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Unformatted text preview: d the other end is attached to a port on the hub. A hub slavishly copies every bit that it receives on each port to every other port. Thus every host sees every bit. Each ethernet adapter has a globally unique 48-bit address that is stored in a persistent memory on the adapter. A host can send a chunk of bits called a frame to any other host on the segment. Each frame includes some ﬁxed number of header bits that identify the source and destination of the frame and the frame length, followed by a payload of data bits. Every host adapter sees the frame, but only the destination host actually reads it. Multiple ethernet segments can be connected into larger LANs, called bridged ethernets, using a set of wires and small boxes called bridges, as shown in Figure 12.4. Bridged ethernets can span entire buildings or campuses. In a bridged ethernet, some wires connect bridges to bridges, and others connect bridges to
A host host hub 100 Mb/s B host X bridge 100 Mb/s 1 Gb/s 100 Mb/s 100 Mb/s host hub host host C host host hub host hub host host bridge Y host Figure 12.4: Bridged ethernet segments. hubs. The bandwidths of the wires can be different. In our example, the bridge-b...
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