Why use two different "H.248 mechanisms" in H.323?

Paul, Manoj mpaul at TRILLIUM.COM
Wed May 30 12:58:38 EDT 2001

Hi Frank,

  H.248 appears in H.323 in three contexts
1) Credit card tones and announcements from Gk.
2) Annex L
3) Endpoints reporting their H248 PackageDescriptors to Gks in RRQ.

Although Annex L defined H.248 messages as Octet Strings, the other
two imported H.248 syntax. There was a proposal in last SG16 meeting
to change them to
Octet Strings as well for the reasons-
 Those who were not willing to support H.248 functionality, would not
have to import the H.248 syntax (For Signals and Pacakges for (1) and (3)

Also these octet strings were proposed to contain PER encoded H.248. (Text
in addition for Annex L) to allow single encoding and decoding scheme,
namely PER for H.323.

I believe, it is due to lightweight reasons (as you pointed out), that
ServiceControlSession also
contained H.248 Signals which could as well be transported using Annex L.


-----Original Message-----
From: Frank Derks [mailto:frank.derks at PHILIPS.COM]
Sent: Wednesday, May 30, 2001 12:24 AM
To: ITU-SG16 at mailbag.cps.INTEL.COM
Subject: Why use two different "H.248 mechanisms" in H.323?

There are two ways in which H.248 can be used in H.323. One way is through
Annex L Stimulus Signalling, which basically "tunnels" H.248 messages in
H.225.0 Call Signalling Messages (although Annex L only speaks about
I assume that "replies" may also be carried).

Another way of carrying H.248 is through the serviceControlSession element,
which can be transported in most of the Call Signalling messages and some of
the RAS messages. Using this mechanism, however, introduces a limitation in
that only H.248 _signals_ may be transported.

If the idea behind the second approach is to have a "lightweight" way of
only some of H.248's functionality, then I wonder why H.248 _events_ were
included as part of the solution.



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