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

IEE 802.11 (a-n, various revisions and tweaks).

The variations define different ways the data can be encoded over the
radio carrier waves.

Different frequency ranges are used in different countries and for
the various protocols. 

The higher the frequency, the higher the throughput, but also more 
suseptable to interferance and limited ranges. But different environments
can actually favor higher frequencies. 

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

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

Because the radio channel frequencies overlap, only a few of the available
channels can actually be used at any one time.

Implemented in half-duplex - a device and either send or recieve but
not both.

Wireless network is a combination of stations (end points) and access
nodes which either function as a bridge into a standard lan network (the
backbone) and/or a bridge to another access node (not common).

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

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

CSMA/CA Carrier sense - multiple access / collision avoidance.
  Rather than monitering the media while broadcasting to sense a 
  collision (CD), the sender broadcast a short ready to send (RTS) packet 
  to reserve the media bandwidth which the receiver acknowledges with a
  Clear to send (CTS). In the process all other nodes are notified of an 
  upcoming communication frame which is terminated with an additional 
  acknowledgement packet that closes the transmisnion frame.
 
  While this may not completely eliminate collisions, it does reduce them
  but at the cost of additional handshaking overhead.
  frame and wait while the frame is transmitted. 

  Generally, faster network speeds and more access points also work to 
  limit collisions.

  If a transaction frame is small enough, it may be sent without using
  the RTS/CTS handshake.

  Part of CSMA/CA is carrier sense. In hardwired ethernet, this is easy
  to implement at the hardware level. In radio broadcasting media, this 
  is expensive and complex.
 
  Instead a type of virtual network sense is implemented by including a
  timing counter,  Network Allocation Vector (NAV), in the RTS packet 
  that tell each node how long it needs to complete the transmision 
  transaction it is announceing. 
 
  The NAV includes time for the CTS, the Frame of data being sent, the
  Acknowledgement from the receiver, and any time spacing between 
  the various parts. The spacing is known as interframe space.

  The CTS reproduces a slightly reduced NAV to make sure all nodes
  heard the time reservation request.