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2.2.1 DTMF Telephony Event

The DTMF telephony event is specified in the event field, as specified in [RFC4733] section 2.3.1, of the DTMF message. In addition to events 0 through 15 (as defined in [RFC4733]), event 16, which is reserved (as defined in [RFC4733]), is also supported. The following is an example of an SDP invite that specifies DTMF event type 0-16 at the end:

 v=0
 o=- 0 1 IN IP4 10.131.32.127
 s=session
 c=IN IP4 10.131.32.127
 b=CT:99980
 t=0 0
 a=x-devicecaps:audio:send,recv;video:send,recv
 m=audio 50006 RTP/AVP 117 114 9 112 111 0 8 116 115 97 13 118 101
 a=x-ssrc-range:727739136-727739136
 a=rtcp-fb:* x-message app send:dsh recv:dsh a=rtcp-rsize a=label:main-audio a=x-source:main-audio a=ice-ufrag:6Gjo a=ice-pwd:NvUIAlyBYxK0xQ+VCXYRc2L/
 a=candidate:1 1 UDP 2130706431 10.131.32.127 50006 typ host
 a=candidate:1 2 UDP 2130705918 10.131.32.127 50007 typ host
 a=x-candidate-ipv6:2 1 UDP 2130705919 2001:4898:1:12:6d0f:ce6a:35a9:c5e0 50002 typ host
 a=x-candidate-ipv6:2 2 UDP 2130705406 2001:4898:1:12:6d0f:ce6a:35a9:c5e0 50003 typ host
 a=x-candidate-ipv6:3 1 UDP 2130705407 2001:4898:0:fff:0:5efe:10.131.32.127 50012 typ host
 a=x-candidate-ipv6:3 2 UDP 2130704894 2001:4898:0:fff:0:5efe:10.131.32.127 50013 typ host
 a=candidate:4 1 TCP-PASS 174455295 131.107.1.53 58849 typ relay raddr 10.131.32.127 rport 50016
 a=candidate:4 2 TCP-PASS 174454782 131.107.1.53 58849 typ relay raddr 10.131.32.127 rport 50016
 a=candidate:5 1 UDP 184547327 131.107.1.53 58555 typ relay raddr 10.131.32.127 rport 50004
 a=candidate:5 2 UDP 184546814 131.107.1.53 59208 typ relay raddr 10.131.32.127 rport 50005
 a=x-candidate-ipv6:6 1 UDP 184546815 2001:4898:9000:6000:fe:1311:700:1053 54003 typ relay raddr 10.131.32.127 rport 50004
 a=x-candidate-ipv6:6 2 UDP 184546302 2001:4898:9000:6000:fe:1311:700:1053 52204 typ relay raddr 10.131.32.127 rport 50005
 a=candidate:7 1 TCP-ACT 174846975 131.107.1.53 58849 typ relay raddr 10.131.32.127 rport 50016
 a=candidate:7 2 TCP-ACT 174846462 131.107.1.53 58849 typ relay raddr 10.131.32.127 rport 50016
 a=x-candidate-ipv6:8 1 TCP-PASS 174453247 2001:4898:9000:6000:fe:1311:700:1053 50226 typ relay raddr 10.131.32.127 rport 50016
 a=x-candidate-ipv6:8 2 TCP-PASS 174452734 2001:4898:9000:6000:fe:1311:700:1053 50226 typ relay raddr 10.131.32.127 rport 50016
 a=x-candidate-ipv6:9 1 TCP-ACT 174845951 2001:4898:9000:6000:fe:1311:700:1053 50226 typ relay raddr 10.131.32.127 rport 50016
 a=x-candidate-ipv6:9 2 TCP-ACT 174845438 2001:4898:9000:6000:fe:1311:700:1053 50226 typ relay raddr 10.131.32.127 rport 50016
 a=candidate:10 1 TCP-ACT 1684794879 10.131.32.127 50016 typ srflx raddr 10.131.32.127 rport 50016
 a=candidate:10 2 TCP-ACT 1684794366 10.131.32.127 50016 typ srflx raddr 10.131.32.127 rport 50016
 a=cryptoscale:1 client AES_CM_128_HMAC_SHA1_80 inline:sW8VgUkKL9a0xVLoRWctybbka87hwg16KknLeyY7|2^31|1:1
 a=crypto:2 AES_CM_128_HMAC_SHA1_80 inline:f29SH3+v3rWEj0hgb3+2a5/a1LG9cW1Yyjma24f3|2^31|1:1
 a=crypto:3 AES_CM_128_HMAC_SHA1_80 inline:a3n9t4OaoJLkwtu9F69U691Xtw8y5fRZikREQlQb|2^31
 a=maxptime:200
 a=rtpmap:117 G722/8000/2
 a=rtpmap:114 x-msrta/16000
 a=fmtp:114 bitrate=29000
 a=rtpmap:9 G722/8000
 a=rtpmap:112 G7221/16000
 a=fmtp:112 bitrate=24000
 a=rtpmap:111 SIREN/16000
 a=fmtp:111 bitrate=16000
 a=rtpmap:0 PCMU/8000
 a=rtpmap:8 PCMA/8000
 a=rtpmap:116 AAL2-G726-32/8000
 a=rtpmap:115 x-msrta/8000
 a=fmtp:115 bitrate=11800
 a=rtpmap:97 RED/8000
 a=rtpmap:13 CN/8000
 a=rtpmap:118 CN/16000
 a=rtpmap:101 telephone-event/8000
 a=fmtp:101 0-16