Subject: [AVT] Non-standard RFC 2833 definition of ANS, /ANS, ANSam and /ANSam

From: Rajesh Kumar <[email-masked]>
Date: Thu, 24 Oct 2002 14:16:41 -0700

Henning,
There are certain issues with the definition of the ANS, /ANS, ANSam and 
/ANSam events that need clarification.

Since at least 450 ms is needed to detect a phase reversal, it is not 
possible to discriminate between ANS and /ANS before 450 ms. However, this 
results in an unacceptable delay in informing the far end that a 2100 Hz 
signal (whatever its variant) has been detected. It takes less than 200 ms 
to detect that fact that this is a 2100 Hz signal.

Question 1: Does RFC 2833 consider it acceptable to send an ANS event (200 
ms) and then an /ANS event (450 ms), thereby using the /ANS event as an 
"update" of the ANS event? The same consideration would apply to ANSam and 
/ANSam.  This would change how you have defined these events in RFC 2833.

Queston 2: Your use of the "bar" or "slash" is at odds with that of the ITU 
V.25. In the ITU specification, /ANS is not a separate signal but refers to 
the 2100 Hz cycle during which phase is reversed. Thus, the RFC 2833 
definition of /ANS corresponds to the following ITU V.25 sequence, where 
each element in the sequence is one cycle:
	ANS, /ANS, ANS, /ANS, ANS, /ANS, ANS

However,  I have no problem with your re-definition of that the "bar" or 
"slash" means. I only want to point out that you say in RFC 2833 that your 
definition is equivalent to the ITU's, when it isn't. Please look at Figure 
3 of ITU V.25 and add the applicable clarification in your document.

Thanks,

Rajesh

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