[NTLUG:Discuss] Ethernet Switches

[Eric Schnoebelen]

Dennis Myhand writes:
- No.  It is a switch if it uses memory to store the packets before
- forwarding them and transistors (or some other suitable electronic
- devices) to make the connections between ports.  It is an hub if
- the connection between ports is always there and the packet from
- one machine on the hub goes to ALL machines on the hub.

	Very close.  The packet doesn't have to be stored before
forwarding (and the mid-range and higher products don't).
Basically, in a switch, a port never sees a packet not addressed
for that port (via the ethernet MAC address.)

	A hub is `classic' ethernet, just stuck into a little box,
so the bus is only three inches long, but the tails are hundreds
of feet.

-                                                         Full-
- or half-duplex merely refers to the speed at which the information
- is moved.

	Nope.. Duplex refers to the ability to transmit while
receiving.  Half duplex can only transmit _or_ receive during a
given timeslice.  Full duplex can transmit and receive
concurrently.

-            The speed at which the information is moved has nothing
- to do with whether it is a switch or hub.

	Hmm, I'll disagree there.  I've never seen a full duplex
hub.  And the nature of an ethernet bus would seem to prohibit
it. (a standard ethernet bus, as defined by 802.<mumble> is
carrier-sense collission detection, which means the card listens
for a collision as it starts to transmit.)

-- 
Eric Schnoebelen		eric at cirr.com		http://www.cirr.com
	"Ford, If I were to ask where in the hell we are, would I
		 regret it?" -- Arther Dent, HHGG