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

John Segers jsegers at LUCENT.COM
Wed Mar 31 07:11:10 EST 1999


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 at lucent.com]
> > Sent: Tuesday, March 30, 1999 2:45 PM
> > To: Arango, Mauricio
> > Cc: 'Greene, Nancy-M [CAR:5N10:EXCH]'; 'ITU-SG16 at mailbag.intel.com';
> > 'megaco at 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 at americasm01.nt.com]
> > > > Sent: Monday, March 29, 1999 8:54 PM
> > > > To: 'ITU-SG16 at mailbag.intel.com'; 'megaco at 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 at 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 at lucent.com)
> > > > Minutes:  taken by Nancy Greene (ngreene at 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 at 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
> > 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:
> > > > 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
> > 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 at baynetworks.com mailing list.
> > > >
> > > > Invitations to audio calls, and audio call minutes will be
> > > > sent to both the
> > > > megaco at baynetworks.com and to the ITU-SG16 at 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
> > 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 at 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 at lucent.com
> > Huizen, The Netherlands  internal http://hzsgp68.nl.lucent.com/
> >

--
John Segers                                  email: jsegers at 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



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