Madge Networks 802.11b Manual do Utilizador descarregar pdf (Página 27)

DCF

• DCF, Distributed Coordination Function

– No central controller; just like Ethernet

– Protocols used are:

• CSMA/CA (CSMA with Collision Avoidance)

– Sense the channel before transmitting. If idle, transmits. It does

not sense the channel while transmitting

– Waits DIFS+RandomTime before transmitting

– Receiver waits SIFS time before acknowledging

– Using duration field in 802.11 frame other nodes backoff this

much amount of time (NAV)

• CSMA/CA with virtual channel

– Perform channel reservation

– RTS alerts and indicates duration of frame for sender’s range

– CTS alerts and indicates duration of frame for receiver’s range

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Madge Networks 802.11b Manual do Utilizador Página 27