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From: kaufman@Neon.Stanford.EDU (Marc T. Kaufman)
Newsgroups: comp.dcom.modems
Subject: Re: IBM dual speed modems
Keywords: IBM modem speeds
Message-ID: <1990Aug16.012436.22491@Neon.Stanford.EDU>
Date: 16 Aug 90 01:24:36 GMT
References: <1990Aug15.140308.25931@cbnewse.att.com>
Distribution: na
Organization: Computer Science Department, Stanford University
Lines: 17

In article <1990Aug15.140308.25931@cbnewse.att.com> mccoy@cbnewse.att.com (earl.mccoy) writes:
.The IBM 5868 and 7868 modems transmit from master to tributary at
.one speed, say 14.4K, and transmit from tributary to master at
.another speed, say 9.6K. My question is: what speed does the master
.modem use across the DTE/DCE interface, i.e. to the FEP? Does
.the modem send back at 9.6K and receive at 14.4K, or does it use
.a single 14.4K speed? If the former the FEP LIC must autobaud, if
.the latter the modem must buffer the frame. I am unable to find
.explicit documentation on this point. Thanks in advance.
.Earl E. McCoy 312-230-4236 attmail!emccoy cuuxb!ntcc!mccoy

Synchronous modems provide clock(s), both TxC and RxC, to the FEP, so no
autobauding is necessary.  The FEP just clocks bits as demanded by the modem.
That is why synchronous modems can shift speed with no specific support by
the FEP.

Marc Kaufman (kaufman@Neon.stanford.edu)