Hi @Ruhail Maqsood
I highly recommend you get yourself a copy of the CWNA Study Guide (specifically the one authored by by David D. Coleman and David A. Westcott). The best way to understand MAC contention resolution is to read chapter 8 of this book on 802.11 Medium Access.
at wikipedia is a good read also.
Wi-Fi clients and Access Points "self organise" to reduce collisions (when two or more stations are transmitting at the same time) by notifying of the likely time (duration) they will be utilising the channel during a transmission. During each contention window (where stations figure out who is transmitting next) various mechanisms and timers take place to reduce the likelihood than any two stations transmissions collide. Random backoff timer, inter-frame spacing as well as the NAV timer are all used to determine the time a station must wait before attempting to transmit.
There is a lot to it but it is fascinating. I recommend the time spent learning and reading up on CSMA/CA and 802.11 Medium Access.
Sent: Aug 27, 2013 07:46 AM
From: Ruhail Maqsood
Subject: Kindly clarify me the Default access mean !!! HELP
Mac contention resolution.... Still confused from last 3days.... unable to understand...
Higly oblige if you clarify me..