Subject: [Megaco] DTMF detection and buffering

From: "CHATRAS Bruno FTRD/DAC/ISS" <[email-masked]>
Date: Wed, 27 Aug 2003 19:18:53 +0200

Hi,
 
A question about digit collection using the Extended DTMF detection
package (H.248.16).
 
Let's assume the following scenario:
 
a) The MGC is notified of the off-hook event and reply with a Modify
command asking for digit collection according to the Extended DTMF
Detection package procedures. The event descriptor includes the xdd/xce
event. The digit map parameter is a pointer to DigitMap1 and the buffer
control parameter indicates that digit buffering shall occur for let's
say 1 minute after the event has been reported. 
 
b) Full match according to DigitMap1 occurs in the MG and the xdd/xce
event is reported to the MGC.
 
c) The MGC replies with another Modify command asking for the detection
of the xdd/xce event, according to another digit map, DigitMap2.
 
Assuming that the buffer is still empty when the second Modify command
is received (because the user dials very very slowly), which DigitMap2
timer is used to wait for the first digit to enter the buffer : T or S ?

The ambiguous point is that this first digit will be the first digit to
be processed by DigitMap2 but will not be the first dialled digit of the
overall dialling procedure. 
 
I guess the answer is T because digit map processing should not depend
on whether a particular DigitMap is processed immediatly after detection
of the off-hook event or after another digit map has been processed.
However H.248.16, section 5.5.1.2 "The start timer (T) is used prior to
any digits having been dialled" is confusing. A more appropriate wording
might be "The start timer (T) is used prior to any digits being
available for processing against the digit map".
 
Any views ?
 
Regards,
 
Bruno Chatras