Switch-hub?

[Jonathan Hutchins]

When you're designing a network for a large installation, you look at how
many of what type of device are in a physical location that the hub will
server.

An Ethernet Segment is a portion of the network on which all traffic for all
nodes is broadcast; the nodes must pick up their own packets from this
stream.  As you get more nodes doing more traffic on the segment, you start
to get more collisions, which starts to degrade the segment's performance.

Older Ethernet systems had a cable that ran from one workstation to another,
connecting them all in a chain.  This made it easy to understand the meaning
of the segment, all of these systems were using the same physical wire.
Nodes connected by Cat5 to a hub are using a different wiring scheme, but
the operation is the same, they're essentially all on the same wire.  Hubs
can be stacked/cascaded until you reach the limit of traffic.

If most of the network traffic is plain text, you can accomodate more notes
on an ethernet segment than if you're running applications off of a server.
I believe that Microsoft recommends keeping it down to around 50
workstations per segment.

A switch, on the other hand, is like a router.  Originally, they were used
to join segments into a larger network while avoiding collision storms by
keeping the segments distinct.  As networks "filled in", adding more nodes
in a given physical area, and as traffic per node increased, switches were
inserted to break up segments and reduce collisions.

All along, techno-geeks have looked at the switch and said - hey, each
connection gets the full network bandwidth to itself - groovy!  They started
out putting high-use nodes like the server directly on the switch, or even
dedicating a switch for all the devices in the computer room.

But of course, they put their own workstations on the switch too, and they
did see better times downloading those image files.

Then some sharp sales technician pitched a switch for the "high end
workstations", "each workstation gets a dedicated ten-meg line"!

As the same process trickled 100m ethernet through the network, the same
forces were at work, putting the servers, then the "important" devices on
the high-speed hubs, and there was already the expectation that some
people's word processors were important enough that they should have a
"dedicated line", so they were put on the switch too.

Nowadays, the equpment is so cheap that you can have an eight-port 100M
switch for your home network and not even think about it.  It's not
justified from a technical cost/benefit analysis, but it's what you want,
and you will see better performance when you're moving large files around
while other people are on the net too.

We have a pretty well engineered plant at UHC, and we've just gone to
switched 10M internet for all workstations, with the switches and servers on
a 100M switch.  There's an improved crispness of response, and overall work
seems more efficient.