Emergency Access Advisory Committee (EAAC) Report on TTY Transition
Emergency Access Advisory Committee (EAAC)
Report on TTY Transition
March 11, 2013
FCC EAAC TTY Transition report
This document is a report to the FCC from the Emergency Access Advisory Committee (EAAC). The
committee was assigned the task to review the sustainability of the TTY communication solutions for text
communication with people with deafness, hard-of-hearing, deafblindness and speech disabilities. In the
task is included to propose solutions if the TTY communication is found to be at risk or by other reasons
need to be replaced or paralleled with new services with similar but improved functionality.
2. Charter .......................................................................................................................................................... 4
2.1 Charter from EAAC ................................................................................................................................. 4
2.2 Extracted goals ....................................................................................................................................... 5
3. Definitions and abbreviations ...................................................................................................................... 5
4. User needs in text based emergency 9-1-1 calling ....................................................................................... 6
5. The current situation for TTY and other PSTN usage ................................................................................... 8
5.1 General information on the TTY ............................................................................................................. 8
5.2. Wireline TTY situation ........................................................................................................................... 9
5.3 Wireless TTY situation .......................................................................................................................... 11
5.4 Specific solutions for users with deaf-blindness .................................................................................. 11
5.5. Solutions for captioned telephony in PSTN ......................................................................................... 11
5.6 Proprietary solutions linking to standardized TTY................................................................................ 12
5.7 TTY Statistics ......................................................................................................................................... 12
5.7.1 TTY usage compared to other accessible service usage in USA .................................................... 12
5.8. Reasons for users to keep on using the TTY ........................................................................................ 14
5.9. Reasons to want to cease use of or support for the TTY .................................................................... 14
6. Theory behind observed transmission problems ....................................................................................... 16
7. Threats to the quality of experience of TTY cal s. ...................................................................................... 19
7.1 Access network threats ........................................................................................................................ 19
7.2 PSTN Core network threats .................................................................................................................. 19
8. Known standards and technical methods intended to transport TTY reliably through IP networks. ........ 20
9. TTY Replacement ........................................................................................................................................ 21
9.1 Features desired by the users .............................................................................................................. 21
9.2 Achievable functionality in IP based implementations ........................................................................ 21
9.3 Standards and technologies in IP networks suitable for TTY replacement .......................................... 23
9.3.1 For native SIP ................................................................................................................................. 23
9.3.2 For IMS used in wireless LTE networks and fixed broadband networks ....................................... 23
9.3.3 For XMPP ....................................................................................................................................... 23
9.3.4 Use of other real-time text protocols ............................................................................................ 24
9.3.5 Routing and addressing by number .............................................................................................. 24
9.3.6 Example from another region ....................................................................................................... 24
9.4 Access to NG9-1-1 ................................................................................................................................ 25
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9.5 Access to legacy 9-1-1 and transition from legacy to NG9-1-1 ............................................................ 26
9.6 Methods for interoperability between TTY and IP based solutions ..................................................... 27
9.6.1 Alternative solutions for interoperability between TTY and TTY replacements. .......................... 28
9.7 Other session control protocols than SIP ............................................................................................. 29
9.8 Solution proposals for interoperability between different IP based solutions. ................................... 29
10. Non real-time text alternatives; Applicability and functionality. ............................................................. 30
10.1 The gap between mainstream provision and accessibility ................................................................ 31
11. Potential problems with the NENA i3 approach for TTY handling. .......................................................... 33
12. Current and emerging policy and regulation support .............................................................................. 33
12.1 Twenty-First Century Communications and Video Accessibility Act of 2010 .................................... 34
12.2 DOJ regulation and guidance on accessible emergency services and TTY access to 9-1-1. ............... 34
12.3 Section 255 of the telecom act........................................................................................................... 34
12.4 Section 508 of the rehabilitation act .................................................................................................. 34
12.5. Draft revised section 255 and 508 .................................................................................................... 35
12.6 Wireless TTY regulation by FCC .......................................................................................................... 36
12.7 FCC TRS regulation. ............................................................................................................................ 36
12.8 TEDP Technology distribution programs. ........................................................................................... 36
12.9 Conclusion on acts and regulations .................................................................................................... 37
13. Concluding Findings and Recommendations ........................................................................................... 37
Rationale for Version 1 and rationale for not being able to agree to Version 2: ....................................... 39
Rationale for Version 2 and rationale for not being able to agree to Version 1: ....................................... 40
14. Entities influenced by the proposals. ....................................................................................................... 41
15. Timeline .................................................................................................................................................... 41
15.1 Timeline of an IP-based replacement................................................................................................. 41
15.2 Timeline of TTY transition .................................................................................................................. 42
16. References ................................................................................................................................................ 43
Appendix A. Background for current usage evaluation ................................................................................. 46
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This document starts from the recommendations from FCC committee EAAC in December 2011 regarding
possible phase out of the legacy TTY communication, explains the situations, the risks for deteriorating
communication quality, and the options to improve functionality by establishing a transition path from TTY
to more modern and higher functionality devices in IP networks.
It recommends protocols and functions for the new communication, and how interoperability with the old
can be achieved. Finally a timeline is provided.
2.1 Charter from EAAC
The TTY Transition group worked with TTY related goals of the main EAAC charter.
EAAC Provision: Deadlines by which interconnected and non-interconnected VoIP service
providers and manufacturers shall achieve the actions . . . where achievable, and for the
possible phase out of current-generation TTY technology to the extent that this technology is
replaced with more effective and efficient technologies and methods to enable access to 9-1-1
emergency services by individuals with disabilities.
The EAAC submitted a set of recommendations in December 2011. The fol owing recommendations were
further worked on by the TTY Transition group:
Recommendation P6.1: No TTY Phase-Out Deadline for PSAP:The EAAC recommends
against imposing any deadline for phasing out TTY at the PSAPs until the analog phone system
(PSTN) no longer exists, either as the backbone or as peripheral analog legs, unless ALL legs trap
and convert TTY to IP real-time text and maintain VCO capability.
Baudot (TTY) Support:The EAAC recommends that Baudot (TTY) be
supported by all PSAPs with VCO and HCO capabilities until there are no more TTYs in use – or
until there is a gateway between every TTY user and the PSAP, that converts TTY into the proper
real-time text format for VoIP systems supported by the PSAPs including support for VCO/HCO
functionality. Because of the risk for deterioration of TTY tones by IP transport, actions to secure
the transmission must be made close enough to the TTY so that no TTY-non-supporting network
path is between the TTY and the securing point. Best practice guidelines should be developed for
Recommendation P6.5: Conditional TTY Waiver: The EAAC recommends that the FCC
remove the requirement for TTY (analog real-time text) support for new IP-based consumer
devices that implement IP-based text communications that include at a minimum real time text or,
in an LTE environment, IMS Multimedia Telephony that includes real-time text. The text must be
possible to use in parallel with voice on the same call so that VCO equivalence is maintained. The
EAAC recognizes real time text provides characteristics that are required by some users in
emergency communications (e.g., sent continuously as it is typed and supports captioned
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Recommendation T2.2: Removal of TTY Requirement:The EAAC recommends that the FCC
remove the requirement for TTY (analog real-time text) support for new IP-based consumer
devices that implement IP-based text communications that include, at a minimum, real time text or,
in an LTE environment, IMS Multimedia Telephony that includes real-time text. The text must be
possible to use in parallel with voice on the same call so that VCO equivalence is maintained. The
EAAC recognizes real time text provides characteristics that are required by some users in
emergency communications (e.g., sent continuously as it is typed and supports captioned
telephony). (This is same recommendation as Recommendation P6.5: Conditional TTY Waiver.)
(See also Recommendation T6.3: Timeline Contingency.)
2.2 Extracted goals
From the charter and background, the following can be extracted as goals of the TTY transition report from
EAAC to the FCC.
1. Functions and modern technology
Provide advice to the FCC about modern technologies that can support the same functional needs
as the TTY does today and how such technologies could be applied both for user an emergency
2. Transition requirements
Provide advice on how a transition can be achieved from TTY usage to usage of the recommended
3. Interoperability requirements and solutions
Provide advice about to what degree interoperability is needed between new technology and TTYs,
as well as between users of new technology, both with users and 911 services, and how such
interoperability can be achieved.
4. Modification of regulations
Provide advice on what modifications may be desirable in the TTY-related regulation to support and
encourage a transition to modern technologies
Provide advice on what timelines should be applied on the actions for TTY transition.
3. Definitions and abbreviations
American Standard Code for Information Interchange. Originally a character code
standard, but in accessible communication used term for text telephony
communication in USA using the Bel 103 modem standard and ASCI character code.
Commercial Mobile Radio Service; a regulatory classification for mobile telephone
service that is provided for profit and makes interconnected service available to the
public, usual y in the form of mobile phone service.
Dual Tone Multi Frequency. Tone coding of numbers used in telephony.
Frequency Shift Keying ( a robust modem technology used in the TIA 825a standard)
Global System for Mobile Communication
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Hearing Carry Over (Audio and text in same call)
Internet Engineering Task Force
Long Term Evolution (wireless technology)
National Deaf-Blind Equipment Distribution Program
National Exchange Carrier Association, Inc.
National Emergency Number Association
Public Security Answering Point
Public Switched Telephone Network
Phone connector standard.
Text transmitted instantly while it is being typed or created. The recipient can
immediately read the sender's text as it is written, without waiting.
Swedish Institute of Assistive Technology
Telecommunications Equipment Distribution Program
Telecommunications Equipment Distribution Program Association
Telecommunication Relay Service
Total Conversation Conversational communication in video, real-time text and voice.
Text telephone based on the TIA 825A standard for an FSK modem, used in the USA.
Technology to be supported as an alternative to the TTY and possible replacement of
the TTY for similar types of conversational situations as the TTY.
U.S. Access Board The Access Board is an independent Federal agency devoted to accessibility
for people with disabilities. The Board develops and maintains design
criteria for the, telecommunications equipment, and for electronic and
information technology and many other areas.
Voice Carry Over (Audio and text in same call) where the cal er can switch between
voice and text or use text in one direction and voice in the other.
Voice over LTE. A profile within IMS for IP based voice and text communication. Real-
time text is included in the specification.
Video Relay Service
World Wide Web Consortium
4. User needs in text based emergency 9-1-1 calling
The EAAC user survey  provides information about how a number of respondents with accessibility
interest views emergency service calling today and in the future. The respondents themselves announced
their interest to participate in the survey. Therefore only brief guiding conclusions can be drawn, but no
reliable extrapolations to the whole population of USA can be done from the material. Some extracts are
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provided here of interest for the judgments in relation to the TTY and other communication methods
The TTY is a technology for text communication combinable with voice in PSTN that has been wide spread.
It is now reducing in usage. A possibility to connect TTYs to wireless handsets exists but is reported to have
very little use.
The fol owing is the user's view of the TTY and other communication including text as a means for 9-1-1
Current TTY usage for 9-1-1 calling
The EAAC user survey  asks in question #13 what communication the users used for calling 9-1-1 during
the last two years.
The response indicates that of the respondents who used means including other modality than voice, 22%
used the TTY. This shows that the TTY stil plays an important role in 9-1-1 calling.
High percentage of reasons to cal 9-1-1 are not fulfil edQuestion #14 shows a scaring reality. 25% of the respondents had reasons to call 9-1-1 during the last two
years but could not do it. Of these, 30% tried but failed and 70% had no suitable means at the site of the
Desired variation in modality of 9-1-1 callsQuestion #15 shows a quite even distribution among respondents of desired modalities to use for 9-1-1
cal s, between text, video, voice, and the combination of text, video and voice together.
From question #16 it is seen that the most favored way of future text communication methods with 9-1-1
among respondents is real-time text. Over 45% of the respondents answered that they wanted that
option, while 10% still wanted the TTY as an option (also providing a kind of limited real-time text).
Question #25 indicates what modality mix the respondents want to use with 9-1-1. 40% of the
respondents want to have the option to use text both ways. 19% want to have the option to use text one
way and voice the other, and 22% want the option to get text captions added to voice communication.
Question #29 shows a very high preference for real-time text over message-wise texting. Of the
respondents wanting to use text communication with 9-1-1, only 13% want to use text messaging.
Question #29 also shows that more than 50% of the respondents want to be able to communicate in text
both ways simultaneously. Thereby they indicate a strong interest to get away from the functional
limitation of the TTY that al ows communication only in one direction at a time.
Wireless and wireline solutions are desiredQuestion #21 shows a high preference for having wireless solutions for calling 9-1-1, but also maintained
interest in having a landline options.
Direct communication with 9-1-1 telecommunicatorQuestion #22 shows a high preference for contacting 9-1-1 directly rather than go through a relay service
with no direct contact with the 9-1-1 telecommunicator.
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Same device and tool for everyday communication as for 9-1-1 cal ing.Question #23 shows that the respondents have an overwhelming desire to use the same communication
tool for 9-1-1 as for everyday calling. 82% indicated that option.
ConclusionsWhen making conclusions, it must be remembered that the method for selection of respondents only
allow brief indications. Only by combination with statistics of other sources, reliable guidance can be
For the conclusions, material has been used from the survey, supported by the EAAC recommendations
and by statistics provided in chapter 5 of this document. :
• The wireline TTY is important and takes 20% of the 9-1-1 accessibility calls.
• A TTY replacement that can be wireless is needed and would increase the number of successful
calling to 9-1-1 when there is a need.
• A TTY replacement shal do away with the limitations of the TTY; Text and voice shal be possible to
use together simultaneously. Text shall be rapid real-time text, with possibility to send text in both
• Some users want video included. It is therefore important that solutions offering only real-time
text and voice are interoperable with solutions offering video, real-time text and voice.
• The solutions for 9-1-1 calling with real-time text and voice need also be wide-spread and
attractive to use for everyday calling.
5. The current situation for TTY and other PSTN usage
5.1 General information on the TTY
TTY is one harmonized technology with strong policy support in USA, implementing a kind of limited real-
time text feature in the PSTN with the goal to enable conversations on distance in text and voice. The users
are mainly persons who cannot use voice fully in communication because of a disability in hearing or
speech. The policy support of the TTY has established a service environment where TTY users can cal each
other and also use relay services and 9-1-1 emergency services.
PSTN, and especial y TTY communication is at threat in the generation shift to Internet protocol
technologies. New technologies outperform the TTY functionally in many ways, while the thorough
harmonization, the interoperability between users of different carriers, the availability of both voice and
text in the same cal , the smooth flow of text while it is typed, the access to 9-1-1 emergency services and
the consistent access to relay services of the TTY system is not yet established by any other technology.
The usage of TTY is declining, but the users in need of consistent accessible communication then often
move to fragmented services with no 9-1-1 access, lacking some of the basic functional features of the TTY,
like the smooth real-time text and the ability to use voice in one direction and text in the other, a form of
communication very important to elders who can speak but not hear and not type wel , especially on small
This document is written from the 9-1-1 access point of view, but deals comprehensively with the
transition to other accessible technologies, since a main principle is that the communication tool and
service that is used for everyday calls should also be the possible to use for 9-1-1 calls in an emergency
situation. In fact, it is important that people be able to call 9-1-1 on the devices they use every day and are
familiar with, rather than expecting them to think of, find, and figure out a new technology in the middle
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of an emergency. Therefore discussion of 9-1-1 and general communication issues are intermingled within
When discussing a replacement or complement for the TTY, a first step should be to look into what
characteristics are important to maintain.
Important capabilities of TTY that should be provided by any replacement technologies include:
a. The ability for users to contact the emergency service PSAP via the same procedure used by voice
callers - e.g. by dialing 9-1-1.
b. The ability to direct 9-1-1 calls that include text (or where text appears in the call after connection) to
PSAP telecommunicators equipped for accessible text communication.
c. The ability to use the same communication devices and methods for 9-1-1 calls as are used for
d. The ability to use the same communication devices and methods for relay service calls.
e. With only minor time delays, text characters must appear on the recipient's display as they are being
typed by the sender.
The ability to intermix both voice and text on the same cal .
g. The ability to support al PSAP functions for accessible text calls that are supported for voice calls.
Call recording including text and voice.
Caller location provision.
Caller location use for call routing to most appropriate PSAP.
A guide for handling of accessible emergency calls and especially TTY calls is found in the DOJ information
athttp://www.ada.gov/911ta.htm"> http://www.ada.gov/911ta.htm . Its service principles must be maintained while the technology
specific parts may be changed when new technologies are introduced.
5.2. Wireline TTY situation
On wireline phone connections where TTY is used, the fol owing features are available.
a) Voice with limited narrow-band quality (300-3400 Hz).
b) TTY for limited real-time-text communication.
i. Also referred to as the “TIA-825A”  standard, using a 45.45 bit/s half duplex FSK modem and a
5-bit character code, also called Baudot.
A cal is set up with general PSTN technology. When answered by a TTY, limited real-time text
communication can take place. Characters typed on one of the TTYs appear on its own display
and on the other's. When text is not transmitted, voice can be transmitted in an adjacent
telephone alternating on using the same line as the TTY.
ii. Limitations of TTY (using TIA-825A (Baudot code)) include:
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• The maximum transmission rate is about six characters per second, which is slower than
many people type.
• Devices are not able to send and receive text at the same time.
• Although users are able to intermix voice and text on same call, simultaneous voice and text
is not supported.
• Case shift is not supported. So the letter transmission is all seen as either upper case or
lower case depending on the terminal display characteristics.
• Only alphanumeric and a few symbols are covered. Many important characters are not
supported, such as the “@” symbol.
• Small transmission errors can cause garbling of the reception, which can carry forward for
up to 72 characters after the error.
• A common reason for garbled reception (but not the only one) is due to the Baudot
presentation protocol having modes. For example, the five-bit code 00001 represents the
letter “E” when the TTY is in Letter Mode, and represents the digit “3” when the TTY is in
Number Mode. It is not uncommon for the sending TTY and the receiving TTY to
temporarily lose mode synchronization, causing the receiving device to display nonsense
• In order to compensate for the risk for garbling by minor communication disturbance, the
devices commonly have a feature for manual request to invert the shift on received and
iii. Many TTYs also support a manufacturer-specific proprietary enhanced text protocol with
advantages over 45 baud TIA 825A, including a faster transmission rate and the ability to interrupt
the typing party with an indication that the other party want to get the turn to type.
Note that, because these more rapid alternative technologies are non-standard proprietary
protocols and only work between TTYs of the same manufacturer, PSAPs are not required to
support them. The PSAP interfaces are required to fol ow only open standards.
Devices capable of these more rapid protocols that fail to receive a “handshake” of its same kind
will default automatically to 45 baud TIA 825A.
c) DTMF (e.g., “If you are in danger and cannot speak, press 1.”)
i. Note that users using a direct connect TTY do not necessarily know how to create the dial tones
with their TTY instead of the normal TTY number tones.
d) Captioned telephony phones, providing rapid real-time text together with a phone cal on another line
by means of a human operated service.
e) "ASCI " text telephone support. Many text relay services and 9-1-1 PSAPs also support text
communication with users with computers and low speed modems. The rate of use is not known
exactly, but is reported to be much lower than for TTY.
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5.3 Wireless TTY situation
Mobile voice channels are not directly suitable for carrying the tones for TTYs successfully. Therefore,
methods for reliable transmission of TTY over wireless networks have been created, cal ed Wireless TTY.
The implementations have so far required connection of a TTY with a cable to the headset interface of the
mobile handset. Different wireless technologies use different ways to encode, transmit and decode TTY
With this arrangement, it is supposed to be possible to have TTY cal s between TTYs connected to mobile
phones and land-based TTYs.
The setup, requiring a TTY and a mobile phone cabled together is regarded inconvenient for a mobile
situation by most users, so this solution is reported to have found very little use. It is difficult to find all the
pieces and cords and connect them all successfully in time to receive a call, as well as being cumbersome
to carry them all about. It has not been possible to get figures either for the real use of the solution, or for
the amount of quality problems that sometimes is said to exist in usage of the Wireless TTY solutions.
There have been indications at the EAAC that there is some use of the wireless TTY solution. The general
impression is however that the current wireless TTY solution with the TTY device attached to the wireless
handset by a cable is very little used, much less than the regular wireline use. Therefore, transitioning to a
TTY replacement technology would cause very little concern for current users as long as the replacement
can connect to TTYs at the far (non-mobile) end of the conversations if the calls terminate on the PSTN.
For the GSM and UMTS wireless technologies, the standards allow for solutions completely built-in to the
handset, but no such implementations have been made commercially available.
For next generation mobile solution, LTE, the real-time text and TTY interoperability solution builds on IP
transmission of text coded text with the same text protocol that is specified for real-time text in NG9-1-1.
This solution can qualify for being a model for the technology to replace TTY. The implementations need
then be built into the handsets including the user interface in order to gain any interest from users.
5.4 Specific solutions for users with deaf-blindness
The National Deaf-Blind Equipment Distribution Program (NDBEDP) enables low-income individuals who
are deaf-blind to access 21st Century communications services.
In this program, launched by the FCC, some of the distributed technology is based on TTY transmission.
When transition is planned for TTY users to improved functionality in more modern environments, it is
important to include the deaf-blind users of the NDBEDP program in the planning, so that suitable
accessible devices are available, and interoperable with what is offered other users.
An advice from the EAAC TTY transition subgroup is therefore that representatives from the NDBEDP get
actively involved in implementing TTY transition measures.
5.5. Solutions for captioned telephony in PSTN
There are captioned telephony phones, providing rapid real-time text together with a phone cal on
another line by means of a human operated service. The text transmission is only from the captioned
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telephony service to the user. Therefore the text transmission part of this solution does not put any extra
requirements on the PSAP communication technology.
IP based variants exist.
The conditions that the captioned telephony communication is only between the service and the user, and
that an IP based alternative exists cause the conclusion that the transition of this type of communication
from PSTN to IP can be left to the discretion of the captioned telephony service provider.
5.6 Proprietary solutions linking to standardized TTY
There are systems providing proprietary communications technology within an organization, converting to
and from TTY transmission in the outside world. Decisions about TTY support in networks and 9-1-1
influences all users of such systems. If these systems are going to be maintained and interwork smoothly
with the TTY replacements and NG9-1-1, it might be desirable to update them with direct links to IP and
adaptation to the TTY replacement protocols.
5.7 TTY Statistics
It is sometimes said that the TTY is obsolete and not used anymore. Looking at statistics from for example
text relay service usage, it can however be seen that the use has fal en dramatical y over the last few years,
but the usage is stil significant and just over half the level of the text IP-relay usage. Thus, over one third
of the text relay traffic is still TTY.
The following are coarse extrapolated approximate figures indicating the size of the TTY population and its
usage 2012. An explanation of the sources of this information is found in Appendix A.
Relative use of different TTY implementations:The statistics provided here is mainly based on relay
service usage statistics. At that point, calls with wireline TTYs, wireless TTYs and proprietary office TTY
solutions look the same, and the statistics does not differentiate between these kinds. The contribution to
the statistics from the Wireless TTY solution is however expected to be close to 0.
Approximate number of current users of TTY in USA: 100 000.
An estimate of the number of emergency cal s from TTY:20,000 per year (See Appendix A).
State of public use of TTY:TTY is a formally accepted way for accessible communication in USA.
Services available:TTY users have access to text relay services for calls with hearing people using voice
phones. Text relay services translate between text and voice. Text relay services for TTY are available at
phone number 711 from the TTY side. It is possible to alternate between text and voice in a relayed call.
(This function is cal ed VCO and HCO)
Trend:The rate of use of the TTY is being reduced by approximately 10% per year. This results in half the
current volume in 7 years, 1/4th the usage in 14 years etc., unless something changes.
5.7.1 TTY usage compared to other accessible service usage in USA
In order to get an indication of the importance of the TTY, an effort is made here to compare its usage with
the usage of other accessible communication solutions.
22.214.171.124 Relay service usage 2010/2011 in USA.
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minutes / year
calls / year
Video Relay (VRS)
100 M minutes 25 M calls
50 M minutes
16 M calls
50 M minutes
16 M calls
Traditional TTY TRS
28 M minutes
9 M calls
California 2010/11 extrapolated with NECA
228 M minutes 66 M calls
Thus TTY based relay calls are about 12% of the total load of relay calls and 36% of the text relay calls.
• VRS -unreliable trends (current decrease, likely temporary)
• IP-relay - decreasing
• Captioned Telephony - Increasing a bit more than the decrease in IP-relay.
• Traditional TTY - Decreasing about 10% per year, to half in 7 years, 1/4th in 14 years etc.
Conclusion: TTY traditional relay is still considerable but lowest in volume, and only about 12% of the total
relay service call volume and approximately 36% of the text relay calls (See Appendix A)
126.96.36.199 User -to - user calls
Of the call types above, only Videophone and TTY are possible to use for direct user-to-user calls.
An estimate from the EAAC survey  early 2011 indicates that TTYs are used for as many user-to-user
calls as for relay calls. That would mean around 9 M TTY calls per year.
There are indications that videophones are used about 5 times more for user-to-user calls than for VRS
relay calls. That would mean around 125 M calls per year in USA.
188.8.131.52 Total calls
The sum of relay calls and user-to-user cal s can then be estimated to be:
18 M calls per year
150 M calls per year
• Captioned telephony 16 M calls per year
• IP text relay
16 M calls per year
• Sum accessible calls
200 M calls per year
The wireline TTY thus seems to be used for about 9% of the accessible calls including other modalities than
Note that these figures are very coarse and only provided to give an approximate view of the current
situation with the degree of precision needed for the discussion in this report.
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5.8. Reasons for users to keep on using the TTY
It is shown in this document that the number of TTY users is decreasing. The functionality is limited, and
the communication problems for TTY are increasing. The wireless TTY solution is said to be close to extinct.
Even so the wireline TTY users select to use the TTY for a cal around 20 mil ion times per year in USA (See
Appendix A). What reasons can the users have to keep on using this communication tool that so often is
said to be out aged and should be made obsolete.
Here is a list of possible reasons for a user to keep using the TTY.
1. The TTY is a robust device capable of surviving 10 years with minimal maintenance. No similar
robust products exist for mobile and IP-networks, where the expected lifetime of a product is
about 2 years.
2. The user has become used to operating the TTY, and is not interested in learning new devices and
new services when the communication needs are sufficiently satisfied with the TTY.
3. The user appreciates the approximately installation-free use of the TTY. It has an acoustic coupling
option, so any traditional y shaped phone receiver on a regular telephone network telephone can
be used to connect the TTY to the network as well as be used for alternating between voice and
text in the cal .
4. The user has only phone-line TTY access and is not interested in changing the phone subscription
to add Internet.
5. The user has other means for daily communication, but maintains a TTY for the case of emergency
at home, when the TTY is the only directly applicable solution.
6. The user has relatives who have only TTY. The TTY is used for communication with them.
7. The user has other means for daily communication, but maintains the TTY for text relay calls with
hearing people in authorities and other organizations.
8. The user is deaf-blind and no solution for deaf-blind people are marketed sufficiently other than
the TTY based solution with Braille display distributed through the deaf-blind equipment program.
9. The user has a number of old friends who mainly use TTY for communication. Some of them have
no Internet so TTY is the only way to reach them.
10. The TTY was provided from the Technology Equipment Distribution Program and the user saw no
reason to not accept it.
11. The user prefers alternating between voice and text during the cal . No other available
communication tool enables that mode.
If products with similar ways of operation, similar robustness, equal interoperability, higher functionality,
better mobility and equal capability to be used for direct 9-1-1 calls were available for IP networks, it is
likely that the transition from TTY to modern communication methods would be more rapid.
5.9. Reasons to want to cease use of or support for the TTY
Wireline carriers, wireless carriers and 9-1-1 centers may find it desirable to cease support of the TTY
because of a number of reasons. Users may find reasons to cease use the TTY. Some of the reasons are
- EAAC Draft TTY Transition report - March, 2013 - Page 14-
Reasons for 9-1-1 centers to want to cease support of TTYs:
1. 9-1-1 TTY calls are rare. In some 9-1-1 centers it is months between the cal s. It is complicated to
maintain the technical capabilities to handle all kinds of TTY calls, when the frequency is so low.
2. It is complicated to maintain PSAP operational competence and preparedness to handle TTY cal s
with all variants including the ways to alternate between voice and text during the call.
3. TTY cal s are often silent from the cal er, expecting the cal ed party to answer with TTY. For 9-1-1
centers this implies that a time consuming procedure needs to take place for each incoming silent
call, so that it is checked if it is a TTY calling before deciding other treatment on the silent call. This
issue is compounded by the infrequency of TTY cal s vs. standard silent calls making them easy to
Possible reasons for wireline carriers to want to cease supporting TTY cal s.
1. Modern communication technologies may have problems to support TTY transmission wel ,
especially when planning for IP transport technology.
2. The need to support TTY transmission requires extra testing, extra engineering, and extra specialist
support actions for a small and decreasing minority of the subscribers that use the TTY.
Possible reasons for wireless carriers to want to cease supporting cal s with TTYs attached to handsets.
1. There seem to be extremely few users of this technology, and there are considerable costs
involved in setting up and maintaining the infrastructure for the few calls made.
2. Each new generation wireless technology requires new specifications and new implementations of
the handset and network support for the wireless TTY solution. With the few users, it seems to be
a lot of resources spent for very little benefit.
3. In certain contexts, providers may get the impression that it would be sufficient to provide the
SMS based "text-to-9-1-1" solution until an NG9-1-1 adapted TTY replacement can be provided.
Possible reasons for users to cease or decrease or not begin using the TTY.
1. There is a desire to be able to call on wireless devices and to wireless devices. The TTY support in
wireless devices is not convenient to use.
2. The functional limitations of the TTY make it inconvenient to use. It is slower than typing speed, it
can only be used in one direction at a time, and it has only capitals or lower case letters, not both.
It has limited set of special characters; voice can only be used alternating with text and not
3. The user wanted to mainly use sign language in communication, so when videophones were
distributed, the user moved to mainly use videophone and sign language.
4. The user wanted to talk and get captions on the incoming voice so the user moved to mainly use
captioned telephony when that service was launched.
5. The IP relay services provide suitable replacement for many of the relay calls that the user used
the TTY for.
- EAAC Draft TTY Transition report - March, 2013 - Page 15-
6. There are many text communication alternatives today making up a patchwork of services through
which it may be possible to have direct communication with many people. So, even if they do not
have the same ubiquitous possibility to reach al , and do not provide full rapidity and
conversational flow as desirable and no possibility to merge voice and text, they are used instead
of TTY in many situations because of their widespread use and mobility.
These reasons may explain the observed reduction in TTY usage. They should be compared with the
reasons for users to maintain use of the TTY listed in previous section.
NOTE: A desire to decrease support for TTY connection to a mobile handset should not be confused the
continued need to support connection to TTYs at the far (non-mobile) end of a call, it if terminates in the
PSTN. In both emergency and daily communication, people (using mobile devices) may need to
communicate in text to people who are on the PSTN. TTY is the ONLY way for text communication to take
place at the PSTN end of the cal . So future TTY replacements on mobile phones must be able to continue
to connect to and work with TTYs on the PSTN or else there wil be no way to communicate in text to
people on the PSTN as there is today.
Also, it needs to be remembered that for PSTN wireline networks, there is no text communication
technology other than TTY. Eliminating TTY support on PSTN wireline networks would eliminate al text
communication to those who only have PSTN wireline networks available to them. (Eliminating all PSTN
wireline networks would address this problem but it is unclear how soon that would happen, and until it
does TTY support on PSTN is needed.)
6. Theory behind observed transmission problems
TTY transport over packet-switched networksOn many packet-switched telecommunication systems, when attempting to transmit 45.45 baud
Baudot TTY signals as audio tones – i.e., when attempting to transmit TTY information via the
same audio protocols and mechanisms that are used for voice – three common types of
transmission impairment at levels that that tend to be acceptable in voice conversations can cause
the TTY character error rate to rise above acceptable levels. They are:
(1) Packet loss
a. Includes packets that are never delivered and packets that arrive too late to be
b. A typical audio packet contains a digital audio recording that is 20 milliseconds in
c. In voice conversations in which the packet loss rate is not extreme, voice-
optimized packet loss concealment algorithms are often able to trick the human ear
into hearing something that wasn’t there – for example, by automatically filling the
gap with “comfort noise” or by acoustically interpolating between the packets on
either side of the gap.
- EAAC Draft TTY Transition report - March, 2013 - Page 16-
d. Voice-optimized packet loss concealment algorithms are not able to trick a TTY
into “hearing” a TTY tone (data bit) that was not received. If any one of the audio
packets containing a TTY tone is lost, the receiving TTY wil be unable to decode and
display that character properly. Some quick math:
i. If a packet size of 20 mil iseconds is assumed, the sequence of audio tones
that comprise a single TTY character spans approximately eight audio packets.
ii. If one assumes that packet loss occurs randomly, as opposed to being
clustered or “bursty”, the expected character error rate will be roughly equal to
the packet loss rate times eight. This means that one can expect to exceed the
one percent character error rate threshold recommended by the FCC when the
packet loss rate is only 0.12% – an amount far below what is often regarded as
acceptable for voice communication.
(2) Audio compression
a. In order to allow telecommunication transmission pipelines to accommodate a
larger number of conversations simultaneously, many systems employ audio
compression techniques that reduce the number of bits-per-second required by
each audio stream.
b. The audio compression techniques that are commonly used in enterprise VoIP
and in wireless systems are voice-optimized. When compared with
uncompressed audio (e.g., audio encoded using ITU-T Standard G.711 ), the
loss of perceived voice quality attributable to these techniques tends to be
noticeable but not objectionable. By contrast, because these techniques are
voice-optimized, the techniques tend to distort non-voice audio information
(such as DTMF and Baudot TTY signals) so badly that the receiving devices are
often unable to decipher the information reliably.
(3) Echo cancellation
a. In telecommunication systems, many factors can cause an undesirable reflection
of signals from a receiving device back to the transmitting device. A simple
example of this problem may be encountered when amplified handsets are
employed: Because the sound coming from the handset’s speaker is amplified,
the sound can be picked up by the handset’s microphone and then echoed back
to the person who is speaking.
b. In telecommunication systems in which the transmission from one person to the
other is virtual y instantaneous, a person who is speaking into a telephone and
receiving these reflected signals will perceive that their own voice sounds a bit
louder to them while there are speaking. The effect can be annoying, but
general y not something that would interfere with the person’s ability to speak.
- EAAC Draft TTY Transition report - March, 2013 - Page 17-
c. In typical IP telecommunication systems, point-to-point transmission times can
be hundreds of mil iseconds. Under these conditions, people who are speaking
will perceive a reflected signal as an obvious echo, time-delayed by an amount
that makes it difficult for people to have a conversation.
d. In order to ensure that voice conversations wil not be disrupted by reflected
signals, IP telecommunication systems have voice-optimized echo cancellation
e. In order to cancel echo, without cancelling desirable signals (e.g., a voice user
trying to interrupt another voice user), signal characteristics that must be
detected and measured by the echo cancel er include: (1) the presence of
transmitted signals with acoustic characteristics that appear to duplicate the
characteristics of the received signal, (2) the difference in amplitude between
the original signal and the duplicate signals, and (3) the time delays between the
original signal and the duplicate signals. Echo cancellation is achieved by
attenuating transmitted signals at levels that align with the measured amplitudes
and time delays of what are determined to be echoes.
f. Voice-optimized echo cancellers may diverge in presence of the relatively long
even tones used in TTY communication. In this situation, the manner in which
signals are attenuated by the echo canceller will be incorrect, thereby causing
TTY transmissions to be inappropriately choked or distorted. An article
describing some of these problems is referenced in 
i. Many voice-optimized echo cancel ation mechanisms assume that a
signal with little acoustic variability is noise (because it cannot be
speech), and wil therefore try to attenuate or block the signal.
ii. If there is intermittent, random noise coming from the endpoint that is
receiving the TTY signal, the echo canceller might assume that the
non-varying TTY signal is noise that should be removed, and that the
intermittent, random noise is a signal that should be retained.
iii. Signal from one end and noise from the other can be taken for cross-
talk. Under cross-talk situations, some echo cancellers freeze their
operational conditions in a way that can lead to diversion, or even
worse, block transmission in one of the directions.
For these reasons, the EAAC advises against methods that transmit TTY information as audio
tones within IP networks. Instead, it is recommended that PSTN gateways transcode between
traditional audio TTY signals on the PSTN side of the gateway, and real-time text packets on the IP
side of the gateway.
- EAAC Draft TTY Transition report - March, 2013 - Page 18-
7. Threats to the quality of experience of TTY calls.
TTY transmission quality is threatened by some development trends in electronic communication.
These threats are assessed in this chapter.
7.1 Access network threats
The network connection where the TTY is connected needs to have characteristics suitable for TTY tone
• Traditional analogue PSTN phone line connections have such suitable characteristics.
• But at an increasing rate such connections are replaced by solutions containing IP based transport
of the audio. Then, a risk for deterioration of the TTY tones appears, resulting in reduced or
destroyed or irregular TTY transmission quality.
This risk appears especially when a user tries to connect a TTY to the phone jack of an interconnected VoIP
connection, but may also possibly appear because changes in the access network behind a PSTN
VoIP operators may have specific settings to apply to connections that the user announces that they
intend to use for TTY.
In order to avoid these risks, information must reach TTY users and potential TTY users explaining the risks
for reduced TTY communication quality in these situations, and possible actions against such deterioration,
if found effective. The TEDPs, the TRS, the TTY resellers and the wireline carriers can share the task to
provide this information.
The TTY Transition subgroup recommends that FCC arranges so that an investigation is performed on to
what degree VoIP transmission technology in the access network causes bad quality on TTY cal s, and to
what degree this is known by carriers and service providers offering connection of PSTN equipment. It
should also be clarified if there are known remedies. This information can then be the base for
requirements to the carriers and service providers to inform users about the suitability of a phone
connection for TTY usage.
7.2 PSTN Core network threats
The PSTN network for telephony is approaching end of life. PSTN-like services will continue for some time,
but the core networks are moving to use IP as the internal technology. This means that users, stil having
regular PSTN RJ-11 jacks and plain old telephone equipment, in an increasing rate will have their calls go
through IP based transmission even if also the other endpoint in the call has a similar PSTN technology
Knowing the extreme sensitivity of audio carried TTY tones in IP networks, where the requirement is that
any echo canceller must not malfunction in presence of TTY tones, and no more packet loss than 0.12%
must occur, there is an apparent risk that IP replacements of the PSTN core network will not always meet
these requirements, and therefore introduce irregular deterioration of TTY call quality.
- EAAC Draft TTY Transition report - March, 2013 - Page 19-
The TTY Transition subgroup recommends that FCC arranges so that an investigation is performed on to
what degree IP transmission technology in the core network causes bad quality on TTY cal s, and to what
degree this is known by carriers and service providers using core network carrying traffic for PSTN devices,
and if there are remedies. This information can then be the base for requirements to the carriers and
service providers to inform users about the suitability of a phone connection for TTY usage.
8. Known standards and technical methods intended to transport TTY
reliably through IP networks.
There has been some efforts to standardize transport between PSTN based TTYs in a reliable way through
IP network segments.
ITU-T Recommendation V.151  This is a standard for transmission of TTY and other text telephone
standard signals over segments of IP networks. This standard is intended to be implemented in gateways
between PSTN and IP. Devices fol owing this standard demodulate TTY tones, and convert them into text
coding sent in IP packets. At the egress side the text is again converted to TTY tones.
• Implementations exist in large gateways, with slight proprietary additions making it required to
have the same make of gateway at both ends of the communication.
• The standard is not intended for communication between a PSTN based TTY and an IP based
• Echo canceller concerns still apply and are not covered by the V.151 standard.
TIA 1001  This is a standard applicable to USA only, because it covers only TTY communication and not
the other text telephone transmission standards used in other countries. The method is similar to the one
used by V.151. This standard is therefore also only applicable to cal s between PSTN based TTYs.
ITU-T Recommendation J.161  This is a standard specified for transmission of IP communication in
cable TV networks. It requires good transmission for TTY tones and also a possibility to use IP based real
time text communication.
IETF RFC 4734 This standard is for detection of tones from e.g. TTYs. It may also be possible to transfer
some tones through IP networks with this standard, but the main idea is to detect and indicate e.g. TTY,
and then move to use of one of the other standards for the transmission of real-time text.
3GPP TS 23.126  The standards for TTY transmission through GSM and UMTS wireless networks also
contain a description on how to handle an al -IP wireless IMS network by IP based real-time text
transmission, called GTT-IP. Even if it is foreseen that most implementations would make the user
interface for text communication built-in to the handset, it is possible to use it also with conversion to a
TTY attached to the handset.
Advice is also sometimes provided for trying to establish network conditions suitable for the transport of
TTY through IP without the standards above. There is no guarantee for success.
The main parts of such advice are:
1. Use a large static jitter buffer for reception after IP transmission.
- EAAC Draft TTY Transition report - March, 2013 - Page 20-
2. Do not use voice error concealment.
3. Use G.711  encoding.
4. Do not use silence detection and comfort noise generation.
5. Use a G.168  line echo canceller that is tested for good performance with TTY tones as
specified in G.168 Test 14 in the actual network conditions. Echo cancellers have less risk to cause
problems if they are set to disable non-linear processing, do no clipping on double-talk detection
and make sure that no G.164 and G.165 functionality are active simultaneously with G.168.
6. Use this way of transmission only in controlled network environments.
Applicability and deployment of these methods for legacy TTY transmission over IP network segments.
Al the methods specified above in this section only aims at reliable transfer of TTY signals over IP network
segments. They thus have the opportunity to prevent the experience of bad quality when crossing IP
networks between legacy TTY terminals, if implemented in both ends of such a connection. They do not
help for connections between TTY and IP based text capable terminals, and have therefore no real place in
a TTY transition plan.
A general protocol suitable for gateway operation including TTY and real-time text is:
ITU-T Recommendation H.248.2Gateway control protocol: Facsimile, text conversation and call
discrimination packages .
Brief descriptions on interoperability between TTY and IP based real-time text can be found in
IETF RFC5194 .
9. TTY Replacement
9.1 Features desired by the users
The EAAC user survey  provides good insight in features and functionality that users find important and
desirable to bring into the TTY replacement. The most relevant features are extracted in chapter 4. This
chapter describes the feasible functions and features and recommends ways to implement them.
9.2 Achievable functionality in IP based implementations
A solution that can replace the functions of the TTY and enable users to move to IP networks should
provide the functionality that is appreciated by the TTY users but eliminate its most apparent limitations.
The fol owing functionality should be provided:
1. Provide smooth, rapid transmission and display of real-time text so that text is transmitted not
more than one second after character submission and without any extra action than typing the
characters, or submitting them in some other way, e.g. through speech-to-text.
- EAAC Draft TTY Transition report - March, 2013 - Page 21-
2. Allow international and national interoperability so that calls can be made with other service
providers or devices. Use agreed interworking standards between providers even if providers may
use different technologies internally. Less functionality does not meet the functional equivalence
3. Make use of any international characters possible with both capital and lower case characters.
4. Provide transmission speed of text above the most rapid typing speed and speed of input of voice-
to-text applications. (at least 30 characters per second )
5. Use a technical method that supports a character error level of not more than 0.2% in network
conditions that are possible to use for voice calls.
6. Use a method that can indicate where text may have been lost.
7. Allow simultaneous speech and text in calls without requiring user actions for alternating between
speech and text.
a. To allow people (especial y elders) who can speak but not hear or hear clearly and who
often cannot type well or at all, to speak to 9-1-1 but get text back from 9-1-1 center.
b. To allow 9-1-1 centers (or callers) to mix text with speech when noise makes it hard to
understand specific words or instructions
c. To allow captioned telephony (where the cal er receives both voice and text captions back
from 9-1-1 center coupled to text caption relay)
d. To enable 9-1-1 services to perceive the background audio from the place of the
emergency situation (while texting is going on) in order to assess the situation rapidly.
8. Support at least ‘erase of last character’ and ‘insertion of line break’ as edit functions.
9. Provide possibility to have calls with TTYs, using calling with the destination phone numbers
between the devices of each environment.
a. TTYs are only able to dial numbers, and are expected to reside in PSTN networks using
phone numbers as identification.
10. Provide possibility to have calls directly with legacy PSAPs who communicate in TTY mode.
11. IP-based TTY replacement (voice and real-time text) is able to interoperate with IP-based total-
conversation devices (voice, real-time-text and video)
12. Enable multi-party calls, with mixing and distribution of both text and audio in the call to other
13. Enable creation of text based IP-relay services for this type of device, and let calling be based on
direct dialing the destination.
14. Initiate the media in a call with a negotiation protocol, so that each side can detect if real-time text
and other media will be supported in the call.
15. Make generation of DTMF tones possible in the audio channel.
16. Arrange visual indication of audio strength in the audio channel.
17. Provide alerting on incoming calls in accessible ways, selectable between visual, tactile and audible
- EAAC Draft TTY Transition report - March, 2013 - Page 22-
18. Provide functionality common for telephony users, e.g. answering machine functionality in real-
time text and audio.
9.3 Standards and technologies in IP networks suitable for TTY replacement
The functional requirements specified above can be met in IP networks through application of existing
standards and provide a good replacement for the TTY. The protocols can be used for interoperability
between service providers as well as for communication with terminals within each service provider's
The recommendation is to use the following specification as the primary set of standards for
interoperability between SIP based accessible communication providers and for replacement for the TTY.
9.3.1 For native SIP
For Native SIP protocol environments that can be used in over-the-top services on wireless networks and
in broadband networks the protocol set is:
• IETF RFCs 3261 SIP  for call control
• ITU-T Recommendation T.140  for real-time text presentation and IETF RFC 4103  for real-
time text transport.
• Suitable audio and wide-band audio codecs commonly used in the implementation environment
and supported by NG9-1-1 PSAPS, e.g. the narrow-band codec ITU-T G.711  to assure
interoperability and a wide band codec included in NG9-1-1.
This case is also described in RFC 5194 .
9.3.2 For IMS used in wireless LTE networks and fixed broadband networks
For IMS, the protocol set is similarly:
• IETF RFC 3261 SIP for call control as contained in the IMS Multimedia Telephony service.
• 3GPP TS 26.114 IMS Multimedia Telephony Codec Considerations for media, including:
o ITU-T Recommendation T.140 for real-time text presentation and IETF RFC 4103 for real-
time text transport.
o AMR and AMR-WB audio.
This set of protocols is collected in a profile defined by the GSM Association, and called GSMA PRD IR.92
“IMS Profile for Voice and SMS” . The real-time text part is described in IR.92 Annex B.
9.3.3 For XMPP
Work is in progress with a standard for real-time text based on the XMPP protocol, cal ed XEP-0301 In-
band real-time text . If the standardization process is successfully completed, it can be a base for TTY
replacement in the XMPP environment properly complemented with audio (with preference for wide-band
audio codec). The native way for adding audio in the XMPP environment is by use of XMPP extension XEP-
0166 Jingle  and XEP-0167 Jingle RTP Sessions .
- EAAC Draft TTY Transition report - March, 2013 - Page 23-
9.3.4 Use of other real-time text protocols
Other real-time text protocols than the above may be used within each service provider's network and
between service providers, as long as the functional goals are met and the protocol set described above is
supported as a fallback for cases when other protocols are not agreed.
It is preferable that terminals also use the same set of protocols as is used between the service providers.
That approach creates the best opportunity for an efficient market of components supporting the TTY
An example of a possible future protocol environment for implementation of calls with real-time text and
voice is in web-based technologies. Standards work is currently going on in this area, called IETF RTCWEB
and W3C WebRTC. Specifications on how to handle real-time text in this environment and how to combine
it with audio (and video) as well as arrange interoperability with other environments and NG9-1-1 is
9.3.5 Routing and addressing by number
Routing mechanisms based on IETF RFC6116 ENUM  can be used for addressing based on numbers in
the international number plan. Other addressing formats may be used within each platform for
9.3.6 Example from another region
When designing a system for TTY replacement, it may be of guidance to look at how the situation is
handled in other countries. Therefore it is described here how this was done in Sweden.
Sweden has a telecommunications equipment distribution program for accessible communication with
some similarities with the TEDP in USA. County council departments procure accessible communication
devices and services based on a joint procurement requirements specification developed by the Swedish
Institute of Assistive Technology, SIAT .
Earlier, PSTN textphones (same idea as TTYs, but with different modem technology) dominated the
procurements, but since around 2003, SIP based Total Conversation devices and softphones dominate
accessible communication procurement in Sweden.
The procurement specification has a SHALL-requirement for interoperability between Total Conversation
devices and PSTN textphones, so that the real-time text and voice functionality of Total Conversation
devices is used also for cal s with PSTN textphones and IP based textphones.
Earlier, Total Conversation terminals having dual network connections, one for PSTN text telephony, and
one for IP connections were common. Lately, it has instead become more common to provide access to
cal s with PSTN textphones through gateways included in the Total Conversation services.
Also lately (2012), it has become common to not procure PSTN textphones anymore, but instead buy IP
based textphones. Both Total Conversation devices and IP based textphones have SHALL requirements for
interoperability through SIP for call control, IETF RFC 4103 for real-time text and common audio codecs for
audio. Both softphones, hardware based products and mobile solutions occur among the IP based
textphones and the Total Conversation devices.
- EAAC Draft TTY Transition report - March, 2013 - Page 24-
Direct access to 112 emergency services is currently provided through the interoperability with PSTN text
telephony. The 112 PSAPs have access for PSTN text telephony and receive real-time text calls from both
the PSTN textphones, the IP based textphones and the Total Conversation devices.
The conclusion is that Sweden is on the way with the textphone replacement evolution and the main
mechanism is a joint procurement specification with strict interoperability requirements between the old
and the new.
9.4 Access to NG9-1-1
The protocols described above for user and service provider usage are also fully in line with the NG9-1-1
specifications. The media chapters in the NG9-1-1 related specifications IETF RFC 6443  and NENA i3
technical specification  both specify use of IETF RFC 4103  for real-time text support.
NENA i3 Technical Specification 08-003  specifies that all PSAP positions shall be capable of handling
real-time text in IP-based SIP calls according to RFC 4103 , together with corresponding specifications
for audio and video and text messages. For TTY access, this specification indicates two options, either
conversion between TTY and RFC 4103 at the border of the PSAP, or handling IP carried audio based TTY
coding in the PSAP work stations. NENA i3 also refers to IETF RFC 5194  for the real-time text
communication and TTY interoperability.
The Internet Engineering Task Force IETF specifies in RFC 6443 "Framework for Emergency Calling Using
Internet Multimedia"  that SIP calls with real-time text as specified in IETF RFC 4103  shall be
supported together with corresponding specifications for audio and video and text messages.
The NG9-1-1 implementations should be developed so that:
• Real-time text with good real-time flow is implemented in the PSAPs.
• Full support of simultaneous real-time text with voice and video included.
• Recording of all media in the call is supported.
• Support for multi-party calls, and call transfer is included for all media.
• Support for invocation of assisting services with text and voice is included.
• Guidance for selection of text transmission method in callbacks is provided.
• Guidance for supporting the differences in functionality between TTY, TTY replacement and text
messaging is provided.
The IMS IP Multimedia Subsystem, an environment for IP based services specifies also that RFC 4103 shall
be supported for emergency calls. This is specified in 3GPP TS 22.101  by referring to the IP based
variant of Global Text Telephony GTT implemented by IMS Multimedia Telephony 3GPP TS 26.114. 
and contained in the profile GSMA PRD ir.92  including its Annex B.
Work is underway for multimedia emergency services in the Multimedia Emergency Services (MMES) work
in 3GPP. The MMES requirements are specified in section 10 of 3GPP TS 22.101 V11.3.0 (2011-09), 3rd
Generation Partnership Project; Technical Specification Group Services and System Aspects; Service
Aspects; Service Principles (Release 11) 
For emergency service access, the procedures for location information provision and call routing described
in IETF RFCs 6442 and 6443 must be implemented by the terminal and the service it is used in.
- EAAC Draft TTY Transition report - March, 2013 - Page 25-
As long as no IMS addition is published for NENA i3 emergency service access, the service must follow the
specification in IETF RFC 6443. The basic functionality of IMS emergency calling is specified in 3GPP TS
22.101 in line with the specification above. ATIS has current work in progress for North American IMS
based emergency cal s that is expected to complete in 2013.
Since the proposed TTY replacement is interoperable with Total Conversation, the advice expressed in ETSI
TR 103 170 Total Conversation Access to Emergency Services  which has been validated in Europe may
provide the template needed for planning PSAP access for the TTY replacement and should be considered
and evaluated on North American networks due to similarity of equipment.
9.5 Access to legacy 9-1-1 and transition from legacy to NG9-1-1
During a period both NG9-1-1 ready PSAPs and legacy PSAPs will exist. Users of the TTY replacement must
not be left without access to emergency services when the geographically most appropriate PSAP is a
legacy PSAP that handles only legacy TTY as text protocol.
There are at least three possible solutions.
1. The TTY replacement service providers are required to provide TTY interworking, for the calls between
TTY replacement and legacy PSAPs.
2. The NG9-1-1 introduction is made so that NG capable PSAPs take TTY replacement calls on behalf of
3. An emergency call transport network is arranged for handling the protocol harmonization, routing,
adaptation to the kind of PSAP to receive the call, and any needed invocation of assisting services. This
network can be made as an extension on the transport network described in the text-to-9-1-1 report.
There are severe limitations with TTY functionality compared to real-time text that wil cause limited
usability in interoperation between the TTY replacement and legacy PSAPs. The most apparent will likely
be the lack of simultaneity of text in both directions and of text and voice. Users and PSAPs wil need
application support to obey the turn-taking habits that are needed for successful TTY communication.
However, organization of PSAPs working on behalf of other PSAPs may cause organizational complexity
that will be hard to overcome. One of these complexities is to keep track of the expected load from TTY
replacement calls in the NG9-1-1 PSAP. Another complexity is that if this is selected to be the only
supported method, then al legacy PSAPs need to have an agreement with an NG9-1-1 PSAP, and that it
will be impossible to start deploying the TTY replacement before NG9-1-1 PSAPs are implemented.
EAAC recommends that the third method for handling the transition period until full NG9-1-1 deployment
are enabled should be examined with highest priority, and that therefore TTY replacement providers are
required to cooperate in establishing the transport network for routing, adaptation and assisting service
invocation of emergency calls.
The EAAC also suggests that a feasibility study is performed to show if it is realistic to provide TTY
interoperability with legacy PSAPs with support for overcoming the functional differences between TTY
and TTY replacement.
- EAAC Draft TTY Transition report - March, 2013 - Page 26-
9.6 Methods for interoperability between TTY and IP based solutions
The most convenient method for interoperability between the TTY and the IP based solutions would al ow
the TTY user to dial a number and reach the IP user and communicate in real-time text and voice. Equal y,
the IP user would dial the number of the TTY user, get connected and communicate.
Gateways in the border between the networks would convert between the transmission and coding forms
for real-time text and voice in the two environments.
It is feasible to produce the required type of gateway action between TTY cal s and IP based cal s with IP-
based real-time text and voice. However, there are apparent obstacles against providing the described
simplicity in reality. The problem concentrates around how to get the required gateway functionality
included in the cal where it is needed.
1. The TTY gateway is needed at the point of conversion to IP. If the cal is al owed to first be converted to
IP and then to RTT somewhere within the IP network then the path where the TTY audio is transported
over IP is a risky path. Audio may be more or less corrupted, and thereby text corrupted.
2. The TTY users are used to moving their equipment between different PSTN connections. The total
number of VoIP gateways in homes, office networks and carrier networks is too high for it to be realistic to
require all VoIP gateways to implement TTY gateway functionality. This is because the VoIP networks had
some years without regulation, and then the VoIP gateways were deployed without TTY gateway
functionality. A TTY call cannot be distinguished from a voice call by any other way than to detect the
typical TTY modem signal timing and frequencies. When answering a call, it is even needed to prompt the
connection with an answering phrase in text in order to cause the calling party to send characters so that a
possibly connected TTY is detected. This makes it slow and resource consuming to detect TTY signals in
VoIP gateways. On the IP side, the opportunities are better. Capability for real-time text is indicated in
session set-up, and requirement for text can be indicated.
Because of this, the TTY owners cannot anymore expect to be able to connect their TTY at any phone
connection point, but rather keep it at a connection where it has proven to achieve suitable transmission
3. Interconnected VoIP services have phone numbers so they should be possible to call and be called if
used for a TTY replacement.
4. The users of the TTY replacement may not be interested to pay extra fees that may be needed by the
service provider to finance the provision of TTY interoperability if the functionality is put on the TTY
Routing and conversion requirementsPSTN calls to the phone number of the IP based TTY replacement terminal shal be routed through a VoIP
gateway with capabilities for conversion between TTY and the TTY replacement. When no text
transmission is going on, voice should be al owed to pass through. The calls to and from the TTY
replacement user may be detected by the service provider to require TTY conversion, so that functionality
can be activated only for calls to and from TTY replacement users.
Calls from the IP based terminal to a PSTN number shal be routed through transcoding equipment for
conversion between TTY replacement and the TTY.
- EAAC Draft TTY Transition report - March, 2013 - Page 27-
The transcoder shall monitor the connection passively. As long as no text flows in either direction, audio
should be al owed to pass through. When text from either side is detected, it shal be converted between
TTY audio coding in the audio channel and the TTY replacement coding of text in a text channel. Text
transmission towards the TTY should only be sent when no text is received from the TTY.
Handling differences in speed, simultaneity and character sets between the solutions.The conversion mechanism needs to adjust for limitations in TTY communication. TTY handles only one
direction of text at a time, cannot handle voice while text is transmitted, is slower than many users type,
supports a limited character set and creates a risk of corruption of up to 72 characters in sequence after a
single character error. These limitations must not hamper a TTY replacement technology when
communicating with other IP based communication tools. An indication of the limitations should be
provided to the user of the TTY replacement technology during sessions with TTYs. The conversion
equipment needs to guide users to stay within the limitations so as to maintain TTY compatibility. For
example, the conversion equipment should store text on the way towards the TTY while the TTY user is
transmitting and make other efforts to span the functionality gap between TTY and TTY replacement.
The conversion equipment should also protect the user of the TTY replacement from receiving TTY tones at
9.6.1 Alternative solutions for interoperability between TTY and TTY
There are a few alternatives for the possibility to have calls between TTY and TTY replacements.
a. Require all VoIP gateways both residential and carrier and office located to introduce support for a
standard for reliable TTY transmission through IP network segments for communication between
TTYs, and conversion between TTY and a TTY replacement protocol for communication between
TTY and IP networks. Even if this is what current regulation requires, it does not look feasible. Too
many VoIP gateways in homes, offices and networks are already deployed without these features
for it to be realistic to require this upgrade.
b. Define small single user gateways for TTYs, which are used local y for connecting TTYs to the VoIP
network and use the TTY replacement protocols. Promote deployment of these single user
gateways for moving TTYs to VoIP subscriptions. For locations with both PSTN and IP connection,
the gateway can select the proper network for each call and activate conversion only on IP calls.
For connection only to VoIP networks, let these gateways (against advice elsewhere in this report)
use best effort audio transmission of TTY signals when they have calls with legacy TTYs.
This solution is mainly of interest for users who want to keep their traditional TTY equipment.
c. Define gateways for conversion between TTY and TTY replacement that are deployed by service
providers of the TTY replacement. When cal s are made between PSTN and a user provisioned to
have TTY replacement, then the gateway functionality is activated seamlessly through routing
analysis in the network. NG9-1-1 calls would need to be regarded as going to a user with registered
interest in TTY calls.
d. Gateways can be arranged for two-step dialing between the two environments. First a call is made
to the gateway where the gateway asks by text communication what number or address the call is
going to be made to. When the cal is completed, the gateway functionality is activated. An
organization already involved in TTY communication, e.g. the TRS services, could be assigned the
task to set up this kind of gateways. . Relay operators would not be involved. The call would go
- EAAC Draft TTY Transition report - March, 2013 - Page 28-
through completely automated without any human intervention. It is just suggested that the same
entities (relay operators) would maintain these automated gateways. This must be regarded a last
resort solution if the more automatic gateway alternatives are not selected. Two-step dialing
through gateways has functional limitations that make it less attractive. One is that electronic
phonebooks cannot be used for the destinations of the cal s. In addition it will be neigh on
impossible and impractically expensive to contact all the TTY users and teach them to dial two
numbers now to make a call when they used to only have to dial one.
e. Ignore the need for interoperability and promote the view that persons interested in
communication with TTYs and TTY replacements should have devices and network access for both
types of communication. This involves providing all TTY users with an IP line, or requiring that they
purchase one on their own. It also causes problems for areas where landline IP is not available
even if the National Broadband Plan is addressing the issue of broadband IP coverage everywhere,
but it may also be a long time before the last PSTN line is vanquished.
Recommendation:The TTY Transition subgroup of EAAC recommends FCC to further explore all
alternatives regarding market interest and costs involved. Without deeper analysis, alternatives b and c
together seems to be the most attractive solution.
9.7 Other session control protocols than SIP
If another session control protocol than SIP is used within a service, it must be specified by the
organization responsible for specifications for the environment how Real-Time text shal be implemented
in that environment and how NG9-1-1 calls shall be handled.
For interconnected VoIP services, it must be specified how real-time text is negotiated and how other
aspects of interoperability with SIP environments are handled.
For the rare case that NENA i3 technical specification is extended for a session control environment with
real-time text, this new way to interact with NG9-1-1 may be used for emergency service sessions with
real-time text according to the target session control environment.
In most cases however, conversion to the protocols already supported by NENA i3 must take place in the
connected service. This is valid both for session control, media handling, multi-party call handling, call
transfer, additional information, location information and routing.
One protocol environment that is mentioned as possible for a future extension for next generation
emergency calling in both IETF RFC 6443 and NENA i3 technical specification is the XMPP protocol. This is a
wide spread protocol for instant messaging. Since work is in progress with a specification of real-time text
in that environment, called XEP-0301 , this may become a possible alternative way for TTY
replacement calls. However, as long as no extension for XMPP is ready for NENA i3 NG9-1-1 access, all
emergency cal s must be provided using SIP  through external conversion by the service provider.
Whatever solution is selected, standardization needs to be forceful in this area if any use of XMPP at all for
emergency calling shall be made possible.
9.8 Solution proposals for interoperability between different IP based
It is recommended that interoperability between communication providers be handled as fol ows:
- EAAC Draft TTY Transition report - March, 2013 - Page 29-
• If two IP based communication environments have interoperability for voice calls, they should also
provide interoperability for text simultaneously with voice in these same calls.
• If at least one of the providers is using SIP as the call control protocol, at least real-time text
according to IETF RFC 4103 is to be provided as an interoperability protocol for text and used as
the TTY replacement if the service providers have no mutual agreement to use another
interoperability protocol for real-time text.
• If none of the environments use SIP as call control protocol, an interoperability protocol for real-
time text needs to be specified by the providers.
Any differences between the real-time text presentation standards used need to be catered for in a best
effort way. There may be differences in supported character sets, editing features, scope of erasures and
corrections, use of emoticons, indications of errors, multi-party handling etc., that may not be possible to
translate exactly between the environments.
10. Non real-time text alternatives; Applicability and functionality.
Lacking convenient mobility, functionality and mainstream availability of TTY communication, many users
in need of text-supported communication have decreased or ceased use of the TTY. A multitude of other
solutions are used instead.
Many of these systems are based on transmission of completed text messages, in contrast with the
continuous flow of characters used by the TTY and real-time text technologies.
Also, many users prefer to move from TTY communication to use of video communication for sign
language, sometimes in combination with real-time text or text messaging.
In these moves, the users currently sacrifice some functionality in order to achieve mobility, higher
functionality and connectivity with the people they want to contact.
The typical sacrificed functions are:
1. No direct 9-1-1 access, instead needing to text to hearing friends to ask them to call 9-1-1, or
finding other inferior solutions.
2. No direct communication with anyone in the International Number Plan, instead using a number
of communication tools and services, and needing to keep track of who is user of what service in
order to maintain a functioning human communication network.
3. No immediate communication in real-time text, instead needing to col ect typed text in messages,
causing delays and risk for crossed dialogue.
4. No communication with the users who are using only TTY for their text based communication,
because interoperability between TTY and new services has not been implemented.
The patchwork of services making up the communications functions includes:
- EAAC Draft TTY Transition report - March, 2013 - Page 30-
1. Proprietary Instant Messaging services, for transmission of text messages, nowadays usually
possible to combine with audio and video, but only working within its closed user group.
2. Standardized Instant Messaging services, mainly based on the IETF XMPP standard, sometimes
providing combination Instant Messaging with audio and video.
3. Short Message Service SMS in the mobile phone systems, offering a way to send text messages to
other mobile phones. There is ongoing Joint ATIS & TIA work to standardize a solution for SMS to
4. IP-relay. Text relay services based on IP technology enabling conversion between voice telephony
and text communication, often in the form of real-time text. This type of service provides numbers
in the North American Number Plan to the text users for communication with hearing users. 9-1-1
calls are allowed and end up as voice calls in the PSAPs. Most of the IP Relay services use real-time
text communication, while some use messaging.
5. Video phones, Video Relay Services and Total Conversation Services, provide possibility to mainly
use sign language instead of text for the communication. This option is preferred by many users
because of the more rapid flow and ease of communication that can be achieved with sign
language compared to typing the conversation. However it is another mode of communication and
further handled in other parts of the EAAC reports. A considerable number of users are not sign
language users and there are situations when video communication is not feasible, technically,
economically or by the situation of the user. Therefore sign language users many times are also
text communication users and rely on provision of modern text communication facilities.
6. IP based captioned telephony services. The captioned telephony services adding real-time text to
voice phone calls are available in IP technology and can be used in 9-1-1 calls for users who prefer
to talk, but need to read a rapidly created real-time text representation of the answers from the
voice phone user.
10.1 The gap between mainstream provision and accessibility
As long as the mainstream provision of services does not meet accessibility requirements, there will be a
gap between these types. Only when the mainstream services are made accessible, this gap will be closed.
As long as the gap exists, some users wil select to use the accessible services, some wil select to use the
mainstream services, and some will use a patchwork of accessible and mainstream services to fulfill their
Real-time text is a feature that has potential to become a mainstream improvement of text messaging
services because of its more rapid delivery of text during typing and the resulting better experience of
contact and efficiency of the communication. The real-time text feature has however not yet received
widespread acceptance in mainstream services. Therefore a gap exists between text messaging services
and real-time text.
When a service with real-time text and voice is offered as a replacement for TTY, it is important for its
success that it gets many users, good functionality and good interoperability with other services.
Thoughts should be given as to what degree the already existing mainstream text messaging services will
be sufficient or not as replacement of the TTY. Many TTY users are also users of such services.
The following facts speak for a conclusion that text-messaging services would or would not be sufficient as
- EAAC Draft TTY Transition report - March, 2013 - Page 31-
Would be sufficient:
a. Many Instant Messaging services are today combined with voice and video options.
b. It is possible to exchange information in text through the service.
c. The most popular services have many users.
d. Two text-messaging standards are specified for NG9-1-1 emergency cal ing by both IETF and
NENA (SIP MESSAGE and MSRP).
Would not be sufficient:
e. Earlier efforts to create interoperability between TTY and text messaging have failed because
the TTY user expects more rapid action and has a tendency to disconnect thinking that there is
an error when no text shows up in a long time while the message user composes a message.
Automatic user guidance by text to avoid this is possible, but not real y feasible because it
dilutes the real conversational text output on the TTY.
f. It is true that two SIP-based text message protocols are specified in the IETF and NENA i3
specifications for next generation emergency services, but enterprise use of SIP-based instant
message is declining in popularity, there are very few consumer services using these two
protocols, and there is no trend towards use of SIP-based instant messaging protocols for
g. Most text messaging services use proprietary methods for messaging, and would need to
establish translation mechanisms to use the standards for the emergency calls.
h. The waiting time during composition of messages can be experienced to be very stressful for
both the sender and the recipient, especial y in an emergency situation. The real-time text
flow corresponds much better to a natural efficient dialogue between humans.
i. The slowness of messaging is also especially stressful and causing inferior access if used in
relay services and in participation in conferences by transcription services.
j. The risk for cross-posting and resulting confusion is high with messaging (reported by EENA in
a report on SMS for 112 emergency services).
k. Even in everyday communication, it has become a common habit among text messaging users
to cut their sentences in short phrase fragments and send them in order to keep the other
side informed. Thus, a pseudo-real-time text method has been created by manual action of
text messaging users. It would better suit these mainstream users if the system automatically
sent the text as typed as it is done in real-time text. This observation makes it less attractive to
propose text messaging as a replacement for TTY when it is already seen not really fulfilling its
mainstream users' needs.
l. Connections to visual or tactile alerting systems are needed for incoming calls to user
terminals. In the PSTN this is done on the phone or directly off the phone line. With VoIP
based communication the old types of ring signals are not commonly used and other ways to
connect o alerting devices and systems need to be provided by terminals or service providers.
This is seldom catered for in the stationary variants of the implementations for the text
At best, a TTY replacement would also become an appreciated mainstream feature. It builds on
mainstream technology. Currently text messaging services are more wide spread as mainstream solutions
- EAAC Draft TTY Transition report - March, 2013 - Page 32-
than real-time text but do not meet all functional requirements of TTY users even if complemented with
voice. Observations indicate that messaging users adopt a pseudo real-time text behavior to make text
messaging more usable for conversation. That is an indication that real-time text could find widespread
usage. However, many earlier TTY users are likely text-messaging users now and will not immediately
adopt the TTY replacement solution. Therefore, the plans to include also text messaging in NG9-1-1 should
be encouraged. Ways should be found to get service providers using text-messaging solutions connected
to the NG9-1-1 with the protocols specified by NENA/3GPP/ATIS-TIA/IETF/XSF.
Conclusion 1: Open standardized services with real-time text and voice should be provided as replacement
for TTY. The existing TTY mandate for VoIP phones should be removed for those phones that implement it.
Conclusion 2: The plans to also provide 9-1-1 access for users of Messaging applications should be
encouraged separately in order to provide 9-1-1 access for current users of these services.
11. Potential problems with the NENA i3 approach for TTY handling.
The main method to handle TTY communication in NG9-1-1 is specified in NENA i3 technical specification
 to be by converting between TTY tone carried text and text coded text in the IP environment according
to IETF RFC 4103 . This conversion is to be done external to the PSAP.
However, an option is described in NENA i3 technical specification; to carry TTY tones in IP transported
audio channels up to the PSAP workstation. This option introduces a multitude of risks and considerations.
1. Having two ways to handle real-time text creates complexity and increased testing for verification
of proper functionality.
2. The sensitivity for packet loss and malfunctioning line echo cancellers for audio carried TTY makes
this option risky. It could potential y be solved by application of any of the standards for securing
audio transport of TTY specified in chapter 8, but it must be questioned if it is feasible to introduce
3. Even if a PSAP could arrange for reliable transport of TTY tones internally, the calls sometimes
need to be transferred to other PSAPs or external assisting organizations. That causes even higher
requirements on planning and implementation efforts to guarantee transmission quality. The
planning must take congestion at major catastrophic situations into consideration, when packet
loss easily is increased over the limits required for TTY audio transmission.
4. Call recording is done in the NG9-1-1 system. If TTY traffic is recorded as audio, there is a risk that
decoding of the recording will show slightly different text than what the PSAP saw in the actual
Regarding these foreseen problems, the EAAC TTY Transition subgroup emphasizes the recommendation
T6.3 of EAAC, to convert TTY to IP carried real-time text at the point of entry to IP networks of the TTY
12. Current and emerging policy and regulation support
Acts and regulations in USA require accessible communication and TTY interoperability in a number of
areas. This is a brief overview of such regulation.
- EAAC Draft TTY Transition report - March, 2013 - Page 33-
Note that this chapter contains extracts of acts and regulations. For full analysis of these acts and
regulations, the extracts need to be read in their original environment.
12.1 Twenty-First Century Communications and Video Accessibility Act of
This is the act that sets the charter for the EAAC, and requires EAAC to recommend protocols for reliable
accessible 9-1-1 calls, timelines for TTY transition and recommendations on more efficient communication
means to replace the TTY.
12.2 DOJ regulation and guidance on accessible emergency services and TTY
access to 9-1-1.
This regulation sets rules for how PSAPs shall handle TTY.
All PSAP workstations shall be able to handle TTY calls using the TIA 825A standard . Since TTY calls are
often silent when calling, there are rules for how to detect if silent calls are calling TTY users.
12.3 Section 255 of the telecom act
Section 255 is the communications equipment part of the telecom act. The currently valid version requires
equipment marketed in USA to be interoperable with TTY or let TTY signals through undisturbed.
Sections 255 and 508 have similar guidelines. See next section.
12.4 Section 508 of the rehabilitation act
Section 508 is the corresponding act for accessible public procurement, with similar requirements as
section 255 but applicable to equipment procured by public authorities.
The detailed rules are found in the guidelines to application of these acts.
The current section 255 guidelines in force are found at:
The current section 508 guidelines in force are found at:
Extracts about TTY from section 255/508 guidelines:
------ copy --------------------------------
§ 1193.3 Definitions.
An abbreviation for teletypewriter. Machinery or equipment that employs interactive text
based communications through the transmission of coded signals across the standard
telephone network. TTYs can include, for example, devices known as TDDs
- EAAC Draft TTY Transition report - March, 2013 - Page 34-
(telecommunication display devices or telecommunication devices for deaf persons) or
computers with special modems. TTYs are also called text telephones.
§ 1193.51 Compatibility.
(d) TTY connectability. Products which provide a function allowing voice communication and
which do not themselves provide a TTY functionality shall provide a standard non-acoustic
connection point for TTYs. It shall also be possible for the user to easily turn any microphone
on and off to allow the user to intermix speech with TTY use.
(e) TTY signal compatibility. Products, including those providing voice communication
functionality, shall support use of all cross-manufacturer non-proprietary standard signals
used by TTYs.
-----end of copy---------------
12.5. Draft revised section 255 and 508
Both section 255 and 508 guidelines described above are under revision.
The U.S. Access Board is developing the new guidelines.
The current drafts for the common guidelines are found at:
The draft sets out basic functional requirements and identifies protocols for usage for interoperability of
real-time text within the PSTN and within IP networks and between these network types.
This is the current draft wording, most essential for the TTY replacement discussion.
------------------copy from draft 255- 508 guidelines, 2011 draft version
E101.2 Equivalent Facilitation.The use of an alternative design or technology that results
in substantially equivalent or greater access to and use of data and information by individuals
with disabilities than would be provided by conformance to a requirement in Chapters 4
through 6 of this document is permitted.
. . .
408.6.3 Interoperability. Where ICT interoperates outside of its closed system, or
where ICT connects to other systems, ICT shall conform to 408.6.3.1 or 408.6.3.2.
408.6.3.1 PSTN. Where ICT interoperates with the PSTN (Public Switched
Telephone Network), real time text shall conform to the TIA 825-A (incorporated by
reference in Chapter 1) Baudot standard for TTY signals at the PSTN interface.
- EAAC Draft TTY Transition report - March, 2013 - Page 35-
408.6.3.2 VoIP Using SIP. Where ICT interoperates with Voice over Internet
Protocol (VoIP) products or systems using Session Initiation Protocol (SIP), they
shall support transmission of real time text that conforms to RFC 4103 (incorporated
by reference in Chapter 1).
-----------------end of copy----------------------------------------------------------------------------
12.6 Wireless TTY regulation by FCC
Wireless communication devices are required to be possible to use for calls with 9-1-1 according to the
wireless TTY regulation from FCC 47 CFR 20.18.
--------------------------copy from wireless TTY regulation------------------------------
47 CFR 20.18 ( Wireless TTY regulation ):
(a) Scope of section. The following requirements are only applicable to CMRS providers,
excluding mobile satellite service (MSS) operators, to the extent that they:
(1) Offer real-time, two way switched voice service that is interconnected with the public
(c) TTY Access to 911 Services. CMRS providers subject to this section must be capable of
transmitting 911 calls from individuals with speech or hearing disabilities through means other
than mobile radio handsets, e.g., through the use of Text Telephone Devices (TTY).
----------------------------end of copy------------------------------------------------------
12.7 FCC TRS regulation.
The FCC has set up regulations for service provision of a number of relay service types. Some of them are
valid for usage with TTY replacement communication. What is needed for TTY replacement use of relay
services is most easily established by modification of the regulation for IP relay services, so that the calls to
emergency services will be according to NG9-1-1 technology.
The TTY Transition subgroup of EAAC recommends the TRS rules to be updated to specifical y support relay
calls based on the protocols used in accessible interchange with NG9-1-1.
12.8 TEDP Technology distribution programs.
TTYs and other accessible communications solutions are provided to users through a network of
Telecommunications Equipment Distribution Programs (TEDP).
- EAAC Draft TTY Transition report - March, 2013 - Page 36-
When defining TTY replacement technology, it is important to coordinate with the TEDPs, so that users in
the TEDP get opportunities to use the TTY replacements. This coordination can be sought through the
TEDP Association TEDPA ahttp://www.tedpa.org/">t www.tedpa.org
12.9 Conclusion on acts and regulations
Based on the experience with the existing TTY rules, the EAAC recommends that any TTY replacement
requirements should ensure that:
• Interoperability with TTYs at the far end of calls is supported, where the cal s terminate on the
PSTN, including access to legacy 9-1-1.
• The functionality of the TTY replacement described in this document is provided in both wireless
and IP wireline environments.
• IP wireline text formats are transcoded to TTY format where IP networks connect to the PSTN
(where only the TTY format is supported).
• The protocols recommended in this document are supported to ensure reliable NG9-1-1 calls.
13. Concluding Findings and Recommendations
In conclusion, the EAAC Subgroup for TTY transition finds and recommends the fol owing:
a. TTY usage in the PSTN is decreasing with around 10% per year but has still approximately 12% of
the accessible communication traffic in USA, 36% of the text relay communication, and is used for
about 20,000 direct 9-1-1 calls per year (See Appendix A.).
b. Even for persons who have ceased using the TTY for everyday cal s, the TTY is often kept because it
is the currently only direct way to reach 9-1-1. This is an unsatisfactory situation.
c. The TTY provides calls in voice intermixed with a limited variant of real-time text in the fixed PSTN
network and is used in communication with persons with deafness, deafblindness, hearing
impairments and speech related disabilities.
d. Consistent implementation of a wel -defined "TTY replacement" as defined in section 9.2 with
higher functionality real-time text, simultaneous voice, and better mobility, is required to fill an
important need in accessible communication for user-to-user calls, relayed calls (including
captioned telephony), and 9-1-1 calls. Deployment of such "TTY Replacement" should be
e. For ease of implementation, the protocols for this purpose included in NENA i3 Detailed Technical
specification 08-003 and IETF RFC 6443 are also recommended for interoperability between
service providers when at least one makes use of IETF SIP for cal control.
The default set of protocols for interoperability is:
• IETF RFC 3261 SIP  for call control
• ITU-T Recommendation T.140  for real-time text presentation and IETF RFC 4103 
for real-time text transport.
• A suitable default audio codec, e.g. ITU-T G.711 .
f. For IMS, e.g. used in the wireless LTE environment, the profile specified in GSMA PRD ir.92 
including its Annex B specifies a similar set suitable to be used as TTY replacement in that
- EAAC Draft TTY Transition report - March, 2013 - Page 37-
environment. It also contains SIP for call control, and RFC 4103 for real-time text, but other
solutions for audio as specified in 3GPP TS 26.114 Multimedia Telephony, Codec Considerations
. The deployment of this technology should be encouraged. A suitable combination with video
as specified in GSMA PRD ir.94  should be considered.
Work underway for multimedia emergency services is the Multimedia Emergency Services (MMES)
work in 3GPP. The MMES requirements are specified in section 10 of 3GPP TS 22.101 V11.3.0
(2011-09), 3rd Generation Partnership Project; Technical Specification Group Services and System
Aspects; Service Aspects; Service Principles (Release 11)
g. Other protocol environments may define their TTY replacement with other protocols as long as the
functional goals are achieved and interoperability is established to the same degree as
interoperability in voice is established. Service providers using such environments should be
encouraged to deploy a wel -defined TTY replacement in their environment including
interoperability with SIP and NG9-1-1.
h. For interoperability of calls between the current TTY in PSTN and the TTY replacement it is most
convenient for the users if gateways are placed in the network, and calls are routed automatically
through them when the cal may contain text. Other alternatives are also considered, and the
subgroup recommends further investigation of the feasibility of the alternatives.
i. The recommendation T6.3 of EAAC, for TTY access to NG9-1-1 to convert TTY to IP carried real-
time text at the point of entry to IP networks is emphasized as the realistic solution. Taking tone-
coded TTY calls all the way to the PSAP has a number of negative side effects and should be
j. Coordination with the U.S. Access Board is recommended. It would be a good outcome if the
current revision of the Access Board’s Sections 255 and 508 Guidelines results in encouraging a TTY
replacement that can be used for NG9-1-1 calls as the current draft sections 255 and 508
k. The TRS rules should be updated to specifical y support relay cal s based on the protocols used in
accessible interchange with NG9-1-1, and include information requested in the NENA i3 technical
specification. The sections on third party invocation describe one scenario to be studied and
adapted by TRS.
l. The Telecommunications Equipment Distribution Programs TEDP should be involved in the TTY
transition, and get opportunities to plan its transition to include the TTY replacement.
m. The National Deaf-Blind Equipment Distribution Program (NDBEDP) should be involved in the TTY
transition, and get opportunities to plan its transition to include TTY replacement products
properly equipped for users with deafblindness.
n. For many users, it may be attractive to often use video, and occasionally use real-time text and
audio. Providers of videophones and VRS services should be encouraged to implement the TTY
replacement features in combination with video so that the same communications tool can be
used for a wide range of communication situations, including NG9-1-1 calls.
o. The plans in NENA to also provide 9-1-1 access for Instant Messaging users should be encouraged
separately from the TTY replacement activities in order to provide 9-1-1 access for current users of
these services related to both accessibility and general needs. But conversion from widely used
Instant Messaging systems by users and service providers to the relatively rarely used protocols
specified by NENA and IETF are needed to be applied by the service providers. Instant messaging
providers should also be encouraged to introduce real-time modes of text communication as well
- EAAC Draft TTY Transition report - March, 2013 - Page 38-
as combination with voice in the same session. During the EAAC work it has been shown that
mainstream users would appreciate that.
p. A timeline of 12 years is proposed for the transition. 3 years for getting the TTY replacement
commonly available, 3 more years until no more legacy TTYs should be deployed, and 6 more years
until support of TTY can close down. This plan can be expedited or slowed down e.g. depending on
appearing problems in the general transition from PSTN to IP.
===== Two alternatives for Recommendation q ==================================
The EAAC could not come to agreement on formulation of Recommendation q about the wireless
solution. Two versions were created. They are presented below with the rationale for the versions
and why the other versions were not acceptable.
Differences are highlighted in bold.
===================Version 1 ============================================
q. It is recommended that both the industry practice and FCC regulations for all IP enabled telephony
move away from TTY and move to TTY replacement as defined in section 9.2. This includes
exempting any handsets (IP wireline or mobile) that implement a Section 9.2 compatible TTY
replacement functionality from any TTY attachment requirements. We do not recommend
dropping TTY requirements without replacing them with an equivalent requirement that would
meet the functionality of the TTY replacement. Far end TTY compatibility in 9-1-1 calls needs
however to be maintained until all calls from TTY replacements to 9-1-1 can be handled using the
NG9-1-1 protocols with TTY replacement functionality. The report describes three alternative
methods to reach this stage. It is recommended that a decision be made on what method should
be used to achieve this.
==================End of Version 1========================================
q) It is recommended that both the industry practice and FCC regulations for all IP enabled telephony
move away from TTY and move to TTY replacement. Far end TTY compatibility in 9-1-1 calls needs
however to be maintained until all calls from TTY replacements to 9-1-1 can be handled using the
NG9-1-1 protocols with TTY replacement functionality. The report describes three alternative
methods to reach this stage. It is recommended that a decision be made on what method should
be used to achieve this.
==================End of Version 2=============================================
Rationale for Version 1 and rationale for not being able to agree to Version 2:
Why Version 1:
Version 1 makes it clear what the term "TTY Replacement" means in the sentence, by tying the term back
to the consensus language in section 9.2 for what a TTY Replacement is. This includes the critical consensus
language that any replacement for TTY should provide real-time text capability mixed with voice and not
just replace TTY with messaging (TTY is real-time text mixed with voice on PSTN).
- EAAC Draft TTY Transition report - March, 2013 - Page 39-
We remind the FCC of the survey results which showed 45% wanting RTT, 22% wanting captioned
telephony (which requires RTT), etc. (see Section 4), as well as the results of the RIM study which showed
the large majority wanting RTT (as reported in the EAAC meeting in August 20111).
Version 1 also provides a strong incentive to implement a TTY replacement, because the older TTY support
requirement stays in place for a phone until a TTY replacement actually shows up on the phone (or an
equivalently enforced requirement for the replacement technology).
Why Version 2 was not acceptable:
First, Version 2 removes all references to 9.2 which describes what “TTY replacement” means. This raises
• If “TTY Replacement” does not mean what we agreed to in 9.2, what does “TTY Replacement” mean?
Version 2 does not specify what the other examples that would qualify as a TTY replacements would
be. Our concern is that a lot of time went into looking at what the old but versatile TTY did and what
the replacement would need to do to replace its function in the IP world. Dropping that list of
functionality could result in people proposing TTY replacements that were not real-time text (like the
TTY is), that didn’t al ow RTT mixed with speech on the same cal (like TTY does - and that is very
important especially for (but not limited to) older late-deafened users who cannot hear or type well,
but want to speak and have text back) and other important functions in the Section 9.2 list. There is a
great concern that there is resistance to a requirement for RTT, or RTT and voice on the same cal .
(Note that 9.2 does not require any particular technology be used for real-time text. Many different real-
time text technologies are described in section 9.3, and any could be used to meet 9.2. )
A second problem with Version 2 is that it deletes the sentence emphasizing that the current regulation
should not be dropped until there is an equally well enforced requirement that meets 9.2 to replace it. Or
that the requirement be kept and that phones be exempted that have TTY replacement functionality.
Consumers and other stakeholders are very worried that allowing removal of this enforced requirement
before a company builds a TTY replacement into their
IPbased voice systems will result in no mechanism
for real-time text on phones for many years, if at all.
Rationale for Version 2 and rationale for not being able to agree to Version 1:
appropriately raised questions about the existing rules or regulations related to the wireless TTY
requirement. The FCC should consider any modifications to the existing rules and regulations for wireless
TTY on a holistic basis that accounts for the limited use of TTY over wireless networks and handsets and
existing text based communications solutions.
=================End of rationales =============================================
- EAAC Draft TTY Transition report - March, 2013 - Page 40-
The means of "encouragements" to implement the recommendations and result in efficient and universal
deployment are left for the decision of the FCC, (e.g. regulation or other means).
14. Entities influenced by the proposals.
The proposals influence a large number of entities who need to get an opportunity to contribute wel to a
good and widespread solution. For example:
• TRS providers
• TTY producers
• Standards organizations
• Telecom Equipment Distribution Program
• National DeafBlind Equipment Distribution Program
• Mobile manufacturers
• Wireless carriers
• Wireline carriers
• Communication service providers
• Originating network providers
• Transport network providers
• Accessibility advocacy groups
There are two timelines of main importance for transition from the TTY.
1. The time when an IP based replacement technology can start to be used.
2. The time when the traditional TTY needs to be abandoned and replaced.
15.1 Timeline of an IP-based replacement.
The reasoning above indicates that the preferred solution is already standardized for the wireless VOLTE
environment using the profile GSMA PRD ir.92  with its Annex B, including interoperability procedures
for calls with TTYs. The timeline only depends on when that solution can be available in terminals and
It is realistic to expect that it will take 24 months to deploy the solution after completion of necessary
standards, resolution of implementation issues, and decision via the FCC NPRM process to recommend the
For Over-The-Top environments, such as SIP in the Internet, deployment can begin in small scale within a
few months after decision and in larger scale within 18 months after decision. Note that it is feasible to
- EAAC Draft TTY Transition report - March, 2013 - Page 41-
have video functionality in these terminals, so that full total conversation can be used in IP networks and
the limited audio and text functionality in calls with TTYs.
The requirements for both these environments are that there are vendors willing to provide terminals or
terminal software, communication services, interoperability services with TTYs, text relay services and 9-1-
1. The access to 9-1-1 may be done through the TTY compatibility function for legacy PSAPs and with NG9-
1-1 protocols for NG enabled PSAPs.
15.2 Timeline of TTY transition
The timeline for TTY transition is divided in three steps.
1. The time when a user can select between IP based functionality and legacy TTY.
2. A time when new TTYs should not be instal ed except in very special exception cases.
3. The time when TTYs need to be made obsolete.
These timelines are depending on how rapid rollout of all-IP networks is, and how many quality problems
appear in these networks. (Unless special IP-based TTY like devices are created that can sit on a PSTN line
and work in conjunction with special gateways to provide IP based telecommunication over PSTN lines – or
some similar such solution that allows removal of all TTYs before there is universal IP network availability.
Such devices should also work on IP lines so that they can continue to be used as PSTN-only places receive
The time when a user can select between IP based functionality and legacy TTY starts when the IP-based
solution is available. That is in limited areas and situations within a few months from decision.
If attractive robust and easily operated terminals are provided, there will be a natural migration to the IP-
based solution and eventual y the number of remaining TTYs so low that the support of them can be
ended. If no time pressure is put on the procedure because of appearing quality problems in the PSTN
network, the complete process can be al owed to take 12 years, with 3 years until TTY replacement
products and services are commonly available, another 3 years to the point when no more new TTYs
should be deployed and yet another 6 years until the support of them can be turned off. The time periods
are selected so that the natural reduction of TTY usage wil have been reduced to manageable numbers
when support is closed.
When the transition is complete, silent cal s by TTY users, without indication that there might be a text
user calling will not appear anymore. That can allow the PSAPs to modify their procedure to handle silent
calls to become less time consuming. Real-time text calls will still be silent, but they will be accompanied
by an indication that text is supported that can be used to alert the telecommunicator that text might be
needed. It is however urgent that the implementation of support for various new communication
modalities and media in NG9-1-1 does not cause new needs for time consuming prompting in case of silent
cal s. It is recommended that the procedures for silent calls in NG9-1-1 are designed early and automated
as far as possible.
When the support is turned off there may stil be 30,000 TTYs in use. It needs to be a col aborative task for
text relay services and equipment distribution programs to trace them down and suggest or provide
- EAAC Draft TTY Transition report - March, 2013 - Page 42-
For the Wireless TTY solutions, where the usage today is close to zero, a more rapid close of the current
system can be considered. The point in time can be as soon as there are deployed solutions for TTY
replacement following the functionality description in this document widely available in wireless networks,
maintaining TTY interoperability, e.g. for 9-1-1 calls ending up in legacy PSAPs
If no usability problems appear in the transition to IP networks, and all kinds of users are satisfied with the
TTY replacement solutions, the transition period can be made shorter if that is seen favorable.
GSMA PRD IR.92 "IMS Profile for voice and SMS"
GSMA PRD IR.94 "IMS Profile for conversational video service"
NENA i3 Detailed Functional and Interface Standards for the NENA i3 Solution
IETF RFC 3261 Session Initiation Protocol (SIP)
IETF RFC 4103 RTP Payload for text conversation
IETF RFC 4734 Definition of Events for Modem, Fax, and Text Telephony Signals
IETF RFC 5194 Framework for text-over-IP using the Session Initiation Protocol SIP.
IETF RFC 6116 The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation
Discovery System (DDDS) Application (ENUM)
IETF RFC 6443 Framework for Emergency Calling Using Internet Multimedia
TIA 825A A Frequency Shift Keyed Modem for Use on the Public Switched Telephone
TIA-1001 Transport of TIA-825-A Signals over IP Networks
ITU-T Recommendation F.700 Framework for Multimedia Service Descriptions
ITU-T Recommendation F.703 Multimedia Conversational Services
ITU-T Recommendation G.168 Digital Line Echo Canceller
ITU-T Recommendation G.711 Pulse code modulation (PCM) of voice frequencies
- EAAC Draft TTY Transition report - March, 2013 - Page 43-
ITU-T Recommendation H.248.2 Gateway control protocol: Facsimile, text
conversation and call discrimination packages
ITU-T Recommendation J.161 Audio and video codec requirements and
usage for the provision of bidirectional audio services over cable
television networks using cable modems
ITU-T Recommendation T.140 Protocol for multimedia application
ITU-T V.151 Procedures for the end-to-end connection of analogue PSTN text
telephones over an IP network utilizing text relay.
Access for 9-1-1 and Telephone Emergency Services. Department of Justice
3GPP TS 22.101 Service characteristics
3GPP TS 23.226 Global Text Telephony, Stage 2.
3GPP TS 26.114 IMS Multimedia Telephony Codec Considerations
North American Numbering Plan.
XEP-0167 Jingle RTP Sessions
XEP-0301: In-band Real-time text ( work in progress)http://xmpp.org/extensions/xep-0301.html"> http://xmpp.org/extensions/xep-
U.S. Access Board Information and Communication Technology (ICT) Standards
ETSI Draft EN 301 549 "European accessibility requirements for public
procurement of ICT products and services"
ETSI TR 103 170 Total Conversation Access to Emergency Services
SIAT Requirement specification for textphones videophones and total conversation
units. (In Swedish).
EAAC, Report on Emergency Calling for Persons with Disabilities Survey Review and Analysis
2011, July 21, 2011
http://transition.fcc.gov/cgb/dro/EAAC/EAAC-REPORT.pdf"> http://transition.fcc.gov/cgb/dro/EAAC/EAAC-REPORT.pdf .
- EAAC Draft TTY Transition report - March, 2013 - Page 44-
"An algorithm for identification of FIR systems with bounded frequency response",
Trump, T. Acoustics, Speech, and Signal Processing, 2002. Proceedings. (ICASSP
apos;02). IEEE International Conference on. . Volume 2, Issue , 2002 Page(s):1713 -
- EAAC Draft TTY Transition report - March, 2013 - Page 45-
Appendix A. Background for current usage evaluation
Relay service usage 2010/2011 in USA.
minutes / year
calls / year
Video Relay (VRS)
100 M minutes 25 M calls
50 M minutes
16 M calls
50 M minutes
16 M calls
Traditional TTY TRS
28 M minutes
9 M calls
California 2010/11 extrapolated with NECA
228 M minutes 66 M calls
Thus TTY based relay calls are about 12% of the total load of calls.
VRS - unreliable trends (current decrease, likely temporary)
IP-relay - decreasing
Captioned Telephony - Increasing a bit more than the decrease in IP-relay.
Traditional TTY - Decreasing about 10% per year, to half in 7 years.
Conclusion: TTY traditional relay is still considerable but lowest in volume, and only 12% of the total relay
User -to - user cal sOf the call types above, only Videophone and TTY are possible to use for direct user-to-user calls.
Estimation from the EAAC survey  early 2011 indicates that TTYs are used for as many user-to-user calls
as for relay calls. That would mean around 9 M TTY calls per year.
A figure from Sweden indicates that videophones are used 5 times more for user-to-user calls than for VRS
relay calls. That would mean around 125 M user-to-user video calls per year in USA.
Total cal sThe sum of relay calls and user-to-user cal s can then be estimated to be:
18 M calls per year
150 M calls per year
16 M calls per year
IP text relay
16 M calls per year
Sum accessible calls
200 M calls per year
A very rough approximation of the frequency of TTY emergency cal s:
The number of TTY cal s to 911 can be roughly estimated to about 20 000 per year, 400 per week or 50
calls per day for all of USA, decreasing with about 10% per year.
- EAAC Draft TTY Transition report - March, 2013 - Page 46-
The highest increase of 911 call types is in people with disabilities contacting friends by any electronic
communications means and asking them to call 911 for them because they do not have any means for
direct 911 contact themselves.
Background for this rough estimation:The EAAC user survey indicates that most TTY users use TRS relay services on rare occasions while still a
considerable number of users use TRS often or daily. Approximately the same answers were given for TTY
usage, indicating that nowadays the TTY is mainly used for relay calls, or at least as often for relay calls as
for person-to-person cal s. A rough estimation of the mean frequency is then two TRS cal per week per
active TTY user.
Also from the user survey it can be extrapolated that a rough mean time between 911 calls for TTY users is
four years, or 200 weeks.
Thus the emergency cal frequency for TTY users is 1/2*200= 1/400 of the TRS usage.
The TRS usage was 9 M cal s per year. Thus the TTY emergency service usage is approximately 9M/400 = 20
000 per year, 400 per week or 50 calls per day for all of USA.
ValidationAnother way to evaluate is to say that there are 300 M people in USA. At top, 1 per mille would have had
and used TTY = 300 000. Now, that rate has fallen to 30% of its original number = 100 000 users.
One emergency call per 4 years of these 100 000 users gives 25 000 emergency TTY calls per year for USA.
This figure is close to the 20 000 estimation above, so it indicates that the approximations are likely in the
A 1 M population area would have 1/300 of the load, giving about 1.5 emergency TTY call per week, or 75
Figures have been provided from Rochester, indicating 3100 TTY emergency calls per year, and Fairfax
County, claiming 0 TTY emergency calls per year in 2010. Both are 1 M population areas, but Rochester has
a concentration of deaf schools and a deaf college, and can therefore be expected to have more load than
Background for the TTY TRS figure
The extrapolation of the figure for traditional TTY TRS was made from California state statistics 2010 this
California Total traditional TRS 870 000 calls = 2.79 M minutes per year from California statistics and mean
call length 3.2 from statistics.
California Interstate and Toll free traditional TRS 175 000 calls per year from California statistics. = 560 000
USA TRS Fund traditional TRS 5.6 M minutes per year from NECA statistics. (www.neca.org)
- EAAC Draft TTY Transition report - March, 2013 - Page 47-
USA TRS fund minutes / California TRS fund minutes = 5.6 M /0.56 M = 10.
(Matches well the populations of California vs. USA)
USA total minutes traditional TRS = 10 * 2.79 = 28 M minutes per year.
The number of calls is estimated by dividing the figures above with 3.2 for text based and 4.0 for video
based calls. These are averages from NECA statistics 2011.
- EAAC Draft TTY Transition report - March, 2013 - Page 48-
- 1. Summary
- 2. Charter
- 2.1 Charter from EAAC
- 2.2 Extracted goals
- 3. Definitions and abbreviations
- 4. User needs in text based emergency 9-1-1 calling
- 5. The current situation for TTY and other PSTN usage
- 5.1 General information on the TTY
- 5.2. Wireline TTY situation
- 5.3 Wireless TTY situation
- 5.4 Specific solutions for users with deaf-blindness
- 5.5. Solutions for captioned telephony in PSTN
- 5.6 Proprietary solutions linking to standardized TTY
- 5.7 TTY Statistics
- 5.7.1 TTY usage compared to other accessible service usage in USA
- 184.108.40.206 Relay service usage 2010/2011 in USA.
- 220.127.116.11 User -to - user calls
- 18.104.22.168 Total calls
- 5.7.1 TTY usage compared to other accessible service usage in USA
- 5.8. Reasons for users to keep on using the TTY
- 5.9. Reasons to want to cease use of or support for the TTY
- 6. Theory behind observed transmission problems
- TTY transport over packet-switched networks
- 7. Threats to the quality of experience of TTY calls.
- 7.1 Access network threats
- 7.2 PSTN Core network threats
- 8. Known standards and technical methods intended to transport TTY reliably through IP networks.
- 9. TTY Replacement
- 9.1 Features desired by the users
- 9.2 Achievable functionality in IP based implementations
- 9.3 Standards and technologies in IP networks suitable for TTY replacement
- 9.3.1 For native SIP
- 9.3.2 For IMS used in wireless LTE networks and fixed broadband networks
- 9.3.3 For XMPP
- 9.3.4 Use of other real-time text protocols
- 9.3.5 Routing and addressing by number
- 9.3.6 Example from another region
- 9.4 Access to NG9-1-1
- 9.5 Access to legacy 9-1-1 and transition from legacy to NG9-1-1
- 9.6 Methods for interoperability between TTY and IP based solutions
- 9.6.1 Alternative solutions for interoperability between TTY and TTY replacements.
- 9.7 Other session control protocols than SIP
- 9.8 Solution proposals for interoperability between different IP based solutions.
- 10. Non real-time text alternatives; Applicability and functionality.
- 10.1 The gap between mainstream provision and accessibility
- 11. Potential problems with the NENA i3 approach for TTY handling.
- 12. Current and emerging policy and regulation support
- 12.1 Twenty-First Century Communications and Video Accessibility Act of 2010
- 12.2 DOJ regulation and guidance on accessible emergency services and TTY access to 9-1-1.
- 12.3 Section 255 of the telecom act
- 12.4 Section 508 of the rehabilitation act
- 1193.3 Definitions.
- 1193.51 Compatibility.
- 12.5. Draft revised section 255 and 508
- 12.6 Wireless TTY regulation by FCC
- 12.7 FCC TRS regulation.
- 12.8 TEDP Technology distribution programs.
- 12.9 Conclusion on acts and regulations
- 13. Concluding Findings and Recommendations
- Rationale for Version 1 and rationale for not being able to agree to Version 2:
- Rationale for Version 2 and rationale for not being able to agree to Version 1:
- 15.1 Timeline of an IP-based replacement.
- 15.2 Timeline of TTY transition
- 16. References
- Appendix A. Background for current usage evaluation
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