Subject: Bearer Descriptions

From: Tom-PT Taylor <[email-masked]>
Date: Mon, 17 Jan 2000 08:57:21 -0500

Now that we have sorted out where media processing should be specified (in
Local and Remote, not in LocalControl) I would like to sort out another
piece of the puzzle: bearer descriptions.  I use the term "bearer" with the
thought that it can be generalized from its traditional usage in TDM
networks, but perhaps I can say it deals with the specification of layers
1-3 of transport.

My basic proposition is that bearer descriptions in this generalized sense
should be provided as much as possible as properties in TerminationState (if
the whole termination can be identified with one bearer) or LocalControl
(where the bearer is stream-specific).  Basically the analysis of where to
put properties and what properties to put there has to be done separately
for each bearer type.  The results have to be reflected in individual
bearer-specific packages.   Since the necessary information is already
specified in Annex C, those packages will have to have cross-references to
Annex C for the binary encoding.  (I would find dispersal of Annex C into
the packages more logical, but that's a battle I lost half a year ago.)

The basic bearer types we have dealt with up to now are analogue, DS-0, IP,
ATM-AAL2, and ATM-other.

It seems reasonable to view analogue and DS-0 bearers as 1-1 mappable to the
terminations they support.  Hence the relevant properties can go into
TerminationState -- they apply to the termination as a whole.  For DS-0
these properties include the sort of thing signalled in the Bearer
Capability, Information Rate, and similar information elements.  For
analogue, I'm not sure if anything is required -- perhaps frequency range.
Echo cancellation and gain have to go into LocalControl, because they are
specific to audio streams.

ATM and IP transport tend to be set up on a per-media flow basis (i.e.
potentially with different characteristics by direction of flow,
individually by stream).  From my point of view, this is a real headache --
the logical conclusion is that they should be specified in Local and Remote.
The truth is that it would be nice to reserve Local and Remote for media
description, as I suggested above, so that we don't have to extend SDP to
carry all sorts of bearer-related stuff it doesn't handle now.  Anyway, the
sort of thing I see as bearer-related is as follows:

For IP: anything to do with QOS

For ATM: all those parameters needed to specify channel characteristics.

Really, how we handle all this stuff is still an open question.  What do
other people think: properties on a per-direction basis in LocalControl, or
extend SDP to handle all of it in Local and Remote?

Tom Taylor
Advisor -- IPConnect Standards
E-mail: [email-masked] (internally, Tom-PT Taylor)
Phone and FAX: +1 613 736 0961

---

From: "Rosen, Brian" <[email-masked]>
Date: Mon, 17 Jan 2000 14:11:38 -0500

I'm baffled.

We went through the discussion of not trying to duplicate in
LocalControl that which you can express in SDP and/or Annex C.
Now you want to go back and do that again.

I don't want to split this up again.  If SDP is missing something,
or Annex C, then that is the place to put it.

Brian

> -----Original Message-----
> From: Tom-PT Taylor [mailto:[email-masked]]
> Sent: Monday, January 17, 2000 8:57 AM
> To: [email-masked]
> Subject: Bearer Descriptions
>
>