Yealink SIP-T48G Administrator's Manual page 280

Administrator's Guide for SIP-T2_Series_T4_Series IP Phones
DTMF Keypad Frequencies:
697 Hz
770 Hz
852 Hz
941 Hz
Three methods of transmitting DTMF digits on SIP calls:
RFC 2833 -- DTMF digits are transmitted by RTP Events compliant to RFC 2833.

INBAND -- DTMF digits are transmitted in the voice band.

SIP INFO -- DTMF digits are transmitted by SIP INFO messages.

The method of transmitting DTMF digits is configurable on a per-line basis.
RFC 2833
DTMF digits are transmitted using the RTP Event packets that are sent along with the
voice path. These packets use RFC 2833 format and must have a payload type that
matches what the other end is listening for. The payload type for RTP Event packets is
configurable. IP phones default to 101 for the payload type, which use the definition to
negotiate with the other end during call establishment.
The RTP Event packet contains 4 bytes. The 4 bytes are distributed over several fields
denoted as Event, End bit, R-bit, Volume and Duration. If the End bit is set to 1, the
packet contains the end of the DTMF event. You can configure the sending times of the
end RTP Event packet.
INBAND
DTMF digits are transmitted within the audio of the IP phone conversation. It uses the
same codec as your voice and is audible to conversation partners.
SIP INFO
DTMF digits are transmitted by the SIP INFO messages when the voice stream is
established after a successful SIP 200 OK-ACK message sequence. The SIP INFO
message is sent along the signaling path of the call. The SIP INFO message can transmit
DTMF digits in three ways: DTMF , DTMF-Relay and Telephone-Event.
266
1209 Hz 1336 Hz
1 2
4 5
7 8
* 0
1447 Hz 1633 Hz
3 A
6 B
9 C
# D