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

[Henning Schulzrinne <[e-mail]>]

I don't think we want a service label for each media type. While  
*today* there are PSAPs that only answer TTY calls, is this likely to  
make sense in an all-IP PSAP environment where the media would  
terminate on the same PC that's used for IM, video and so on? Why  
would you do this?

Rather than trying to put SDP in a URN, maybe the better solution is  
to route to one PSAP for the emergency service and have that PSAP  
then redirect the call based on the full SDP information, if this  
becomes necessary. That way, you can deal with situations where the  
caller can handle a variety of means of communications, albeit with  
different ease, and the PSAP has access to the full media information.

Since this could be added on later if necessary, once we know whether  
anybody actually needs this, maybe it's better to avoid gratuitous  
complexity, both in terms of protocol operation, testing (yet another  
thing a mapping protocol has to test) and user agents.

Henning

On Feb 15, 2006, at 6:52 PM, Gunnar Hellstrom wrote:

> What would sos.police.tty  do and how would it be invoked?
>
> If it could lead to a text capable IP terminal, it should be called  
> sos.police.real-time-text    or so.
>
> If it helps to find a PSTN based PSAP with text capabilities, it  
> could be called sos.police.txp
>
> tty is a US term.
>
> Gunnar
>
> ---------------------------------------------------------------------- 
> -------
> Gunnar Hellström, Omnitor
> [e-mail]
> Mob: [phone]
> Phone: [phone]
> www.omnitor.se
> -----Original Message-----
> From: Brian Rosen [mailto:[e-mail]]
> Sent: Thursday, February 16, 2006 12:17 AM
> To: 'Gunnar Hellstrom'; [e-mail]; 'Aquil, Kamran'; 'François  
> D. Ménard'
> Cc: 'Gregg Vanderheiden'
> Subject: 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
>
>
>
> From: Gunnar Hellstrom [mailto:[e-mail]]
> Sent: Wednesday, February 15, 2006 5:47 PM
> To: [e-mail]; 'Aquil, Kamran'; [e-mail]; 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
>
> ---------------------------------------------------------------------- 
> -------
>
> Gunnar Hellström, Omnitor
>
> [e-mail]
>
> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]]On  
> Behalf Of François D. Ménard
> Sent: Wednesday, February 15, 2006 5:14 PM
> To: [e-mail]; 'Aquil, Kamran'; [e-mail]
> 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" <[e-mail]> wrote:
>
> Within the scope of our work, I don’t 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 doesn’t 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 don’t 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
>
>
> From: [e-mail] [mailto:[e-mail]] On  
> Behalf Of Aquil, Kamran
> Sent: Wednesday, February 15, 2006 10:31 AM
> To: [e-mail]
> 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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>
>
>
> -- 
> Francois D. Menard
> [e-mail]
>
>
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