Brian,
Your argument for the second approach (separate terminations for each of the streams) makes sense. I agree that it's not very nice to have each termination describe audio, video and data parameters. Can't we have set the audio termination's video and data parameters to "null", allowing the MGC to know that it represents the audio stream?
Note that in this approach, there are multiple terminations (the H.320/audio, H.320/video, H.320/data) associated with one physical endpoint. This suggests having all terminations as ephemeral entities, one of their properties being the transport addresses and type of network they use. I realize that this is rather a large step away from the current protocol document. But is there another way to solve this?
In my previous message I showed a diagram in which the video stream was split up over two ports. If we want to model such a multi-port video stream by means of one termination, the termination has to be associated to multiple ports. This is currently not possible, but I see no other way to do it. Any thoughts?
John
Brian Rosen wrote:
I'm in favor of the second approach.
You could have a termination class H.320 with H.320/audio H.320/video and H.320/T.120. There would be 3 contexts, each with different media. There is a slight ugliness where the termination class would define all the parameters for all of the streams as one big list, and each of the terminations would have all of them. Unfortunate, but it works.
Christian did not want to infer anything from the name. We would need to have some way for the MG to know which media was on which termination if we couldn't infer it from the name.
I like this approach because from the MGC, whether the three streams are on one gateway, or multiple gateways, it operates on them the same way, only the names are changed (to protect the innocent). The MG is built differently in these cases, but I don't see any way around that.
BTW, the H.320 stream could be multi-ported, so you could have H.320/7/video.
-----Original Message----- From: John Segers [mailto:jsegers@lucent.com] Sent: Tuesday, March 30, 1999 10:27 AM To: megaco@BayNetworks.COM; ITU-SG16@mailbag.cps.intel.com Subject: H.320 gateways
People,
In yesterday's conference call, the subject of H.320 GWs was raised briefly. In my opinion, the connection model and protocol should be able to deal with H.320. I would like to continue discussion on it on
the
mailing list.
H.320 allows a user to have a session with both audio and video on a
single 64 kbit/s channel such as an ISDN B-channel. The same
channel
carries some signalling information (frame alignment, bitrate allocation). To a MG supporting H.320, this means that on a single endpoint, three streams can come in, carrying different types of media. The current connection model of megaco/H.gcp does not cater to this. I see two possible solutions:
The first is to allow multiple media in one context and to describe for terminations the logical streams they carry. In a picture:
+----------+ | | | +--------- signalling (FAS, BAS) | |B-channel ==========+ +--------- audio (16 kbit/s) | | | +--------- video (46.4 kbit/s) | | +----------+
The second solution is to have separate terminations for the
different
streams. They would all "connect to" the same physical endpoint.
In
order to properly identify the terminations, it is necessary to have
logical names for them. The physical endpoint they connect may have the hierarchical name proposed in the megaco document.
Another example of a H.320 session is the case of two B-channels
being
used for an audiovisual call. The following frame structure is then
possible.
+--------------------------++-----------------------+ | Channel 1 || Channel 2 | +-----+--+--+--+--+--+--+--++--+--+--+--+--+--+--+--+ |Bit 1|B2|B3|B4|B5|B6|B7|B8||B1|B2|B3|B4|B5|B6|B7|B8| +-----+--+--+--+--+--+--+--++--+--+--+--+--+--+--+--+ 1 | a1 |a2|a3|a4|a5|a6|v1|F ||v2|v3|v4|v5|v6|v7|v8|F | 2 | a7 |a8|a9|a |a |a |v9|F ||v |v |v |v |v |v |v |F | 3 | a |a |a |a |a |a |v |F ||v |v |v |v |v |v |v |F | 4 | a | | | | |a |v |F ||v | |v |F | 5 | a | | | | |a |v |F ||v | |v |F | 6 | a | | | | |a |v |F ||v | |v |F | 7 | a | | | | |a |v |F ||v | |v |F | 8 | a | | | | |a |v |F ||v | |v |F | +---------------------------------------------------+ 9 | a | | | | |a |v |B ||v | |v |B | 10 | a | | | | |a |v |B ||v | |v |B | 11 | a | | | | |a |v |B ||v | |v |B | 12 | a | | | | |a |v |B ||v | |v |B | 13 | a | | | | |a |v |B ||v | |v |B | 14 | a | | | | |a |v |B ||v | |v |B | 15 | a | | | | |a |v |B ||v | |v |B | 16 | a | | | | |a |v |B ||v | |v |B | +---------------------------------------------------+ 17 | a | | | | |a |v |v ||v | |v |v | . . . 80 | a | | | | |a |v |v ||v | |v |v | +---------------------------------------------------+
(a=audio, v=video, F=FAS, B=BAS).
We see that the video stream is split up over two channels. In order to cater to this, it seems we have to allow terminations to receive
media
from and send it to multiple physical endpoints. The two approaches
outlined above can both be extended to allow this. Both extensions will lead to the introduction of logical names for terminations. In the first approach there will be one termination "containing" two B-channels on one side and three logical streams on the other. In the second approach there will be three terminations, the one for the video stream referencing both B-channels, the ones for signalling and audio referencing only channel 1.
The second approach allows us to keep separate contexts for
different
media types. It is then easy to delete, for instance, the video part of a session (session used loosely to desribe the contexts for the
audio
and video).
The first approach groups the streams coming from/going to one user,
making it possible to remove a user from a context more easily.
Personally, I can't decide which approach I would prefer. How do others feel about these ideas?
Regards,
John Segers
John Segers email:
jsegers@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
-- John Segers email: jsegers@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