Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

The Bell standards were the first modem communications protocols. The first of these standards was Bell 103, which paved the way for today's complex and efficient modem standards, such as V.32bis and V.42bis. While AT&T largely controlled the standardization of the original modem standards, the CCITT (Consultative Committee for International Telegraph and Telephone), established as part of the United Nations' ITU (International Telecommunications Union), controls most standardization today. The Bell standards are summarized here:

• Bell 103    Supports 300-baud full-duplex asynchronous modem transmissions.


• Bell 113A and 113D    A originates calls, and D answers calls.


• Bell 201B    Supports synchronous 2,400-bits/sec full-duplex transmissions.


• Bell 202    Supports asynchronous 1,800-bits/sec full-duplex transmissions.


• Bell 208    Supports synchronous 4,800-bit/sec transmissions.


• Bell 209    Supports synchronous 9,600-bit/sec full-duplex transmissions.


• Bell 212A    Supports 1,200-bit/sec full-duplex transmissions (equivalent CCITT V.22 standard).

Many other standards have been developed since these initial standards, such as the CCITT "V dot" series standards. Microcom, a modem and communications software vendor, developed several standards on its own that have also come into widespread use or been integrated into ITU standards.

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
All rights reserved under Pan American and International copyright conventions.