by January 11, 1999 0 comments

ISDN connections can support 64, 128, or 384 kbps data transfer rates. All ISDN devices are referred to as TE-1 (Terminal Equipment). All non-ISDN devices such as analog telephones, referred to as TE-2 devices, can be connected to ISDN terminal adapters and routers

In the article “Affordable ISDN is Here” we
talked about ISDN and how to get an ISDN connection. Now let’s take a look atthe
various devices you can connect on an ISDN line.

One of the basic difference between an analog telephone and ISDN is that you can add
multiple devices on the latter. However, the more the number of devices, the more
complicated it becomes to configure your line. So the first step is to know what devices
to install. There’s a whole range of ISDN products available, and there’s also a
lot of jargon associated with these.

All devices that connect to an ISDN line are called TE-I’s (Terminal Equipment I).
All analog devices like telephones and fax machines are called TE-II (Terminal Equipment
II). These analog devices can be used on an ISDN line through TE-I devices. For example,
you could connect an analog telephone to an ISDN line through a terminal adapter or
routers that have analogue telephone jacks.

Network Termination (NT1)You can daisy chain multiple NT1 boxes to add more ISDN devices
Once you get your ISDN connection, the
telecom department extends an ISDN line called a U-interface, till your premises. This
interface connects to a switch at the telephone exchange and has a single pair of wires
that can handle full-duplex communication for a single ISDN device. At your end you need
to terminate the line with an NT1. Usually, it’s not recommended to directly connect
another ISDN device to the U-interface. ISDN wiring and connection beyond the NT1, in your
premises is referred to as S/T or S-bus interface. The NT1 converts the two-wire,
U-interface into 4-wire S/T interface or the S-bus. This provides two pairs of wires for
transmitting and receiving, so that multiple devices can be attached for performing
full-duplex communication. The telecom department usually provides this device, but you
can also purchase your own.

In affect, the NT1 box actually works as a multiplexer that
allows multiple ISDN devices to share the line. Without this device, your ISDN line is an
ordinary single phone line. One NT1 box usually has support for two ISDN devices. However,
you can daisy chain multiple NT1 boxes to add more devices. We’ll see how to connect
the NT1 in the article “how to setup an ISDN router”.

Terminal adapter
A terminal adapter (TA) is to ISDN what
a modem is to a telephone line. A TA connects your system to the ISDN line. But, unlike
the modem, a TA doesn’t need to convert analog signals into digital and vice versa,
since ISDN is already a digital connection.

A terminal adapter is similar to an analog modem. In fact, some vendors call their TAs ISDN modemsLike a modem, a TA connects to the Net by connecting to your
machine’s serial port, and has drivers that need to be installed. A TA uses simple
dial-up networking. However, if you’re using a 128 kbps TA, then you’ll need to
enable the multi-link option in dial-up networking.

As ISDN connections become common, you’ll soon find office PCs shipping with
built-in ISDN adapters. A terminal adapter can let only one PC enjoy ISDN connectivity,
unless you set up a proxy server on it .

ISDN router
If you want to share your ISDN
connection with other machines on a network, one way is to use a terminal adapter and a
software proxy server. However, on a network it’s advisable to use an ISDN router
because of better manageability and lower costs. A typical ISDN router connects to a network port and has in-built DHCP and gateway services along with filtering capabilities

An ISDN router is similar to Webramp or hardware
proxy server using analog telephone lines. It performs all the functions of a TA and goes
beyond that. Like a TA, it acts as a gateway to the Internet. It also has in-built DHCP
services. The other advantage is that the router connects directly to your network and
doesn’t need a dedicated machine for maintaining it.

Other devices
There are various other products that
you can connect to your ISDN line. These include a feature phone, a video telephone, G4
fax terminal, an ISDN PC card, etc. As ISDN is digital, it won’t be compatible with
your ordinary analog telephone instruments. So you’ll need an ISDN feature phone.
This phone offers you features like call diversion, call identification, call waiting,
answering machine, etc. You could also attach teleconferencing instruments to your ISDN
line. The capability of ISDN to support all forms of transmission gives you the benefit of
seeing the person you’re talking to over the phone instrument itself, provided the
other party has a Webcam and a bandwidth to match your digital line.

An ISDN feature phone can offer many advanced functions over a regular ISDN handset To send and receive faxes, you could also connect a digital fax
machine called the G4 fax machine to your line, which lets you transmit high-resolution
images too. An ISDN PC card is a counterpart of an internal modem in the analog setup.
It’s an internal ISDN terminal adapter that fits into one of the slots in your PC.

As the usage of ISDN expands, more and more ISDN ready devices are expected to hit the
market. 
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