's entirely possible that neither of these scenarios actually
work. But I don't see in the discussion of outbound anything about WHY
they wouldn't work, which means that the requirements language (the
MUST in outbound) is unsupported. I don't like unsupported
requirements in a specification.
--
Dean
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