3618170
| 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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