lab 11 The comparison of 802.11b DCF and 802.11e EDCA

understand the mechanism of 802.11b DCF and 802.11e EDCA

• CSMA/CA
  802.3 use the carrier sense multiple access/collision detectionthe packets need to detect the channel is idle or busy.If the collision occurs, the jan signal will send.It not easy to the detect
  the collision in wireless networks. The signal gets weak and the hidden terminal problem.
• Distribution coordination function(DCF)
  Definition in the IEEE 802.11b protocol
  point coordination function (PCF)
  -contention free period : special node to control the time use in the channel.
  -contention period : each node in contention.
• DIFS: Distributed Inter-Frame Space, the time need to wait if the channel is idle.
• RTS/CTS is not regulated in the IEEE standard.
  
  
• Enhanced Distribution Channel Access(EDCA)
• To get better QoS. The priority of the data is defined, such as audio, video, best effort...etc.
  

ns2 simulation

three wireless node n0-->video---> n1, n1--->FTP flow--->n2, n2--->exponential traffic--->n0
priority1-video
priority2-ftp flow
priority3-exponetial traffic

802.11b results










802.11e results









Observation of two results.

average psnr 32.8(802.11b)<34.8(802.11e)
average delay 1.04(802.11b)>0.08(802.11e)