RE: [Ecrit] ECRIT support for TTY/TDD calls

All I get out of this for ecrit is that we need entries for sos.police.tty
in the service registry

Brian

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From: Gunnar Hellstrom [mailto:gunnar.hellstrom@omnitor.se] 
Sent: Wednesday, February 15, 2006 5:47 PM
To: ecrit@ietf.org; 'Aquil, Kamran'; br@brianrosen.net; François D. Ménard
Cc: Gregg Vanderheiden
Subject: RE: [Ecrit] ECRIT support for TTY/TDD calls

It is quite widely accepted now that real-time text transmitted with its own
text coded RTP payload RFC 4103 is used to carry text that may be gatewayed
to/from TTY/TDD/textphones in PSTN.

It is discussed in
http://www.ietf.org/internet-drafts/draft-ietf-sipping-toip-03.txt

And it is documented in
http://www.ietf.org/internet-drafts/draft-sinnreich-sipdev-req-08.txt

Also other standardisation bodies have picked up the real-time text concept
in IP networks, and pointed at RFC 4103 (or its compatible predecessor
RFC2793 ). E.g. 3GPP and ETSI.

A couple of years ago we had an intensive discussion in the SIMPLE mail list
about the possibility to use MSRP to carry the real-time text medium, but we
concluded that it would cause too much overhead or too much delay for the
users, so that RTP was recommended instead. The most common use of MSRP is
to not transmit until end of sentence, while for real time text,
transmission is required with at most 500 ms interval as long as there is
anything to transmit in order to maintain the real-time feeling of being in
touch in a conversation through this medium.

Quite commonly you will connect a text RTP stream and an audio RTP stream
and possibly a video RTP stream in the same call, so that you will get an
enhanced multimedia phone call with all supported media 

The ecrit requirements also mentions this correspondence

in www.ietf.org/internet-drafts/draft-ietf-ecrit-requirements-03.txt

   Re4.  Multiple Modes: Multiple communication modes, such as audio,
      video and text messaging MUST be supported.

      Motivation: In PSTN, voice and text telephony (often called TTY or
      textphone in North America) are the only commonly supported media.
      Emergency calling must support a variety of media.  Such media
      should include voice, conversational text (RFC 4103 [9]), instant
      messaging and video.

I am working in a European group where one of the goals is to agree on
handling text users'  requirements on emergency calling in IP networks. Of
course we want to agree on global solutions if possible.

Address mapping is one important and tricky question for text users. It is
true that different countries have different approaches on emergency calling
with PSTN Text telephones (TTYs). Some have the same number as voice users,
while others have specific numbers. On the SIP side it would be good to have
the same URL and make any required routing based on declared media, mode and
language capabilities and preferences. 

Text capable gateways are not at all as common as VoIP gateways, so if the
PSAP is still in PSTN, there is a need to have a good mechanism for routing
emergency calls from SIP into PSTN through a text capable gateway. I cannot
say that the mechanisms for finding the right gateway and make the proper
address mapping to a PSTN number is solved yet for the text calls, and it
would be excellent if we could have that topic in mind in the discussions
and get proper methods documented.

I have drafted, but not yet submitted a registration of a SIP URL and an
ENUM subservice for real-time text. It might be helpful for finding text
gateways and mapping addresses and (text) numbers, but I would like to see
some scenarios thoroughly discussed before adding SIP URL and another ENUM
subservice.

Would there be any benefit of being allowed to enter TXP:112    or having
ENUM to find an appropriate address if I   call 112 from a SIP multimedia
phone declaring text capabilities with m=text in sdp?

Gunnar

----------------------------------------------------------------------------
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Gunnar Hellström, Omnitor

gunnar.hellstrom@omnitor.se

-----Original Message-----
From: ecrit-bounces@ietf.org [mailto:ecrit-bounces@ietf.org]On Behalf Of
François D. Ménard
Sent: Wednesday, February 15, 2006 5:14 PM
To: br@brianrosen.net; 'Aquil, Kamran'; ecrit@ietf.org
Subject: Re: [Ecrit] ECRIT support for TTY/TDD calls

I made a contribution to CISC NTWG on use of SIP for transporting TDD
traffic:

http://www.crtc.gc.ca/cisc/COMMITTE/N-docs/NTCO0338.doc

I think it may be relevant to ECRIT.

-=Francois=-

On 2/15/06 10:51 AM, "Brian Rosen" <br@brianrosen.net> wrote:

Within the scope of our work, I dont see how TDD services are impacted
until we get to the architecture effort, which probably has to have some
sections on that subject.
With respect to the mapping protocol, I do not believe there is any impact
at all.
With respect to the sos service urn, I do not believe there is any impact at
all

Ecrit doesnt have scope to talk about any kind of gateways or codec
support.

Ah!  My BCP on phones and proxies may need some mention, although this is
the IETF, and I dont think the ploy of forcing the entire PSTN to support
TDD just so 9-1-1 TDD will work.  That effort would have to be in the
general SIP arena.

Brian

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From: ecrit-bounces@ietf.org [mailto:ecrit-bounces@ietf.org]
<mailto:ecrit-bounces@ietf.org%5d>  On Behalf Of Aquil, Kamran
Sent: Wednesday, February 15, 2006 10:31 AM
To: ecrit@ietf.org
Subject: [Ecrit] ECRIT support for TTY/TDD calls

Folks,

Like to know if there are specific ECRIT requirements recognizing support
for Telecommunications Device for the Deaf (TDD) services for the hearing
impaired. If not is this left for VOIP/SIP gateways to perform this
requirement of translating the TDD calls to Text and Speech encoding. Wanted
to make sure how ECRIT meet requirement for TDD services.

Regards,
Kamran Aquil
Intelligent Transportation Systems- Division
Mitretek Systems.

  _____  

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