Re: Multimedia (was Re: Megaco Protocol - IETF/ITU conf call minutes) - sg16-avd

31 Mar 1999


      I want to add the issue of T.120 to the multimedia discussion. An effort is
made in SG16 Q3 to try to develop T.120 as the control interface for audio
graphic conferences using PSTN. So far we talk about h.323 and H.245 but
what about T.120

Roni Even
Accord Video Telecommunication.
email:roni_e@accord.co.il
-----Original Message-----
From: John Segers <jsegers@LUCENT.COM>
To: ITU-SG16@MAILBAG.INTEL.COM <ITU-SG16@MAILBAG.INTEL.COM>
Date: éåí øáéòé 31 îøõ 1999 14:13
Subject: Re: Multimedia (was Re: Megaco Protocol - IETF/ITU conf call
minutes)
...
Mauricio,
You are right that single medium contexts are simpler to reason about
services and call flows.  But we must take care that we don't end up
with a protocol that cannot be extended to cover multimedia GWs.  If
multimedia applications are within scope, the protocol document should
not contain a connection model that handles only audio.
What do others think?  Is multimedia in the scope of megaco/H.gcp?  And
if so, is Paul's proposal general enough?  Doesn't it lead to too much
overhead for single media GWs?  I'd be interested to hear opinions.
John Segers
"Arango, Mauricio" wrote:
...
Please disregard my previous message which by mistake I sent without
erasing
...
editing. Apologies to the list members.
Paul,
I understand the rationale for your multiple media context. My preference
is
the single medium context because it seems simpler for thinking about
services and call flows. This seems to require more discussion. I suggest
we
advance the protocol as proposed with single-medium contexts and revisit
this later if necessary.
Mauricio
...
-----Original Message-----
From: Paul Sijben [mailto:sijben@lucent.com]
Sent: Tuesday, March 30, 1999 2:45 PM
To: Arango, Mauricio
Cc: 'Greene, Nancy-M [CAR:5N10:EXCH]'; 'ITU-SG16@mailbag.intel.com';
'megaco@baynetworks.com'
Subject: Multimedia (was Re: Megaco Protocol - IETF/ITU conf call
minutes)
Mauricio,
you write:
...
It could be good idea to have some entity that ties
together multiple
contexts, this was our experience in the Touring Machine
and we referred to
it as "session". However, it may not be necessary for the
most common audio
only operations, and for the sake of simplicity it may be
better to leave it
as an option.
I think you are absolutely right. We have been doing some
work on that and
have come up with the following which seems like a sensible
extention to
the H.gcp/MEGACOP work:
Problem definition:
 For multimedia calls you will have multiple media streams
representing
each of the users. these streams need to be appropriately
processed (maybe
mixed or something more clever) and synchronised.
The current definition in the MEGACO I-D specifies that each
context only
has one type of medium. This makes the logical grouping of
terminations
belonging to one user difficult, creates issues with synchronisation
between media. It also makes it difficult to remove one user
or an entire
conference in one command.
We have gone over several possible solutions, you can group
terminations
per user, and/or per medium and/or make some kind of links between
terminations or contexts which signify the synchronisation.
What seems like a workable model is to allow multiple media
in one context
and have a matrix binding the terminations to the right
medium/user. So you
would get something like:
context
medium1 | M2 | ....| Mn
------------------------------
user1 |  x    |     |    | x
user2 |       | x   |    | x
..........
usern |  x    | x
   where x==termination
such a matrix could be a "scap paper" used by the MGW and MC
to keep track
of to which user and which medium each termination belongs.
One could set a
flag on terminations that one wants to synchronise.
Naturally you would not need this for simple voice gateways so the
extentions needed to the protocol for this youl be optional.
The extentions would look like:
Commands:
  We now have a command structure that states:
ContextID
    *Command(TerminationID ....)
we would get:
ContextID
   [UserID]
    *command( [MediaID] Termination ID....)
so for example:
ContextID=3
  UserID=2
   add (MediaID=Video3,  TerminationID=RTP:32424, ....)
   modify (MediaID=Video3, TerminationID=*, SychWith:MediaID=Audio2)
etc.
A context could have the following properties:
 - mode (unidirectional, bidirectional, mix, choose...)
 - maxNumberOfUsers (e.g. 3)
 - maxNumberOfMedia (e.g. 1 for a simple voice gateway)
This extention would allow the removal of one medium or one
user from a
conference but not hamper "simple" operations.
Paul
"Arango, Mauricio" wrote:
...
Nancy,
Thanks for preparing the minutes.
...
b. Raised by Mauricio Arango: you may want to be able to
create a context
with parameters before adding any terminations to it - (e.g.
turing machine)
I want to clarify that I was not referring to Alan Turing's
...
to something colleagues and I did some years ago in
multimedia call control,
called "Touring Machine". This effort developed a
connection model similar
to the one in MEGACO's protocol and could be worth keeping
in mind as
previous experience to help this effort.
The January 1993 of the Communications of the ACM has an
...
Touring Machine. Following is an excerpt desribing its
connection model
(page 71):
"The logical topology of a session is specified as a set of
typed connectors
(see Figure 2). A connector represents a multiway transport
connection among
endpoints (logical ports). A connection is an abstraction of a
communications bridge, including point-to-point (two way) as well as
multipoint connections. Since bridging is a medium-specific
operation,
connectors are typed by medium. A session may have one or
more connectors
per medium, with souce and sink endpoints from
...
endpoint represents a connector termination point. Endpoints are
distinguished by medium, direction of flow, and the client
receiving or
providing transport."
In the above excerpt a "connector" is equivalent to
MEGACO's context and an
"endpoint" is equivalent to MEGACO's termination.
...
c.  Raised by a few people: we need to see whether we need a
meta definition
of a "call" in the MG, so that the MG can link together
related contexts.
May be needed for lipsynch between a call's video context and
its audio
context. Instead of introducing a callId, this could be done using
parameters on each context referring to the other one.
Benefit of a callId
is that the MGC can bring down the entire call by just
referring to the
callId. (Note: "call" may be the wrong word - if we need it,
let's try to
invent a new name).
It could be good idea to have some entity that ties
together multiple
contexts, this was our experience in the Touring Machine
and we referred to
it as "session". However, it may not be necessary for the
most common audio
only operations, and for the sake of simplicity it may be
better to leave it
as an option.
Regards,
Mauricio Arango
...
-----Original Message-----
From: Greene, Nancy-M [CAR:5N10:EXCH]
[mailto:ngreene@americasm01.nt.com]
Sent: Monday, March 29, 1999 8:54 PM
To: 'ITU-SG16@mailbag.intel.com'; 'megaco@baynetworks.com'
Subject: Megaco Protocol - IETF/ITU conf call minutes
Here are the minutes from the call today. Please email me any
corrections. I
tried to pair comments made with the person that made them -
I may have made
some errors, and I know I missed the names of some of the
people commenting.
Nancy (ngreene@nortelnetworks.com)
-----------------------------------------------------------
Megaco Protocol presentation to IETF megaco and ITU SG16
...
...
March 29/99 10am-12pm EST
=================================================
Present: The number of ports being used went as high as 47,
and was about 45
on average. Number of participants was higher since a number
of people were
sharing ports.
Chair of the call: Glen Freundlich (ggf@lucent.com)
Minutes:  taken by Nancy Greene (ngreene@nortelnetworks.com)
NOTE: In keeping with IETF and ITU procedures, the audio call
cannot make
binding decisions. It is a tool for the chairs and
editors, and the
participants of both the IETF and ITU working groups, to
gauge support for
the protocol, and to raise issues with the protocol. Issues
may be raised in
either an audio call, or on the mailing list
(megaco@baynetworks.com). These
minutes are going to both the Megaco and ITU-SG16 mailing lists.
Meeting summary:
--------------------------
Glen Freundlich summed up results of the meeting. The goal of
the meeting
was two fold:
1) it was the first opportunity for people to look at the
output from the
Megaco protocol design/drafting group.
2) it was an opportunity for people to pose questions on
...
...
He saw no opposition to the connection model proposed in the
Megaco protocol
I-D
(ftp://www.ietf.org/internet-drafts/draft-ietf-megaco-protocol
-00.txt).
To date, the Megaco protocol I-D has been run through audio
call scenarios
for 3-way call, for call waiting, ... However, it needs to be
tested with
multimedia scenarios. Any input in this area is appreciated.
Because there seems to be agreement on the connection model,
Bryan Hill, the
H.gcp editor, will start pulling related sections from the
Megaco protocol
I-D into H.gcp.
Glen will hold another audio call next week to see where we
stand, and to
look towards adding more sections to H.gcp from the Megaco
protocol I-D.
For the ITU-T SG16 May meeting, H.gcp needs to contain:
- a connection model
- a set of commands
- a start on parameters for those commands
- generic syntax
- and a list of issues to resolve.
Protocol timetable:
--------------------------
IETF Megaco:
- Proposed Standard by summer/99
- interoperability testing in fall/99
- Draft Standard in Feb/2000
This matches up closely with the ITU-T SG16 schedule:
- planning to get H.gcp determined in May/99
- planning to get H.gcp decided in Feb/2000
IETF/ITU collaboration:
-------------------------------
Question raised: will the two protocols be identical?
Tom Taylor proposes two options:
1) SG16 and Megaco completely agree on the protocol
requirements. If this is
the case, the protocol will be identical
2) Each group has some requirements that are different from
the other group.
In this case, there would be agreement on a core
...
...
additional parts would be defined by each group.
BUT how to do this in practice? Tom said that if a huge
roadblock comes up
again, we would form a new design team to work out a solution.
Tom asked whether the group on the call agreed that the
Megaco protocol I-D
was a reasonable basis for H.gcp. Feeling was that it is, but
that we need
to do multimedia call walkthroughs. Mike Buckley had some
concern about the
definition of a context, but thought that the basic model
is workable.
Mauricio Arango thought it was a good model for multimedia.
Ami Amir raised
issue about associating contexts. Glen asked the H.320
experts to look at
the protocol and see if we need to modify the connection model.
Next audio call:
----------------------
Probably next Thursday April 8/99, same time. Confirmation of
date & time
and the call details will be out later this week.
Use of mailing lists:
---------------------------
It was agreed that we would try to keep all technical
discussion of the
Megaco protocol on the megaco@baynetworks.com mailing list.
Invitations to audio calls, and audio call minutes will be
sent to both the
megaco@baynetworks.com and to the ITU-SG16@mailbag.intel.com
mailing lists.
Tom Taylor took the action of posting to each list, how to
join the other
one.
Detailed minutes:
------------------------
Brian Rosen presented the Megaco protocol draft
(ftp://www.ietf.org/internet-drafts/draft-ietf-megaco-protocol
-00.txt). He
first noted that this draft is open for discussion. It is not
cast in stone.
If changes need to be made to any part, they will be
made, if they are
deemed necessary to satisfy the requirements of the protocol,
and agreed to
by the group.
1. New connection model
- concept of a termination - have permanent (e.g. DS0) and
ephemeral (e.g.
RTP port) terminations
- a termination is named with a terminationId, this name can
have wildcards,
for example to allow the MG to choose the actual physical
termination, or to
request notification of an event that occurs on any DS0
- concept of a context - can add, subtract, modify
terminations in a
context. A context is created when the first termination is
added to it, and
goes away when the last termination is subtracted from it.
- a context can have parameters associated with it - for
example, a video
mixing context may have parameters to describe how the video
is to be mixed
- mosaic, or current speaker/last speaker, ...
- a termination class defines parameters on a typical
termination - e.g. DS0
Termination Class, RTP Termination Class
- Signals can be attached to a termination class, events can
occur at a
termination class, and the MGC can specify which ones it
wants to be
notified about.
- packages define signals and events
- a termination class can have more than one package that
apply to it
- event naming structure allows package name to be put in
front of the event
name
- question: how do you apply a call waiting tone? - answer -
it is a signal
that you apply to a termination
1.1 Proposed Changes and Issues:
a. Tom Taylor proposed a more general definition for
context: every
termination in a context has connectivity with all other
terminations in the
context.
b. Raised by Mauricio Arango: you may want to be able to
create a context
with parameters before adding any terminations to it - (e.g.
turing machine)
- may want to mark a context with the max # of terminations
at creation
time. - BUT this may bring lack of flexibility - may be
better to let the MG
decide, as new terminations are added to a context, whether
it is able to
mix them in. For example, instead of marking a context with
one particular
type of codec, it is more flexible to let the MG decide what
transcoding
needs to be done in a context as a function of the types of
terminations
added to it.
c.  Raised by a few people: we need to see whether we need a
meta definition
of a "call" in the MG, so that the MG can link together
related contexts.
May be needed for lipsynch between a call's video context and
its audio
context. Instead of introducing a callId, this could be done using
parameters on each context referring to the other one.
Benefit of a callId
is that the MGC can bring down the entire call by just
referring to the
callId. (Note: "call" may be the wrong word - if we need it,
let's try to
invent a new name).
d. Raised by Steve Davies: with H.320, the MG has one
physical termination
with audio, video and data on it - can a termination be in
more than one
context? no - so need to separate the different media out of
this physical
termination before creating the contexts.
e. Raised by Tom Taylor: need to see whether it is
feasible to have
decomposed H.320 gateways - if it is necessary (people say
yes), then need
to be sure the Megaco protocol can handle it.
2. Commands
- grouped into commands within an action per context, and
one or more
actions are grouped into a transaction. Transaction is
all or nothing.
- Add, Modify, Subtract each can contain local and remote
terminiation
descriptors, signalling descriptor, an events descriptor, and
a digit map
descriptor
- question on how to change an event description for a
termination - answer:
use Modify - can do it within a context, or outside a context
- if it is
outside the context (i.e. using the NULL context), then that
is how you
change the default parameters for that termination.
- MGCP's NotificationRequest is now covered in Modify
3. Multimedia and Contexts and Terminations
- a termination only belongs to one context
- for multimedia, there is one context per media type
- just as you have separate RTP flows for different media
types, you have
separate contexts.
3.1 Issues
a. Paul Sijben noted that when you try to use the Megaco
grand work but
article on the
participating clients. An
participants
the draft.
protocol, and then
protocol with
...
...
H.320, there may be problems with the model - Paul will bring
these up on
the mailing list.
Also, see Issue c in 1.1 above.
4. H.245 & SDP
- Tom Taylor explained that H.245 has at least 2 purposes: 1)
for capability
negotiation, and 2) for specification of open logical
channel. The scope of
the Megaco protocol is 2). Capability negotiation may use
H.245 between
MGCs, but the Megaco protocol is between MGC and MG. SDP may
be good enough
to be used between the MGC and the MG. Discussion still open
here. Need to
allow for an environment where H.245 may not be involved.
- with H.263 - H.245 provides a tag to link together 2 RTP
streams - need to
be able to carry this tag from the MGC to the MG.
5. underspecifying termination descriptors
- can be used as a way to tell the MG to use default
values for the
termination
- a termination learns its default values at MG boot-up time
- MGC can change these values using Modify with context
set to NULL.
6. underspecifying terminationIds
- provides a way of setting default parameters for a T1
for example
7. Case: two audio contexts - in different MGs, and in the same MG
- can the connection model handle this? Yes
- protocol should need to keep track of where resources are.
- it is up to the MGC to know what contexts are associated
with a call.
8. overview of Audit, Notify, ServiceChange
- ServiceChange - MG can use it upon reboot, to register
itself with an MGC
- MG knows which MGC to send this msg to from some method
outside the scope
of this protocol (pre-provisioned, for example).
- MGC learns capabilities of MG using Audit. - can learn codecs
8.1 Issue
- need a way for MGC to learn the QUANTITY of codecs an MG has!
9. overview of Security
- this is security between an MGC and an MG
- interim method is specified for when an MG does not have IPSEC
10. Question on scope of the protocol
- check the requirements draft:
ftp://standards.nortelnetworks.com/megaco/docs/minn99
- Steve Davies brought up point that some aspects of the
Megaco protocol
overlap with Policy server protocol proposals.
11. Can MG do coded renegotiation?
- David Featherstone asked if an MG can negotiate use of a
new codec on its
own
- Brian Rosen answered that with AAL2 profiles, the MG can
Issue:
a. MGC may need to be involved - for example if the Quality
goes down too
low, call may no longer be billable. Solution - create an
event to notify
the MGC for this case.
12. How does the MGC find out RTP interfaces?
- should be able to do this using Audit in the NULL context.
13. IVR - still open for discussion
- view IVR as a termination
- issue is how much signalling effort do you need to add to
the protocol?
- simply playing msgs is ok - they just look like events
- problem is when you want to put time and money values into
it for example,
you have x minutes left on your calling card. - this may be
out of the scope
of the Megaco protocol
14. QoS reservation
- needs more discussion
****see Meeting summary above for audio call conclusions.
end of minutes.
--------------------------------------------------------------
------------
Nancy M. Greene
Internet & Service Provider Networks, Nortel Networks
T:514-271-7221 (internal:ESN853-1077) E:ngreene@nortelnetworks.com
--
Paul Sijben              Telno:+ 31 35 687 4774 Fax:+31 35 687 5954
Lucent Technologies      Home telno: +31 33 4557522
Forward Looking Work   e-mail: sijben@lucent.com
Huizen, The Netherlands  internal http://hzsgp68.nl.lucent.com/
--
John Segers                                  email: jsegers@lucent.com
Lucent Technologies                                        Room HE 344
Dept. Forward Looking Work                      phone: +31 35 687 4724
P.O. Box 18, 1270 AA  Huizen                      fax: +31 35 687 5954

Re: Multimedia (was Re: Megaco Protocol - IETF/ITU conf call minutes)

Roni Even

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