For most of the life of electronic/electrical communication, the primary method of communication
has been the telephone. As a result, there exists a network
of cables and connection throughout the
world that dwarfs the Internet in both number of connections and miles of wire. Wouldn't it be
wonderful if we could take advantage of the already existing network? Well, we can. This comes to us
in the form of a system called Integrated Services Digital Network, or ISDN.
ISDN is one of
the fastest growing technologies, particularly in Europe. Local telephone companies are offering it
as a replacement (or addition) to conventional telephone lines. Until recently, the German phone
company was offering cash incentives for businesses and private individuals to switch to ISDN.
primary benefit (at least to most end users) is that you can simultaneously send data across the
same lines as your phone. For example, while you are speaking to a customer, you can be faxing them
the spec sheets on your latest product across the same phone line. Although such
functionality for both partners requires ISDN
connections on both ends, your phone could be talking
to their conventional phone and your fax could be talking to their conventional fax. However, from
your office to the phone company is a single telephone connection.
If both sides are using
ISDN, they need to be communicating in a fashion similar to a network
(like with TCP/IP or IPX/SPX).
Therefore, both sides know who is calling. Image getting a call from a customer and having your
database automatically call up the record on that customer, even before you pick up the phone! This
ability to integrate all these different services from voice to fax to data communication gives ISDN
The key concept in ISDN
is the idea of a digital data pipe
between the end device
and the service provider. Note that I didn't say between the two participants. This allows the
service provider (the phone company) to switch between the ISDN
connection on one side to the analog connection on the other. At the receiving end (your office) will
be something similar to a switch box. As the packets come in from the service provider, this switch box
will route the packets to the
appropriate device. Each device is set with a particular ID number. This works conceptually the same way as SCSI IDs.
As of this writing, three types of connections have been standardized. The
first is often referred to as the "basic" rate as it provides the necessary service for basic users
such as homes and small businesses. This provides two 64 kbps channels for voice or data and one
channel for "out-of-band" signaling. In some cases, you could use these two channels simultaneously
and get 128 kbps. However, this would be considered two phone calls.
The "primary" service
provides 23 voices or data channels, instead of just two. In Europe, this is increased to 30
channels. The third type provides a 4 KHz analog phone channel along with a 8 or 16 kbps data
channel. This allows you to use your old analog phone along side the new ISDN
is not just for data communication. As I mentioned the German phone company subsidized the transfer
from the old analog system to ISDN.
I have an ISDN connection at home. Using the same wires as my
old phone line, the ISDN
line comes into a telecommunications box, which converts the signal so that
my normal analog phones can work.
ISDN support is provided by isdn4linux, which is a set of
kernel modules. The main module (isdn) communicates with the driver for the particular card. As of
this writing, there is a limited number of cards that are supported. However, many cards are
supported that don't have "official" drivers for them. For example, the AVM A1 (Fritz) card
is supported using the Teles driver. For more information, check out the /pub/isdn4linux directory
on ftp.franken.de. This not only has many of the drivers, but also a very extensive
If you have a 2-0 or later kernel,
then you are in luck. ISDN
support is included by
default. When you run 'make config', you are prompted to incldue/activate it along with several different
options. There are only a few cards mentioned by name. However, I know that many other cards will work
with the drivers that are included.