Contents

1 Basics

• Designed by the CCITT in 1988 as a WAN technology, althought it can be used in the last-mile (residential access).
• Circuit-switching technology.
• Dedicated lines.
• Depending on the required capacity, it can use standard telephone copper wires, optical fiber, microwave, etc.
• Transports voice and data, simultaneously.
• Full-duplex (TDM).
• ISDN tariffs are based on a per-B(earer) channel basis and are similar to those of analog voice connections.
• There are two types of CBR channels:
  1. A B-channel that transports 64 Kbps. Usually used for data.
  2. A D(delta)-channel transports 16 o 64 Kbps. Usually used for call setup and other purposes.

2 BRI (Basic Rate Interface) (2B+D)

• Three channels consisting of two 64 Kbps B-channels (B1 and B2), and a 16 Kbps D-channel. The TDM has nine timeslots, which are repeated in the sequence shown in the figure.

• BRI has a call setup time that is less than a second.

3 PRI (Primary Rate Interface)

• A B-channel transports 64 Kbps. A D-channel transports 64 Kbps.
• The implementation of the PRI differs depending on the country:
  1. In North America and Japan the PRI service is delivered on one or more T1 carriers (often referred to as 23B+D) of 1544 Kbps (24 channels).
  2. In the rest of the world, the PRI service is carried over an E1 (30B+D = 2048 Kbps).