It can not carry voice data. One pair of wires is capable of carrying one or two B channels and one D channel . Like ISDN , DSL carries data over standard copper telephone wires, but has the capacity for speeds much greater than ISDN . Due to the fact that ISDN is a type of DSL , they are often compared. Many people think that ISDN has no future and that DSL is the only way to go.
Some people even go so far as to state that it is competing technology to cable modems.
Unlike cable technologies, DSL is a dedicated line so it has the benefits of maintaining high speeds without being affected by other users in the neighborhood. The speed of the communication transfer can vary. DSL speeds have been quoted as being anywhere from 30 to 100 times faster than a modem and 10 times faster than an ISDN connection. Also, ISDN has only one possible upgrade. Like ISDN , DSL is capable of two-channel connections, one for voice, one for data connection and can be used simultaneously.