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MEDIA ACCESS METHOD (MULTIPLE ACCESS METHOD (Random Access protocols…

- - - - was designed to be used on a radio(wirekess) Local Area Network
      - Every station need to send frame to the base station before it relays it to destination
      - The data from the two station collide and become garbled
    - - To minimize the chance of collision
      - Increase the performance
    - - If the station hear the collision, it send a jam signal to the line to inform other station
      - All the station discard the part of the frame received
    - - collision are avoided through 3 strategies
        
        The Interframe Space (IFS)
        
        Gap time before sending frame
        
        The IFS also can be used to define the priority of a station or a frame
        
        Contention Window
        
        An amount of time divided into slots
        
        A station chooses a random number of slots as its wait time
        
        Acknowledgment
        
        The positive acknowledgment and the time-out timer can help guarantee the receiver has received the frame
  - - - A station need to make a reservation before sending data
      - If there is N stations in the system, so there are N reservation mini slots in reservation frame
      - When a station needs to send a data frame, it make reservation in its own mini slot.
      - The station that have made reservations can send their data frames after the reservation frame
    - - If primary want to receive data, it asks the secondaries if they have anything to send (polling)
      - If primary want to send data, it tell secondary target to ready receive (SELECTING)
      - Work with topologies in which one device designated as a primary station and other secondary
    - - Each station has a predecessor and a successor
      - Predecessor is the station which is logically before the station in the ring
      - The stations are organized in a logical ring
        
        Star ring topology
        
        Bus ring topology
        
        Dual ring topology
        
        Physical ring topology
      - Successor is the station which is after the station in the ring
      - The current station is the one that is accessing the channel now