[ns] there are many different between Mac/802_11 and article of IEEE802_11

[reza mohammadi]

hello 
i study the  article "IEEE 802.11 Wireless LAN Medium Access Control (MAC) and 
Physical Layer (PHY) Specifications"
and compare the frames and structure of MAC protocol with MAC/802_11 in NS2 but 
there are many different between article and simulated Mac protocol in NS2
can any body help me about this problem?
Thanks
best regards