Four main ways of using a relay service
Feb. 19th, 2018 11:12 pmFour main modes for using a relay service.
I have explained the basics of how textphones and relay works including calling-out info in my post Deaf and speech impaired people's access to telephones which you should read before this post.
This post has been edited to reflect changes since 2014 with the introduction of BT's Next Generation Text-Relay, known as NGT but probably needs restructuring entirely to make more sense.
This post explains a little bit more about the roles the caller, relay operator and recipient make in three different types of call using relay.
Textphone to Telephone
Voice Carry Over (VCO)
Hearing Carry Over (HCO)
Textphone to Textphone via TextRelay
1. Textphone to Telephone via TextRelay
This is one of the most common ways of using a relay service with the relay operator typing for the textphone user and speaking for the telephone user.

1. The textphone user types their words out on a textphone which are read by the relay operator to the telephone user.
2. The telephone user hears the relay operator speaking on their phone handset and once it is their turn to speak speaks their reply back to the relay operator.
3. Relay operator types out the telephone user's spoken reply as best as they can (but they aren't verbatim typists) which appears as text on the textphone user's screen.
Each person has to say Go Ahead or "over" or type GA (GA means go ahead) to end their turn and allow the other person to speak or type. Calls are ended with SK SK which means "stop keying" from telegraphy. There are other shortcodes in varying levels of use e.g Plz, thx.
Since the introduction of NGT Lite in 2014 most computers running Windows, MacOS, or linux, or tablets and smartphones running iOS or Android can act like a textphone.
Historically hardware textphone users could not access the audio of the call. Since NGT was introduced the user may now be able to access the audio during the call. The telephone users still cannot see the typed words.
2. Voice Carry Over (VCO)
Voice carry over (VCO) mode is usually used by people who cannot hear but wish to speak for themselves. This requires a textphone which has a handset like one of the ones below or NGT-Lite software.


The first image shows a woman using a Uniphone branded textphone holding the handset in the usual way but reading the relayed text from the screen.
The second image shows a woman using a Screenphone which does not have a keyboard but has a larger screen. The close up zoom in of the screen shows the words "Hello Geoff, how are you today".

The textphone user speaks (voices) for themselves into their textphone or telephone handset. The telephone user can hear the textphone user speaking as usual but cannot just reply instantly as usual. When the textphone user has finished speaking they have to let the operator know they've finished by saying Go Ahead. This is an improvement on the old-textphone-system where a button had to be pressed with a 1-2 second 'change over time'.
When the telephone user has finished speaking they say "Go ahead" or "over" and the relay operator will let the deaf person know they can now speak again.
Historically textphone users could not access the audio of the call, but that has now changed with NGT. NGT was designed with the intention of encouraging more people to use voice carry over mode although I am not sure this has happened in practice.
3. Hearing Carry Over

Hearing Carry Over (HCO) is usually used by people who cannot or do not wish to speak but can hear what is said. Like with voice carry over this requires a textphone with a handset or NGT Lite.
The textphone user types what they wish to say and the relay operator speaks this to the telephone user. When the textphone user has finished typing they type GA so the operator knows to tell the other person they can speak and be heard by the speech impaired caller. When the telephone user has finished speaking they say "go ahead" or "over" and the textphone user will know it is their turn to type again.
NGT has eliminated the 1-2 second mode switching.
4. Textphone to Textphone (with and without relay)

The call connects with each textphone connecting by BT Text Direct (service provider of TextRelay)'s servers.
These days deaf people tend not to use textphone to textphone to communicate with one another as it has been superseded by SMS, text and video chat of various kinds etc.
The main reasons people will use this mode are to get the 60% call rebate; get clearer call progress messages and if their textphone isn't compatible with the other person's (TextRelay eliminates this issue).