Subject: RE: [Megaco] Local- and Remote descriptors for multiplexed TDM st reams

From: "Tom-PT Taylor"<[email-masked]>
Date: Mon, 11 Mar 2002 10:47:25 -0500

We have two sets of descriptors to play with: those on the supporting
bearers and those on the multiplexing descriptor.  I think this gives you
what you need.  Here's the schema as I see it for an H.324 connection based
on a single TDM bearer (hence with no intervening H.226 multiplex):

Based on my SDP draft, the Local and Remote descriptors for the TDM bearer
appear as follows, assuming the inbound Q.931 indicated Information Transfer
Capability = "video", User Layer 1 Protocol = "Recommendations H.223 and
H.245".  I wouldn't be surprised if other values are used in practice, in
which case I'll modify my example.

Local (and Remote) ={
v=0
o=- 7736844526 7736842807 IN IP4 125.125.125.111
s=-
t= 0 0
b=AS:64
c=TDM NUL xxxx
m=application 1 TDM h324i
}

Preparation of this example has forced me to face the fact that the Local
and Remote descriptors for the multiplexing termination are problematic.
I'm not sure what transport to assign to them.  I suspect that transport has
to be multiplex-specific, since it is the multiplex which determines the
format of the raw media samples.  That means we are going to have to define
SDP for each of the multiplex types we support.  Let me hazard a guess at
what an audio + video H.324 conference will look like:

Local (an Remote) ={
v=0
o=- 7736849657 7736850233 IN IP4 125.125.125.111
s=-
t= 0 0
c=H223 NUL xxxx
m=control 0 H223 H245
m=audio 1 H223 PCMU
[possible audio attributes]
m=video 2 H223 H263
[possible video attributes]
}

Here the ports are the H.245 logical channel numbers.

Thoughts on this?

-----Original Message-----
From: Christer Holmberg [mailto:[email-masked]]
Sent: Monday, March 11, 2002 3:13 AM
To: [email-masked]
Subject: [Megaco] Local- and Remote descriptors for multiplexed TDM
streams

Hi,

No matter which method (SDP or something else) is used to describe the
Local- and/or Remote descriptors for a TDM termination, how do we handle
multiplexed TDM streams, which may include multiple streams with
different codecs etc... ?

One argument could be that in this case the descriptors should not be in
the TDM termination, but in the MUX termination. Since each
demultiplexed channel is represented by a H.248 Stream, each Stream
descriptor in the MUX termination would then define the Local- and/or
Remote descriptors for each channel.

However, there may still be specific Local- and/or Remote descriptors
which the TDM termination needs, so in this case we could have two sets
of TDM descriptors within the same context....

Any ideas/comments on this?

Regards,

Christer Holmberg
Ericsson Finland

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---

From: Christer Holmberg <[email-masked]>
Date: Tue, 12 Mar 2002 07:55:39 +0200

Hi Tom,

> bearers and those on the multiplexing descriptor.  I think this gives
> you what you need.  Here's the schema as I see it for an H.324
> connection based on a single TDM bearer (hence with no intervening
> H.226 multiplex):
>
> Based on my SDP draft, the Local and Remote descriptors for the TDM
> bearer appear as follows, assuming the inbound Q.931 indicated
> Information Transfer Capability = "video", User Layer 1 Protocol =
> "Recommendations H.223 and H.245".  I wouldn't be surprised if other
> values are used in practice, in which case I'll modify my example.
>
> Local (and Remote) ={
> v=0
> Preparation of this example has forced me to face the fact that the
> Local and Remote descriptors for the multiplexing termination are
> problematic.  I'm not sure what transport to assign to them.  I
> suspect that transport has to be multiplex-specific, since it is the
> multiplex which determines the format of the raw media samples.  That
> means we are going to have to define SDP for each of the multiplex
> types we support.  Let me hazard a guess at what an audio + video
> H.324 conference will look like:
>
> Local (an Remote) ={
> v=0

You seem to define the LCNs for each media type in the m= line. That is
not possible in the way you've done it, since you may different LCN
values in each media direction. To make it work, you would need
something like:

m=audio 1 H223 PCMU  (LCN = 1)
a=recv
m=audio 2 H223 PCMU  (LCN = 2)
a=send

Also, for which Stream did you specify the Local/Remote descriptor? The
"input" stream to the multiplexer (which in most cases will be the
multiplexed TDM stream)?

Since the audio and video bytes will be demultiplexed into separate
channels, represented by separate H.248 streams, another option would be
to use TWO sets of Local/Remote descriptors, each within a separate
Stream Descriptor (each Stream representing a demultiplexed channel).

I am not sure we need the m= line for the control channel, since the LCN
is always 0 for that, but that's details.

I am still not sure I like the idea of using SDP for TDM terminations,
but the way Tom uses it for the MUX termination looks interesting, so I
think that's something we should maybe look more into :)

Is this something people would like to spend time discussing in
Minneapolis?

Regards,

Christer Holmberg
Ericsson Finland

---

From: Christer Holmberg <[email-masked]>
Date: Tue, 12 Mar 2002 07:55:39 +0200

Hi Tom,

Regards,

Christer Holmberg
Ericsson Finland

---

From: Christer Holmberg <[email-masked]>
Date: Tue, 12 Mar 2002 08:29:04 +0200

Hi,

One more question on Tom's proposal.

> Here the ports are the H.245 logical channel numbers.

In you define this Local descriptor for the input stream to the
multiplexer, how will you map each demultiplexed stream into separate
H.248 Streams (in the example you only define the LCN for each media; 1
for audio and 2 for video)?

Regards,

Christer Holmberg
Ericsson Finland

---

From: Christer Holmberg <[email-masked]>
Date: Tue, 12 Mar 2002 08:29:04 +0200

Hi,

Regards,

Christer Holmberg
Ericsson Finland