Integrated Services Digital Network

(I-S-D-N)

A telephone standard designed to replace analog connections with digital. ISDN started as a recommendation in the 1984 ITU Red Book. It comes in differing connection speeds and bandwidth:

• DS0 (64 kbps and 1 channel PCM)
• T1 or DS1 (1.54 Mbps and 24 channels PCM)
• T1C or DS1C (3.15 Mbps and 48 channels PCM)
• T2 or DS2 (6.31 Mbps and 96 channels PCM)
• T3 or DS3 (44.736 Mbps and 672 channels PCM)
• T4 or DS4 (274.1 Mbps and 4032 channels PCM)

Channel, as used here, is one voice channel. A common ISDN assignment is a Basic-Rate Interface (BRI) which uses one D-channel (call-control info) and two B-channels for voice/data at 64 Kbps each.

It has not widely caught on in the United States due to spotty and differing implementations of the international standards.

More Information

• ISDN Tutorial
• National ISDN Council
• ISDN Tutorial