Hubs, Bridges, Switches

Hubs, Bridges, Switches

1. Hubs

   • Physical Repeater
     • Receives an electrical signal on one interface it repeats it by sending it on all its other interfaces
   • No intelligence
   • Physical layer of OSI
   • Can get collisions
     • More computers then the more likely you will get collisions. More collisions means your throughput will go down

2. Bridge

   • Has "intelligence"
   • Data link layer of OSI
   • Makes decisions on where to send Ethernet frames by looking at their MAC addresses
   • Forwards Ethernet frames on ports where they are needed
   • Filter Ethernet frames (discard them)
   • Flood Ethernet frames (send them everywhere)
   • Only have a few ports
   • Slow

3. Switches

   • Switch is an evolved Bridge
     • Bridge on steroids
   • Many ports
     • Different port speeds - FastEthernet or Gigabit
   • Fast Internet switching
   • Large buffers
   • Different switching modes
     • Cut-Through
       • Will start forwarding the frame before the whole frame has entered the switch
       • Only needs to know the destination MAC address before forwarding
       • Fast but less reliable if you have corrupt frames
     • Store-and-forward
       • Receives the complete frame, checks for errors then forwards
         • If its corrupt it will be discarded
     • Fragment-free
       • Checks the first 64bytes
       • Trade off between cut-trough and store-and-forward switching