Sending Out-of-Band DTMF to an IKON Gateway

[PeterInFrankfurt]

I need to send Out-of-Band DTMF to an extension, but the snomone appears to transcode the DTMF to in-band. (The "extension" is really an IKON gateway which only supports out-of-band DTMF.) Here's a part of the logfile:

 

[6] 2013/09/10 13:19:40: Call port 121: Different Codecs (local telephone-event/8000, remote PCMA/8000), callid f419f99b@pbx, falling back to transcoding

[6] 2013/09/10 13:19:40: Received DTMF *, call type attendant

[8] 2013/09/10 13:19:40: Attendant: Ignoring the DTMF * in the state connected

 

How can I make the pbx forward the DTMF as an RTP-event to the "extension"?

In case it's relevant, here's the INVITE etc.

 

2013/9/10 13:19:39 Tx: udp:172.27.66.105:5067 (959 bytes)

INVITE sip:240@172.27.66.105:5067 SIP/2.0

Via: SIP/2.0/UDP 172.27.66.106:5060;branch=z9hG4bK-abb91ea6476deec2bab243dd796c1b78;rport

From: "Svalbard MER1" <sip:401@localhost;user=phone>;tag=51546

To: "MSG Control Room" <sip:240@localhost>

Call-ID: 57a2ef9c@pbx

CSeq: 27025 INVITE

Max-Forwards: 70

Contact: <sip:240@172.27.66.106:5060;transport=udp>

Supported: 100rel, replaces, norefersub

Allow-Events: refer

Allow: INVITE, ACK, CANCEL, BYE, REFER, PRACK, INFO, UPDATE

Accept: application/sdp

User-Agent: snomONE/5.1.0

Alert-Info: <http://127.0.0.1/Bellcore-dr3>

Content-Type: application/sdp

Content-Length: 329

 

v=0

o=- 63349 63349 IN IP4 172.27.66.106

s=-

c=IN IP4 172.27.66.106

t=0 0

m=audio 41036 RTP/AVP 8 0 9 2 3 101

a=rtpmap:8 PCMA/8000

a=rtpmap:0 PCMU/8000

a=rtpmap:9 G722/8000

a=rtpmap:2 G726-32/8000

a=rtpmap:3 GSM/8000

a=rtpmap:101 telephone-event/8000

a=fmtp:101 0-16

a=rtcp-xr:rcvr-rtt=all voip-metrics

a=sendrecv

 

and here's the OK back

 

2013/9/10 13:19:39 Rx: udp:172.27.66.105:5067 (820 bytes)

SIP/2.0 200 OK

Via: SIP/2.0/UDP 172.27.66.106:5060;branch=z9hG4bK-abb91ea6476deec2bab243dd796c1b78;rport

From: "Svalbard MER1" <sip:401@localhost;user=phone>;tag=51546

To: "MSG Control Room" <sip:240@localhost>;tag=802229

Call-ID: 57a2ef9c@pbx

CSeq: 27025 INVITE

Contact: <sip:240@172.27.66.105:5067>

Allow: REGISTER,SUBSCRIBE,NOTIFY,INVITE,ACK,PRACK,OPTIONS,BYE,CANCEL,REFER,INFO,UPDATE

Content-Length: 149

Content-Type: application/sdp

Server: (innovaphone H323/[unknown])

Supported: replaces,100rel,sec-agree,answermode

P-Preferred-Identity: <sip:240@172.27.66.105:5067>

Remote-Party-ID: <sip:240@172.27.66.105:5067>;party=called;screen=no;privacy=off

 

v=0

o=- 49 1 IN IP4 172.27.66.105

s=-

c=IN IP4 172.27.66.105

t=0 0

a=sendrecv

m=audio 8184 RTP/AVP 8 0

a=ptime:20

a=silenceSupp:off - - - -

[Vodia PBX]

Well the SDP in the response says "okay, you can send me aLaw and uLaw"; but nothing about telephone-event (which is RFC2833 a.k.a. RFC4733 out of band). Maybe there is a setting on the gateway that needs to be turned on to offer the DTMF codec as well?

[PeterInFrankfurt]

Thanks for the reply. I can find no relevant settings on the gateway. I noticed that a=fmtp:101 0-16 is not mentioned in the gateway's reply. However, RFC 2833 says:

Since all implementations MUST be able to receive events 0 through   15, listing these events in the a=fmtp line is OPTIONAL.

Are you saying the snomone pbx insists the gateway response explicitly includes a=fmtp... ?

[Vodia PBX]

snom ONE does not need the FMTP line, but it needs a a-line like a=rtpmap:101 telephone-event/8000.

 

The FMTP line provides additional information about a codec (parameters). The one above looks like a telephone-event parameter (DTMF), and it says send everything from 0-9, #, *, A, B, C, D and also hook-flash (according to RFC2833).

 

But anyway this is the right corner. If it is sending the fmtp line, it actually must also send the a=rtpmap:101 line.

[PeterInFrankfurt]

I've found a way to make the gateway behave correctly - it works now! Many thanks for your help.

[Vodia PBX]

Can you tell us what the trick was? Then others may find this here on the forum and don't have to go through a similar experience...