hi paul,
Thanks for your detailed mail.
Regds
John A
----- Original Message -----
From: "Paul Kyzivat" <[EMAIL PROTECTED]>
To: "Jhon miller" <[EMAIL PROTECTED]>
Subject: Re: [Sip-implementors] Query on SUBSCRIBE
Date: Mon, 20 Dec 2004 11:50:53 -0500
>
>
>
> Jhon miller wrote:
> > hi all,
> > I have Proxy(namely P1) with 10 valid Users.I have a separate
> > Proxy(namely P2) with 4 Valid users.
> > I want to send only one SUBSCRIBE from P1 to P2 on behalf of that
> > 10 users.(I dont want to maintain 10 Subscribe)
> > Is it possible to Bulk Subscription.(ie a Proxy send a Subscribe
> > on behalf of the valid users)
>
> The simple answer is NO. But some further explanation and nuances
> are appropriate:
>
> You aren't too specific about the use case. Lets assume that the
> users are named:
> - sip:[EMAIL PROTECTED]
> - ...
> - sip:[EMAIL PROTECTED]
> - sip:[EMAIL PROTECTED]
> - ...
> - sip:[EMAIL PROTECTED]
>
> and then assume that everybody wants to get the presence of everybody else.
>
> In general, there will be a separate authorization decision for
> each user. (So y4 may permit only x1,x2,y3, while x1 only permits
> x10,y1.)
>
> The only defined way to handle this situation is for every
> subscription to be handled independently, so it may be authorized,
> or refused.
>
> Also, notifications are not supposed to be sent unless there is a
> subscription. Were the proxy to initiate the subscriptions, then
> the UAs would have none, and so could not receive notifications.
> And, if the proxy initiated a subscription, it wouldn't be a proxy
> - it would be a UA.
>
> However there are some other possible approaches to this.
>
> It may be that each UA wants to minimize its outbound
> subscriptions. It can do this by storing a buddy list on a server -
> perhaps the same server that acts as its proxy. The buddy list is
> an instance of what is called a resource list - a list of URIs.
> This list can have a URI of its own, and a SUBSCRIBE may be
> directed to it. E.g.
>
> SUBSCRIBE sip:[EMAIL PROTECTED]
>
> In this case the server (p1) is acting as a special UA (a Resource
> List Server - RLS) which is a sort of B2BUA. When it receives one
> subscribe to a list, it fans it out into multiple subscribes to all
> the entries in the list, and directs all the NOTIFY responses back
> to the subscriber.
>
> This helps x1, but it doens't decrease the total number of
> subscriptions in the system, unless the RLS does some proprietary
> optimizations. For instance, if it is also the presence server for
> x1...x10, it might be able to respond on their behalf without
> actually subscribing. But it is more problematic when crossing
> domains.
>
> If p1 was acting as an RLS for x1...x10, it could conceivably
> generate a single subscribe to each of y1...y4, using its own
> credentials, and then provide the results back to any of x1...x10
> that have requested it. This doesn't provide the best of results,
> because the results received will reflect what the y users are
> willing to disclose to p1 rather than to the actual subscribers. It
> also still requires one subscription to each user in the foreign
> domain.
>
> To resolve the latter problem, it would be necessary to have some
> agreement between P1 and P2, so that P2 maintained a buddy list for
> the benefit of P1, listing all of P2's users that P1 is interested
> in. Then P1 could subscribe to that buddy list.
>
> None of this is very appealing. The only thing that provides good
> confidentiality properties is individual subscriptions.
>
> Paul
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