The 802.11 MAC
One of the best important aspects of the 802.11 accepted is the rules laid
bottomward for Media Admission Control (MAC). Regardless of the concrete
bandage 802.11 is implemented on (2.4-GHz ISM band, 5-GHz UNII band, and so
on), the MAC rules break the same.
Distributed Coordination Function
The 802.11 accepted specifies two modes in which MAC can operate:
altercation chargeless and altercation based. In contention-based MAC, stations
basically action for admission to the media. Agnate to Ethernet, aback a base
wants to address first, it checks to see if addition base is application the
wire. In an Ethernet network, a base waits until the media is not in use and
afresh transmits the packet. If addition base transmits at the aforementioned
time, it will ascertain the blow and about aback off. This makes Ethernet a
carrier faculty assorted access/collision apprehension (CSMA/CD)–based
algorithm.
When 802.11 is operating in
contention-based mode, it uses a agnate technique. The better aberration is
that best 802.11 cards alone accept one radio, which agency they can address or
receive, but not both at the aforementioned time, authoritative blow
apprehension impossible. Instead, 802.11 needs to apply blow avoidance,
authoritative the agreement CSMA/CA - based, not CSMA/CD. This mode, accepted
as the Distributed Coordination Function (DCF), is the approach that about all
802.11 networks accomplish under. In DCF mode, the base waits until the media
is bright and afresh transmits data. After commutual the transmission, the base
waits for an acceptance bulletin from the almsman to announce the abstracts was
accustomed successfully. If the acceptance bulletin is not received, the
abstracts is retransmitted and apparent to let the almsman apperceive the base
is sending the abstracts again.
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