Lectures

Wikipedia topic : Wi-Fi

Wireless - broadcast network implemented over short* distance radio
communication. WLan

See both WiFi and 802.11 on Wikipedia.

IEEE 802.11 (1991) (a-n, various revisions and tweaks).
  3 major variations and several tweaks.

  2.5 GHz and 5 GHz bandwidth. About 20 meter radius from access point.

  * 3.6(7) GHz - wide area wireless - U.S. only.

  * 60 GHz - very high speed but generally only within a room.

Home frequencies vary by country.

Higher frequency, higher data throughput but shorter range.
  But may favor environments with many obstacles.

Major frequency is divided into sub-ranges or channels which 
  allows multiple devices or stations to use the same access point.  

  * 2.4 GHz - 2.412, 2.417, 2.422, 2.427, 2.432, 2.437, 2.442, 2.447,
              2.452, 2.457, 2.462, 2.467, 2.472, 2.484

  * Similar to how the television broadcast spectrum is broken into channels.

  * Consider switching channels if you WiFi under performs.

Because channel frequencies overlap, only a few channels useful.
  One access point will use channels at least 25MHz apart.
   
Implemented in half-duplex - a device can either send or receive but
  not both at same time.

Wireless network is combination of stations (end points) and access nodes.
  Access nodes usually interconnected using standard copper LAN.
  But can be directly bridged to create a truly wireless network.

Also wireless stations can be set up peer to peer without an access node,
  but then network is truly private.

Wireless access points are configured so that they appear to have a 
  common link layer (same local network id - SSID).

  SSID - service set identification - 32 octet ID which IDs/ensures the 
     interaction between an access node and a station that has established
     a connection to it.
     * This allows different devices to connect to different nodes/networks.
       a type of network name.
     * Often human readable.

Multiple devices can interleave communication packets on a particular
  channel and follow the CSMA/CA protocol when competing for band width.

Wireless is considered less secure than current implementations of wired.

But can use TLS (Transport Layer Security) to provide encrytion of data
before leaving devices. (WEP, WPA, WPA2).