Status of H.323 Annex L

Frank Derks frank.derks at PHILIPS.COM
Tue May 29 13:50:48 EDT 2001


UserInputSupportIndication was added to an earlier version of H.245 (v2)
before UserInputCapability (v3). The latter is now the prefered means of
indicating what type of UII one supports, but the former must also be
supported for backward compatibility. BTW, UserInputSupportIndication came
about because it was generally conceded early on but too late to modify
H.245v1 that it was a mistake to have specified GeneralString in UII because
the character set was way too large and would have imposed an unreasonable
burden on receivers when we mostly just wanted to convey a rather small
character set.

The general issue here is that there is a great deal of character-set
overlap between these types, e.g., GeneralString can encode everything that
IA5String can encode but not vice versa, so the type is not necessarilly
sufficient to indicate exactly what characters to expect. Basically, we
screwed up in the beginning and have been trying to fix it ever since. :-)

Paul Long
ipDialog, Inc.

-----Original Message-----
From: Mailing list for parties associated with ITU-T Study Group 16
[mailto:ITU-SG16 at mailbag.cps.INTEL.COM]On Behalf Of Frank Derks
Sent: Tuesday, May 29, 2001 10:00 AM
To: ITU-SG16 at mailbag.cps.INTEL.COM
Subject: What is the purpose of UserInputSupportIndication in
UserInputIndication and where are the string types used?

Through the UserInputCapability (during the capabilities exchange), an EP
can signal
which string type(s) it supports for "user input". The
UserInputSupportIndication in
the UserInputIndication message carries similar information, but it is not
for what purpose it is included in the UserInputIndication.

Furthermore, the "signal" element in the UserInputIndication can only carry
IA5String type and the extendedAlphanumeric element can only carry strings
of type
GeneralString, so what is the purpose of informing the other party about
string types that will never be used anyway?



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