How to check in-band and out-band DTMF in SIP traces

[shahhussainkhattak]

Hello guys,

I hope you all will be doing great. I want to check in-band and out-band dtmf (rfc-2833) in sip traces. I am able to see from telephony event 101 fields that the dtmf is being passed properly, but i am not able to see if that dtmf was passed in-band or out-band. Suppose from below mentioned media attributes in the SDP, i can tell that telephony event 101 is being sent to handle dtmf tones, but i dont know if its inband dtmf or outband dtmf:

( My test client is a 3CX-Softphone, i have enabled RFC -2833 and Inband DTMF on this softphone)

v=0

o=3cxVCE 41540925 32973495 IN IP4 10.60.0.16

s=3cxVCE Audio Call

c=IN IP4 10.60.0.16

t=0 0

m=audio 40042 RTP/AVP 0 8 3 101

a=rtpmap:0 PCMU/8000

a=rtpmap:8 PCMA/8000

a=rtpmap:3 GSM/8000

a=rtpmap:101 telephone-event/8000

a=fmtp:101 0-15

a=ptime:20

a=sendrecv

m=video 40040 RTP/AVP 34

c=IN IP4 10.60.0.16

a=rtpmap:34 H263/90000

a=fmtp:34 QCIF=1;CIF=1;SQCIF=1;CIF4=1

a=sendrecv

I was reading in some discussion for rfc-2833, that:

rtp-nte = rfc2833 , no rtp-nte = not rfc 2833

but where can i find all this detail in a packet capture file? I would really appreciated your thights and feedback on this.

Thank you.

[Sambit Khuas]

Hello Hussain,

Afaik, inband dtmf cannot be seen in CUCM traces.

I would say the best way to check DTMF is in packet captures.

I found the following article that gives some idea on how to understand DTMF in a wireshark capture:

http://anetworkerblog.com/2011/02/06/dtmf-on-voip/

Please check it it helps.

Regards

Sam

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[shahhussainkhattak]

Dear Sambit,

Thank you very much sir, this is a great article indeed!

But here i have two questions:

1: If i have enabled Supprot for RFC-2833 and Inband DTMF, how it will be shown in my invite SDP? Because on my test client i have enabled both features, but dont see any visible parameters in the SDP, only see telephony event 101, which to my knowledge is used with G.711 (or any good codec, not prone to distoring dtm tones) to handle inband dtmf. But i dont see any parameter in Invite SDP showing whether rfc-2833 parameters were sent in it or not!

2: So, can i conclude, if i dont see any RFC-2833 related RTP - Events in a sip trace,it would be a call in which inband signalling was in action? Like from where i can verify the parameters like  rtp-nte and no rtp-nte in a sip trace?

Looking forward for your thoughts on this.

Regards,

Shah Hussain

[Ayodeji Okanlawon · Accepted solution]

Shah,

Telephone event 101 is RFC2833..When you see the ff lines in your SDP, then you are doing RFC2833..

a=rtpmap:101 telephone-event/8000

a=fmtp:101 0-16

RFC2833 transports DTMF inside RTP stream using Payload type 101...This ha snothing to do with G711, because G711 is a payload on its own..

Please refer to this doc to understand DTMF negotiation better

https://supportforums.cisco.com/docs/DOC-33944

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[shahhussainkhattak]

Thank you sir ( Aokanlawon), yes checked and verified from traces!

      |(17542)  ---------------------------------------------------------->  (13860)  |

13   |51.308776|                   |         RTP (RTPType-101) DTMF One 1  |                   |                   |RTP Num packets:14  Duration:0.260s SSRC:0x18BE

     |         |                   |(17542)  ---------------------------------------------------------->  (13860)  |

13   |51.308776|                   |         RTP (RTPType-101) DTMF One 1  |                   |                   |RTP Num packets:14  Duration:0.260s SSRC:0x18BE

     |         |                   |(17542)  ---------------------------------------------------------->  (13860)  |

13   |51.308776|                   |         RTP (RTPType-101) DTMF One 1  |                   |                   |RTP Num packets:14  Duration:0.260s SSRC:0x18BE

Regards,

Shah Hussain

[Ritesh Desai]

Hey @Ayodeji, Can you please attach document. The URL redirects to page not found. Thanks. regards, Ritesh Desai.