Download QH16-03010

ITU - Telecommunications Standardization Sector
QH16-03010
Study Group 16 – Question 11, H
Location:
Streatley, Berkshire, UK. 18th – 20th March 2003
Source:
Michael J Day
Title:
A proposal for the integration of PSTN and IP textphone communications
Contact:
Michael J Day
Tel:
+44 20 8546 1601
Email: [email protected]
ABSTRACT
This contribution proposes a general methodology for the integration of PSTN and future IP
textphones. The principle that forms the basis for this proposal is that while the legacy textphone
should be supported the future is with IP. The main objective is to allow textphone users to benefit
from new technologies and mainstream products by facilitating their migration to IP based textphones
while maintaining a means by which they can connect to existing legacy textphones.
Through the use of local PSTN/IP gateways the proposal allows calls to be made from a PSTN
textphone to a PSTN textphone, from an IP textphone to an IP textphone and between the PSTN
textphones and IP Textphones. The gateways could also support for locally available textphone
protocols and provide interoperability between incompatible textphone protocols.
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TABLE OF CONTENTS
1
Introduction ..................................................................................................................................... 3
2
The Local Textphone Network ....................................................................................................... 3
2.1 Gateway In and Gateway Out ..................................................................................................... 3
2.2 The Local Textphone Intranet ..................................................................................................... 3
2.3 Directory ..................................................................................................................................... 4
2.4 Relay ........................................................................................................................................... 4
2.5 Emergency .................................................................................................................................. 4
2.6 Services ....................................................................................................................................... 4
2.7 Router.......................................................................................................................................... 4
2.8 Changes Needed.......................................................................................................................... 4
3
The Customer’s Perspective............................................................................................................ 4
3.1 From a PSTN Textphone or Telephone ...................................................................................... 4
3.2 From an Internet, Mobile or Wireless Terminal ......................................................................... 4
3.3 From a PC ................................................................................................................................... 5
3.4 Connecting a Relay ..................................................................................................................... 5
4
Conclusion ...................................................................................................................................... 5
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1
Introduction
There has been a lot of discussion about standards and protocols but not much about how they could
work together, the migration or interoperation and possibly more important convergence i.e. the
ability to use other terminals.
In the US the discussion focuses on transmitting Baudot across a network. While this is very
understandable given their regulatory situation it does have a flaw as a method for the future of
textphone communications because it assumes that all textphones communicate using compatible
protocols.
This document describes a gateway based solution for the future of textphone communications. This
is a high level description of a solution that both allows textphone users to benefit from new
technologies while maintaining and improving the facilities available to legacy textphones.
The heart of the solution is The Internet and Internet Protocols (IP). In order to help understanding it
is necessary to clarify some of the terms used in the diagram attached and explain how they relate to
the customer’s equipment.
2

Textphones, TTYs and Telephones – domestic analogue terminals connected to a telephone
line; this would include PCs with modems that are being used as textphones.

Internet terminals – any terminal connected to The Internet, this would include PCs that are
directly connected using ADSL and those using a dial-up connection via ISDN or the
telephone network (PSTN).

Mobile terminals – GSM and GPRS terminals connected using a data channel.

Local wireless terminals – PDAs and PCs connected via a local wireless network such as
WiFi, 802.11b, etc.
The Local Textphone Network
The Local Textphone Network (LTN) could be provided on a country or state basis and designed to
meet the needs of the textphone users within its catchment area.
The composite parts are:
2.1
Gateway In and Gateway Out
This is where the Telephone Network (PSTN) interconnects to the Local Textphone Intranet. It
provides both PSTN textphone and PSTN voice connections. Ideally this would be ITU-T V.18 based
however because this is a local access point it may only be required to support those protocols
available locally. The gateway function provides connectivity with The Internet for the PSTN
textphones and voice telephones removing the need for any changes to be made to the terminals, it
would also provide the ability for incompatible textphones to communicate.
2.2
The Local Textphone Intranet
The Local Textphone Intranet (LTI) is the backbone of the textphone communications using
internationally supported protocols for call set up, and transmission of text and voice. These protocols
would be used for communications between LTNs and from LTNs to Internet connected terminals.
Providing the LTI as a segment of The Internet means that textphone conversations are provided with
the required level of speed to facilitate textphone communication that must of course include a voice
element. LTIs could be interconnected independent of The Internet in order to maintain the required
speed and provide a level of resource sharing that would ensure service availability while providing a
cost effective solution. Such a service could be access to a language not support by the local relay, in
this situation a suitable relay could be accessed via The Internet.
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2.3 Directory
With the dynamic nature of The Internet comes the need for some form of directory server, the basic
function being to lookup telephone numbers and translate them to IP addresses when available. This
could be a simple lookup directory like that used for Microsoft NetMeeting or the type described
within the SIP recommendation.
2.4
Relay
The standard voice to text and text to voice function but accessible from the LTN with access being
requested by a gateway or Internet terminal when required.
2.5
Emergency
Access to standard emergency services.
2.6
Services
With the LTN being the focus for textphone communications comes the ability to provide services
such a network based text/voice answering machine, the number of the last person to call the user, etc.
2.7
Router
Basic Internet router functionality, this isolates the LTN calls from The Internet traffic allowing the
communication speed to be maintained.
2.8
Changes Needed
For a gateway function to work textphone calls from the telephone network need to be routed through
the gateway. The easiest way of achieving this is to prefix the dialled telephone number with an
access code, this could be automatically added by the textphone. However this is not the only way it
could work, a telephone line could be set-up to automatically connect to the gateway when the phone
goes off hook, or automatically route a call to a textphone user via the LTN gateway.
3
The Customer’s Perspective
Below is a brief description of how a call would be made:
3.1
From a PSTN Textphone or Telephone

Dial the access code and the telephone number required

Call connects to the Gateway

The Gateway looks up the telephone number in the Directory

If an IP address is available the call is connected via The Internet

If no IP address is available then the call is connected via Telephone Network
3.2
From an Internet, Mobile or Wireless Terminal

When the users connects to The Internet they log into the Directory with their telephone
number and current IP address

To make a call the textphone application running on their Internet Terminal checks with the
Directory to see if the person they want is connected to The Internet

If the other person is connected to The Internet then the textphone application will connect
direct to the other Internet Terminal
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
3.3
If they are not connected to The Internet then the call is routed via a LTN Gateway
From a PC
If the user is using a PC then there are two possible ways to make a call. Either to use it as a PSTN
textphone as above or to connect to The Internet via their Internet Service Provider (ISP) and then
make a call in the same way as the Internet Terminal above.
3.4
Connecting a Relay
If a relay service is required then the Gateway or textphone application running on the Internet
Terminal would connect to the Relay Service.
4
Conclusion
With the move to higher data rates available on The Internet there comes the ability to have
simultaneous text and voice in both directions and it would also allow control functions that could
provide handshaking between the terminals. Two possible scenarios for this come to mind:
1. If a user is more comfortable with the characters appearing a word at a time, or they need to slow
down the text because the sender is typing too fast they could set their terminal to control the
flow. This would of course delay their response to any conversation and the sender could wonder
what was going on. However if the two terminals could communicate then the sender would see a
message saying 'The other person is reading' until the recipient has finished the whole sentence.
2. If one user wanted to use voice then the 'Voice' button would send a request to the other terminal
which could be set to reply automatically dependent on the terminal's ability, speaker or
microphone plugged in, or the user's ability.
The gateway approach has a number of further benefits:

It enables access for legacy textphones to new protocols and terminals without modification
to either textphone or terminal.

Possibly the biggest benefit is that only the gateways need to know about textphone protocols.
Should a new protocol be introduced within a country then only the LTNs in that country
would need to be changed. The same is true for the network, any changes would be tested
between LTNs and would not require testing between textphones. Ideally all gateways would
allow the same protocols to be used from and to the PSTN but it need not be the case local
proprietary protocols could be supported.

Incompatible terminals can talk to each other such as a textphone to GPRS terminal. All that
is needed is for the terminals to be able to talk to the gateway.

Internet to Internet terminals can communicate without touching the telephone network, e.g. a
mobile terminal to an internet terminal would not require a gateway function or changes to the
network infrastructure.

New technologies would just have to be able to communicate with the gateways to be
accessible to textphone users. No more testing against every available textphone.

Access to services such as relay and emergency from Internet connected terminals would not
need to go via the telephone network.
These are potential benefits the initial benefit is a dramatic increase in the number of terminals that
can support real-time text communications.
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The Internet
Services
Relay
Emergency
Local
Textphone
Network
Internet
terminals
Router
Local
Textphone
Intranet
Directory
Gateway In
Gateway
Out
Mobile
terminals
Telephone
Network
Local
wireless
terminals
Textphones,
TTYs, etc.
PSTN
connected
products
Local Textphone Network
Telephones
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