Subject: Re: Summary of Megaco Meetings

From: Nancy-M Greene <[email-masked]>
Date: Tue, 16 Nov 1999 09:34:00 -0600

Taking the picture from Brian's email:
       MGC     ---   SIP/ISUP/H.323   ---   MGC
          |                                                   |
      Megaco                                       Megaco
          |                                                   |
        MG      ---   RTP/AAL2/....       ---   MG

Altering to show interaction with a SIP client, as in Pyda's email below:

       MGC     ---   SIP       ---------------   SIP UAC (i.e. SIP IP Phone)
          |                                                   |
      Megaco                                         /
          |                                             /
        MG      ---   RTP/AAL2/....  ------/

In this case the RTP/AAL2 goes from the MG to the SIP IP Phone. The SIP UAC
is a peer to the MGC. The SIP UAC does not need to know that the MGC uses
Megaco to talk to its MG.

Note that here we do not get SIP and Megaco overlapping - they are happening
in different places.

Nancy
--------------------------------------------------------------------------
Nancy M. Greene 
Internet & Service Provider Networks, Nortel Networks
T:514-271-7221 (internal:ESN853-1077) E:[email-masked]

> ----------
> From:         Pyda Srisuresh[SMTP:[email-masked]]
> Sent:         Tuesday, November 16, 1999 10:06 AM
> To:   [email-masked]
> Subject:      Re: Summary of Megaco Meetings
> 
> --- Lyndon Ong <[email-masked]> wrote:
> > Hmm, maybe I can ask for more context on Henry's email:
> >
> > -- SIP could be used for transport, but it uses application layer
> framing in
> > the same way that Megaco over UDP would use application layer framing,
> so
> > there's no advantage, is there?
> >
> 
> I believe, the advantage is that the MGC is able to work with a SIP
> network.
> I.e., MGC (telephony gateway) and SIP UAC(say, IP phone) will simply be
> clients to SIP network.
> 
> cheers,
> suresh
> __________________________________________________
> Do You Yahoo!?
> Bid and sell for free at http://auctions.yahoo.com
>

---

From: Henry Sinnreich <[email-masked]>
Date: Wed, 17 Nov 1999 07:59:51 -0600

RE: Summary of Megaco MeetingsNancy's drawing adds the important point of
MEGACO gateways talking to SIP clients and together with Brian's provides
the graphics for an architectural background, such as:

MEGACO in the Context of the The Internet Multimedia Conferencing
Architecture [x] (attached)
=====================================================================
SIP clients can be IP telephony gateways, using MEGACO as shown in figure1 .
In this architecture, any SIP client, such as IP phones, PCs or palm tops do
not need to know the PSTN protocol when the other party is on the PSTN.
Gateways and clients can also use H.323 in an H.323 environment.
Call flows for SIP clients and gateways are given in [y].

                               Figure 1

In the particular case when both SIP clients are IP telephony gateways as
shown in Fig. 2,

       MGC  --- SIP/ISUP(BICC)/H.323  --- MGC
          |                                                   |
      Megaco                                       Megaco
          |                                                   |
        MG      ---   RTP/AAL2/....       ---   MG

                            Figure 2

there are two options:

A. The gateways use SIP signaling as with any other client (SIP in the
middle model).

B. The gateways use SIP as a transport vehicle to carry PSTN signaling
between them, such as ISUP across the IP network. This case is applicable
when both sides understand the same PSTN protocol variant [z].

My apology if all this seems obvious to some, but the discussions on the
list have shown that such an introductory note would be quite useful.
I suppose H.248 documents could carry similar references for good balance.

References:
[x] The Internet Multimedia Conferencing Architecture by M. Handley/J.
Crowcroft/C. Bormann/J. Ott
     <draft-ietf-mmusic-confarch-02.txt> (have attached it here below)

[y] SIP Telephony Call Flow Examples by Alan Johnston, et al.

http://search.ietf.org/internet-drafts/draft-johnston-sip-call-flows-00.txt

    (PBX and Centrex like services are given in

http://search.ietf.org/internet-drafts/draft-sparks-sip-service-examples-00.
txt )

[z] SIP Best Current Practice for Telephony Interworking
    http://search.ietf.org/internet-drafts/draft-zimmerer-sip-bcp-t-00.txt
    This document obseletes the 'SIP+: Inter-MGC Protocol'

Thanks, Henry
  -----Original Message-----
  From: Media Gateway Control (megaco)
[mailto:[email-masked]]On Behalf Of Nancy-M Greene
  Sent: Tuesday, November 16, 1999 9:34 AM
  To: [email-masked]
  Subject: Re: Summary of Megaco Meetings

         MGC     ---   SIP       ---------------   SIP UAC (i.e. SIP IP
Phone)
            |                                                   |
        Megaco                                         /
            |                                             /
          MG      ---   RTP/AAL2/....  ------/

  In this case the RTP/AAL2 goes from the MG to the SIP IP Phone. The SIP
UAC is a peer to the MGC. The SIP UAC does not need to know that the MGC
uses Megaco to talk to its MG.

  Note that here we do not get SIP and Megaco overlapping - they are
happening in different places.

  Nancy

    ----------

framing in
so

    cheers,
    suresh

---

From: Chip Sharp <[email-masked]>
Date: Wed, 17 Nov 1999 09:23:09 -0500

Good.  Then we can close the issue of using SIP as a transport protocol for
H.248/megacop (i.e., we don't).  In other words, SIP isn't used to carry
megaco messages between the MGC and MG.

Using SIP between MGCs is another matter and currently isn't in the scope
of megaco.

Supporting interworking between MGCs and SIP clients/servers has always
been an application intended to be supported as far as I'm concerned (and
many other people as well).

BTW, I see you've added BICC in there.

Chip

At 07:59 AM 11/17/99 -0600, Henry Sinnreich wrote:
>Nancy's drawing adds the important point of MEGACO gateways talking to SIP
>clients and together with Brian's provides the graphics for an
>architectural background, such as:
>
>SIP clients can be IP telephony gateways, using MEGACO as shown in figure1
>. In this architecture, any SIP client, such as IP phones, PCs or palm
>tops do not need to know the PSTN protocol when the other party is on the
>PSTN. Gateways and clients can also use H.323 in an H.323 environment.
><http://search.ietf.org/internet-drafts/draft-johnston-sip-call-flows-00.tx
>t>http://search.ietf.org/internet-drafts/draft-johnston-sip-call-flows-00.txt
>
><http://search.ietf.org/internet-drafts/draft-sparks-sip-service-examples-0
>0.txt>http://search.ietf.org/internet-drafts/draft-sparks-sip-service-examp
>les-00.txt )
>
><http://search.ietf.org/internet-drafts/draft-zimmerer-sip-bcp-t-00.txt>htt
>p://search.ietf.org/internet-drafts/draft-zimmerer-sip-bcp-t-00.txt
>>----------  From:   Pyda
>>Srisuresh[SMTP:[email-masked]]  Sent:   Tuesday, November 16, 1999
>>10:06
>>AM  To:     [email-masked]  Subject:        Re:
>>Summary of Megaco Meetings
>>
>>--- Lyndon Ong <[email-masked]> wrote:  > Hmm, maybe I can ask
>>for more context on Henry's email:  >  > -- SIP could be used for
>>transport, but it uses application layer framing in  > the same way that
>>Megaco over UDP would use application layer framing, so  > there's no
>>advantage, is there?  >
>>
>>network.  I.e., MGC (telephony gateway) and SIP UAC(say, IP phone) will
>>simply be  clients to SIP network.
>>
>>cheers,  suresh  __________________________________________________  Do
>>You Yahoo!?  Bid and sell for free at
>><http://auctions.yahoo.com>http://auctions.yahoo.com

Support NetAid!  http://www.netaid.org
--------------------------------------------------
Chip Sharp                 Consulting Engineering
Cisco Systems              Telco Bio-region
Reality - Love it or Leave it.
--------------------------------------------------

---

From: Michael Thomas <[email-masked]>
Date: Wed, 17 Nov 1999 07:51:51 -0800

> Using SIP between MGCs is another matter and currently isn't in the scope

I've been watching this with some amount of
confusion in my flu-induced haze. I'm not entirely
sure I'd characterize that SIP is outside of the
scope of MEGACO, per se. Back from SGCP,
Christian's original architecture showed the
functional decomposition of the media gateway, and
where SGCP fit into that architecture. Christian,
I believe, only used H.323 as an example of the
call processing's signaling protocol between two
MGC's, but with the ascendency of SIP it has
always been clear in my mind that SIP is the
equivalent of H.323 in that functional
decomposition. SIP, like H.323, and MEGACO are
quite orthogonal.

I hope that this is all that this disagreement (if
any) is about. Al Varney brought up a good analogy
to the circuit switched world, which is that
MEGACO is much like GR-303, though far more rich
in its capabilities of controlling the "DLC" (303
being very, very simple and lineside oriented). It
is definitely *not* like Q.931, even if Q.931 is
being used in a very simple manner (eg, overlapped
dialing, etc).

This is a pretty fundamental thing to understand
about the MEGACO and MGCP architecture.

                Mike

---

From: Chip Sharp <[email-masked]>
Date: Wed, 17 Nov 1999 13:05:47 -0500

>  > Using SIP between MGCs is another matter and currently isn't in the scope

Flu seems to be one of the main outcomes of the IETF meeting. ;-\

>decomposition. SIP, like H.323, and MEGACO are

I see you snipped part of my message without noting the deletion.
Tsk-Tsk.  I'll mark this down as part of your flu-induced haze.

Below is the relevant part.

 >Supporting interworking between MGCs and SIP clients/servers has
 >always been an application intended to be supported as far as
 >I'm concerned (and many other people as well).

I assumed it was clear to everyone that SIP was an important part of the
overall application.