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Chapter 10: Principles of Data Communication
An ISDN TA/V provides an interface between the digital world of an attached
computer, and that of the ISDN service, and also between the analogue world
of a telephone handset and the ISDN service. In this chapter we take a
moment to explain why its use is necessary to enable a communication to take
place, and explain some of the terminology that you’ll find in later chapters.
We also outline how the ISDN TA/V’s command language is used to initiate
and accept calls to/from other devices over the ISDN service.
10.1 How the ISDN TA/V Works
The digital signals received on the DTE interface are passed over the ISDN
line using the first available B channel. An incoming data call on the ISDN
is identified as being a data call, and is automatically passed to the DTE
interface. An incoming voice call on the ISDN is identified as such and is
automatically passed to the telephone-handset circuitry, converted from its
digital format into an analogue format, and output via the handset interface.
Vice versa an outgoing analogue voice call is converted into digital format by
the ISDN TA/V before being passed over the ISDN service.
10.1.1 C
ONTROLING THE
ISDN TA/V
Your ISDN TA/V, like most ISDN terminal adaptors and modems available
today, uses a deviant of the industry standard set of commands known as AT
codes to control all aspects of its operation. Control over the ISDN TA/V can
then be initiated directly using the commands, via a communications-software
program, or via the
Intro
software program installed in the DTE interface
attached PC, (providing that the DTE interface is configured to accept
asynchronous command).
Direct command to the ISDN TA/V is possible either by using your DTE
interface attached computer in terminal-emulation mode (providing that the
DTE interface is configured to accept asynchronous commands), or from a
dedicated terminal/PC attached to the
CONTROL
interface—in either case
you can control the ISDN TA/V by entering the relevant AT command at
your keyboard. Although this method of operation requires a greater
understanding than when using communications software or the
Intro
program, the terminal mode offers the greatest flexibility of customisation
and fine control over the ISDN TA/V’s parameters.
When using a communications-software program, or the supplied
Intro
software, in the DTE interface attached computer to control the ISDN TA/V,
providing that the DTE interface is configured to accept asynchronouus
commands, a friendlier interface containing menu selections is presented to
the user. ISDN TA/V command is then executed by selecting options from
the menu structure, then the software automatically builds the appropriate
10. Principles of Data Communication
