IEEE 802.3 (CSMA/CD) protocol

  As implemented on Ethernet 

  Anyone on network can talk whenever they want.

  

  source : https://en.wikipedia.org/wiki/Carrier_sense_multiple_access_with_collision_detection

Advantages 
  If no-one else using connection, unlimited access.

  Technology cheap.

  Layout very flexible (star, bus, tree)

Disadvantage
  Single machine can dominate bandwidth.

  Also as more devices attempt to access, 
    All time wasted in collision handling.

  If machines very far apart, increases chance of not detecting busy until
    collision.

  Tends to have an inverse exponential transmission success rate as number
    of nodes on network increase. As nodes added, the chance of failure
    increases roughly exponentially.

  In worst case scenario, no device can get anything sent because of 
    collisions.

  Tends to have a normal curve for total throughput.

  Modern systems use switching hubs that avoid collisions, but added cost.
    If source/target on same switch, it creates a virtual p to p connection. 

    If different sources are not competing for same target, establishes 
     parallel connections. Number of these may be limited.

    If larger tiered local network, isolates communication to source/target
      portion of network.

    Queue/buffer packets to avoid collisions if target busy.