Neil Croft wrote in a message to Mike Bilow:
 MB> (slightly incorrectly) called a "hub."  When you use a concentrator,
 NC> I would question the "(slighty incorrectly)" bit here. If
 NC> 3Com et al call them hubs in their catalogues then a hub is
 NC> quite likely /a/ correct name for them. If you consider the
 NC> topology of a hubbed Ethernet and then think of a hub on
 NC> say, an old wagon wheel, then that sounds right too. My
 NC> dictionary also defines a hub as "a centre of activity"
 NC> which also sounds about right. 
The distinction is subtle, but important.
A "concentrator" is a multiport repeater.  It operates at the Physical Layer 
and consists of electrical buffer amplifiers.  It does not read or understand 
any kind of addresses, nor even know about anything other than bits.
A "hub" is a store-and-forward device.  It operates at the Link Layer and can 
do rudimentary things based on knowledge of the protocol, such as discard 
frames with bad CRC.  An intelligent hub that can forward frames based upon 
their destination addresses is called a "switch."  A switch that has only two 
ports is usually called a "bridge."
Although concentrators are often called hubs, sometimes it is necessary to 
distinguish exactly what is meant.
 
-- Mike
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