Administrator’s Guide for SIP-T2 Series/T19(P) E2/T4 Series IP Phones
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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 default payload type for RTP Event packets is 101 and the payload type
is configurable. The IP phones use the configured value 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.
Procedure
Configuration changes can be performed using the following methods.
Central Provisioning
(Configuration File)
Configure the method of transmitting DTMF
digit and the payload type.
Parameters:
account.X.dtmf.type
account.X.dtmf.dtmf_payload
account.X.dtmf.info_type
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