On Wed, 2009-05-27 at 15:57 -0400, Mark Gertsvolf wrote:
> The current behavior of directed call pickup feature is to extend dialog
> event subscription to all the registered sets of a user in question and
> on top of that follow the whole call forwarding tree in parallel. So, if
> user 200 has a rule to forward calls to user 201, then pickup plug-in
> sends subscription to all the phones of user 200 and user 201, which
> translates into all the phones of user 201 and so on. This is causing
> issues as described in http://track.sipfoundry.org/browse/XTRN-622. The
> subscription is also sent to the user's voicemail deposit URI, which is
> yet another issue altogether: http://track.sipfoundry.org/browse/XX-4830
> 
> However, regardless of the actual specifics of why the pickup is failing
> in this case, I think the call pickup conceptually should not follow the
> call forward tree.
> 
> People invoke directed call pickup when they hear somebody's phone ring
> or when they have a BLF key for another user and they see the call for
> that user. The intention is to pick the call that appears on the sets of
> a specific user right now. It is irrelevant that the call happens to
> also ring phones belonging to 10 other people because of the user's call
> forward rules.
> Also if the call stops ringing the phone of the user in question and
> rolls to the next destination in the forwarding tree - pickup should
> fail. If the next target is user Y, then it should be able to pick this
> call up using directed call pickup for user Y.
> 
> My proposal is to restrict the target audience of the subscription to
> only user's registered sets using "sipx-userforward=false" parameter in
> R-URI.

I think that's worth trying, but I'm concerned that it's a very large
change to make very late in the release cycle.  It also may have
significant backwards-compatibility issues in that it will change which
phones are followed, and therefor may cause operations that worked
before to stop working.

I think that the configuration in XTRN-622 that caused the failure is
pretty unusual (significantly more forks than most lines will have), so
my inclination is to say that this should be deferred to 4.0.2.

I like the suggestion [1] that the pickup redirector pre-construct the
authentication (we do this in at least one other case that I know of),
but I don't think it's urgent enough to do now.

I also think that we should add an Expires header to the SUBSCRIBE so
that all branches are cleared out quickly (N minus 1, where N is the
pickup timer).

[1] 
http://track.sipfoundry.org/browse/XTRN-622?focusedCommentId=39694&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#action_39694

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