DTMF problem

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Asterisk Users 2 Comments

19 sep 2011 kl. 01:51 skrev Zeeshan A Zakaria:

> This DTMF problem has always been there and there is no real solution for it, other than using those expensive PBX systems like that from Avaya, Cisco, etc. This problem happens when you are sending inband DTMF tones. Via softphone you are sending out-of-band DTMF which is basically SIP messages.

Just to correct the latest part of your statement:

The default way to send DTMF in SIP calls is using DTMF as a codec called telephony-event in the RTP stream. This sends DTMF as events. Most hard and soft phones support this – usually called RFC2833 DTMF mode. Asterisk supports it by default.

Sending DTMF in the audio usually gets messy when using an IP network. Especially if you use codecs that compress the audio. I do recommend you to use RFC2833. We have built very large IVR services and have no issues with DTMF being received in Asterisk so it’s doable.

There are other issues with Asterisk DTMF, but that’s another issue 🙂


2 thoughts on - DTMF problem

  • You can emulate this feature from the Expensive PBX system by setting:
    in the case of SIP, option may vary with Techology.

  • Dear,

    Huawei softx3000 sends the dtmf with undefined content-type(sscc) and format, so the asterisk can not recognize the digits, maybe changing the source code of asterisk be a good solution, but I am looking for a better way.

    would you please let me know if you have a better solution.


    < --- SIP read from UDP: --->
    INFO sip:050111111@ SIP/2.0
    Via: SIP/2.0/UDP;branch=z9hG4bK2d421b56a6bf8d240ecb4592d Call-ID: SBCb0l9t89ql920b0y1rsps2gsr8sy9ggl0@SoftX3000
    From: ;tag=srtysnby-CC-23
    To: ;tag=as12188ab0
    CSeq: 2 INFO
    Max-Forwards: 70
    Content-Length: 9
    Content-Type: application/sscc

    < ------------->
    — (9 headers 1 lines) –