jjj@batgirl.hut.fi (Joni Jaakko J{rvenkyl{) (07/04/90)
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)
--
jjj@niksula.hut.fi mbaX> Fnab vgr "wrrf", c|yw{!
jjj@otax.tky.hut.fi ubaX>tnixon@hsfmsh.UUCP (Toby Nixon) (07/10/90)
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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