Summary:ASTERISK-15230: RFC 2833 DTMF Events Generated by Polycom IP Phone Running v3.2.1 F/W Not Recognized by Asterisk 1.4
Reporter:Jamuel Starkey (jamuel)Labels:
Date Opened:2009-11-28 15:04:34.000-0600Date Closed:2009-11-30 13:42:08.000-0600
Versions:Frequency of
Environment:Attachments:( 0) spip_dtmf_issue-fw-3.1.3.pcap
( 1) spip_dtmf_issue-fw-3.2.1.pcap
Description:A Polycom SP IP 450 phone running firmware version 3.2.1 configured with the default configuration settings generates an rtpmap for DTMF events that is apparently not recognized by Asterisk.

Run the same phone against Asterisk 1.6.1 no problem.

Run the phone on version 3.1.3 firmware against Asterisk 1.4 or 1.6 and no problem.

In the SDP exchange we are seeing a different rtpmap # for telephone-event/8000 generated by the Polycom with the 3.2.1 version of firmware as compared v3.1.3

I will attach packet captures showing that the in the INVITE's SDP the SPIP generates rtpmap:127 telephone-event/8000 when running fw v3.2.1 and rtpmap:101 telephone-event/8000 when running v 3.1.3

v3.1.3 works without issue with Asterisk 1.4.27 but while running the Polycom on v3.2.1 Asterisk does not seem to recognize the rtmap:127 value and does not respond in-kind in its SDP.

rtpmap:127 is the default value set in the Polycom configuration files (sip.cfg) for f/w 3.2.1  <DTMF tone.dtmf.rfc2833Payload="127" /> versus in v3.1.3 f/w <DTMF tone.dtmf.rfc2833Payload="101" />

I realize this sounds like it's a Polycom issue but if rtpmap:127 is a valid payload type for 2833 RTP telephony-events, then this is a bug in Asterisk 1.4
Comments:By: Dan G (dan g) 2009-11-29 17:34:39.000-0600

I'm experiencing the same issue with  DTMF from the Polycom IP670 with v3.2.1 does not work with

When I downgrade to, it works fine with v3.2.1.  If I change the Polycom sip.cfg file to say: tone.dtmf.rfc2833Payload="101", then works fine.

I noticed there are lots of changes in chan_sip.c between and, so I built, but with the chan_sip.c file from, and it works fine.  There's something new in chan_sip.c that doesn't like the new payload of 127.

By: Leif Madsen (lmadsen) 2009-11-30 13:42:07.000-0600

This should be fixed in the next set of releases, due out later today.