TORNADO WEBJET 128
Allied Data Technologies
5
1.
ISDN, Data Communication, the Internet
This chapter starts off with a brief explanation of ISDN and the function of the Tornado WebJet 128.
After that, the concept of Data Communication is described.
ISDN
The introduction of ISDN (Integrated Services Digital Network) has made it possible to send information in a digital
format. This helps improve speed and reliability. ISDN was set up to integrate the existing speech, data and telex
telephone networks into one network. Apart from this integration, a separate signaling net was added to speed up
connection. Establishing a connection through the PSTN network (telephone net) by modem took about 15 seconds; this
has been reduced to just 2 or 3 seconds by using a terminal adapter through the ISDN network.
Figure 1: Possible ISDN Configuration
In ISDN, only one connection is needed for communication devices like faxes, telephones and terminal adapters. An ISDN
device only responds to an incoming call if the call is actually destined for it. For instance, if a call is made by a terminal
adapter, only a terminal adapter will respond; the fax and telephone will not. This is possible because information is sent
along about the kind of telecommunication service. This means a beeping fax on the line is a thing of the past.
With an ISDN2 or BRI (Basic Rate Interface) connection, you have two so-called B channels (64 Kbps) and a D channel (16
Kbps) at your disposal. Both the B channels are data channels, whereas the D channel gives access to the signaling net
and is used to make a connection. It is possible to connect eight ISDN devices to an ISDN2 connection, with a maximum
total cable length of 200 meters between devices and ISDN2 connection.
Setting up a connection
Setting up a data connection through the ISDN network is almost the same as doing so by modem. Once a protocol has
been selected, a number can be dialed using the ATD command. The Tornado WebJet 128 will now establish a
connection through the D channel. If the same protocol is selected on both sides, a data connection is set up through one
B or possibly both the B channels.