Broadcast vs. Point to Point.
  Wans tend to use point to point connections between major nodes and 
    hang "leaf" broadcast LANs off these.

  Broadcast - Message broadcast to all machines, addressed to one.
    All machines monitor (listen), only destination machine responds.

    Most common physical broadcast protocols are Ethernet and Wi-Fi.

      CSMA/CD (Ethernet) - carrier sense multiple access / collision detection.
      10 Mbit or 100 Mbit (now 1Gbit available, fiber or high quality copper)
         Modern Ethernet equipment is able to avoid collisions altogether.

      Technology in public domain and tend to be cheap and fairly simple.

      With right connections, it can be arranged as a:
        Linear bus, Tree, or Star