Gunnar Hellström and Kelvin Currie
Voice telephony has become an important means of communication holding our society together, but it can not be used directly by everyone. For people with hearing or speech disabilities, alternative communi-cation services must be available on equal terms. One important such service is text telephony which provides text conversation in real time through telecommunication networks. It can be combined in various ways with voice telephony and with proper implementation will also be found to be very useful by non disabled people.
Currently available text telephone methods are nationally implemented and mutually incompatible. None of these has sufficient functionality to become the global standard which is urgently needed. The European Union of the Deaf have issued a resolution with a strong request for a uniform standard for text telephony and user involvement in the standardization process. Not until standards are established, can text telephone users be given the same accessibility to communication as voice telephone users have.
This chapter describes the need for further standardiza-tion, development and service provision in the area of text telephony and indications on the current status and some directions for possible solutions following the main trends in telecommunications development.
Relay services which provide a link between voice telephony and text telephone users, are also described and their development is indicated.
When a globally standardized and convenient text telephone service is available, everyone may find it useful to have the option to express something in writing during a voice telephone call.
However, the primary users of text telephony are people who are hearing impaired, deaf or deaf-blind or speech impaired, including their families and all social relations. As always in the disability area, it is hard to draw limits and evaluate numbers, but it can be anticipated that this presumptive user group is 0.5-1% of the population in any country. This means 2-4 million presumptive primary users in Europe.
Indirectly, anybody can become a text telephone user. For communication with people who only have a voice telephone available, the relay services play an important role translating between spoken and written dialogue, thus enabling conversations between voice telephone users and text telephone users.
The purpose of text telephony is to offer capabilities for real time text conversation through telecommunications networks. Text telephony should be combinable with voice telephony and video telephony as many users may want to combine these modes in the conversation.
The functionality of the network used should be available to text telephones. Any supplementary services (like call waiting and call when free) should also be easily accessible from a text telephone.
Interworking with current text telephones
Automatic interworking should be provided with the current text telephones. When operating in interworking mode, the functionality may be limited to what the emulated current text telephone normally offers.
The display of sent and received text should be presented in separate areas, so that a natural dialogue can be supported. A limited set of editing and control functions shall be provided to the user. Both caller and reader should have a synchronized view of the dialogue.
Call progress and session status
Call progress information, call status information and events during the session shall be presented visually to the user. Visual, tactile and audible alerting on incoming calls should be provided.
Identification when calling and answering
In the telephone network a calling text telephone shall produce a standardized calling signal that can be identified both audibly and by automatic answering equipment. In the telephone network an answering text telephone shall produce a standardized answering signal that can be identified both audibly and presented visually. In other networks, like ISDN, where there are procedures for signalling required capabilities, it is desirable to implement a more secure selection procedure.
For all network environments users are depending on incoming calls being announced by visual or tactile alerting systems.
The connection procedure should be safe and not require unrealistic decision capabilities from the user. This means, for example, not requiring the user to select between different text telephone methods or parameters when initiating a connection. Technical decisions on how to establish the connection should be taken by the equipment.
For users it is very important to be able to use their national characters in the written dialogue. The character set used shall be usable at least for Europe. This implies using rich standardized character sets and a standardized way to negotiate and control character set usage. The ISO 8859 family that is popular in modern computing and ISO 10 646 that has the ambition to cover the whole world's needs of characters are preferred character sets.
Combine text and speech
It shall be possible to use text and speech in combination in a session in a convenient way. This can mean simultaneous text and speech in some situations, and alternating between text and speech mode in other. A call can be set up in either mode. There should be simple procedures to switch mode or add the other mode during the call.
Emergency services should be safely reached through text telephony.
Relay services for conversion between voice telephony and text telephony are important for communication between the users of the two systems.
Directory services and information services
The text telephone users should have access to directory services through a text telephone. Any service provider like banks and commercial services should regard text telephony as an important medium for providing their services.
Audiovisual and multimedia services
In multimedia communication services and video-telephony, text conversation should be supported concurrently with voice and video. Videotelephony is of great importance for many text telephone users. Smooth introduction of videotelephony requires text telephony to be usable with the same equipment.
Interworking throughout networks
There should be established and supported standards for text telephony in all networks where voice telephony is supported. Interworking methods should be established to text telephony in the other networks. (Specifically this is valid for GSM, ISDN, PBX and networks and future mobile networks). Interworking methods should also be established to similar functions i.e. applications for distant co-operation, all audiographic conferencing.
According to UN standard rules on equal opportunities, text telephone users should have availability to equipment and services for communication on equal terms with voice telephone users. This implies a need for both very small text telephones that can easily be carried, being mobile or attachable to telephones, and a need for public text payphones.
Some important factors are worth mentioning. Factors that are more implementation dependent, but that will influence the success of different text telephone products as well as the whole text telephone system.
A technical solution is needed that allows an inexpen-sive user terminal implementation.
The text telephone is usually a device with a screen, a keyboard and a network connection. It is therefore tempting to imagine other applications of interest that can use the same equipment. Some users may find it useful to have in the same terminal a combination of functions for text telephony, telefax and data communi-cation (for BBS, information services, electronic mail, Internet etc.). Well integrated, user friendly applications are required to make use of this capability.
Connection to other equipment
The greater the proportion of population where direct contacts are possible without using a relay service the more it is of value. Therefore, equipment capable of performing text dialogues that is widely spread in the general public is of interest for contacts. It should for example be possible to connect in text telephone mode to personal computers equipped with ordinary modems. In this case a lower functionality than in the native text telephone mode is accepted.
Unsuccessful voice calls can be diverted to voice mail services. Diversion of unsuccessful text telephone calls should be possible to mail services.
There are text telephone users who cannot use ordinary keyboards or ordinary displays because of disabilities. Text telephone products should be adaptable to other means for input and display in order to make it economically reasonable to establish text telephony for these users.
(Table 4-1) List of Basic requirements on a standardized text telephone system.
The Current Methods
Table 4-2 briefly presents the most important text telephone methods in the world. All of them use the existing telephone networks. All methods have their pros and cons. The main problem of this multitude of methods is international incompatibility, and small markets per type of text telephone. More information is found in the references.
Method - Main Characteristics - Used in
Minitel - V.23 modem. 1200/75 bit/s, videotex protocol- France
EDT - V.21 110 bit/s one channel, carrier only while sending - Germany, Switzerland, Austria, Italy, Spain, Malta
Nordic V.21 - V.21 300 bit/s full duplex, 7 bit, even parity, one stop bit - Sweden, Norway, Finland
British V.21 - V.21 300 bit/s full duplex - UK
DTMF - Combination of tone dialling codes into characters - Denmark, Holland
Baudot or TDD - FSK method with 45.45 bits/s and 1400/1800 Hz - USA, Ireland, Iceland and partly UK
Bell - 300 bit/s full duplex - USA
(Table 4-2) Most widely used text telephone methods
Standardization and Development Today
Is there any way out of this confusion ?
Yes. Right now there are some activities which, if handled properly, can provide for a better situation in the future.
All text telephones contain a modem, that sends and receives the signals in a form suitable for the telephone network. A modem for text telephony has been recently standardized in ITU-T Study Group 14. The standard is named V.18, the features of which are given in Table 4-3.
Work going on in ITU-T Study Group 14 is in the area of a symmetric connection procedure and modem princi-ples for simultaneous text and voice. The goal is to include these capabilities that are urgently needed by text telephone users in future versions of V.18.
Current modem aspects cover only the lowest level of a text telephone design. For interworking possibilities, presentation and control aspects must be standardized. Such work has been recently initiated in the European Telecommunications Standards Institute (ETSI) starting from the user needs and a general service description. This work has been initiated in the Human Factors committee of ETSI. Text telephone terminal aspects are handled in ETSI terminal equipment committee.
In multimedia communication, the protocols for audio-visual services and audiographic conferencing currently do not contain any protocol for text conversation. Work in this area must be initiated in order not to block out the user group from multimedia communication. Multimedia communication contains all other elements needed for text telephony and should therefore be regarded as an environment for future text telephony.
The Basic Idea of V.18
The idea is to introduce a new text telephone method, while retaining controlled compatibility with the current methods. If one V.18 modem is connected to another V.18 modem, both modems will recognize this situation. They will then adjust themselves to the new method and report this fact upwards, to the higher layers in their respective terminals. They will then rapidly go into contact for the exchange of text.
If, instead, a V.18 modem is connected to one of the present text telephones, the modem will find out which standard this text telephone adheres to, and adjust to this method. In this way, text telephones with the new modem can be introduced without causing confusion. They will coexist well with present text telephones. They should become attractive in the market, because of their good facilities for international communication and modern conversation implementation.
(Table 4-3) Main feature of ITU -V18 text telephone modem standard.
A Vision of Future Text Telephony
Text telephony has now been around for many years. It is time to draw conclusions from the experience gathered. The introduction of a world-wide standard for modems offers a great chance to create a better text telephony system. With both standards and products adhering to the new standard, improved text telephony can be introduced while still being able to carry out conversations with all the old text telephones. This is a one-time chance. The characteristics chosen with the introduction of this new standard are something that the users will have to live with for many years to come.
It is important therefore, that decisions are made as to what exactly a text telephone is to be like. A whole family of standards are required for:
- the modem negotiation (decide on working mode and speed);
- the modem (interworking with older systems, trans-mission, interworking with speech and picture transmission);
- the data transmission (character by character, flow control, transmission checking)
- session control (connection and disconnection)
- presentation (separation in panels, character code, formatting, etc.);
- dialogue control (taking turns);
- implementation of text telephony in other networks. (GSM, ISDN, etc.).
As there are other networks than the analogue telephone network, e.g. mobile telephone networks, ISDN, and Local Area Networks (LAN), it must be possible to carry out text telephone calls in several of these. The standard can then be same in the upper layers, while the lower ones will be network-specific.
The text telephone users should be provided with a text telephone service containing different kinds of terminals, interworking methods with different networks, relay services for translation between speech and text, connec-tion possibilities to emergency services, supplementary services, and information on the system and its users.
Therefore V.18 should just be the beginning of an important standardization effort taking place in different groups of ETSI and ITU-T. Some activities in this direction are taken, among others from the European co-operation groups COST 219 and COST 220.
Today, in most cases, a text telephone has one screen, where texts from both parties are mixed. We take turns in the dialogue using special codes like "*" or "GA" (Go Ahead). One person is writing at a time. The whole procedure is a bit inflexible, and the limitations will hamper the dialogue flow.
A window-separated presentation can be obtained (COST 219, 1991), and if the other party can see the same picture, it is possible to relinquish the requirement for taking turns in the present formal way. The right to write can pass from one communication partner to the other in a natural way, and while one of the parties is writing a long passage, the other one can produce a sort of small acknowledgement like "sure", "Oh, really ?", "Yes, I know" and so on. This does not disturb the dialogue. On the contrary, it enhances the feeling of contact.
The opportunity should be taken to switch over to a new modem standard, to also change to a more human-friendly form of dialogue !
Combining Text and Speech
Standards are now in development for modems supporting voice and data connections simultaneously on one single telephone connection. Products supporting this are on the market, but in order to be useful as part of a standard, they must of course be standardized. This is of course of high interest for a future text telephone standard. One possibility is to continue the work on V.18, to include a method for voice-data as the native mode when two V.18s are in touch.
All the current text telephone methods are symmetric in their connection procedure. They just have to be activated to be able to start using them. The future text telephone method should also be symmetric. Regular modems are not, and V.18 is currently not. When starting regular modems, they must be told to work in originate mode or answer mode. On a connection, the two parties must select one mode each. There are many cases in modern telephony when it is not obvious what mode should be selected. One simple example is when a user has been talking for a while on the telephone and then wants to enter text mode. One simple operation, "enter text mode" should be enough.
This need also exists in the voice-data case. Therefore standards are under development for a symmetric modem connection procedure that is possible to activate both initially and during a voice call.
It is very important for the smooth operation of V.18 to incorporate the emerging standard for symmetric modem connection procedures.
Is text telephony satisfactory as it is ? No !
Are changes really needed ? Yes, the current situation of many incompatible national methods gives rise to at least four major problems:
- the users can not call internationally, which amounts to segregation
in the internationalizing process;
- there is no good advice to give to "new" countries wanting to start with text telephony;
- the products tend to be expensive and not well developed because of the fragmented market;
- the current dialogue method of one common screen causes an unuser friendly dialogue.
Can text telephony be replaced with telefax ?
Telefax is now in many countries in widespread use in the commercial sector and has started to enter the home market. It therefore offers an excellent opportunity for direct communication with companies and authorities. But some forms of communication are very hard to do in the message oriented fashion that telefax offers. The direct dialogue offered by voice telephony and text telephony is definitely needed, and telefax is only a good complement.
Is screen based telephony an alternative ?
An ideal situation would be for everybody to have equip-ment which could be used for both voice telephony and text telephony. Everybody would have some apparatus with a display and a keyboard capable of performing text telephone functions.
There are some companies moving in this direction. Bellcore in the USA has formulated a standardization proposal for screen based telephony called ADSI (Analogue Display Services Interface), which is aimed at just that - a telephone with screen and keyboard as extras.
What the designers of ADSI have primarily in mind is visual support for the telecommunication services and information services like number information and bank services. Unfortunately, the present ADSI proposal does not mention anything about direct communication from one user device to another, but only between such a device and an information centre.
The idea of visual support for telephone network services is of great interest to the text telephone users.
If ADSI is considered to be part of an important trend, that could lead to widespread use, action should now be taken to include text dialogue directly from one ADSI user terminal to another.
ADSI is incompatible with all the old text telephone methods. A study should therefore be carried out to see if the advantages of ADSI and V.18 can be combined.
Internet offers conversation applications:
Why not use internet instead ?
It is true that conversation applications are available on Internet. But only people who are already logged in can be reached. What text telephony offers is a direct replace-ment of the telephone, with possibilities to call to a person and send an awareness signal (a ring or a flash) to tell him that a call is waiting.
So far, Internet does not offer any realistic capability for transmission of sound and data together with quality and economy in the same range as a direct modem connection.
Use of electronic mail
Electronic mail has the same limitation as Internet conversation. It is not normal to send any awareness signal to a person not logged in to the mail service. And it also lacks the direct conversation mode that is important in many situations.
Use of a PC and currently available modems
This solution has many limitations. Firstly it is only the Nordic, the French and the British V.21 solutions that are compatible with modems and the modems must be selected very carefully. Secondly, current modems give too few indications on the call progress. It is very hard to judge why some calls do not get through. Thirdly, a regular modem is not easily handled together with voice telephony.
But of course it is of interest to the text telephone users to be able to contact other persons with regular PCs and regular modems.
Use of videotelephony instead
It is true that most of the current text telephone users are deaf people longing for the availability of good quality videotelephony to conduct conversation in their native sign language. But that is not at all the whole pre-sumptive text telephone user group. Many users with hearing impairment or speech impairment do not use sign language and are therefore not helped by a videophone.
Therefore, videotelephony is not an alternative, but a service of high interest to the same user group. When selecting the standardized method of text telephony, the standard protocols for mixing video, voice and data should also be judged as a presumptive carrier of the text dialogue.
What is a Relay Service ?
The basic purpose of a telephone relay service is to provide a method of communication between people who need to use text telephones (or videophones) because they cannot hear (or speak) and the rest of the world who do not need, and therefore do not use text telephones.
When using text terminals, communication is only possible if both ends of the conversation have text terminals that are compatible. Unfortunately, this back-to-back mode of operation excludes the text customer from contacting the majority of hearing customers.
The relay solution
By using a telephone relay, deaf and speech impaired people who have a textphone can now call a hearing third party, the relay operator, who themselves have a textphone. The relay operator then makes a second call to a hearing person and relays the information typed onto their screen from the deaf customer by speaking it to the hearing customer. The responses from the hearing customer are then typed to the deaf customer.
Typical relay operation
A deaf person wishing to make a call first calls the relay service on their text access number. The operator at the relay service who answers the call checks where they are calling from and the number they wish to call. The operator then proceeds to make a call on a separate line to the hearing customer and explains the service to them. Once both parties are on-line, the operator reads out the text from the deaf customer to the hearing customer, and types the hearing customer's reply to the deaf customer. This is in essence is the relay process. Deaf people who have good voices may, if they wish, and if the relay has the facility, talk directly to the hearing person. This facility is known as "talk through" or "talk over".
This may be achieved in a number of ways, some relay services raise their own bills for the calls, whereas others will bill through the telecommunications providers. Ideally, the call charge structure should be such that the calling customer is charged as if they had made the call directly, and not through the relay. This brings equality to the text user when compared with the rest of the telecommunications world.
The full relay service should offer the text user calls to any number that a hearing person can call. This would include full international service, Premium Rate calls, mobile telephones, etc. Calls may be made for business or personal reasons, so that there is no discrimination.
As the operator is party to the conversation, all relay staff should sign a declaration of confidentiality as part of the contract of employment. Most relay operators take this aspect very seriously.
Relay services may be funded in a number of different ways:
- direct funding by telecommunications operator, and run by them
or a third party;
- funding by a statutory levy on all telephony customers, the fund being centrally managed and the service being awarded to a suitable operator by tender;
- direct government funding.
In any of the above cases, it is essential to include the customers in the construction of the operating principles of the relay. Studies of existing relays in the US and Canada showed that deaf customers resented the imposition of a relay service by the telecommunications operator, and that they would prefer to run the relay service themselves or at least have a major say in the way it is operated. This is why many of the options for funding and running the relay services have resulted in the operation being carried out by a major deaf peoples' organization, or being jointly run through such an organization and a telecommunications operator.
Typical relay parameters
From the above, the following ideal parameters result, although they may be modified to suit local geographical or cultural requirements.
The Relay Service should:
a) be national;
b) offer 24 hour 365 day service;
c) be compatible with as many types of terminals as possible;
d) offer equal billing for the equivalent call made by speech users;
e) be professionally staffed and managed;
f) be open to any text user who wishes to use it;
g) carry any type of call to any telephone number that is accessible to hearing customers.
The competence needed to handle written dialogue is of interest in relation to the relay services. The prelingually deaf users often have sign language as their primary language. The educational systems vary widely in success in teaching written language. Under these circumstances, the written language produced in the real time conversion on the text telephone is often heavily influenced by the grammar and structure of sign language.
This means that operators have to be trained in "deaf awareness" which gives them an enhanced ability to understand the different syntax and grammar which originates from sign language customers typing. These skills are over and above those of basic typing skills which are required to be a relay service operator.
It can be seen that this is not really a task suited to a traditional telephone operator who has communication rather than interpretation skills.
Access to Emergency Services
Access for text customers to the emergency services (e.g. Police, Fire, Ambulance, etc.) has long been a problem. In some instances this has been solved by the emergency dispatch operators having text telephones, but there can be problems with this. In particular, the large number of line standards available in any one country may make the text telephone more complex and expensive. However, the major difficulty is likely to be the unfamiliarity of the dispatch operator with the needs of deaf people. The low number of calls is likely to be insufficient for keeping the communications skills up to a reasonable level and the written language ability of prelingually deaf people can cause problems for an inexperienced operator. This may waste vital seconds in an emergency situation.
To provide suitable text access to emergency services, it may be better to provide it through the relay system so that the every day experience of the operators can be brought to bear on the problems outlined above.
A lot of effort in research and development is currently being put into the field of multimedia communications, creating interesting opportunities for people who cannot use voice telephony. By careful design and standardiza-tion, text conversation applications can be created in these mainstream developments, better satisfying the needs of the text telephone users than current text tele-phones do. The recently standardized text telephone modem can be used as the bridge for smooth inter-working with the current text telephones. Unified forces are needed to keep the trends together in a system of standardized interworking solutions so that text tele-phone users can get the universal access to telecommunications they have been denied so far.
With proper implementation, text telephony could be found useful as an add on for voice telephone users. Still, the need for the service comes from people with disabilities and in the development process the needs of these primary users must never be forgotten.
COST 219, Ed. von Tetzchner S. (1991). Issues in Telecommunications and Disability. Chapter. 29: A Conversation-Oriented Text Telephone program for IBM Compatible Computers. ISBN 92-826-3128-1.
COST 220 reports, Ed. Reefman, P. (1993). A text telephone service for Europe. ISBN 92-826-6198-9.
COST 219, Ed. Olesen K.G. (1992). Survey of text telephones and relay services in Europe, 1992 ISBN 92-826-4395-6.
ETSI TSC HF, (1995). DTR/HF-02015, Text telephony, User needs. Draft Technical Report.
ITU V.18 Operational and interworking requirements for modems operating in the text telephone mode.