Path: utzoo!utgpu!watserv1!maytag!xenitec!zswamp!root
From: root@zswamp.uucp (Geoffrey Welsh)
Newsgroups: comp.dcom.modems
Subject: Over 1000 cps with PEP?
Message-ID: <244.2861EA83@zswamp.uucp>
Date: Fri, 21 Jun 91 03:13:28 EDT
Organization: Izot's Swamp BBS (FidoNet), Kitchener, Ontario

In a letter to All, Bruce Klein (brucek@emperor.scs.com ) wrote:

 >How are you people achieving this?

   Actually, if you want to use YMODEM-G, I'm sure that you'll exceed 1000 CPS 
by a significant margin.

 >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.  

   Problems:

1) With 9600 bps serial ports, you're limited to 960 CPS, no matter what.  
Switch to 19,200 bps and you stand a chance of going over 1000 CPS.

2) I'm led to believe that the T1000 is not as fast as the T1800 (TB+) or 
T2500.

 >Using xmodem and the telebit xmodem support (s111=20) I was 
 >able to achieve 500 cps.

3) XMODEM is a slow protocol, period... and few programmers bother to code it 
very efficiently as a result.  In fact, even at 115,200 bps over a null modem, 
I have not been able to reach 1000 CPS with XMODEM!

 >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?)

   Yes, your computer-modem interface was not correctly configured and data 
was being lost.  Consult your manuals on the subject of handshaking.  RTS/CTS 
(hardware) handshaking is preferred, but XON/XOFF will do fine in almost all 
aplications.

   Note that each computer and its modem must be using the same handshaking 
technique (and the cable must support the relevant pins), but the two modems 
may be using a different apporach (e.g. the Sun and its modem may be using 
XON/XOFF while the Mac and its modem may be using RTS/CTS).
 

--  
Geoffrey Welsh - Operator, Izot's Swamp BBS (FidoNet 1:221/171)
root@zswamp.uucp or ..uunet!watmath!xenitec!zswamp!root
602-66 Mooregate Crescent, Kitchener, ON, N2M 5E6 Canada (519)741-9553
"He who claims to know everything can't possibly know much" -me