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From: tnixon@hsfmsh.UUCP (Toby Nixon)
Newsgroups: comp.dcom.modems
Subject: CCITT standard on multistandard modem handshake?
Message-ID: <3478@hsfmsh.UUCP>
Date: 10 Jul 90 13:15:48 GMT
Sender: daemon@hsfmsh.UUCP
Organization: Hayes Microcomputer Products, Inc.  Norcross, Georgia
Lines: 47

In article <1990Jul4.123905.29321@santra.uucp>, Joni Jaakko J{rvenkyl{ 
asks:

- What is the status of the CCITT standard for multistandard modem handshake?
- 
- And what shall it probably be like - from highhest to lowest or are they
- going to make some 'universal handshake' procedure so that probably 'all'
- async modems could negotiate the highest speed with just one procedure?
- (so that v32-v22bis-v21 handshake mess wouldn't be required anymore)

The "Automode procedure", as it is known, has been defined as an 
appendix to Recommendation V.32 (and V.32bis, by reference).  It 
specifies how combined V.32/V.22bis modems (it doesn't reference 
V.21 or any other standard) can automatically select the highest 
common speed between them and other combined, V.32-only, or 
V.22bis-only modems.  It works "fast" if the calling V.32 modem 
follows the rule that it should begin handshaking as soon as the 
2100Hz answer tone is heard (most do); otherwise, after the answer 
tone, it sends a couple of seconds of V.22bis handshake (unscrambled 
binary ones), before reverting to the normal V.32 handshake.  

Because of the need to interwork with existing modems made according 
to these standard, we couldn't define an entirely new mechanism (a 
"universal handshake", as you call it).  It was considered, but 
rejected, mainly on the basis that it could be included only in new 
designs, and it is the intention of SG XVII to probably create only 
ONE MORE modem standard (after V.32bis and V.17), which will 
hopefully standardize modulation at 19,200bps or higher.

In the USA, the national standards committee on modems (TIA TR-30) 
is extending the CCITT-defined V.32/V.22bis handshake to include 
automatic interworking with Bell 103, Bell 212, V.21, V.22, and V.23 
modems.  Because of the inclusion of US proprietary standards, this 
work won't be taken forward to the CCITT, but is nevertheless 
expected to be widely used by modem manufacturers who include these 
industry standards in their products.

	-- Toby

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