Subject: [AVT] DTMF interoperability: In-band, RFC 2833 or SIP INFO

From: "Murat Artun" <[email-masked]>
Date: Wed, 20 Jun 2007 11:45:12 +0300

Hello all,

I want to ask about the interoperability issues for DTMF sending.

There exist three ways for DTMF sending: In-band (I use this term
meaning in audio as a voice data), RFC 2833 (currently 4733 obsoletes,
but no change to previous procedure exists) and SIP INFO.

Among these three ways, I know that only RFC 2833 is announced in the
SDP of a VoIP application when it is ready to receive DTMF events as
RFC 2833 packets.

I have a few points to be clarified in the sense of interoperability issues:

- Is it preferred that DTMF is also sent in-band and as SIP INFO when
the remote VoIP application announces that it is ready to receive RFC
2833 packets?

- What if the remote VoIP application does not announce that it is
ready to receive RFC 2833 packets? Which method should be preferred,
In-band or SIP INFO, or both for reliability purposes?

- I have observed that sending DTMF as RFC 2833 packets is mostly
preferred considering that sending DTMF In-band requires the remote
VoIP application to perform tone detection in RTP level which requires
considerable processing overhead as RFC also states. Is there a known
issue about SIP INFO method for DTMF sending?

Thanks in advice...

-- 
M u r at  A r t u n, MSc.
   Design Engineer

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

---

From: "Gaurav Kheterpal" <[email-masked]>
Date: Wed, 20 Jun 2007 15:19:24 +0530

My comments below:-

> the remote VoIP application announces that it is ready to receive RFC

GK>> I believe that if you advertise RFC 2833 in SDP & it is negotiated
successfully, you should send/receive DTMF as RFC 2833. However,
theoretically speaking, nothing prohibits you from using SIP INFO or in-band
mechanisms. It's merely a waste of negotiating something that you would not
eventually use.

> In-band or SIP INFO, or both for reliability purposes?

GK>> SIP INFO marks a textual way of sending DTMF so it provides codec
independence. Moreover, it provides transport of DTMF digits along with
signaling path as opposed to the media path.

SIP INFO was primarily introduced to support the transport of mid-call ISUP
messages which could not be mapped to any other SIP request. OTOH, it's also
believed that its "content-free framework" is the root cause to discourage
the use of SIP INFO (see draft-rosenberg-sip-info-harmful-00). So, SIP INFO
has it's share of pros & cons.

> issue about SIP INFO method for DTMF sending?

GK>> You are right that with in-band DTMF, you need to perform tone
detection at RTP level which isn't exactly an ideal scenario.

KPML is another mechanism for DTMF processing that you may want to explore.

>From an interoperability stand point, it's good to support at least RFC 2833
& in-band modes.

My 2 cents,
Gaurav

> -----Original Message-----
> From: [email-masked] [mailto:sip-
> [email-masked]] On Behalf Of Murat Artun
> Sent: Wednesday, June 20, 2007 2:15 PM
> To: [email-masked]; [email-masked]
> Subject: [Sip-implementors] DTMF interoperability: In-band,RFC 2833 or SIP
> INFO
> 
> Hello all,
> 
> Sip-implementors mailing list
> [email-masked]
> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors

---

From: Peter Saint-Andre <[email-masked]>
Date: Wed, 20 Jun 2007 13:17:08 -0500

> but no change to previous procedure exists) and SIP INFO.

FWIW, in Jingle we use an XML format for DTMF information:

http://www.xmpp.org/extensions/xep-0181.html

However, use of RFC 2833 (RFC 4733) can be negotiated.

The XML format should be interoperable (through a gateway or other
transformational agent) with the SIP INFO method. We'll document that
when we write the forthcoming specification on SIP-Jingle interworking.

Peter

-- 
Peter Saint-Andre
XMPP Standards Foundation
http://www.xmpp.org/xsf/people/stpeter.shtml

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From: "Meir Leshem" <[email-masked]>
Date: Wed, 20 Jun 2007 12:51:53 +0300

Hi Murat,
Note that the in-band method for DTMF tones transfer through the VoIP
network has additional significant drawback:  the classification of DTMF
digits which are received in-band is not reliable when compressed voice
codec is used (different than G.711).

Regards
---------------------------------------
Meir Leshem
System Engineer
Veraz Networks
--------------------------------------- 

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]] On Behalf Of
Murat Artun
Sent: Wednesday, June 20, 2007 11:45 AM
To: [email-masked]; [email-masked]
Subject: [Sip-implementors] DTMF interoperability: In-band,RFC 2833 or
SIP INFO

Hello all,

I have a few points to be clarified in the sense of interoperability
issues:

Thanks in advice...

---

From: "Vishal Mathur" <[email-masked]>
Date: Wed, 20 Jun 2007 16:44:28 +0530

Hi Murat,

SIP INFO based DTMF is useful when state full proxy want to take some
action if DTMF digits are pressed by the parties. So if the call is By
pass mode (media is not passing thru server) and user press any DTMF
digit, both the method (in band and TFC 2833) will be passing this
information directly between UAC and UAS. Even in this case SIP INFO
will still be pass thru state full proxy and hence proxy can take
certain decision like forwarding, conference initiation etc.

Regards,

Vishal Mathur
Symantec Corporation
www.symantec.com
_________________________________
Office: +91-20-66067655

-----Original Message-----

Hello all,

Thanks in advice...

---

From: "Meir Leshem" <[email-masked]>
Date: Wed, 20 Jun 2007 12:51:53 +0300

Hi Murat,

Regards

-----Original Message-----

Hello all,

Thanks in advice...

---

From: "Vishal Mathur" <[email-masked]>
Date: Wed, 20 Jun 2007 16:44:28 +0530

Hi Murat,

Regards,

Vishal Mathur
Symantec Corporation
www.symantec.com

-----Original Message-----

Hello all,

Thanks in advice...