Re: Long ethernet


glen herrmannsfeldt wrote:
grisley wrote:
Hi,
We have to connect 32 dataloggers, separated 500m from each other (16km
total) with an ethernet LAN. We're going to place 32 fiber optic
switches close to each datalogger, and an utp link from switch to the
datalogger.

I think this network is excesively long due to ehernet inherent CSMA/CD
timing considerations, and that we should split the network up using
routers into smaller sub-networks. On the other hand, traffic is going
to be quite low.

If the long links are full duplex, then there is no CSMA/CD problem.
Otherwise, for 10baseFL (10 megabit/s) you should be fine unless you
daisy chain them.

You will need to provide further details however:-

Assuming that the switches are:-

Full Duplex on the Fiber Optic ports at 10 or 100 or 1000 Mbps
OR
Are 10 Mbps

There there is no problem with CSMA/CD

The only way there could be an issue is with 100 HD where
the max length is 200M (IIRC)

The standard (IEE 802.1d) does say however that the maximum
network diameter is 8 bridges (bridge=switch pretty much).
This though really applies to the Spanning Tree Protocol
and I think that unless you need STP for redundant links
then there will be no problem.

Even if you want to use STP I find it hard to imagine that
it will not work since the standard was written years ago
and took into account slower links and lower capacity
switches.

I have never tried a network of > a few switches in diameter.

AH! Oh yes I have. Years ago my company used to test
switches by configuring them with a lot of vlans with
two ports in each. These VLANs were then connected
by crossover cables making a very long network and
a pair of PCs were used to ping through the lot.
It worked. This was done with dozens of VLANs.

If you do want to stick to the standard you will
need 4 routers to break the 32 nodes into 4 x 8 switch
(approx) sections.

.

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