subject: ISDN Connection [print this page] For those requiring faster access, or for companies who require several or even many users to access the net simultaneously, a simple MODEM-based connection won't do. Instead it's possible to have what's called an ISDN or integrated Services Digital Network Connection. With this type of set up you need a special connection to your house or business which can handle the higher bandwidth. For example, ISDN2, one of the systems, which are supplied by British Telecoms, consists of two twisted-pair copper cables. This combination can supply two 64Kbps channels plus a third 16Kbps data channel which acts as a control for the other two channels. This is quite versatile because you can use the normal phone at the same time as transferring computer data. This facility alone is often enough to please some serious suffers who work from home, and are thus often in competition with other family members for telephone access! The basic ISDN2 channel can be configured such that you can use the two 64Kbps. The cost of using the system varies, but it's usual to find a much higher quarterly rental, otherwise the cost of the phone calls is identical. However, don't forget that you can transfer data much faster, and therefore spend much less time on the phone - at 128Kbps you would obviously spend about a quarter of the money on phone bills for the same data transferred via a typical 33.6Kbps MODEM.
Function of a MODEM is to modulate the digital signals into an analogue form ready for transmission over the normal telephone link. With an ISDN connection the line can handle the digital signals as it's designed to be able to do so. Therefore, you don't need a MODEM anymore. Instead you need what's called a Terminal Adapter or TA, also known as ISDN TA. This has the function of interfacing your computer with the ISDN line. TAs usually comes in parallel, serial or PCMCIA (i.e. portable computer interface) type. Other devices like faxes can also be connected to appropriate ISDN links. ISDN lines have no dial tone so they sound dead when you pick up a telephone receiver! However, dial the number and the connection is made in a fraction of a second - this is quite a shock if you are used to dialing with a conventional MODEM and telephone line.
