Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!MATHOM.CISCO.COM!BILLW
From: BILLW@MATHOM.CISCO.COM (William "Chops" Westfield)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: SLIP, IP Routers and Named Pipes
Message-ID: <12628737090.25.BILLW@mathom.cisco.com>
Date: 10 Oct 90 19:24:44 GMT
References: <1990Oct9.221843.20145@bnrgate.bnr.ca>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 39


    > 
    > Really?  FTP is slow?  Our experience at cisco (with our own terminal
    > servers, of course) was that FTP was quite zippy - the sliding window
    > of TCP bought you much more than you lost from the big headers.  Compared
    > to DEC-20 to PC kermit, FTP's FTP over slip was nearly twice as fast.

    Care to share the test configuration with us?  I use SLIP over a
    Microcom AX/9624c MNP Class 6 modem and a cisco terminal server.  I
    see the modem lights grinding away, waiting..., grinding away,
    waiting..., etc.  It's almost as though the VJ algorithms were
    throttling...  I found I could get more files through by starting 2-3
    FTPs so that one is still running when the other 1-2 are stalled.
    Sort of round-robin FTP transfers; doesn't work if I've only got one
    file to transfer though... :^(


The configuration was a 286 based PC clone running either (old, non-sliding
window, 92 byte packet) MSDOS kermit or FTP software's package v 1.16,
connected vai a 19.2kbps direct line to aa cisco terminal server (v6.1
software?  This was slightly before SLIP was released on the cisco TS)
We were talking to either HPUX or TOPS20 (no VJ algorthims in sight!)

FTP software was configured with a window size of 1024, and an MSS of 512,
if I remember correctly.  It's sort of important (with no slow start) that
the number of MSS packets in a window be both larger than 1 and smaller than
the effective queue-size on the terminal server (then 3, now settable). (Your
description of the problem sounds exactly like the MSS is > window/2, so that
you end up operating lock-step instead of sliding windows, by the time SWS
algorithms come into play.)

FTP file transfer speeds were about 13kbps, while kermit was about half that.

I haven't done those tests in a couple of years, though - I would hope that
everything still works at least as well as it did then!

Bill Westfield
cisco Systems.
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