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From: hall@state.enet.dec.com (Dan Hall)
Newsgroups: comp.dcom.modems
Subject: Re: New Modems
Message-ID: <2038@mountn.dec.com>
Date: 28 Nov 90 19:00:44 GMT
References: <1990Nov28.042729.8077@jwt.UUCP> <1990Nov21.221114.11850@unixland.uucp> <9842@discus.technion.ac.il> <1990Nov26.062122.24546@sbcs.sunysb.edu>
Sender: news@mountn.dec.com
Reply-To: hall@state.enet.dec.com
Organization: Digital Equipment Corporation, Merrimack, NH
Lines: 51

In article <1990Nov28.042729.8077@jwt.UUCP>, john@jwt.UUCP (John Temples)
|> From: john@jwt.UUCP (John Temples)
|> Newsgroups: comp.dcom.modems
|> Subject: Re: New Modems
|> 
|> >The PC Mag test was measuring the ability to hold the line
|> >when using V.32/V.42/V.42bis and not PEP.
|> 
|> That's not what the article says.  Quoting here: "The Telebit modem
|> did not perform well under any of our degraded-line tests using
|> either its V.32 or PEP mode."  However, beyond this statement, there
|> were no further references indicating that the reviewers used or
|> tested PEP.
|> 

You missed another small oblique reference.  Quoting from page 329:

"Unfortunately, the Telebit modems were not able to complete the data
transfer tests under any of the EIA-standard impairment conditions.
We saw similar problems using these modems under their native PEP mode."

The article included 3-D bar graphs showing throughput of various file
types, and except for the baseline tests, there were conspicuous holes
where the Telebit performance should have been, because of their inability
to complete any of the 1V32 through 6V32 impairment tests.  BTW, someone
asked recently what those tests are.  They are combinational channel
impairment tests established by the EIA for V.32 modems, as described in
EIA/TIA standard 496-A.  The baseline tests used by PC Magazine simulated
a typical U.S. long-distance circuit, with the following impairment levels:

Input level:	-10 dBm
Output level:	-23 dBm
IMD, 2nd-level:	 52 dB
IMD, 3rd-level:  50 dB
Frequency shift: 1.25 Hz
Phase jitter:	 8 degrees

No level for white noise was given (should have been about 32 dBrn), nor
did they mention any gain or delay filtering (flat line?).

|> John W. Temples -- john@jwt.UUCP (uunet!jwt!john)
|> 

-Dan
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