Subject: Comments on the "FAX and Modem Package for MEGACO Protocol"

From: Hung Bui <[email-masked]>
Date: Mon, 8 Nov 1999 15:54:32 -0500

Dear all,

I would like to thank Roy Spitzer for the draft.  It is great to see such a
draft so we can move forward with the fax protocol.

I agree that we should treat the voice to fax switching operation like a
codec switching.  I could see in a short term requirements for:

-   voice to fax switching from a voice codec into T.38 fax relay
-   voice to fax switching from a compressed codec such as G.729a, G.723 to
a higher speed codec such as G.711.

For the purpose of this email, I would like to comment on the T.38
operation, as the switching to G.711 is much simpler and can be added later.

Here are my comments:

1.      The use of UDP is mandatory, TCP is optional.

2.      The proposal does not specify when and how T.38 fax relay session is to
be set up if T.38 is the codec selected for fax/modem transfer.  E.g. What
are the UDP ports for T.38 session?  At which stage of the call would MGC
specify to MG the UDP ports for T.38 data streams.

3.      At the detection of the CED (for CED fax detection) or V.21 flags (for
V.21 flag fax detection), the answering side needs to Notify the Call Agent
but should not need to signal the remote endpoint.  The Call Agent then
sends Modify Codec commands to both endpoints to set up the fax call.

4.      It seems to be unnecessary to send fax signaling using RTP DTMF between
the two endpoints once the T.38 has been set up.  T.38 has the means to
transport these signals in T.38 packets.  There should be no RTP and RTP
streams active during T.38 fax session.

I hope this will have enough information for us to discuss on Wednesday.

Regards,

   =========
  ===========   Hung Bui                   mailto:[email-masked]
 ============   Principal Engineer         http://www.salix.com
 ============   SALIX Technologies, Inc.
 ==  ==== ==    904 Wind River Lane        TEL:  (301) 417-0017
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   The statements contained herein are strictly those of
   their author, and unless otherwise specifically indicated
   should not be attributed to SALIX(r) or its management.

---

From: Gunnar Hellstrom <[email-masked]>
Date: Tue, 9 Nov 1999 12:47:22 +0100

The described actions for Fax look straightforward. Very similar actions are
needed for text telephone signal detection, as described in the text
conversation part of the packages dockument.

Answering from the PSTN
-----------------------
On the called gateway end, Fax detection, and text telephone detection must
co-reside. (and modem detection if there is any interest for modem access)
We have to decide if this shall be expressed in one common call type
discrimination package, or if we dare to describe it in separate packages
and know that they are interleaved in implementations.

If separate, can we both say that we extend the simple line signal detection
packages and rely on getting a chance to split the job of fax and textphone
signal detection properly?

And, I assume that you can have a V.8 based and V.8 bis based handshaking
faxes, where you need rapid decisions and transmission of handshaking
signals from both ends. Textphones may also have V.8 or V.8 bis handshaking,
so these handshaking procedures should be common for activation from both
packages.

There is a need for a common call type discrimination plan.

Calling to the PSTN
--------------------
On the gateway end calling out to the PSTN, the situation is simpler. If
T.38 is applied in a call, then Fax functionality is activated in the PSTN
termination. If RTP-Text or T.140-TCP is signalled in a call, then text
telephone functionality is activated in the PSTN termination.
So, for that case you can be selective with the discrimination functionality
applied in the call.

Gunnar Hellström

------------------------------------------
------------------------------------------
Gunnar Hellstrom
LM Ericsson

E-mail [email-masked]
Tel +46 8 556 002 03
Mob +46 708 204 288
fax +46 8 556 002 06

-----Ursprungligt meddelande-----
Från: Media Gateway Control (megaco)
[mailto:[email-masked]]För Hung Bui
Skickat: den 8 november 1999 21:55
Till: [email-masked]
Ämne: Comments on the "FAX and Modem Package for MEGACO Protocol"

Dear all,

Here are my comments:

2.      The proposal does not specify when and how T.38 fax relay session is
to
be set up if T.38 is the codec selected for fax/modem transfer.  E.g. What
are the UDP ports for T.38 session?  At which stage of the call would MGC
specify to MG the UDP ports for T.38 data streams.

3.      At the detection of the CED (for CED fax detection) or V.21 flags
(for
V.21 flag fax detection), the answering side needs to Notify the Call Agent
but should not need to signal the remote endpoint.  The Call Agent then
sends Modify Codec commands to both endpoints to set up the fax call.

4.      It seems to be unnecessary to send fax signaling using RTP DTMF
between
the two endpoints once the T.38 has been set up.  T.38 has the means to
transport these signals in T.38 packets.  There should be no RTP and RTP
streams active during T.38 fax session.

Regards,

   =========

---

From: James Rafferty <[email-masked]>
Date: Tue, 9 Nov 1999 10:12:41 -0500

To all -

As Tom Taylor has noted, there have been discussions in the ITU-T Study Group
8 about the support for fax and IP fax within Megaco.  I have been involved
in that work
as well as monitoring this list.   Some related comments follow:

>draft so we can move forward with the fax protocol.
Yes,  I agree that Roy document has a lot of useful content in
areas like call flows and helps get this work going.
>a higher speed codec such as G.711.
I see about 4 related topics for fax and data packages, which may show up
in single or more likely (IMO)
in multiple documents.

- IP fax package (supports T.38 and fall back to G.711)
- G3 fax package (deals with recognition of G3 fax signalling - i.e. CNG,
CED, V.21 w flags
- data modem package (switch to data modem)
- interaction between voice, data and fax (how to distinguish between these
calls; map out the most
important call flow scenarios)

Roy's draft touches on all of the topics above.   I believe that all of
these elements need to be dealt with
in the package work, but it is probably cleaner to break them down into
smaller documents.

>1.      The use of UDP is mandatory, TCP is optional.
T.38 states that support for both UDP and TCP are required.   If this profile
has a different assumption, the reasons would have to clearly stated.
(for
between
>streams active during T.38 fax session.
Yes.   It is a common misunderstanding that fax relay requires RTP.   T.38
does not use RTP, so there are no needs to have active RTP streams to support
a T.38 fax session.
>I hope this will have enough information for us to discuss on Wednesday.
I assume the discussion Wed. will be on putting together a roadmap for
the fax/data package work.   I am certain that the interested parties
involved in the
SG8 T.38 work(such as Glenn Parsons, myself and others) can work with Roy
and this WG
to put together the necessary package and interaction documents.

Regards,

James

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