Subject: RFC 2833 on Tones

From: RFC Editor <[email-masked]>
Date: Thu, 18 May 2000 15:48:08 -0700

A new Request for Comments is now available in online RFC libraries.

        RFC 2833

        Title:	    RTP Payload for DTMF Digits, Telephony Tones and
                    Telephony Signals
        Author(s):  H. Schulzrinne, S. Petrack
        Status:     Standards Track
	Date:       May 2000
        Mailbox:    [email-masked],
                    [email-masked] 
        Pages:      30
        Characters: 68786
        Updates/Obsoletes/SeeAlso:  None

        URL:        ftp://ftp.isi.edu/in-notes/rfc2833.txt

This memo describes how to carry dual-tone multifrequency (DTMF)
signaling, other tone signals and telephony events in RTP packets.

This document is a product of the Audio/Video Transport Working Group
of the IETF.

This is now a Proposed Standard Protocol.

This document specifies an Internet standards track protocol for
the Internet community, and requests discussion and suggestions
for improvements.  Please refer to the current edition of the
"Internet Official Protocol Standards" (STD 1) for the
standardization state and status of this protocol.  Distribution
of this memo is unlimited.

This announcement is sent to the IETF list and the RFC-DIST list.
Requests to be added to or deleted from the IETF distribution list
should be sent to [email-masked].  Requests to be
added to or deleted from the RFC-DIST distribution list should
be sent to [email-masked].

Details on obtaining RFCs via FTP or EMAIL may be obtained by sending
an EMAIL message to [email-masked] with the message body 
help: ways_to_get_rfcs.  For example:

        To: [email-masked]
        Subject: getting rfcs

        help: ways_to_get_rfcs

Requests for special distribution should be addressed to either the
author of the RFC in question, or to [email-masked].  Unless
specifically noted otherwise on the RFC itself, all RFCs are for
unlimited distribution.echo 
Submissions for Requests for Comments should be sent to
[email-masked].  Please consult RFC 2223, Instructions to RFC
Authors, for further information.

Joyce K. Reynolds and Sandy Ginoza
USC/Information Sciences Institute

...

Below is the data which will enable a MIME compliant Mail Reader 
implementation to automatically retrieve the ASCII version
of the RFCs.

---

From: "Bratakos, Maroula" <[email-masked]>
Date: Wed, 31 May 2000 08:59:04 -0700

I agree that if bandwidth is a problem then you probably only want to send
one representation for the signaling event/dtmf digit.  However, the RFC
2833 says you should (not MUST but SHOULD) send signaling events as both
named signals and tone representation and if you can't send the tone
representation then you should sent regular audio.  My point was that if you
are going to send both then I think it needs to be formated in the redundant
format of 2198.

> I have a question about the last paragraph in section 2 that discusses
> gateways which send signaling events via RTP.  It states: 
> 
> If a gateway cannot present a tone representation, it SHOULD send the
> audio tones as regular RTP audio packets (e.g., as payload format
> PCMU), in addition to the named signals.
>
> If the audio tones are sent along with named signals then shouldn't the
> redundant method of RFC 2198 be used?

That would cause 'issues' (to put it mildly) if you're on any sort of
bandwidth allocation or near the saturation point for the access link,
such as with DSL or cable.

For example, if the admitted calls are currently consuming nearly
all of the upstream bandwidth, then doubling the bandwidth consumed
when someone touches a DTMF keypad will cause problems for the other
calls using that link.

-Dan Wing