Path: utzoo!utgpu!watserv1!maytag!xenitec!zswamp!root
From: root@zswamp.uucp (Geoffrey Welsh)
Newsgroups: comp.dcom.modems
Subject: Tuning slip on a T2500/NextStation
Message-ID: <231.285ED74C@zswamp.uucp>
Date: Tue, 18 Jun 91 12:48:30 EDT
Organization: Izot's Swamp BBS (FidoNet), Kitchener, Ontario

In a letter to All, Booker Bense (benseb@grumpy.sdsc.edu ) wrote:

 >- Well, I've been banging on a version of slip for the NeXT 
 >for about a month. The connection is t2500 to t2500 and I
 >generally run it in  pep mode. 

 >- A back of the envelope calculation reveals:

 > (19200 / 8 ) = 2400 bytes/sec * (2/3 data/tcp packet length 
 >) = 1.6
 >Kbytes /sec ftp transfer rate.

 >Or in other words , I shoud expect an optimal ftp rate of 
 >about 1.5 Kb/sec.

 >- When I first started I was seeing about a 0.4 kb/sec 
 >coming in and 0.6 going out.

Lesson #1: don't use half-duplex or asymmetrical channels for SLIP.  Use V.32 
mode in stead of PEP.

Lesson #2: when manufacturers say that the modem is capable of "up to" 19200 
bps, they mean it has done this on cooked files which don't even faintly 
resemble real world data.

   V.32 "back of the envelope calculation": 9600 bps / 8 = 1200 bytes/sec 
(neglect MNP or LAP-M overhead) * 2/3 TCP data/packet = 800 CPS.

   That's theory; I'm sure that Larry will have realistic figures for us.

 >- The line is not the greatest , the pep connection has to 
 >retrain about every hour or so. Varying the modem settings
 >does not seem to have much effect.

  This may indeed pose a problem; perhaps you'd best stick with PEP and your 
best configuration so far.

 >I'm not really concerned with interactivity, fast
 >ftp is much more important!!

   TCP/IP is an interactive protocol, so to speak (it has a limited window 
size and must receive ACKs before it continues transmitting); you can't 
separate the issues.
 

--  
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