Subject: ITU-T SG11 Q.1950 and H.248 alignment

From: Mark Watson <[email-masked]>
Date: Fri, 2 Feb 2001 16:01:32 -0000

All,

As everyone will be aware from the communication sent to this list from
ITU-T SG11 on 6 December, ITU-T SG11 is standardising a new protocol, known
as Call Bearer Control protocol, based on H.248. This has been determined in
ITU-T as draft recommendation Q.1950.

Whilst aligned with H.248/Megaco in many respects, there is one important
difference in the manner in which 'bearer control' information is passed
from MG up to MGC and then back to the other MG. Several organisations in
ITU-T expressed concerns about this difference and as a result the
forthcoming 'editing' meeting in Gold Coast was given the remit to look at
this particular issue.

Nortel Networks plans to make a detailed proposal to this meeting, and we
are seeking support from other ITU-T member companies and comments from
anyone with an interest.

The rationalle for alignment is simply to avoid there being essentially two
versions of H.248 and the additional complexity this entails for both
service providers and equipment suppliers.

The particular different between H.248 and Q.1950 concerns the transport of
'bearer control' information between MGs in the case of IP networks. Whilst
H.248, at least the text encoding, assumes the use of SDP exchanged between
gateways for this purpose, Q.1950 instead defines a generic 'Tunnelling
Package' which would allow any format of information to be used. Whilst this
is a valuable enhancement in itself, ironically, the only format of
information defined for use in BICC network by ITU-T SG11 is essentially SDP
(see below).

Our proposal is simply, then, that when the information to be transported is
SDP, then the existing elements carrying SDP in H.248/megaco should be used.
The generic 'tunnelling' package would remain for use if/when other formats
of information need to be carried.

Additionally, we propose enhancing the H.248 Annex C native tags which
support individual lines of SDP, with an additional tag supporting an entire
SDP string. This will allow alignment of the bearer control information
format between the text and binary encodings.

You can find our proposal at:

http://people.itu.int/~watsonm/Q1950_proposalv5.pdf

[[Note this is a Nortel proposal only - it has no official status in the
ITU-T at present]]

Q.1950 is available at:

http://people.itu.int/~watsonm/pl-090r1.pdf

Note that the 'Tunnelling Package' in Q.1950 specifies that in BICC network
the tunnelled data format is defined by new recommendation Q.1970 ('BCTP').
This specifies a short header giving the format of the subsequent
information. Only one format is defined, and this is described in new
recommendation Q.1990 ('IP BCP'). This in turn references SDP and specifies
certain mandatory SDP elements to be used for this application.

Draft Q.1990 is available at:

http://people.itu.int/~watsonm/pl-092.pdf

and Draft Q.1970 is available at:

http://people.itu.int/~watsonm/pl-072.pdf

Comments ?

Regards,

Mark Watson
Nortel Networks