Media Access Methods
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Media Access Methods



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Media Access Methods Media Access Methods Presentation Transcript

  • MEDIA ACCESS METHODS An access method is a set of rules governing how the network nodes share the transmission medium. The rules for sharing among computers are similar to the rules for sharing among humans in that they both boil down to a pair of fundamental philosophies: 1) first come, first served and 2) take turns. These philosophies are the principles defining the three most important types of media access methods:
    • Contention. (CSMA/CD Carrier Sense Multiple Access with Collision Detection ,
    • CSMA/CA Carrier Sense Multiple Access with Collision Avoidance )
    • Token passing.
    • Demand Priority.
  • Contention
    • Competition for resources.
    • The term is used specially to describe the situation where two or more nodes attempt to transmit message across the same wire at the same time.
  • MEDIA ACCESS METHODS CSMA/CD Carrier Sense Multiple Access with Collision Detection CSMA/CA Carrier Sense Multiple Access with Collision Avoidance Contention . (“listen before talking”)
  • MEDIA ACCESS METHODS Token passing :- IEEE 802.5 standard deals with Token Ring networks Token passing is implemented on a token-ring network.
  • MEDIA ACCESS METHODS Demand Priority. Demand priority is an access method used with the new 100Mbps 100VG-AnyLAN standard. Although demand priority is officially considered a contention-based access method, demand priority is considerably different from the basic CSMA/CD Ethernet. In demand priority, network nodes are connected to hubs, and those hubs are connected to other hubs. Contention, therefore, occurs at the hub. (100VG-AnyLAN cables can actually send and receive data at the same time.) Demand priority provides a mechanism for prioritizing data types. If contention occurs, data with a higher priority takes precedence.