Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!elroy.jpl.nasa.gov!decwrl!netcomsv!gandrews
From: gandrews@netcom.COM (Greg Andrews)
Newsgroups: comp.dcom.modems
Subject: Re: Over 1000 cps with PEP?
Summary: Don't use a T1000, use a T2500 or TB+.
Message-ID: <1991Jun19.051429.5731@netcom.COM>
Date: 19 Jun 91 05:14:29 GMT
References: <1991Jun19.003439.7587@emperor.scs.com>
Organization: Netcom - Online Communication Services  UNIX System {408 241-9760 guest}
Lines: 51

In article <1991Jun19.003439.7587@emperor.scs.com> brucek@emperor.scs.com (Bruce Klein) writes:
>
>How are you people achieving this?
>
>I have a number of Telebit modems here.  For this experiment, I called
>a T2500 with a T1000 using the PEP protocol.  The modems were connected
>to their hosts through 9600 baud serial ports.  
>
>Using xmodem and the telebit xmodem support (s111=20) I was able to achieve
>500 cps.
>

I regularly get 900+ cps with xmodem spoofing through T1000s.  I wonder if
your modems were REALLY getting the spoofing negotiated...  Just turning
on a register doesn't do the trick; the modems must negotiate the feature
properly or it won't get turned on.

>
>Next I tried zmodem.  With a Sun on one end and a Mac Plus running Zterm
>on the other (same two modems) I was able to achieve peak thruput of 700
>cps.  I was unable to sustain this though, and on average it delivered
>about 400 cps.  There may be something wrong with my sz binary--on EVERY
>file it produces a CRC error at bytes 6144, 13312, 20480, 27648, ....
>(Anyone have any ideas about that?)
>

Errors in a streaming Zmodem transfer usually point to a flow control
problem.  The problem could be at your end of the signal chain, or at
the Sun's end.  Every error caused by bad flow control means data must
be transmitted again - slowing down the average throughput numbers.

You should also make sure that the modem's spoofing is turned OFF for
zmodem transfers.  Otherwise, spoofing can cause interference.

>
>Are these figures reasonable?  If not, what could be the problem?  The
>two phone lines in this instance were part of the same Centrex system,
>and thus should be of good quality.  
>

Getting throughputs higher than 950-960 cps isn't possible with a T1000
(unless your transfer protocol performs compression).  That's because the
T1000's PEP mode is limited to 9600 bps throughput.  To get higher rates,
you need to use full-speed PEP modems like the T2500, TB+, or T2000.


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 |  Greg Andrews   |       UUCP: {apple,amdahl,claris}!netcom!gandrews    |
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