Physical Layer - List of Services

List of Services

The major functions and services performed by the physical layer are:

  • Bit-by-bit or symbol-by-symbol delivery
  • Providing a standardized interface to physical transmission media, including
    • Mechanical specification of electrical connectors and cables, for example maximum cable length
    • Electrical specification of transmission line signal level and impedance
    • Radio interface, including electromagnetic spectrum frequency allocation and specification of signal strength, analog bandwidth, etc.
    • Specifications for IR over optical fiber or a wireless IR communication link
  • Modulation
  • Line coding
  • Bit synchronization in synchronous serial communication
  • Start-stop signalling and flow control in asynchronous serial communication
  • Circuit switching
  • Multiplexing
    • Establishment and termination of circuit switched connections
  • Carrier sense and collision detection utilized by some level 2 multiple access protocols
  • Equalization filtering, training sequences, pulse shaping and other signal processing of physical signals
  • Forward error correction for example bitwise convolutional coding
  • Bit-interleaving and other channel coding

The physical layer is also concerned with

  • Bit rate
  • Point-to-point, multipoint or point-to-multipoint line configuration
  • Physical network topology, for example bus, ring, mesh or star network
  • Serial or parallel communication
  • Simplex, half duplex or full duplex transmission mode
  • Autonegotiation

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