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From: jbvb@VAX.FTP.COM (James Van Bokkelen)
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re: Fast ethernet card for PC
Message-ID: <8907201545.AA02055@vax.ftp.com>
Date: 20 Jul 89 15:45:47 GMT
References: <11306@cit-vax.Caltech.Edu>
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Compare apples to apples, not apples to tomatoes.  The WD8003/A, the
3C523, the NI5910 and other Microchannel cards can handle 2.5Mb/sec
*TCP* transfer rates, with reliable, ordered, acknowleged data
delivery.  The delivered data rate is 25% of the available bandwidth,
the Acks and headers probably bring the actual usage up to nearly 30%.
Even Van Jacobsen's experiments, with much faster processors, have not
gotten the delivered data rate above about 80% of the available
bandwidth, and that was between a pair of 68K boxes alone on a cable.

16-bit busses (either on-board or in the host PC) will almost always
out-perform 8-bit busses.  Buffer size doesn't matter too much with
TCP/IP, unless you've got broadcast storm problems.  The LAN
controller chip matters a good deal, but I haven't seen much variation
among them.  The vendor's supporting hardware also matters, but not
that much.

Packet loss due to inadequate LAN hardware will increase with network
load.  This ought to be compensated for by the TCP retransmit code
(note that the RPC/NFS has to do this on its own), but not everyone
understands retransmit very well.  Packet loss also increases with
broadcast and multicast load, because of software driver and buffer
overloading (rwho, RIP and Ethertalk are all suspects).

If the TCP/IP vendor supplies any sort of low-level statistics display,
you can see if it indicates excessive retransmits.  This indicates a
problem, but without a LAN monitor and an understanding of the protocols
involved, it is hard to tell inadequate hardware from low-quality software,
or from broadcast storms or other network congestion.

James B. VanBokkelen		26 Princess St., Wakefield, MA  01880
FTP Software Inc.		voice: (617) 246-0900  fax: (617) 246-0901