Perhaps I have not stated the problem well. When a Media Gateway receives a call from the PSTN and it is using RFC2833/4733 for DTMF, it typically suppresses the sending of the DTMF tone as encoded audio and sends only the RTP event. It takes some time for the Media Gateway to actually detect the DTMF tone before it can suppress the encoded audio. During that time, some of the DTMF tone can leak into the encoded audio. The leakage can be reduced by additional buffering but this in turn adds latency. I'm trying to determine if there is a generally acceptable range for this leakage. I have seen values ranging from 5ms which is not too significant, up to 50ms, which is quite significant and which creates problems for some VoIP applications.
Thanks, James -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Wednesday, May 02, 2007 9:16 PM To: [email protected] Subject: Re: [Sip-implementors] RFC2833 Implementations - Inband Leakage vs. Latency ? From: [EMAIL PROTECTED] In case of DTMF digits, a single RFC 4733 packet carries a single DTMF digit in my understanding. Triple redundancy is the basic means to target RTP packet losses, i.e. the receiver must receive at least one out of three. Be careful -- An RFC 4733 packet carries state information about a DTMF sound, either that the sound is on (and if so, how long it has been on) or that the sound has stopped. E.g., it is up to the recipient to decode this information into DTMF digits, and in some cases, to distinguish how long the digit was. Multiple packets are used to defeat packet loss, but also to allow transmitting the initiation of the digit before the finish of the digit has been seen, and to allow the transmission of the real length of the digit. Dale _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
