ISDN-Like DigitalSubscriber Line (IDSL)

DSL refers to a pair of modems installed on the last mile of line, which facilitate high data speeds. Network providers use the existing wires and add the DSL modems to increase the through-put. DSL modems offer duplex operations. The speed of a DSL modem may be 128 Kbps on copper at distances up to 18,000 feet using the twisted pair wires.

The bandwidth used is from 0 to 80 kHz. IDSL uses the 128-Kbps full-duplex basic rate interface (BRI). The IDSL technique is all digital, operating at two channels of 64 Kbps for voice or non-voice operation and a 16-Kbps data channel for signaling, control, and data packets.

ISDN was very slow to catch on, but the movement to the Internet created a whole new set of demands. Now more ILECs and the CLECs offer ISDN services. As the deployment of IDSL was speeding up on the local loop, the providers developed a new twist, called always on ISDN, mimicking a leased set of channels that are always connected. Bonding the channels together, users can surf the Net at speeds of 128 Kbps. Note that this is a symmetrical digital subscriber line.