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DTMF before 200 OK - Printable Version

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DTMF before 200 OK - Pirmin - 04-03-2019 06:13 AM

Hello. It seems like Yealink phones would not support to send DTMF before they have received a 200 OK message. We tested this on a T46S with firmware and with all possible settings for account.X.dtmf.type.

In our case the phone gets a 183 Session Progress with the SDP listed bellow. (All necessary things for sending DTMF are negotiated and sendrecv is set in the SDP, so there is no reason why the phone could not send any DTMF sequences). In Switzerland there are some telephony services for which one needs to confirm with some DTMF digits that the call should be established after an announcement has been played back about how much the call will cost (some quite expensive 0900 services), so this is quite an issue here...

Is there a config option that can be set on the phone to enable DTMF before 200 OK? It's working without any issues with devices from other manufacturers.

The SDP:

Content-Type: application/sdp
Content-Length: 223

o=- 20137 20139 IN IP4
c=IN IP4
t=0 0
m=audio 15314 RTP/AVP 8 101
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16

FYI: this seems to be a Firmware 84.X issue. A downgrade to fixed the issue. An upgrade to didn't help. (Like mentioned we originally tested with So can you please fix this in fimre 66.84.0.X?