Megaco Protocol - IETF/ITU conf call minutes

Arango, Mauricio MArango at RSLLA.COM
Mon Mar 29 21:38:21 EST 1999


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.


Mauricio Arango

> -----Original Message-----
> From: Greene, Nancy-M [CAR:5N10:EXCH]
> [mailto:ngreene at]
> Sent: Monday, March 29, 1999 8:54 PM
> To: 'ITU-SG16 at'; 'megaco at'
> 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
> -----------------------------------------------------------
> 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
> Minutes:  taken by Nancy Greene (ngreene at
> 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 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
> (
> -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 mailing list.
> Invitations to audio calls, and audio call minutes will be
> sent to both the
> megaco at and to the ITU-SG16 at
> 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
> (
> -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:
> - 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

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