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carrier sense multiple access with collision avoidance (CSMA/CA)

The CSMA/ CA method is a multiple access with line polling and collision avoidance. CSMA/CA avoids collisions by using a priority scheme in which the access right is signaled by the stations.

When a station is ready to transmit, it eavesdrops on the transmission medium for a specified time. In the case of WLANs, the transmission medium is the radio channel that is listened to for a certain time, the interframe space( IFS). In addition to the interframe space, there are other parameters that influence the CSMA/CA access method. These include the Network Allocation Vector( NAV), the Distributed Coordination Function( DCF), the Point Coordination Function( PCF), and the MAC acknowledgement mechanism.

The transmission mechanism is based on Request to Send/Clear to Send( RTS/ CTS) and kicks in when the transmission medium is free. Then a station sends a request to send (RTS). The RTS signal is received by all other stations, which then defer any transmit requests. The receiving station sends a ready to transmit (CTS), whereupon the stations can transmit the data. The end of the transmission is signaled by an acknowledgment( ACK). The collision-free method is particularly suitable for transmissions on media that do not react to collisions, such as radio channels.

CSMA/CA is used, among other things, in WLANs according to 802.11.

Informations:
Englisch: carrier sense multiple access with collision avoidance - CSMA/CA
Updated at: 28.05.2014
#Words: 216
Links: carrier sense multiple access (CSMA), contingency analysis (CA), method, line, polling
Translations: DE
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