Switches 
  Generally, a connection device is classified as a 'switch' if the 
    protcol on the incoming and out-going lines are the same. Modern switches
    are capable of at least some routing and traffic control.

Minimal switching.  
  Layer 1 - hubs and repeaters.

    Used to consolidate multiple local connections into a single
    shared line.

    And/or to replicate and boust a signal.

    Ethernet 
      Requires keyed connections - data lines positionally important.

    Early designs (hubs) were dumb. 
      Often broadcast frames to all devices on hub.

      Slowest connection set max speed of hub.

      Also used different configuration for line going out to next hop.

    Current designs include minimal processing power.
      Capable of discovering MAC on each port and routing frames to 
        appropriate port rather than broadcasting to all nodes on switch.

      Can work with each port at its node's optimal speed.

      Can identify and properly electronically switch data lines.

  Layer 2 - network bridge
    
    Used to connect two physically separated collection of nodes (sub-net).

    Uses point to point interface between two sub-net of nodes.

    Treats all nodes as single local network.

    Discovers MACs on each side of bridge so sub-nets only get valid frames.
 
  Layer 3 - some routing functions.
    Besides being able to target port where MAC is known, can handle 
      multi-casting. 

Full blown network switch
  Layers 4 and up.
    Capable of load balancing.
   
    May provide advanced caching such as web caching.

    May interface with several different local neworks.
     * these will be of the same protocol type.

    Although they may they may also switch phyical transmission.
      e.g 100 Mb ethernet over copper wire to each node 
        to 1 GB ethernet fiber to switch in another building. 

     * note briding and rouuting functionality.
  
Gateway routers.
   Device or system that isolates local networks and routes packets
     into and out of each local network based on IP protocols.

   Provides a singe 'gate' into/out of local network. 
     tied to a point to point connecton which then connects to a router.
     * if it connected to another gateway, it could be views as a bridge.
  
   May use same protocol on both sides of gateway. 
 
   Your DSL (hi-speed) Modem is essentially a Gateway router.

Routers
  Layer 3 and up

  Provides traffic control between local networks or other routers.  

  Often capable of handling different network protocols on differnt ports.
    Ethernet, FDDI, Token Ring, ATM, etc.

  Often designed for a large number of ports.

  Robust processing capabilities (RISC)

  Selective packet routing (IP)

  Congestion control.

  Monitoring.

  Security such as firewall.  

  NAT - network address translation.