Doug Karl Lecture

  1. Modulation Basebase/Broadband. Modulation on wires/colors in fiber allow multiple channels
  2. Wireless loses at a much higher rates then wires (or fiber). TCP had a very long timeout. Packet loss REALLY slowed thing down. This is an example of why knowing low level is VERY useful.
  3. Water absorbs 2.4 GHz frequency. So rain can be a real problem.
  4. Multipath problem - can make signal hard to interprete
  5. These are reason packet loss is high.
  6. Hidden Node Problem:
    • Causes packet collision, thus packet loss
    • Possible solutions: Round robin (polling), send multiple packets, intelligent polling
    • Another Solution: RTS/CTS. Small sync packets are used to request access, with lower probability of collision. RTS and CTS have packet length, so other stations know how long to wait.
  7. WDS - Allows multple APs to interconnect. Problems - all share the same frequency, lots of opportunity for collision or lose
  8. Ad Hoc - everything is point to point amoung a group of clients.
  9. Mesh - similar to ad hoc - Group of clients, shared frequency, at least one connected to Internet. May require that packets be forwarded to reach the client connected to Internet. Required a type of dunamic routing. No single point of failure, so used in military. Works great for low packet rate, but high bandwidth problem with conllisions (hidden node problem).
  10. VLANS - A special packet header which includes in the options field a VLAN number. This allows a physical network to be logically segmented into separate virtual networks which achieves isolation amount virtual LANS. The VLAN switches MUST support VLAN, and only send packets to the right clients.
    WiFi capable AP's can have multiple SSID's, where each SSID sends to a different VLAN. Thus you can have different classes of users, which end up on different virtual networks.
-- JimSkon - 2011-09-27
Topic revision: r3 - 2013-07-15 - JimSkon
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