Media Access Control and Collision Domains
- Ethernet is a multiple access area network
- the available communications capacity is shared between the nodes that are connected to the same media
- Media access control (MAC) refers to the methods a network technology uses to determine when nodes can communicate on shared media
- Ethernet uses a contention-based MAC system
- each network node connected to the same media is in the same collision domain
- Network segment where nodes are attached to the same shared access media
- such as a bus network or Ethernet hub
- when two nodes transmit at the same time, the signals collide and neither reaches its destination
- Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is the Ethernet protocol governing contention and media access
- collision is state when a signal is present on an interface’s transmit and receives lines simultaneously
- when collision detected, the node broadcasts a jam signal
- each node that was attempting to use the media then waits for a random period before attempting again
- collision detection mechanism means only half duplex transmission is possible
- in 10BASE-T star topology, each node is connected to a hub
- hub repeats signals to each node
- thus, each host is in the same collision domain