LinuxSA Mailing list archives

  From: Adrian Butterworth <adrian@econ-outlook.com.au>
  To  : linuxsa@linuxsa.org.au
  Date: Mon, 15 Nov 1999 19:12:53 +1030

Re: LAN Speed...

Hi all
This thread seem a bit clouded with mythology

On Mon, 15 Nov 1999, Andrew Whyte wrote:
> MWP wrote:
> > 
> > Hi all...
> > 
> > The "server" is a RH6.0 box and the other machine is a Celeron 433 running
> > Win98.
> > The NIC's are crappy realtek PCI 10Base2 cards, over a 5 metercoax cable.

.. in my experience realtek network cards are not particularly crappy   
.. there was a problem with the Windows driver for realtek 8029's
  which causes problems unless you apply the fixed driver available
  from their site.  

> > 
> > What sustained speeds do you think I should expect transferring files from   
> > the linux box to the win98 box using FTP??

.. 900K or more - see the test below

> > 
> > At the moment, I get around 450Kbytes/s.
> > 
> > BTW... the server is running BeroFTPD if it makes any difference.
> > 
> 
> You're getting what you should be expecting ofer 10base2.
> 
> It's only a 10Mbits medium, which is 1.25MB / sec at best.
> however, 10base2 which is a CMSA/CD setup, basic rule is that
> every node you add will half the total available bandwitdh.

.. There is no such "rule"
.. You can have a virtually unlimited number of hosts without effecting
  transfer rates as long as they are not colliding.
.. if only two machines are active at the same time there will be few if
  any collisions 

A test I just ran on an actual FTP transfer between two linux machines
with realtek PCI cards each connected to hubs which are joined by
10base2 (thinnet coax) on a active segment containing 9 hosts and a
router. It achieved 9.7e+02 Kbytes per second
The file was 19,532,163 bytes (jdk1.2pre-v2.tar.bz2)
and transfered in 19.7 seconds
I chose a highly compressed file to eliminate any compression
opportunities.

NFS transfers are much slower (aprox half this speed) due to protocol
differences 

> 
> IF you are using a Crossover cable directly between the boxes,
> you'll get the same through put as a hub, 350-450KB/sec
> If you through a switch in there, you'll get much better performance,
> somewhere around 850-1250KB/sec.

.. A crossover cable will give you maximum transfer rate possible between
  the two interfaces. And unlike coax you can get full duplex transfers.

.. A switch can't make things faster, it will in fact introduce a small
  latency as it buffers at least the start of the ethernet packet to 
  determine which segment it has to be switched to.

.. on a network with only one active transfer a hub is faster than a
  switch  

.. a switch helps in a congested network by dynamically breaking the  
  network into smaller segments which can transfer data independently  
  of one another. It does this by learning the ethernet addresses of
  the network cards on each leg(socket) and storing them in an
  internal table.

  When an ethernet packet comes through the swich looks for the ethernet
  address of the destination and checks this against its table,
  buffering the data. If it finds a match it knows which leg to sent
  the packet out on and doesn't put the signal out on the other legs.

  This reduces keeps those other legs bandwidth free. If on the
  otherhand it doesn't have a entry for the destination it has to   
  broadcast in on all legs much like a hub but with a small delay from  
  the buffering.

  Thus a switch helps only while a network is saturated and then only
  when there are at least 4 legs active as when host1 on leg1, is
  talking to host 2 on leg 2, while host 3 on leg 3, is talking to host
  4 on leg 4. 

  <snip>...

Regards
Adrian

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