IDSL is short for ISDN DSL. Technically speaking, it is DSL running over an ISDN line. ISDN (Integrated Services Digital Network) is one of the oldest and well-established standards for delivering "high-speed" data transmission over regular phone lines.

Since it uses the same protocols as ISDN, it is useful to look at how ISDN works.

How ISDN Works
When a phone line is converted to ISDN, the line is capable of transferring 144 kilobits/second (Kbps). This speed is divided into three sections called channels.

There are two 64 Kbps channels (called "B channels") and one 16 Kbps channel (called a "D channel"). The two B channels are used to transmit data. The D channel controls the two B channels.

The two B channels can be "bonded" to provide a 128 Kbps connection.

However, since ISDN replaces the existing phone line, all voice, fax, and other phone line communication must be carried over one of the B channels.

This means that if you receive or place a call while connected to an Internet service, one of the B channels must drop the Internet connection to handle the call. Consequently, the speed of the connection will be cut in half (to 64 Kbps).

IDSL Differences
One of the primary difference between ISDN and IDSL is that IDSL uses a completely separate phone line. This means that the IDSL line is a separate phone line dedicated just for Internet access.

Another primary difference is the type of connection. ISDN travels through the same network as regular phone calls. Thus, you still need to tell your ISDN equipment to dial-in to you Internet provider.

With IDSL, the connection is routed through the same high-speed network used for DSL. This means the IDSL connection is like an extended network connection--connecting you computer right into StarNet's network.