MODULE 4

• Data Link Layer

  Layer of the OSI model that prepares network data for the physical network
• Data Link Layer

  Responsible for network interface card (NIC) to network interface card communications
• IEEE 802 LAN/MAN Data Link Sublayers


  • Logical Link Control (LLC)
  • Media Access Control (MAC)
• Types of Topologies


  • Physical
  • Logical
• Common Physical WAN Topologies


  • Point-to-point
  • Hub and spoke
  • Mesh
• Half-duplex communications


  Exchange data in one direction at a time
• Full-duplex communications


  Send and receive data simultaneously
• Contention-based multi-access networks


  All nodes operating in half-duplex
• Contention-based access methods

  • CSMA/CD for bus-topology Ethernet LANs
  • CSMA/CA for WLANs
• Parts of a Data Link Frame


  • Header
  • Data
  • Trailer
• Frame Fields


  • Frame start and stop indicator flags
  • Addressing
  • Type
  • Control
  • Data
  • Error detection
• Data Link Addresses


  Also known as physical addresses
• Data Link Addresses


  Only used for link local delivery of frames