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A+: ISDN, Hardware & Connections

ISDN (Integrated Services Digital Network) was originally developed to provide an all-digital method for connecting multiple telephone and telephony-type devices. such as fax machines, to a single telephone line and to provide a faster connection for teleconferencing for remote computer users. A home/small office-based connection can also provide an all-digital Internet connection at speeds up to 128Kbps. Line quality is a critical factor in determining whether any particular location can use ISDN service. If an all-digital connection cannot be established between the customer’s location and the telephone company’s central switch, ISDN service is not available or a new telephone line must be run (at extra cost to you!).

The telephone network was originally designed to support analog signaling only, which is why an analog (dial-up) modem that sends data to other computers converts digital signals to analog for transmission through the telephone network. The receiving analog modem converts analog data back to digital data.

To make an ISDN connection, your PC (and any other devices that share the ISDN connection) needs a device called an ISDN terminal adapter (TA). A TA resembles a conventional analog modem. Internal models plug into the same PCI, ISA, and PC Card slots used by analog modems, and external models use USB or serial ports. External TAs often have two or more RJ-11 ports for telephony devices, an RJ-45 port for the connection to the ISDN line, and a serial or USB port for connection to the computer.
Setting Up an ISDN Connection
ISDN connections (where available) are provided through the local telephone company. There are two types of ISDN connections, the Primary Rate Interface (PRI) and the lesser Basic Rate Interface (BRI).

A PRI connection provides 1.536Mbps of bandwidth, whereas a BRI interface provides 64Kbps (single-channel) or 128Kbps (dual-channel) of bandwidth. BRI is sold to small businesses and home offices; PRI is sold to large organizations. Both types of connections enable you to use the Internet and talk or fax data through the phone line at the same time.

A direct individual ISDN connection is configured through the network features of Windows with the same types of settings used for an analog modem connection. Configuring a network-based ISDN connection is done through the network adapter’s TCP/IP properties window. 
Most telephone companies have largely phased out ISDN in favor of DSL, which is much faster and less expensive.



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