We're revising draft-ietf-bliss-call-completion-02 in the
Call-Completion committee of BLISS.  It turns out that our design can
be simplified and made more robust toward various difficulties in the
Real World if the the recipient of a SUBSCRIBE request could take the
>From header of the request into consideration when determining the
entity/events that are to be sent in NOTIFYs.

But it does look like having a subscription affected by the From value
has not done before, so we're extending the practice of SIP, if not
the letter of the law.  Use of the From value is not described in RFC
3265, but as one member pointed out, "It doesn't say you can't,
either."

What do people think of this?

The use case:  We want to be able to correlate an incoming SUBSCRIBE
with a previous incoming INVITE from the same UA.  The original idea
was that the SUBSCRIBE should specify in some manner the Call-Id of
the INVITE, but it turns out that in real SIP networks, SBCs often
change the Call-Id, so the caller doesn't know the Call-Id that the
callee sees.  However, it's rather reliable that the From headers of
the two requests will match, as SBCs are likely to change both of them
in the same way.

Dale
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