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TR41.4/00-11-061VON_Text_Telephony_GH2

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Text Telephony and Total Conversation

in the IP revolution

Gunnar Hellström, Omnitor AB

Gunnar.Hellstrom@omnitor.se+46 8 708 204 288

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Accessibility opportunities in IP networks

• IP networks take over telecomm traffic• Opportunity:

– Combine text, video and voice– Interworking between many ways to access the network– Next generation mobile will have IP capabilities

• Important points to consider– Interworking with Textphones in the Telephone

Network is desired. – IP Transit for textphones requires special consideration – A simple IP textphone is needed

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Total Conversation standards

• Text conversation need standards as well as video and audio.

• Work is close to completion in ITU-T and IETF to define extension of video telephony to Total Conversation with video, text and voice

• Subsets are possible for text telephony

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Example of a Total Conversation Terminal

Voice

Text in videocall

Sign language

Text telephony

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Opportunities with Total Conversation

• Deaf: sign, type or lip-read as the situation calls for.• Adult deaf: speak and see and get text back.• Hearing impaired – Hear and lip-read as far as possible,

revert to text when needed.• Video relay services: Transfer phone number to call• Speech impaired: Hear and type. Or hear and speak and

revert to typing when needed.• Anyone: Communicate in preferred mode, type when

needed for names, phone numbers etc.

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Further opportunities with local additions to Total Conversation

• Screen reader and Braille display makes text conversation accessible to deaf-blind users.

• Voice recognition can make voice conversation convenient with adult deaf users.

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T.140, the common base for text conversation

• Standardised in ITU-T 1998• Extremely simple end-to-end text chat protocol• User input to Unicode UTF-8 coded transmission• UTF-8 transmission to display• Safe and easy to include everywhere

What is the street address? Alameda 34

User

T.140

Channel

T.140 text protocol• Character by character transmission• Character code for any language:

ISO 10646 (= Unicode). • Control from ISO 6429:

– Erase last character,

– New line,

– Nelect graphic rendition

– Alert in session

• Transport channel must be specified for each environment.

T.140

Channel

User application

Network

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Text Telephony, a subset of Total Conversation

• IP Telephony builds on IP Multimedia technology.

• IP Text Telephony builds on IP Total Conversation technology– ITU-T H.323 Annex G Text Conversation and

Text SET. IP telephone extension with text– IETF RFC 2793 transport for text in IP

networks– Usable in IETF multimedia protocol SIP

Text in IP networks

• H.323 Annex G = text in the dominating IP telephony protocol H.323

• SIP text conversation also possible without further specfikation

IP Textphone orTotal Conversation

terminal IP textphone

T.140Text

RTP

T.140Text

RTP

Text in IP networks

Audio

RTP

Audio(and

Video)

RTP

IP Network

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Total Conversation -a complete family

V.18

Text telephony

Transparent

Equal-izers

T.140

PSTN

H.223

V.34/V.80

AL1 H.245

H.324

T.140Voice

andvideo

PSTN

H.221

Networkaccess

H.320

H.224

T.140Voice

andvideo

ISDN

H.323

Networkaccess

T.140Voice

andvideo

IP

H.324Mobile system

H.223

Mobiletransmission

Voiceand

video

AL1 H.245

T.140

MOBILE

T.124GCC

T.134

T.120 Dataconferencing

T.123

T.140

H.248 Annex F. Text - aware Gateway For decision in ITU 13 Nov. 2000

Ready Ready Ready Ready Ready Ready

RTP

DATA

TCP/ RTP

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V.18 An automoding modem - a bridge to mono media text

Can be used in gateways and servers

USA, UKUSAHollandGermanyFranceAnywhereSweden, UK

Example of use

Text telephone interworking• T.140 is also used in standardised text telephony.

• V.18 enables communication with a huge number of existing text telephones

T.140 equalizers for legacy modes

T.140 ready transmission in V.18 mode

T.140

V.18 text telephone modem

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PSTN Interworking• Gateways need to have V.18 capabilities, to

connect PSTN text telephone calls with Total Conversation or IP Text Telephone terminals

• Gateways need to be T.140 aware

PSTNTextphone

Gateway H.323Annex G

T.140 text in IP channel

RTP/Audio

Gateway example V.18 - H.323

V.18 compa-tible text V.18

/T.140 T.140

alternatingwith voice

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Textphone gateway call between Telephone network and IP

network

IP network Telephone network

IP Gateway

Text telephone

V.18 port RTP port

T.140

H.323 or SIP IP textphone

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Textphone call in telephone network passing through IP

network

IP transit network

IP Gateway

V.18 port

RTP port

T.140

IP Gateway

V.18 port

RTP port

T.140

RTP-Text

Textphone Text-phone

Figure: IP transit network in textphone call

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IP gateway standardisationITU-T H.248 and IETF Megaco

• Current hot topic – huge efforts.• Text telephone and text conversation

additions.• Integration of text – fax – modem additions• Possible use – same port for voice, text, fax

and modem, automatic identification of mode and invocation of proper packetization.

Conclusions

• Video telephony is complemented with text to form Total Conversation

• Text Telephony is linked in through a standardised bridge – V.18

• Work is centered in ITU-T SG 16 with Q9-Accessibility as initiator

• Many companies and organisation have contributed• Standards are in place, implementations emerge

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Standards support for Total Conversation and text telephony

F.MCVS Service Description

Text telephony (PSTN)

V.18

Text, video and voice

ISDN- H.320H.224

Text, video and voice (IP)

H.323 Annex GRTP-Text

Text, video and voice (PSTN)

H.324

Mobile textH.324M

GatewayH.248

Text conversation T.140

Data conferencingT.120, T.134