Frank,

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@mailbag.cps.INTEL.COM]On Behalf Of Frank Derks Sent: Tuesday, May 29, 2001 10:00 AM To: ITU-SG16@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 clear for what purpose it is included in the UserInputIndication.

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

Regards,

Frank

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