Networking / Beginners

The Physical Layer

Sometimes called the PHY layer or layer 1, this is the hardware layer and deals with the transmission of bits over a channel. Typical problems are what voltages (or change of voltages) or colour and intensity of light pulses should be used to signify a one and a zero; how long (in time) a bit should be; how many wires to use in a cable; what each wire is for. This is an electrical or optical or mechanical or other specification that transmits a continuous stream of bits (if we chose to use bits). Note that this layer might be radio or any other transmission medium rather than copper wire or optical fibre.

This layer is sometimes divided into two sublayers for extra flexibility:

  1. Physical Media Dependent (PMD) sublayer for actual hardware like optical transceivers or copper wire. For example, 10Gb Ethernet has two kinds of optical transceiver for short- and long-range networks.
  2. Physical Coding Sublayer (PCS) or Physical Layer Convergence Procedure (PLCP) sublayer is for how bits are encoded on the PMD. For example, 10Gb Ethernet uses a 64B/66B encoding.
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In this tutorial:

  1. Layering Models
  2. The Seven Layer Model
  3. The Physical Layer
  4. The Data Link Layer
  5. The Network Layer
  6. The Transport Layer
  7. The Session Layer
  8. The Presentation Layer
  9. The Application Layer
  10. How the Layers Fit Together
  11. Why Layers and Encapsulation?
  12. The Internet Model
  13. The Link Layer
  14. Models and Protocols
  15. Comparing OSI and Internet Models