Virtual ring  - Token passing  (token bus)
  Uses the broadcast style connections.
 
  Each node is assigned a sequence id which may or may not match 
  the physical layout of node.

  And each node takes its turn based on id.
    Like Token Ring, token passed between nodes based on their Id.
    But like Ethernet, token is broadcast to all nodes.

    Does not need a physically connected ring.


     But the overhead for virtual sequencing may take some additional 
       bandwidth.

      Requires each node to know the physical or logical address of next 
        node in 'ring'.

     Also, insertion of new node or removal of existing node challenging
       because logically adjacent nodes need updating.
       * Like updating a linked list.

   Long gone in the PC world,
     Was very popular for monitoring type networks (fire/intrusion).

     Guarantees all nodes contacted in known time frame.

  Arcnet 2.5 Mib/sec. 1976-mid 90's. Could sometimes provide faster throughput
    than 10Mib Ethernet on networks with a large number of machines.

    www.arcnet.com

    Originally developed to Network Accessed Storage on 8" floppy drives.
 
    Arcnet Plus 20 Mib/sec.

    Capable of 2000 ft. runs between active hubs using coaxial cable.

    Although rarely used for new networks, a number of legacy systems still
      exist.

  M.A.P. - Manufacturing Automation Protocol (G.M.) 1982-2004 - allowed for
    single protocol between GM and suppliers, Boeing also used for a while.

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  FDDI/CDDI (fiber/copper )- another token ring implementation - 
    Uses a pair of rings for redundancy and can even "heal". 

    Nodes were a logical position on 'ring' that did not need to 
      align with physical position.

    100 Mib/s.
    If fiber, 200 Km range.
    thousands of users possible.

    Useful as a backbone for a MAN.

    Dual ring for routers, tree structure for leaf nodes.

    Fast Ethernet out performs.