Network problem

[bscott at ntisys.com]

On Thu, 28 Aug 2003, at 7:20pm, s_ingham at comcast.net wrote:
> Warning: Many cheap multi-port 10/100 "switches" are not true switches but
> are really two repeaters plus a 2 port switch.  A 10Mbit and a 100Mbit
> repeater connected to all ports

  FYI, any "dual speed repeater" operates this way (more or less).  There's
really no such thing as a "dual speed repeater".  A given Ethernet bus runs
at a single speed.  So, to get a "dual speed repeater", a manufacturer
packages two repeaters in one unit.  Each repeater is potentially connected
to each port, and the right repeater is electrically connected when the
speed of the connection is negotiated.

  A bridge of some kind connects the two repeaters together.  This is
traditionally a simple bridge, i.e., one that does not do learning or
filtering.  Apparently, some manufacturers have been using a learning
bridge, and thus passing the unit off as a "switch".  That's highly bogus.

  A true switch is much more sophisticated then a repeater (which is why
they used to cost so much more).  Each port in a switch is a full Ethernet
transceiver.  Frames are received on a port, and the logic in the switch
decides what to do with each frame.  A typical store-and-forward switch will
buffer each frame, decide what port the frame is destined for, wait for that
port to become available (if needed), and transmit the frame out that port.  
If the destination port is the same as the source port, the frame is not
forwarded.  Only if the destination port is unknown will the switch transmit
the frame on all ports.

-- 
Ben Scott <bscott at ntisys.com>
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