Access to the medium

  • Support and in conjunction with upper-level services

    • Allows the upper layer to access the media using various techniques such as framing
    • Use techniques such as media access control and error detection to place data on and receive data from media

  • Two sub-layers of the data link layer

    • The data link layer is the connection layer between the software processes on the upper layer and the physical layer below
    • The data link layer is usually split into two self-layers:
      • Logical Link Control (LLC), which encapsulates the network layer into frames and identifies the network layer protocol
      • Media Access Control (MAC), marking the start and end of a frame

  • Data link layer standard

Media access control technology

  • Media access control for shared media

    • For shared media, there are two basic media access control methods
      • Controlled: Each node has its own time to use the media
      • Contention: All nodes freely compete for the use of media
    • Full duplex and half duplex
      • Half-duplex communication: The device can send and receive over this medium, but cannot perform it simultaneously
      • Full-duplex communication: Both devices can send and receive data over media
    • Physical topology and logical topology
      • Physical topology: Is the layout of nodes and the physical connections between them
      • Logical topology: Is the network’s way of transferring frames from one node to another

  • Point-to-point topology

    • A point-to-point topology connects two nodes directly together
    • A virtual circuit is a logical connection created between two network devices in a network

  • Multiple access topology

    • CSMA/CD (Ethernet)orCSMA/CA (802.11 Wireless)
    • CSMA/CD(Listen and speak -> Listen and speak -> In case of conflict -> hear immediately -> Wait for time -> Speak again)

  • Ring topology

    • Token passing (fetch before issue -> send in order -> Send back after use)