Networking
 
Three views
  Local area network (LAN)
    Individual nodes are recognized by their hardware id.

    Relatively small area coverage (room, building, or complex).

    Tends toward one type of technology. 

    Broadcast communication.

  Wide area network (wan)
    Nodes given a symbolic address supported by public protocol.

    World wide.

    Highly variable technology.

    Point to Point communication via gateways to large portions of network.
 
Third view
  Metropolitan area network (man)
    Networking concept originated with the phone company.

    In between - city wide or sparsely distributed over distance.

    Dissimilar technologies for sub-nets.

    Pretty much conceptually replaced by private wan.

    NIU is a man.
      Multiple sub-nets.

      Different technologies, Token ring, Ethernet, Applenet, ATM, 
        Fast Ethernet, FDDI  (mostly variations of Ethernet)

    Connection in/out of campus
      45 Mb OC3, Discontinued 30 Mb T3 p to p out of campus.
 
Broadcast - Message broadcast to all machines, 
  All machines monitor (listen), only destination machine responds.

  CSMA/CD (Ethernet) - carrier sense multiple access - collision detection.
  10 Mbit or 100 Mbit (now 1Gbit available, fiber or high quality copper)

  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 

Ethernet Algorithm 
  Anyone on network can talk whenever.
    Listen for no traffic.

    If no traffic, 
      Then broadcast while continuing to listen.

    Else (collision) 
      Stop and immediately try again.
   
      While collision
        Wait a short time and try again    

      Endif 

      Then broadcast while continuing to listen.

    Endif 

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

Disadvantage
  If someone else keeps beating you to the punch, you don't get on.

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

  Tends to have a statistically normal curve of use.

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

Token ring - invented by IBM
  Proprietary and somewhat more complex and twice as expensive.

  Physically arranged as a ring, with right connection some flexibility.

  Behaves almost like a ring of point to point connections.

  4 MBits/sec.

  Each machine has a single card.
    But card is designed to allow traffic to come in from one direction 
    and out the other.

  A single token is generated as system comes up.

  The token is passed from device to device around the ring.

  For a set period of time, a device in possession of the token can 
    communicate with any other devices on ring.  
  
  If device does not wish to communicate or its time is up,
    It passes token to next device.
 
  Advantage:
    Each device guaranteed a chance to communicate, no matter how many 
    devices on network.

  Disadvantage:
    Proprietary (IBM) technology - license fee.

    More complex electronics $.

    Very large rings run extremely slow even if no load.

Virtual ring  - (Arcnet)
  Uses the broadcast style connections.
 
  Each device is assigned a sequence id which may or may not match 
  the physical layout of devices.

  And each device takes its turn based on id.
    Like token ring, token passed between devices based on their id.

    Does not need a physically connected ring.

     But the overhead for virtual sequencing may take some additional 
       bandwidth.
    
Network Packets
  Network nodes communicate via packets.
   
  Packet consists of address, data, & control.
    Data - information being transferred along with "address" of
    application sending and "address" of application being talked to.

    Address
      Card Hardware ID - MAC @ - Media access code.

    Control - CRC error checking.