Subject: RE: [SIP] DTMF

From: "Arnoud van Wijk (ETM)" <[email-masked]>
Date: Fri, 11 Aug 2000 09:16:40 +0200

I want to alert you people that text communications is still going to be very important.
Deaf/hearing impaired people will depend on text communications. I am deaf, so I have no need for voice communications (well..I can talk, but receiving voice is useless for me). I would love to see that any SIP device that is used/will be used has support for text. (if it links through a brain socket with my brain etc..then we can skip text  :-))
So..I'd like to see one clear agreement on how we implement it.
My knowledge into DTMF is very low. (I understand they are touch tone, if so, they are currently used by relay operators all over the world via the boudot protocol).

Arnoud

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ERICSSON TELECOMMUNICATIE BV
Arnoud van Wijk
Research & Development
ETM/BL/RE
Fax: +31-161 247569
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-----Original Message-----
From: Henning Schulzrinne [mailto:[email-masked]]
Sent: Thursday, August 10, 2000 9:47 PM
To: [email-masked]
Subject: [SIP] DTMF

Besides the philosophical arguments, can somebody please succinctly and
technically characterize why RTP transport of digits does not work or is
not sufficient, given that

- sending a 'tones' RTP packet incurs no more (and plausibly less)
overhead at sender or receiver than a SIP packet

- sending keyboard input as envisioned here has nothing to do with
session setup or control or signaling

- RTP with redundancy is at least as reliable as SIP transport

- REFER and 3pcc can be used to redirect RTP streams wherever they are
needed, either separate from or jointly with the audio stream

- a number of implementations already support the RFC 2833 mechanism -
why should they support another mechanism?

As Colin points out and has been raised on the list before in a
different context, if we're into text communications (full keyboard
set), the RTP text payload type may also be appropriate. 

Thank you.
-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs

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