Cover Page by Andrew S. Tanenbaum, David J. Wetherall

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2THE PHYSICAL LAYER

In this chapter we will look at the lowest layer in our protocol model, the physical layer. It defines the electrical, timing and other interfaces by which bits are sent as signals over channels. The physical layer is the foundation on which the network is built. The properties of different kinds of physical channels determine the performance (e.g., throughput, latency, and error rate) so it is a good place to start our journey into networkland.

We will begin with a theoretical analysis of data transmission, only to discover that Mother (Parent?) Nature puts some limits on what can be sent over a channel. Then we will cover three kinds of transmission media: guided (copper wire and fiber optics), wireless (terrestrial radio), ...

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