Fred Sending to Barney, While Betty Sends to Wilma

Fred Sending to Barney, While Betty Sends to Wilma

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This example shows two devicesFred and Bettysending a frame at the same time. With a hub, only one device could send at a time. With two devices sending at the same time, the capacity of the LAN to forward frames doubles!

The original Ethernet specifications define a 10-Mbps transmission rate. In Figure 6-3, two separate transmissions occur, each at 10 Mbps. In one way of thinking, this LAN has 20 Mbps of capacity because it allows two concurrent transmissions at 10 Mbps. Now imagine a switch with 24 ports, with the device on port 1 sending to the device on port 2; the device on port 3 sending to the device on port 4; and so on. All 12 of the odd-numbered ports are sending frames in this case, so this switch supports 12 x 10 Mbps, or 120 Mbps, of capacity.