The integrated Service Digital Network is a digital method of using copper analogue phone lines to increase bandwidth. Examples of this are ISDN 2 and Home Highway. An ISDN line will normally consist of
2 x 64k channels. Each channel may carry voice or data allowing up to 128k transfers if both channels are used for data transmission.
The same line, using a conventional V90 modem has a theoretical maximum of 56k, although in reality, 48k is the norm - thus ISDN can be expected to be 3 times faster when downloading than a conventional modem.