Several important points deserve consideration.
One, since the ISDN equipment will belong to you and you bear the risk of economic
loss if it is damaged by lightning or power surges on the telephone line, ensure that
your service provider installs a lightning protector with a proper ground. This means
the structural metal framework of an office building, the metal (not plastic!) water pipe
of a residence, or a driven copper ground rod with an effective resistance of under 25
ohms (ideally under 5 ohms).
If your installation is in a suburban or provincial area, then consider to install a better
protector than offered by either TOT or TelecomAsia; otherwise your expensive ISDN
hardware may fry in the first electrical storm. Such a device (called the Multi-Protector)
is actually manufactured in Thailand for export and may be obtained from Goham
(Thailand) Co. Ltd. Refer to the hardware vendors section below.
Second, if your Terminal Adapter includes a frame ground connection, be certain to
connect it to the same ground as is used by the lightning protector or Multi-Protector.
This will protect the Terminal Adapter from incoming overvoltages and ensure no
"ground potential difference" arises which can occur if the Terminal Adapter and light-
ning protector use separate grounds. And ensure that your computer’s third (ground)
power pin goes to the same ground. (The one the installer broke off, remember?)
Third, if you will be using your ISDN service for mission-critical work, develop a
backup power plan. If you need only phone service, you may use a special ISDN
telephone instrument which will be powered from the ISDN line in case of commercial
power failure. Such instruments, available from several local ISDN hardware vendors,
offer numerous whiz-bang convenience features but are expensive at 5,000 to 10,000
baht per device.
An alternative is to use analogue telsets from a Terminal Adapter’s R port, but main-
taining telephone service through a commercial power failure requires installing an
Uninterruptible Power Supply in front of the Terminal Adapter, unless it contains an
internal backup battery. Only one unit presently sold in Bangkok has this internal
backup battery feature.
Fourth, decide whether you need to rent (or buy) an NT-1. This expense can be avoid-
ed by using a Terminal Adapter with an embedded NT-1; some have and some don’t.
Fifth, be alerted that you cannot report an ISDN circuit failure to TOT using the stan-
dard 1177 call procedure, since the interactive voice response system has not yet been
programmed to accept ISDN numbers. You must select the "speak to a service repre-
sentative" option, input a phony number, inform the service representive you fooled his
robot to access a human, and then give him the actual ISDN number. (TelecomAsia’s
reporting mechanism already works right on the first try.)
The flip side is that every NT-1 has an inbuilt responder allowing the Central Office
instantly to check the line (one of the many clever customer-friendly design features of
ISDN). Several similar technologies are inexpensively available for immediate verifica-
tion of standard analogue phone lines and have been offered many times by many ven-
dors to both TOT and TelecomAsia. However both have declined to take up these
technologies on the ground that they benefit the customer more than the provider so
the expense is not justified.
5
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