Telephone Company WAN Technologies: Circuit Switching
The telephone company provided circuit-switching technology for a Wide Area Network (WAN) solution is so widely used because data delivery is almost guaranteed. Circuit-switched solutions are characterized by connections that are established temporarily to send data. If you are using a circuit-switched solution, each time you send data to a location, you must establish the connection, send the data, and close the connection.
This process is done automatically to addresses that are predefined by your telephone company and for which your router is configured. When you use circuit switching, your data always takes the same path and is guaranteed to arrive in order and intact. For these solutions, you contract the amount of bandwidth you require, and this bandwidth is yours, so you do not share it with other customers.
Because you must pay for this bandwidth, this option may be appropriate for low-bandwidth solutions, but it becomes costly as bandwidth needs increase.
The main example of circuit-switched solutions is Integrated Services Digital Networks (ISDN), which is a solution that uses digital connections to carry either computer data or voice traffic.
This solution uses two types of channels to carry data, B-channels and D-channels. A B-channel is capable of carrying data at a rate of 64 Kbps. A D-channel carries signaling data at a rate of 16 Kbps or 64 Kbps. Here are the main kinds of ISDN services In North America:
Basic Rate Interface (BRI): The implementation of BRI supports two 64-Kbps B-channels to carry data at a combined rate of 128 Kbps. The signaling channel (D-channel) for BRI is 16 Kbps.
Primary Rate Interface (PRI): The implementation of PRI supports up to 23 64-Kbps data channels (B-channels) to carry data at a combined rate up to 1.45 Mbps, while having one additional 64-Kbps D-channel carry the signaling information.