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

1 Apr 1999

      Tom,
I agree with your analysis.  We have to investigate the co-ordination
problems in the case of multiple contexts for one multimedia
conference.
There's another problem related to multimedia, viz. multimedia on the
circuit side.  How do we with H.320 streams into the megaco/H.gcp
connection model? When H.320 is used, it is posAs I see it, it will
require changes to the definition of termination.
In fact,
"Taylor, Tom-PT [CAR:5V00-I:EXCH]" wrote:
...
Single-medium contexts as a representaion scheme are orthogonal to the
question of multimedia.  Multimedia implies
(a) multiple media types
(b) coordination between them.
If I have multiple contexts, each devoted to one medium, that satisfies (a).
One suggestion on the call was to do that, then add a context attribute
which linked together different contexts.  This is a possible solution to
(b).
My personal feeling is that the single-medium context is a good direction to
explore, because in the degenerate (audio-only) case it turns out simply.
The open question, of course, is whether it introduces too many problems of
coordination.  I'm hoping to work through the two test cases I posed before
the Minneapolis meeting to see.
...
-----Original Message-----
From: John Segers [SMTP:jsegers@LUCENT.COM]
Sent: Wednesday, March 31, 1999 7:11 AM
To:   ITU-SG16@MAILBAG.INTEL.COM
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
grand work but
...
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
article on the
...
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
participating clients. An
...
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
participants
...
...
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:

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
the draft.
...
...
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:

SG16 and Megaco completely agree on the protocol

requirements. If this is
the case, the protocol will be identical

Each group has some requirements that are different from

the other group.
In this case, there would be agreement on a core
protocol, and then
...
...
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.

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.

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

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
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.

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.

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.
...
...

underspecifying terminationIds

provides a way of setting default parameters for a T1

for example
...
...

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.

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!

overview of Security

this is security between an MGC and an MG
interim method is specified for when an MG does not have IPSEC

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.

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.

How does the MGC find out RTP interfaces?

should be able to do this using Audit in the NULL context.

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

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
--
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