Subject: Re: [Sipping] Comments on BLA draft

From: "Dale Worley" <[email-masked]>
Date: Wed, 3 Aug 2005 17:52:51 -0400

> From: Jeroen van Bemmel [[email-masked]]
>
> I understand that the draft is about sharing a single resource. However,
as
> I read the draft this resource is virtual / logical, it does not
(necessarily)
> represent a single physical resource. So the restriction to associate each
of
> the calls with a unique line id is artificial, not mandated by anything
besides
> the requirement in the draft. I can understand where the idea comes from,
you
> are emulating a telephone system with a fixed (limited) number of physical
> lines. But why emulate the restrictions of such a system if there is no
need
> for it?

Though it is true that BLA is imitating a legacy architecture that was
invented based on the physical limitations of copper-wire-pair PSTN
networks, the concepts are more useful than they first appear.

Yes, the "line" (or really, "sub-line", reserving "line" as a term for an
AOR) is just a virtual resource, but it plays a vital role as an identifier
of a particular dialog that can be easily transmitted to other users in the
BLA group.

As an identifier, you need to consistently restrict all calls (that
participate in that BLA line), incoming and outgoing, to have unique values
of the identifier.

What you are getting hung up on, I think, is the idea that the *user* needs
to select the sub-line ID before he can start making an outgoing call.  As
you note, that's pointless.  The *UA* needs to allocate the sub-line ID
before making an outgoing call, so that it knows an ID is available.  But
there's no reason that the UA cannot search for and reserve the sub-line ID
automatically (or ask the state agent to do so for it).  Since that is a UA
operational feature, nobody has written about it in the I-D, but it should
be kept in mind as the most likely implementation technique.

> I guess what I am saying is that I see the use case for incoming calls,
but
> don't really see it for outgoing calls (at least in the above scenario).
> The outgoing call here could be made without asking permission, the only
> feature that the attendant would loose is the ability to put the call on
hold
> for someone else to pick it up. But that could be arranged using other
> mechanisms as well, if it is really desired.

Well, yes, but the whole point of using BLA for an outgoing call is to
support putting the call on hold in a way that another user can pick it up
based on a small integer identifier.

Dale

_______________________________________________
Sipping mailing list  https://www1.ietf.org/mailman/listinfo/sipping
This list is for NEW development of the application of SIP
Use [email-masked] for questions on current sip
Use [email-masked] for new developments of core SIP

---

From: "Jeroen van Bemmel" <[email-masked]>
Date: Thu, 4 Aug 2005 00:18:24 +0200

> based on a small integer identifier.

OK, so how about postponing the allocation of a line ID until the moment 
that the user wants to put the call on hold? That way you don't 
unnecessarily restrict the number of simultaneous outgoing calls, just the 
number that can be put on hold simultaneously

> to select the sub-line ID before he can start making an outgoing call

Actually, what I was "getting hung up on", is the idea that the user needs
to select the sub-line ID *before he can start making an outgoing call*.

With a physical line it is required before the call is made, but if you only 
need an ID for transfer then it seems the allocation can be postponed - or 
am I again missing something here?

Regards,

jeroen