[4015] in linux-net channel archive
Re: Question on performance
daemon@ATHENA.MIT.EDU (ATPlack)
Thu Aug 15 05:03:51 1996
Date: Tue, 13 Aug 1996 15:01:16 -0500
From: ATPlack <ATPlack@scj.com>
To: buttice@elecomm.net, kris10an@internet.dk, linux-net@vger.rutgers.edu
Please remember that a PC using an ISA bus is limited in bandwidth.
3COM estimates that 380k/sec is the peak for an ISA bus and their card.
NE2000 lists about 185k/sec. This is with the Novell ODI stack in DOS.
PCI bus or EISA bus cards are better.
Sounds like Linux is beating these DOS tests by a landslide. 500k sounds
good to me. :) However, Novell servers have shown an 800k throughput or
more with an ISA card on fast machines so it is not incredible.
A little lesson on Ethernet to dispel myths:
Networks have two major performance factors. Throughput and Utilization.
Throughput for 10BaseT Ethernet is rated at 10Mb/sec simplex (20Mb/s duplex
which is new for concentrators or if you use it point to point in 10BT).
Each workstation transmits at this full rate of 10Mb/sec. However, since
there are only a maximum of 1.5k bytes in each packet, you end up with less.
The full rate is still 10Mb/sec and each packet gets to use that. If you
want more explanation I can give it to you. Suffice to say, most people
measure throughput on the networks in the number of packets/sec. This is
assuming a full packet (a ping is usually 56 bytes which is smaller than the
1.5k) or that the average packet size is known.
Ethernet is designed with a gap between each packet. That way your packet
does not get mixed up with someone else's packet (a collision). The bigger
that gap, the less utilization is on the network. The theory is that if I
have 1000 packets to send, I will get them out in as short of a time as
possible with the smallest gap as possible. Therefore, utilization of the
network is measuring how much of the 10Mb/sec we are using (smaller
inter-packet gaps meaning more traffic).
A really good network with little noise can achieve 95% utilization. Most
only see 75% due to noisy connections (EMF, dirty contacts, poor wire).
That is what the Base in 10BaseT gives us. Baseband transmission is
susceptible to noise.
The fun thing is that at 75% utilization with 1.5k packets you only have a
little over 600 packets/sec on the wire. With a standard pings (56 bytes),
you get 16,700 packets/sec. Utilization remains the same at 75%.
>>In real world cases Ethernet isn't a 10Mbit net, more like a 3-4 Mbit net.
This could not be true actually, but might seem true in a noisy network.
Thin-net(Cheap net) sees this regularly. Mainly due to poor cabling,
terminators and connectors.
----------
From: kris10an@internet.dk
To: linux-net@vger.rutgers.edu
Subject: Re: Question on performance
Date: Tuesday, August 13, 1996 1:11PM
On Thu, 8 Aug 1996, Emanuele Buttice wrote:
> I have never been able to get more than 500KB transfer rate between any
> of my PC's, Is this normal ?
>
> I have about 5 pc's running Linux 1.2.13 mostly P5's with >= 16meg Ram
> and ISA 3ccom 3c509TP cards. The network traffic is very light and my
> tests are done when no one is working. I have done transfers using ftp
> and tcpspray but the results are simular.
That's very normal, actually it's pretty high.
About 300KB/s is normal for a network in good condition, with some
traffic.
In no cases schould it be slover than that, and on a small network with
little or no traffic, schould you be able to see higher rates.
Getting near 10Mbit/s will only happen with absolutely no disturbing
traffic, and short exellent connections. Like two machines connected
without a hub.
In real world cases ethernet isn't a 10Mbit net, more like a 3-4 Mbit net.
***********
Kristian Elof Soerensen http://www.gbar.dtu.dk/~c948632
kris10an@internet.dk 45 93 92 02 2:236/447.19
