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IETF RFC 3351
User Requirements for the Session Initiation Protocol (SIP) in Support of Deaf, Hard of Hearing and Speech-impaired Individuals
Last modified on Wednesday, August 14th, 2002
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Network Working Group N. Charlton
Request for Comments: 3351 Millpark
Category: Informational M. Gasson
Koru Solutions
G. Gybels
M. Spanner
RNID
A. van Wijk
Ericsson
August 2002
User Requirements for the Session Initiation Protocol (SIP)
in Support of Deaf, Hard of Hearing
and Speech-impaired Individuals
 Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright © The Internet Society (2002). All Rights Reserved.
Abstract
This document presents a set of Session Initiation Protocol
(SIP) user requirements that support communications for deaf, hard of
hearing and speech-impaired individuals. These user requirements
address the current difficulties of deaf, hard of hearing and
speech-impaired individuals in using communications facilities, while
acknowledging the multi-functional potential of SIP-based
communications.
A number of issues related to these user requirements are further
raised in this document.
Also included are some real world scenarios and some technical
requirements to show the robustness of these requirements on a
concept-level.
Charlton, et al. Informational PAGE 1 
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
Table of Contents
1. Terminology and Conventions Used in this Document................2
2. Introduction.....................................................3
3. Purpose and Scope................................................4
4. Background.......................................................4
5. Deaf, Hard of Hearing and Speech-impaired Requirements for SIP...5
5.1 Connection without Difficulty................................5
5.2 User Profile.................................................6
5.3 Intelligent Gateways.........................................6
5.4 Inclusive Design.............................................7
5.5 Resource Management..........................................7
5.6 Confidentiality and Security.................................7
6. Some Real World Scenarios........................................8
6.1 Transcoding Service..........................................8
6.2 Media Service Provider.......................................9
6.3 Sign Language Interface......................................9
6.4 Synthetic Lip-reading Support for Voice Calls...............10
6.5 Voice-Activated Menu Systems................................10
6.6 Conference Call.............................................11
7. Some Suggestions for Service Providers and User Agent
Manufacturers...................................................13
8. Acknowledgements................................................14
Security Considerations.........................................14
Normative References............................................15
Informational References........................................15
Author's Addresses..............................................15
Full Copyright Statement........................................17
1. Terminology and Conventions Used in this Document
In this document, the key words "MUST", "MUST NOT","REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in BCP 14,
RFC 2119[1] and indicate requirement levels for compliant SIP
implementations.
For the purposes of this document, the following terms are considered
to have these meanings:
Abilities: A person's capacity for communicating which could include
a hearing or speech impairment or not. The terms Abilities and
Preferences apply to both caller and call-recipient.
Preferences: A person's choice of communication mode. This could
include any combination of media streams, e.g., text, audio, video.
Charlton, et al. Informational PAGE 2
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
The terms Abilities and Preferences apply to both caller and
call-recipient.
Relay Service: A third-party or intermediary that enables
communications between deaf, hard of hearing and speech-impaired
people, and people without hearing or speech-impairment. Relay
Services form a subset of the activities of Transcoding Services (see
definition).
Transcoding Services: A human or automated third party acting as an
intermediary in any session between two other User Agents (being a
User Agent itself), and transcoding one stream into another (e.g.,
voice to text or vice versa).
Textphone: Sometimes called a TTY (teletypewriter), TDD
(telecommunications device for the deaf) or a minicom, a textphone
enables a deaf, hard of hearing or speech-impaired person to place a
call to a telephone or another textphone. Some textphones use the
V.18[3] protocol as a standard for communication with other textphone
communication protocols world-wide.
User: A deaf, hard of hearing or speech-impaired individual. A user
is otherwise referred to as a person or individual, and users are
referred to as people.
Note: For the purposes of this document, a deaf, hard of hearing, or
speech-impaired person is an individual who chooses to use SIP
because it can minimize or eliminate constraints in using common
communication devices. As SIP promises a total communication
solution for any kind of person, regardless of ability and
preference, there is no attempt to specifically define deaf, hard of
hearing or speech-impaired in this document.
2. Introduction
The background for this document is the recent development of SIP[2]
and SIP-based communications, and a growing awareness of deaf, hard
of hearing and speech-impaired issues in the technical community.
The SIP capacity to simplify setting up, managing and tearing down
communication sessions between all kinds of User Agents has specific
implications for deaf, hard of hearing and speech-impaired
individuals.
Charlton, et al. Informational PAGE 3
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
As SIP enables multiple sessions with translation between multiple
types of media, these requirements aim to provide the standard for
recognizing and enabling these interactions, and for a communications
model that includes any and all types of SIP-networking abilities and
preferences.
3. Purpose and Scope
The scope of this document is firstly to present a current set of
user requirements for deaf, hard of hearing and speech-impaired
individuals through SIP-enabled communications. These are then
followed by some real world scenarios in SIP-communications that
could be used in a test environment, and some concepts of how these
requirements can be developed by service providers and User Agent
manufacturers.
These recommendations make explicit the needs of a currently often
disadvantaged user-group and attempt to match them with the capacity
of SIP. It is not the intention here to prioritize the needs of
deaf, hard of hearing and speech-impaired people in a way that would
penalize other individuals.
These requirements aim to encourage developers and manufacturers
world-wide to consider the specific needs of deaf, hard of hearing
and speech-impaired individuals. This document presents a
world-vision where deafness, hard of hearing or speech impairment are
no longer a barrier to communication.
4. Background
Deaf, hard of hearing and speech-impaired people are currently
often unable to use commonly available communication devices.
Although this is documented[4], this does not mean that developers or
manufacturers are always aware of this. Communication devices for
deaf, hard of hearing and speech-impaired people are
currently often primitive in design, expensive, and non-compatible
with progressively designed, cheaper and more adaptable communication
devices for other individuals. For example, many models of textphone
are unable to communicate with other models.
Additionally, non-technical human communications, for example sign
languages or lip-reading, are non-standard around the world.
Charlton, et al. Informational PAGE 4
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
There are intermediary or third-party relay services (e.g.
transcoding services) that facilitate communications, uni- or bi-
directional, for deaf, hard of hearing and speech-impaired people.
Currently relay services are mostly operator-assisted (manual),
although methods of partial automation are being implemented in some
areas. These services enable full access to modern facilities and
conveniences for deaf, hard of hearing and speech-impaired people.
Although these services are somewhat limited, their value is
undeniable as compared to their previous complete unavailability.
Yet communication methods in recent decades have proliferated:
email, mobile phones, video streaming, etc. These methods are an
advance in the development of data transfer technologies between
devices.
Developers and advocates of SIP agree that it is a protocol that not
only anticipates the growth in real-time communications between
convergent networks, but also fulfills the potential of the Internet
as a communications and information forum. Further, they agree that
these developments allow a standard of communication that can be
applied throughout all networking communities, regardless of
abilities and preferences.
5. Deaf, Hard of Hearing and Speech-impaired Requirements for SIP
Introduction
The user requirements in this section are provided for the benefit of
service providers, User Agent manufacturers and any other interested
parties in the development of products and services for deaf, hard of
hearing and speech-impaired people.
The user requirements are as follows:
5.1 Connection without Difficulty
This requirement states:
Whatever the preferences and abilities of the user and User Agent,
there SHOULD be no difficulty in setting up SIP sessions. These
sessions could include multiple proxies, call routing decisions,
transcoding services, e.g., the relay service Typetalk[5] or other
media processing, and could include multiple simultaneous or
alternative media streams.
Charlton, et al. Informational PAGE 5
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
This means that any User Agent in the conversation (including
transcoding services) MUST be able to add or remove a media stream
from the call without having to tear it down and re-establish it.
5.2 User Profile
This requirement states:
Deaf, hard of hearing and speech-impaired user abilities and
preferences (i.e., user profile) MUST be communicable by SIP, and
these abilities and preferences MUST determine the handling of the
session.
The User Profile for a deaf, hard of hearing or speech-impaired
person might include details about:
- How media streams are received and transmitted (text, voice, video,
or any combination, uni- or bi-directional).
- Redirecting specific media streams through a transcoding service
(e.g., the relay service Typetalk)
- Roaming (e.g., a deaf person accessing their User Profile from a
web-interface at an Internet cafe)
- Anonymity: i.e., not revealing that a deaf person is calling, even
through a transcoding service (e.g., some relay services inform the
call-recipient that there is an incoming text call without saying
that a deaf person is calling).
Part of this requirement is to ensure that deaf, hard of hearing
and speech-impaired people can keep their preferences and abilities
confidential from others, to avoid possible discrimination or
prejudice, while still being able to establish a SIP session.
5.3 Intelligent Gateways
This requirement states:
SIP SHOULD support a class of User Agents to perform as gateways for
legacy systems designed for deaf, hard of hearing and speech-impaired
people.
For example, an individual could have a SIP User Agent acting as a
gateway to a PSTN legacy textphone.
Charlton, et al. Informational PAGE 6
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
5.4 Inclusive Design
This requirement states:
Where applicable, design concepts for communications (devices,
applications, etc.) MUST include the abilities and preferences of
deaf, hard of hearing and speech-impaired people.
Transcoding services and User Agents MUST be able to connect with
each other regardless of the provider or manufacturer. This means
that new User Agents MUST be able to support legacy protocols through
appropriate gateways.
5.5 Resource Management
This requirement states:
User Agents SHOULD be able to identify the content of a media stream
in order to obtain such information as the cost of the media stream,
if a transcoding service can support it, etc.
User Agents SHOULD be able to choose among transcoding services and
similar services based on their capabilities (e.g., whether a
transcoding service carries a particular media stream), and any
policy constraints they impose (e.g., charging for use). It SHOULD
be possible for User Agents to discover the availability of
alternative media streams and to choose from them.
5.6 Confidentiality and Security
This requirement states:
All third-party or intermediaries (transcoding services) employed in
a session for deaf, hard of hearing and speech-impaired people MUST
offer a confidentiality policy. All information exchanged in this
type of session SHOULD be secure, that is, erased before
confidentiality is breached, unless otherwise required.
This means that transcoding services (e.g., interpretation,
translation) MUST publish their confidentiality and security
policies.
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RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
6. Some Real World Scenarios
These scenarios are intended to show some of the various types of
media streams that would be initiated, managed, directed, and
terminated in a SIP-enabled network, and shows how some resources
might be managed between SIP-enabled networks, transcoding services
and service providers.
To illustrate the communications dynamic of these kinds of scenarios,
each one specifically mentions the kind of media streams transmitted,
and whether User Agents and Transcoding Services are involved.
6.1 Transcoding Service
In this scenario, a hearing person calls the household of a deaf
person and a hearing person.
1. A voice conversation is initiated between the hearing
participants:
( Person A) <-----Voice ---> ( Person B)
2. During the conversation, the hearing person asks to talk with the
deaf person, while keeping the voice connection open so that voice
to voice communications can continue if required.
3. A Relay Service is invited into the conversation.
4. The Relay Service transcodes the hearing person's words into text.
5. Text from the hearing person's voice appears on the display of the
deaf person's User Agent.
6. The deaf person types a response.
7. The Relay Service receives the text and reads it to the hearing
person:
( ) <------------------Voice----------------> ( )
(Person A ) -----Voice---> ( Voice To Text ) -Text-> (Person B )
( ) <----Voice---- (Service Provider) <-Text- ( )
8. The hearing person asks to talk with the hearing person in the
deaf person's household.
9. The Relay Service withdraws from the call.
Charlton, et al. Informational PAGE 8
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
6.2 Media Service Provider
In this scenario, a deaf person wishes to receive the content of a
radio program through a text stream transcoded from the program's
audio stream.
1. The deaf person attempts to establish a connection to the radio
broadcast, with User Agent preferences set to receiving audio
stream as text.
2. The User Agent of the deaf person queries the radio station User
Agent on whether a text stream is available, other than the audio
stream.
3. However, the radio station has no text stream available for a deaf
listener, and responds in the negative.
4. As no text stream is available, the deaf person's User Agent
requests a voice-to-text transcoding service (e.g., a real-time
captioning service) to come into the conversation space.
5. The transcoding service User Agent identifies the audio stream as
a radio broadcast. However, the policy of the transcoding service
is that it does not accept radio broadcasts because it would
overload their resources far too quickly.
6. In this case, the connection fails.
Alternatively, continuing from 2 above:
3. The radio station does provide text with their audio streams.
4. The deaf person receives a text stream of the radio program.
Note: To support deaf, hard of hearing and speech-impaired people,
service providers are encouraged to provide text with audio streams.
6.3 Sign Language Interface
In this scenario, a deaf person enables a signing avatar (e.g.,
ViSiCAST[6]) by setting up a User Agent to receive audio streams as
XML data that will operate an avatar for sign-language. For outgoing
communications, the deaf person types text that is transcoded into an
audio stream for the other conversation participant.
Charlton, et al. Informational PAGE 9
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
For example:
( )-Voice->(Voice To Avatar Commands) ----XMLData-->( )
( hearing ) (deaf )
( Person A)<-Voice-( Text To Voice ) <--------Text-------- (Person B)
( ) (Service Provider) ( )
6.4 Synthetic Lip-speaking Support for Voice Calls
In order to receive voice calls, a hard of hearing person uses lip-
speaking avatar software (e.g., Synface[7]) on a PC. The lip-
speaking software processes voice (audio) stream data and displays a
synthetic animated face that a hard of hearing person may be able to
lip-read. During a conversation, the hard of hearing person uses the
lip-speaking software as support for understanding the audio stream.
For example:
( ) <------------------Voice-------------->( )
( hearing ) ( PC with ) ( hard of )
( Person A) -------Voice-----> ( lip-speaking)---->( hearing )
( ) ( software ) ( Person B)
6.5 Voice Activated Menu Systems
In this scenario, a deaf person wishing to book cinema tickets with a
credit card, uses a textphone to place the call. The cinema employs
a voice-activated menu system for film titles and showing times.
1. The deaf person places a call to the cinema with a textphone:
(Textphone) <-----Text ---> (Voice-activated System)
2. The cinema's voice-activated menu requests an auditory response to
continue.
3. A Relay Service is invited into the conversation.
4. The Relay Service transcodes the prompts of the voice-activated
menu into text.
5. Text from the voice-activated menu appears on the display of the
deaf person's textphone.
6. The deaf person types a response.
Charlton, et al. Informational PAGE 10
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
7. The Relay Service receives the text and reads it to the voice-
activated system:
( ) (Relay Service ) ( )
( deaf ) -Text-> (Provider ) -Voice-> (Voice-Activated)
( Person A ) <-Text- (Text To Voice ) <-Voice- (System )
8. The transaction is finalized with a confirmed booking time.
9. The Relay Service withdraws from the call.
6.6 Conference Call
A conference call is scheduled between five people:
- Person A listens and types text (hearing, no speech)
- Person B recognizes sign language and signs back (deaf, no speech)
- Person C reads text and speaks (deaf or hearing impaired)
- Person D listens and speaks
- Person E recognizes sign language and reads text and signs
A conference call server calls the five people and based on their
preferences sets up the different transcoding services required.
Assuming English is the base language for the call, the following
intermediate transcoding services are invoked:
- A transcoding service (English speech to English text)
- An English text to sign language service
- A sign language to English text service
- An English text to English speech service
Note: In order to translate from English speech to sign language, a
chain of intermediate transcoding services was used (transcoding and
English text to sign language) because there was no speech-to-sign
language available for direct translation. Accordingly, the same
applied for the translation from sign language to English speech.
Charlton, et al. Informational PAGE 11
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
(Person A) ----- Text ----> ( Text-to-SL ) --- Video ----> (Person B)
---------------------- Text --------------------> (Person C)
----- Text ----> (Text-to-Speech) --- Voice ----> (Person D)
---------------------- Text --------------------> (Person E)
----- Text ----> ( Text-to-SL ) --- Video ----> (Person E)
(Person B) -Video-> (SL-to-Text) -Text-> (Text-to-Speech) -> (Person A)
---- Video ----> ( SL-to-Text ) ---- Text ----> (Person C)
-Video-> (SL-to-Text) -Text-> (Text-to-Speech) -> (Person D)
--------------------- Video --------------------> (Person E)
---- Video ----> ( SL-to-Text ) ---- Text ----> (Person E)
(Person C) --------------------- Voice --------------------> (Person A)
Voice->(Speech-to-Text)-Text->(Text-to-SL)-Video->(Person B)
--------------------- Voice --------------------> (Person D)
---- Voice ----> (Speech-to-Text) ---- Text ----> (Person E)
Voice->(Speech-to-Text)-Text->(Text-to-SL)-Video->(Person E)
(Person D) --------------------- Voice --------------------> (Person A)
Voice->(Speech-to-Text)-Text->(Text-to-SL)-Video->(Person B)
---- Voice ----> (Speech-to-Text) ---- Text ----> (Person C)
---- Voice ----> (Speech-to-Text) ---- Text ----> (Person E)
Voice->(Speech-to-Text)-Text->(Text-to-SL)-Video->(Person E)
(Person E) -Video-> (SL-to-Text) -Text-> (Text-to-Speech) -> (Person A)
--------------------- Video --------------------> (person B)
---- Video ----> ( SL-to-Text ) ---- Text ----> (Person C)
-Video-> (SL-to-Text) -Text-> (Text-to-Speech) -> (Person D)
Remarks: - Some services might be shared by users and/or other
services.
- Person E uses two parallel streams (SL and English Text).
The User Agent might perform time synchronisation when
displaying the streams. However, this would require
synchronisation information to be present on the streams.
- The session protocols might support optional buffering of
media streams, so that users and/or intermediate services
could go back to previous content or to invoke a
transcoding service for content they just missed.
- Hearing impaired users might still receive audio as well,
which they will use to drive some visual indicators so
that they can better see where, for instance, the pauses
are in the conversation.
Charlton, et al. Informational PAGE 12
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
7. Some Suggestions for Service Providers and User Agent Manufacturers
This section is included to encourage service providers and user
agent manufacturers in developing products and services that can be
used by as wide a range of individuals as possible, including deaf,
hard of hearing and speech-impaired people.
- Service providers and User Agent manufacturers can offer to a deaf,
hard of hearing and speech-impaired person the possibility of being
able to prevent their specific abilities and preferences from being
made public in any transaction.
- If a User Agent performs auditory signalling, for example a pager,
it could also provide another signalling method; visual (e.g., a
flashing light) or tactile (e.g., vibration).
- Service providers who allow the user to store specific abilities
and preferences or settings (i.e., a user profile) might consider
storing these settings in a central repository, accessible no
matter what the location of the user and regardless of the User
Agent used at that time or location.
- If there are several transcoding services available, the User Agent
can be set to select the most economical/highest quality service.
- The service provider can show the cost per minute and any minimum
charge of a transcoding service call before a session starts,
allowing the user a choice of engaging in the service or not.
- Service providers are encouraged to offer an alternative stream to
an audio stream, for example, text or data streams that operate
avatars, etc.
- Service providers are encouraged to provide a text alternative to
voice-activated menus, e.g., answering and voice mail systems.
- Manufacturers of voice-activated software are encouraged to provide
an alternative visual format for software prompts, menus, messages,
and status information.
- Manufacturers of mobile phones are encouraged to design equipment
that avoids electro-magnetic interference with hearing aids.
- All services for interpreting, transliterating, or facilitating
communications for deaf, hard of hearing and speech-impaired people
are required to:
Charlton, et al. Informational PAGE 13
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
- Keep information exchanged during the transaction strictly
confidential
- Enable information exchange literally and simply, without
deviating and compromising the content
- Facilitate communication without bias, prejudice or opinion
- Match skill-sets to the requirements of the users of the service
- Behave in a professional and appropriate manner
- Be fair in pricing of services
- Strive to improve the skill-sets used for their services.
- Conference call services might consider ways to allow users who
employ transcoding services (which usually introduce a delay) to
have real-time information sufficient to be able to identify gaps
in the conversation so they could inject comments, as well as ways
to raise their hand, vote and carry out other activities where
timing of their response relative to the real-time conversation is
important.
8. Acknowledgements
The authors would like to thank the following individuals for their
contributions to this document:
David R. Oran, Cisco
Mark Watson, Nortel Networks
Brian Grover, RNID
Anthony Rabin, RNID
Michael Hammer, Cisco
Henry Sinnreich, Worldcom
Rohan Mahy, Cisco
Julian Branston, Cedalion Hosting Services
Judy Harkins, Gallaudet University, Washington, D.C.
Cary Barbin, Gallaudet University, Washington, D.C.
Gregg Vanderheiden, Trace R&D Center University of Wisconsin-Madison
Gottfried Zimmerman, Trace R&D Center University of Wisconsin-Madison
Security Considerations
This document presents some privacy and security considerations.
They are treated in Section 5.6 Confidentiality and Security.
Charlton, et al. Informational PAGE 14
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
Informational References
[3] International Telecommunication Union (ITU), "Operational and
interworking requirements for DCEs operating in the text
telephone mode". ITU-T Recommendation V.18, November 2000.
[4] Moore, Matthew, et al. "For Hearing People Only: Answers to Some
of the Most Commonly Asked Questions About the Deaf Community,
Its Culture, and the Deaf Reality". MSM Productions Ltd., 2nd
Edition, September 1993.
[5] http://www.typetalk.org.
[6] http://www.visicast.co.uk.
[7] http://www.speech.kth.se/teleface.
Authors' Addresses
Nathan Charlton
Millpark Limited
52 Coborn Road
London E3 2DG
Tel: +44-7050 803628
Fax: +44-7050 803628
EMail: nathan@millpark.com
Mick Gasson
Koru Solutions
30 Howland Way
London SE16 6HN
Tel: +44-20 7237 3488
Fax: +44-20 7237 3488
EMail: michael.gasson@korusolutions.com
Charlton, et al. Informational PAGE 15
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
Guido Gybels
RNID
19-23 Featherstone Street
London EC1Y 8SL
Tel: +44-20 7296 8000
Textphone: +44-20 7296 8001
Fax: +44-20 7296 8199
EMail: Guido.Gybels@rnid.org.uk
Mike Spanner
RNID
19-23 Featherstone Street
London EC1Y 8SL
Tel: +44-20 7296 8000
Textphone: +44-20 7296 8001
Fax: +44-20 7296 8199
EMail: mike.spanner@rnid.org.uk
Arnoud van Wijk
Ericsson EuroLab Netherlands BV
P.O. Box 8
5120 AA Rijen
The Netherlands
Fax: +31-161-247569
EMail: Arnoud.van.Wijk@eln.ericsson.se
Comments can be sent to the SIPPING mailing list.
Charlton, et al. Informational PAGE 16
RFC 3351 SIP for Deaf, Hard of Hearing and Speech Impaired August 2002
Full Copyright Statement
Copyright © The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
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included on all such copies and derivative works. However, this
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English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Charlton, et al. Informational PAGE 17
User Requirements for the Session Initiation Protocol (SIP) in Support of Deaf, Hard of Hearing and Speech-impaired Individuals
RFC TOTAL SIZE: 33894 bytes
PUBLICATION DATE: Wednesday, August 14th, 2002
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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