Re: H.245 alphanumeric support required?
From: Rich Bowen[SMTP:rkbowen@CISCO.COM] H.323 v2 section 6.8.2.1 says, "Transmitters shall limit the content of their transmitted information to that which the receiver has indicated it is capable of receiving."
This was written back when "transmitted information" did not include H.245 messages. It referred only to the streams of video, audio, and data. That's why it seems to contradict the following, which was added much later:
H.245 v3 section 7.12.6 says, "Endpoints shall use the alphanumeric indication to convey DTMF user input if the other endpoint has not indicated the ability to receive DTMF using UserInputCapability."
o Every endpoint is required to indicate capability of receiving alphanumeric user input (not likely), or --
o Every endpoint is assumed to have the capability to accept alphanumeric user input; i.e., each endpoint *implicitly* indicates that it has this capability. Or --
o I'm interpreting H.245 v3 too strictly. What it really means is that endpoints shall use alphanumeric if the remote endpoint did not indicate DTMF capability but it did indicate alphanumeric capability; otherwise don't send user input at all.
Is any of these interpretations correct?
The second one.
Can someone please clarify the requirements here?
First, the intent was that all H.323 terminals have at least a basic ability to signal "DTMF." In fact, this is a requirement. 6.2.8/H.323v2: "An H.245 indication, userInputIndication, is available for transport of user input alphanumeric characters from a keypad or keyboard, equivalent to the DTMF signals used in analogue telephony... H.323 terminals shall support the transmission of user input characters 0-9, "*", and "#". Transmission of other characters is optional."
All endpoints must be able to receive all of the H.245 messages, including userInputIndication (6.2.8/H.245v3: "H.323 terminals shall be capable of parsing all H.245 MultimediaSystemControlMessage messages..."); however, note that there is no requirement to do anything with this information on the receive side. Just like with the PSTN, it is up to special-purpose terminals to decide whether and how to interpret these signals, but all terminals are required to send them.
Paul Long Smith Micro Software, Inc.
Paul,
Thanks for clearing this up for me.
Rich ---------------------------------------------------------------------------- Richard K. Bowen Cisco Systems, Inc. rkbowen@cisco.com Research Triangle Park, NC ---------------------------------------------------------------------------- Paul Long wrote:
From: Rich Bowen[SMTP:rkbowen@CISCO.COM] H.323 v2 section 6.8.2.1 says, "Transmitters shall limit the content of their transmitted information to that which the receiver has indicated it is capable of receiving."
This was written back when "transmitted information" did not include H.245 messages. It referred only to the streams of video, audio, and data. That's why it seems to contradict the following, which was added much later:
H.245 v3 section 7.12.6 says, "Endpoints shall use the alphanumeric indication to convey DTMF user input if the other endpoint has not indicated the ability to receive DTMF using UserInputCapability."
o Every endpoint is required to indicate capability of receiving alphanumeric user input (not likely), or --
o Every endpoint is assumed to have the capability to accept alphanumeric user input; i.e., each endpoint *implicitly* indicates that it has this capability. Or --
o I'm interpreting H.245 v3 too strictly. What it really means is that endpoints shall use alphanumeric if the remote endpoint did not indicate DTMF capability but it did indicate alphanumeric capability; otherwise don't send user input at all.
Is any of these interpretations correct?
The second one.
Can someone please clarify the requirements here?
First, the intent was that all H.323 terminals have at least a basic ability to signal "DTMF." In fact, this is a requirement. 6.2.8/H.323v2: "An H.245 indication, userInputIndication, is available for transport of user input alphanumeric characters from a keypad or keyboard, equivalent to the DTMF signals used in analogue telephony... H.323 terminals shall support the transmission of user input characters 0-9, "*", and "#". Transmission of other characters is optional."
All endpoints must be able to receive all of the H.245 messages, including userInputIndication (6.2.8/H.245v3: "H.323 terminals shall be capable of parsing all H.245 MultimediaSystemControlMessage messages..."); however, note that there is no requirement to do anything with this information on the receive side. Just like with the PSTN, it is up to special-purpose terminals to decide whether and how to interpret these signals, but all terminals are required to send them.
Paul Long Smith Micro Software, Inc.
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