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From: tnixon@hsfmsh.UUCP (Toby Nixon)
Newsgroups: comp.dcom.modems
Subject: Re: What is CCITT V.22 mode?
Message-ID: <3428@hsfmsh.UUCP>
Date: 5 Jul 90 15:10:09 GMT
Sender: daemon@hsfmsh.UUCP
Organization: Hayes Microcomputer Products, Inc.  Norcross, Georgia
Lines: 42

In article <49570@iuvax.cs.indiana.edu>,
herrj@silver.ucs.indiana.edu (Jon Herr)  asks:

- I was checking out the AT command summary in the user's manual and ran
- accross this "mode" for the B/B0 commands.  What is it?

The International Telegraph and Telephone Consultative Committee
(French acronym, CCITT) is part of the International
Telecommunications Union (ITU), which is the United Nations
organization with responsibility for setting worldwide
communications standards and policies.  One of the Study Groups in
the CCITT, Study Group XVII, sets standards for data transmission on
the telephone network.  All of these standards are designated by the
letter "V" followed by a period and a number. 

Until the Carterfone decision that allowed non-Bell equipment to be
hooked to the phone network, AT&T controlled what modems could be
connected, and they followed Bell standards.  After Carterfone, the
USA joined the rest of the world in emphasizing international
standards (CCITT).  So, at 2400bps and higher, both the US and the
rest of the world use primarily CCITT standards, but at 1200 and
below we in the USA still use primarily the Bell standards (103J for
300bps, 212A for 1200bps). 

V.22 is the CCITT standard for full-duplex data transmission at 1200
bits per second. V.22 is very similar to, but somewhat different
than Bell 212.  Modems that support both of these need a command
to allow the DTE to specify which type of modulation to use at
1200bps, which is B0/B1.  Many have another command [B15/B16 in
Hayes modems] to select between CCITT V.21 and Bell 103 at 300bps.

  -- Toby Nixon, Principal Engineer, Hayes Microcomputer Products
     (Hayes' representative in the CCITT)

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