Er... hmmmm
rfc2543, "SIP: Session Initiation Protocol," that was obsoleted by rfc3261, "SIP: Session Initiation Protocol"
that was published as rfc2543, "SIP: Session Initiation Protocol"
3261 and 2543 are not encoding standards but SIP itself.
Perhaps you are referring to RFC 2833 (
RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals)? As the title suggests, RFC2833 describes how to transmit DTMF and call-signalling information in an RTP packet, as opposed to transmitting it
out-of-band (in the SIP header, usually referred to as
info or
sip-info), or transmitting it
in-band as an undifferentiated part of the overall audio signal. The only thing you really need to know about this stuff is that both sender and receiver should be setup to use the same method and that you can't use
in-band with a compressive codec (i.e. with anything other than G711
law).
Kind Regards
S