Administrator’s Guide for SIP-T2 Series/T19(P) E2/T4 Series IP Phones830Three 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 2833DTMF 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 otherend is listening for. The default payload type for RTP Event packets is 101 and the payload typeis configurable. The IP phones use the configured value to negotiate with the other end duringcall establishment.The RTP Event packet contains 4 bytes. The 4 bytes are distributed over several fields denoted asEvent, End bit, R-bit, Volume and Duration. If the End bit is set to 1, the packet contains the endof the DTMF event. You can configure the sending times of the end RTP Event packet.INBANDDTMF digits are transmitted within the audio of the IP phone conversation. It uses the samecodec as your voice and is audible to conversation partners.SIP INFODTMF digits are transmitted by the SIP INFO messages when the voice stream is establishedafter a successful SIP 200 OK-ACK message sequence. The SIP INFO message is sent along thesignaling path of the call. The SIP INFO message can transmit DTMF digits in three ways: DTMF,DTMF-Relay and Telephone-Event.ProcedureConfiguration changes can be performed using the following methods.Central Provisioning(Configuration File).cfgConfigure the method of transmitting DTMFdigit and the payload type.Parameters:account.X.dtmf.typeaccount.X.dtmf.dtmf_payloadaccount.X.dtmf.info_type
