draft-ietf-sipping-toip-06.txt   draft-ietf-sipping-toip-07.txt 
SIPPING Workgroup A. van Wijk, Editor SIPPING Workgroup A. van Wijk, Editor
Internet Draft G. Gybels, Editor Internet Draft G. Gybels, Editor
Category: Informational August 16, 2006 Category: Informational August 30, 2006
Expires: February 17, 2007 Expires: March 3, 2007
Framework for real-time text over IP using the Session Initiation Framework for real-time text over IP using the Session Initiation
Protocol (SIP) Protocol (SIP)
draft-ietf-sipping-toip-06.txt draft-ietf-sipping-toip-07.txt
Status of this Memo Status of this Memo
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will be disclosed, in accordance with Section 6 of BCP 79. will be disclosed, in accordance with Section 6 of BCP 79.
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This Internet-Draft will expire on February 17, 2007. This Internet-Draft will expire on March 3, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document lists the essential requirements for real-time Text- This document lists the essential requirements for real-time Text-
over-IP (ToIP) and defines a framework for implementation of all over-IP (ToIP) and defines a framework for implementation of all
required functions based on the Session Initiation Protocol (SIP) and required functions based on the Session Initiation Protocol (SIP) and
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Table of Contents Table of Contents
1. Introduction....................................................2 1. Introduction....................................................2
2. Scope...........................................................3 2. Scope...........................................................3
3. Terminology.....................................................3 3. Terminology.....................................................3
4. Definitions.....................................................4 4. Definitions.....................................................4
5. Requirements....................................................6 5. Requirements....................................................6
5.1 General requirements for ToIP................................6 5.1 General requirements for ToIP................................6
5.2 Detailed requirements for ToIP...............................7 5.2 Detailed requirements for ToIP...............................7
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5.2.1 Session set-up and control requirements..................7 5.2.1 Session set-up and control requirements..................7
5.2.2 Transport requirements...................................8 5.2.2 Transport requirements...................................8
5.2.3 Transcoding service requirements.........................9 5.2.3 Transcoding service requirements.........................9
5.2.4 Presentation and User control requirements..............10 5.2.4 Presentation and User control requirements..............10
5.2.5 Interworking requirements...............................11 5.2.5 Interworking requirements...............................11
5.2.5.1 PSTN Interworking requirements......................12 5.2.5.1 PSTN Interworking requirements......................12
5.2.5.2 Cellular Interworking requirements..................12 5.2.5.2 Cellular Interworking requirements..................12
5.2.5.3 Instant Messaging Interworking requirements.........12 5.2.5.3 Instant Messaging Interworking requirements.........12
6. Implementation Framework.......................................13 6. Implementation Framework.......................................13
6.1 General implementation framework............................13 6.1 General implementation framework............................13
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12.1 Normative references........................................24 12.1 Normative references........................................24
12.2 Informative references......................................26 12.2 Informative references......................................26
1. Introduction 1. Introduction
For many years, real-time text has been in use as a medium for For many years, real-time text has been in use as a medium for
conversational, interactive dialogue between users in a similar way conversational, interactive dialogue between users in a similar way
to how voice telephony is used. Such interactive text is different to how voice telephony is used. Such interactive text is different
from messaging and semi-interactive solutions like Instant Messaging from messaging and semi-interactive solutions like Instant Messaging
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in that it offers an equivalent conversational experience to users in that it offers an equivalent conversational experience to users
who cannot, or do not wish to, use voice. It therefore meets a who cannot, or do not wish to, use voice. It therefore meets a
different set of requirements from other text-based solutions already different set of requirements from other text-based solutions already
available on IP networks. available on IP networks.
Traditionally, deaf, hard of hearing and speech-impaired people are Traditionally, deaf, hard of hearing and speech-impaired people are
amongst the most prolific users of real-time, conversational, amongst the most prolific users of real-time, conversational,
text but, because of its interactivity, it is becoming popular amongst text but, because of its interactivity, it is becoming popular amongst
mainstream users as well. Real-time text conversation can be combined mainstream users as well. Real-time text conversation can be combined
with other conversational media like video or voice. with other conversational media like video or voice.
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d. description of ToIP interworking with other text services. d. description of ToIP interworking with other text services.
3. Terminology 3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14, RFC 2119 [7] and indicate requirement levels for compliant BCP 14, RFC 2119 [7] and indicate requirement levels for compliant
implementations. implementations.
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4. Definitions 4. Definitions
Audio bridging: a function of an audio media bridge server, gateway or Audio bridging: a function of an audio media bridge server, gateway or
relay service that sends to each destination the combination of audio relay service that sends to each destination the combination of audio
from all participants in a conference excluding the participant(s) at from all participants in a conference excluding the participant(s) at
that destination. At the RTP level, this is an instance of the mixer that destination. At the RTP level, this is an instance of the mixer
function as defined in RFC 3550 [4]. function as defined in RFC 3550 [4].
Cellular: a telecommunication network that has wireless access and can Cellular: a telecommunication network that has wireless access and can
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Text relay service: a third-party or intermediary that enables Text relay service: a third-party or intermediary that enables
communications between deaf, hard of hearing and speech-impaired communications between deaf, hard of hearing and speech-impaired
people and voice telephone users by translating between voice and people and voice telephone users by translating between voice and
real-time text in a call. real-time text in a call.
Text telephony: analog textphone service. Text telephony: analog textphone service.
Total Conversation: a multimedia service offering real time Total Conversation: a multimedia service offering real time
conversation in video, real-time text and voice according to conversation in video, real-time text and voice according to
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interoperable standards. All media streams flow in real time. (See interoperable standards. All media streams flow in real time. (See
ITU-T F.703 "Multimedia conversational services" [6].) ITU-T F.703 "Multimedia conversational services" [6].)
Transcoding service: a service provided by a third-party User Agent Transcoding service: a service provided by a third-party User Agent
that transcodes one stream into another. Transcoding can be done by that transcodes one stream into another. Transcoding can be done by
human operators, in an automated manner, or by a combination of both human operators, in an automated manner, or by a combination of both
methods. Within this document the term particularly applies to methods. Within this document the term particularly applies to
conversion between different types of media. A text relay service is conversion between different types of media. A text relay service is
an example of a transcoding service that converts between real-time an example of a transcoding service that converts between real-time
text and audio. text and audio.
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SRTP Secure Real Time Transport Protocol SRTP Secure Real Time Transport Protocol
TDD Telecommunication Device for the Deaf TDD Telecommunication Device for the Deaf
TDMA Time Division Multiple Access TDMA Time Division Multiple Access
TTY Analog textphone (Teletypewriter) TTY Analog textphone (Teletypewriter)
ToIP Real-time Text over Internet Protocol ToIP Real-time Text over Internet Protocol
URI Uniform Resource Identifier URI Uniform Resource Identifier
UTF-8 Universal Transfer Format-8 UTF-8 Universal Transfer Format-8
VCO/HCO Voice Carry Over/Hearing Carry Over VCO/HCO Voice Carry Over/Hearing Carry Over
VoIP Voice over Internet Protocol VoIP Voice over Internet Protocol
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5. Requirements 5. Requirements
The framework described in section 6 defines a real-time text-based The framework described in section 6 defines a real-time text-based
conversational service that is the text equivalent of voice based conversational service that is the text equivalent of voice based
telephony. This section describes the requirements that the framework telephony. This section describes the requirements that the framework
is designed to meet and the functionality it should offer. is designed to meet and the functionality it should offer.
5.1 General requirements for ToIP 5.1 General requirements for ToIP
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and audio. and audio.
Deaf, hard-of-hearing and mainstream users may invoke ToIP services Deaf, hard-of-hearing and mainstream users may invoke ToIP services
for many different reasons: for many different reasons:
- because they are in a noisy environment, e.g., in a machine room of - because they are in a noisy environment, e.g., in a machine room of
a factory where listening is difficult; a factory where listening is difficult;
- because they are busy with another call and want to participate in - because they are busy with another call and want to participate in
two calls at the same time; two calls at the same time;
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- for implementing text and/or speech recording services (e.g., text - for implementing text and/or speech recording services (e.g., text
documentation/ audio recording) for legal purposes, for clarity or documentation/ audio recording) for legal purposes, for clarity or
for flexibility; for flexibility;
- to overcome language barriers through speech translation and/or - to overcome language barriers through speech translation and/or
transcoding services; transcoding services;
- because of hearing loss, deafness or tinnitus as a result of the - because of hearing loss, deafness or tinnitus as a result of the
aging process or for any other reason, creating a need to replace or aging process or for any other reason, creating a need to replace or
complement voice with real-time text in conversational sessions. complement voice with real-time text in conversational sessions.
In many of the above examples, real-time text may accompany speech. In many of the above examples, real-time text may accompany speech.
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R1: It SHOULD be possible to start conversations in any mode (real- R1: It SHOULD be possible to start conversations in any mode (real-
time text, voice, video) or combination of modes. time text, voice, video) or combination of modes.
R2: It MUST be possible for the users to switch to real-time text, or R2: It MUST be possible for the users to switch to real-time text, or
add real-time text as an additional modality, during the conversation. add real-time text as an additional modality, during the conversation.
R3: Systems supporting ToIP MUST allow users to select any of the R3: Systems supporting ToIP MUST allow users to select any of the
supported conversation modes at any time, including in mid- supported conversation modes at any time, including in mid-
conversation. conversation.
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R4: Systems SHOULD allow the user to specify a preferred mode of R4: Systems SHOULD allow the user to specify a preferred mode of
communication in each direction, with the ability to fall back to communication in each direction, with the ability to fall back to
alternatives that the user has indicated are acceptable. alternatives that the user has indicated are acceptable.
R5: If the user requests simultaneous use of real-time text and audio, R5: If the user requests simultaneous use of real-time text and audio,
and this is not possible because of constraints in the network, the and this is not possible because of constraints in the network, the
system SHOULD try to establish text only communication. system SHOULD try to establish text only communication.
R6: If the user has expressed a preference for real-time text, R6: If the user has expressed a preference for real-time text,
establishment of a connection including real-time text MUST have establishment of a connection including real-time text MUST have
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is possible to use. is possible to use.
R11: Real-time text transmission from a terminal SHALL be performed R11: Real-time text transmission from a terminal SHALL be performed
character by character as entered, or in small groups of characters, character by character as entered, or in small groups of characters,
so that no character is delayed from entry to transmission by more so that no character is delayed from entry to transmission by more
than 300 milliseconds. than 300 milliseconds.
R12: It MUST be possible to transmit characters at a rate sufficient R12: It MUST be possible to transmit characters at a rate sufficient
to support fast human typing as well as speech-to-text methods of to support fast human typing as well as speech-to-text methods of
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generating real-time text. A rate of 30 characters per second is generating real-time text. A rate of 30 characters per second is
regarded as sufficient. regarded as sufficient.
R13: A ToIP service MUST be able to deal with international character R13: A ToIP service MUST be able to deal with international character
sets. sets.
R14: Where it is possible, loss or corruption of real-time text during R14: Where it is possible, loss or corruption of real-time text during
transport SHOULD be detected and the user should be informed. transport SHOULD be detected and the user should be informed.
R15: Transport of real-time text SHOULD be as robust as possible, so R15: Transport of real-time text SHOULD be as robust as possible, so
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R20: It MUST be possible to negotiate the requirements for transcoding R20: It MUST be possible to negotiate the requirements for transcoding
services in mid-call, for the immediate addition of those services to services in mid-call, for the immediate addition of those services to
the call. the call.
R21: Communication between the end participants SHOULD continue after R21: Communication between the end participants SHOULD continue after
the addition or removal of a text relay service, and the effect of the the addition or removal of a text relay service, and the effect of the
change should be limited in the users' perception to the direct effect change should be limited in the users' perception to the direct effect
of having or not having the transcoding service in the connection. of having or not having the transcoding service in the connection.
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R22: When setting up a session, it MUST be possible for a user to R22: When setting up a session, it MUST be possible for a user to
specify the type of relay service requested (e.g., speech to text or specify the type of relay service requested (e.g., speech to text or
text to speech). The specification of a type of relay MUST include a text to speech). The specification of a type of relay MUST include a
language specifier. language specifier.
R23: It SHOULD be possible to route the session to a preferred relay R23: It SHOULD be possible to route the session to a preferred relay
service even if the user invokes the session from another region or service even if the user invokes the session from another region or
network than that usually used. network than that usually used.
R24: It is RECOMMENDED that ToIP implementations make the invocation R24: It is RECOMMENDED that ToIP implementations make the invocation
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carry over (VCO) and hearing carry over (HCO)"). carry over (VCO) and hearing carry over (HCO)").
5.2.5.2 Cellular Interworking requirements 5.2.5.2 Cellular Interworking requirements
As mobile communications have been adopted widely, various solutions As mobile communications have been adopted widely, various solutions
for real-time texting while on the move were developed. ToIP services for real-time texting while on the move were developed. ToIP services
should provide interworking with such services as well. should provide interworking with such services as well.
Alternative means of transferring the Text telephony data have been Alternative means of transferring the Text telephony data have been
developed when TTY services over cellular were mandated by the FCC in developed when TTY services over cellular were mandated by the FCC in
the USA. They are a) "No-gain" codec solution, b) the Cellular Text the USA. They are the a) "No-gain" codec solution, and b) the Cellular
Telephony Modem (CTM) solution [8] both collectively called "Baudot Text Telephony Modem (CTM) solution [8] both collectively called
mode" solution in the USA. "Baudot mode" solution in the USA.
The GSM and 3G standards from 3GPP make use of the CTM modem in the The GSM and 3G standards from 3GPP make use of the CTM modem in the
voice channel for text telephony. However, implementations also exist voice channel for text telephony. However, implementations also exist
that use the data channel to provide such functionality. Interworking that use the data channel to provide such functionality. Interworking
with these solutions should be done using text gateways that set up with these solutions should be done using text gateways that set up
the data channel connection at the GSM side and provide ToIP at the the data channel connection at the GSM side and provide ToIP at the
other side. other side.
R44: a ToIP service SHOULD provide interworking with mobile text R44: a ToIP service SHOULD provide interworking with mobile text
conversation services. conversation services.
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Native V.18 text telephones support full duplex and separate display Native V.18 text telephones support full duplex and separate display
from reception and transmission so that the full duplex capability can from reception and transmission so that the full duplex capability can
be used fully. Such devices could use the ToIP split screen as well, be used fully. Such devices could use the ToIP split screen as well,
but almost all text telephones use a restricted character set and many but almost all text telephones use a restricted character set and many
use low text transmission speeds (4 to 7 characters per second). use low text transmission speeds (4 to 7 characters per second).
That is why it is important for the ToIP user to know that he or she That is why it is important for the ToIP user to know that he or she
is connected with an analog text telephone. The session description is connected with an analog text telephone. The session description
[10] SHOULD contain an indication that the other endpoint for the call [10] SHOULD contain an indication that the other endpoint for the call
is a PSTN textphone (e.g. connected via an ATA or through a text is a PSTN textphone (e.g. connected via an ATA or through a text
gateway). This means that the other user may be used to formal turn gateway). This means that the textphone user may be used to formal
taking during the call. turn taking during the call.
6.2.5.2 Mobile Interworking 6.2.5.2 Mobile Interworking
Mobile wireless (or Cellular) circuit switched connections provide a Mobile wireless (or Cellular) circuit switched connections provide a
digital real-time transport service for voice or data. The access digital real-time transport service for voice or data. The access
technologies include GSM, CDMA, TDMA, iDen and various 3G technologies include GSM, CDMA, TDMA, iDen and various 3G
technologies as well as WiFi or WiMAX. technologies as well as WiFi or WiMAX.
ToIP may be supported over the cellular wireless packet switched ToIP may be supported over the cellular wireless packet switched
service. It interfaces to the Internet. service. It interfaces to the Internet.
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