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This chapter is from the book

The Role of the Physical Layer

We have already discussed the most popular cabling used in LANs—UTP. But to fully understand the operation of the network, you should know some additional basic concepts of the physical layer.

The OSI physical layer accepts a complete frame from the data link layer and encodes it as a series of signals that are transmitted onto the local media.

The delivery of frames across the local media requires the following physical layer elements:

  • The physical media and associated connectors
  • A representation of bits on the media
  • Encoding of data and control information
  • Transmitter and receiver circuitry on the network devices

There are three basic forms of network media on which data is represented:

  • Copper cable
  • Fiber
  • Wireless (IEEE 802.11)

Bits are represented on the medium by changing one or more of the following characteristics of a signal:

  • Amplitude
  • Frequency
  • Phase

The nature of the actual signals representing the bits on the media will depend on the signaling method in use. Some methods may use one attribute of a signal to represent a single 0 and use another attribute of a signal to represent a single 1. The actual signaling method and its detailed operation are not important to your CCNA exam preparation.

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