08

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cwna CWNA Flashcards on 08, created by rowelld on 30/09/2015.
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Flashcards by rowelld, updated more than 1 year ago
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Created by rowelld over 8 years ago
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Resource summary

Question Answer
DCF Distributed Coordination Function Mandatory access method in 802.11 standard.
4 main components of DCF Inter frame space Duration/ID field Carrier Sense Random back timer
IFS Interframe Space. Period of time between wireless frames.
6 Types of IFS Reduced Interframe space (RIFS) Short interframe space (SIFS) PCF interframe space (PIFS) DCF interframe space (DIFS) Arbitration interframe space (AIFS) Extended interframe space (EIFS)
Duration/ID Field Field in MAC header. Represents time to transmit a frame. How long the RF medium will be busy.
Carrier Sense Checking if medium is busy
Two ways carrier sense is performed Virtual carrier sense Physical carrier sense
Virtual carrier sense Uses Network Allocation Vector (NAV) Based on duration value. NAV is a countdown timer. STA cannot contend until NAV = 0
Physical carrier sense Listens to channel to detect energy. Known as Clear Channel Assessment (CCA)
Random Backoff Timer Randomly selected duration by STA. Selects from a contention window range. Multiple by the slot time value. Final timer used before STA transmits.
Hybrid Coordination Function Added in 802.11e Defines ability for radio to send multiple frames when transmitting in an allotted time called Transmit Opportunity (TXOP).
TXOP Transmit Opportunity. An allotted time to send frames. Uses frame bursts. SIFS between each frame.
Two channel-access methods used by HCF Enhanced Distributed Channel Access (EDCA) HCF Controlled Channel Access (HCCA)
EDCA Enhanced Distributed Channel Access. D
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