Distributed coordination function: Difference between revisions

Revision as of 23:10, 3 March 2012

Revision as of 19:52, 8 October 2012

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'''Distributed coordination function''' ('''DCF''') is the fundamental [[Media Access Control|MAC]] technique of the [[IEEE 802.11]] based [[wireless LAN| WLAN]] standard. DCF employs a [[CSMA/CA]] with [[binary exponential backoff]] algorithm.

DCF requires a station wishing to transmit to listen for the channel status for a [[DIFS]] interval. If the channel is found busy during the DIFS interval, the station defers its transmission. In a network where a number of stations contend for the wireless medium, if multiple stations sense the channel busy and defer their access, they will also virtually simultaneously find that the channel is released and then try to seize the channel. As a result, collisions may occur. In order to avoid such collisions, DCF also specifies random backoff, which forces a station to defer its access to the channel for an extra period. The length of the backoff period is determined by the following equation:

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DCF includes a positive acknowledge scheme, which means that if a frame is successfully received by the destination it is addressed to, the destination needs to send an ACK frame to notify the source of the successful reception.

DCF is defined in subclause 9.2 of the IEEE 802.11 standard and is the de- facto default setting for Wi-Fi hardware.

The IEEE 802.11 standard also defines an optional access method using a [[Point Coordination Function]] (PCF). PCF allows the [[Wireless access point|access point]] acting as the network coordinator to manage channel access. The [[IEEE 802.11e]] amendment to the standard enhances the DCF and the PCF, through a new coordination function called Hybrid Coordination Function (HCF).

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[[Category:Media access control]]

[[Category:Wireless networking]]

[[Category:IEEE_802IEEE 802.11|D]]

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