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Re: [K12OSN] 100Mbit switch vs. 100Mbit hub



Rob Owens wrote:
I've been on this list long enough that I've heard "use a switch, not a
hub" about a hundred times.  But I have a question about the reasoning:

The server has the most traffic going to/from it.  So if you were using
a switch, the server port of the switch would be saturated first--as
soon as 100Mbit/sec is going to/from the server.  If
you instead used a hub, the only difference I see is that *all* of the
ports would saturate at the same time--as soon as 100Mbit/sec is going
to/from the server.
Since there is no traffic going from one terminal
to another, it seems like a 100Mbit/sec hub would become a bottleneck at
the same time that a 100Mbit/sec switch would.  What am I missing?

What people are generally recommending is a switch with a gig uplink and 100M to the clients, but even with 100M on all ports there is a big difference. With TCP traffic, the receiver has to acknowledge the data at least within the transmit window size or the sender will wait. So for about every 3 packets or less that the server sends, an ack must come back from a client. When the link is saturated by the server, on a hub the clients are going to have collisions and delays sending the acks. On a full duplex switch, the directions are independent so nothing has to wait for anything else.

--
  Les Mikesell
   les futuresource com


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