802.11e Channels ====================== .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What is IEEE 802.11e?** IEEE 802.11e is an amendment to the 802.11 standard that adds Quality of Service (QoS) enhancements to the MAC layer. :contentReference[oaicite:0]{index=0} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **Does 802.11e define new wireless channels?** No — 802.11e operates over existing physical channels (as defined in the PHY standards like 802.11a/b/g etc.). It adds new MAC features (channel access functions) but doesn’t change frequency/channel definitions. :contentReference[oaicite:1]{index=1} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **How does 802.11e influence how a channel is accessed?** It introduces *EDCA* (Enhanced Distributed Channel Access) and *HCCA* (HCF Controlled Channel Access) to provide prioritized / parameterized access to the medium (channel). :contentReference[oaicite:2]{index=2} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What are Access Categories (ACs) in EDCA?** EDCA uses four priority categories — Voice, Video, Best Effort, Background — each with different channel access parameters. :contentReference[oaicite:3]{index=3} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What is a Traffic Specification (TSPEC)?** TSPEC is used in 802.11e to define QoS parameters for a traffic stream (bandwidth, delay, jitter etc.), often related to HCCA. :contentReference[oaicite:4]{index=4} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What does “Hybrid Coordination Function” (HCF) mean?** HCF is a QoS-enabled coordination function in 802.11e. It includes both EDCA and HCCA to manage channel access. :contentReference[oaicite:5]{index=5} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What is the difference between EDCA and HCCA?** EDCA is contention-based (devices compete fairly but with priorities). HCCA is a polling or controlled access method allowing stricter QoS guarantees. :contentReference[oaicite:6]{index=6} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **How does 802.11e ensure high priority traffic gets faster channel access?** By assigning smaller contention windows (CWmin/CWmax), shorter arbitration inter‑frame spaces (AIFS), and possibly larger TXOPs to high‑priority access categories. :contentReference[oaicite:7]{index=7} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What is TXOP (Transmission Opportunity)?** It’s a time duration during which a station (after gaining access to the channel) may transmit multiple frames without releasing the channel. In 802.11e this helps reduce overhead for high priority traffic. :contentReference[oaicite:8]{index=8} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **Does 802.11e alter the physical modulation or frequency used?** No, 802.11e does **not** change modulation or frequency; it works with whatever the underlying PHY supports. :contentReference[oaicite:9]{index=9} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What is a QoS‑enabled Station (QSTA)?** A station (client) that supports 802.11e QoS features (EDCA/HCCA) and can utilize QoS service. :contentReference[oaicite:10]{index=10} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What is a QoS‑enabled Access Point (QAP)?** An AP that supports 802.11e QoS and can act as a hybrid coordinator (HC) for HCCA, manage EDCA settings etc. :contentReference[oaicite:11]{index=11} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **Can 802.11e guarantee strict latency and bandwidth?** Partially — under HCCA, yes, for parameterized traffic; EDCA provides prioritization but not hard guarantees. :contentReference[oaicite:12]{index=12} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What is contention window (CW) in 802.11e?** It is the range from which a random backoff time is chosen before attempting to access the channel. Lower CWmin means faster average access for that AC. :contentReference[oaicite:13]{index=13} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What is Arbitration Inter Frame Space (AIFS)?** A time interval a station waits after the medium is sensed idle before starting its backoff; shorter AIFS gives higher priority. :contentReference[oaicite:14]{index=14} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What effect do these access parameters have on lower priority traffic?** They may have to wait longer, suffer more delay or jitter, if high priority traffic heavily uses the channel. :contentReference[oaicite:15]{index=15} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **Does 802.11e define how many channels an AP uses?** No — that is defined by the PHY and regulatory rules. 802.11e focuses on how traffic uses whichever channel is assigned. (i.e. it doesn’t pick or create channels). — answer inferred. .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **How does 802.11e deal with “virtual collisions”?** Virtual collisions happen when two different access categories within the same station attempt to transmit; 802.11e resolves them by giving the channel to the higher priority AC. :contentReference[oaicite:16]{index=16} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **How are channels “seen” or sensed by 802.11e?** Through the same Clear Channel Assessment (CCA) mechanism. 802.11e does not change how physical channel sensing works. — answer inferred based on facts. .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **Does 802.11e support using multiple channels simultaneously?** Not inherently at MAC level; that’s more a feature of multi‑radio systems or newer standards. 802.11e itself doesn’t define multi‑channel operation. — answer inferred. .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **Does 802.11e require special hardware for QoS?** Yes — both APs and stations need to support 802.11e features (EDCA / HCCA) to benefit. Legacy devices without support will not gain QoS features. :contentReference[oaicite:17]{index=17} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **Is 802.11e the same as WMM?** WMM (Wi‑Fi Multimedia) is a certification/interoperability profile derived from 802.11e (specifically EDCA). It provides QoS in many consumer devices. :contentReference[oaicite:18]{index=18} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **How does 802.11e affect channel utilization?** By allowing high priority traffic to use the channel more efficiently (fewer delays, possibly longer TXOPs), but if overloaded, low priority traffic may see longer wait times. — inferred. .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What happens if a QoS‑enabled and non‑QoS device share the same channel?** The non‑QoS device follows legacy MAC rules; QoS devices may have an advantage in access delays. However, fairness and overall performance depend on deployments. :contentReference[oaicite:19]{index=19} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **Can 802.11e reduce collisions on a busy channel?** It can help reduce contention collisions via parameter tuning, but cannot eliminate them entirely. — inferred. .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **What is meant by “contention periods” and “contention-free periods” in relation to 802.11e?** EDCA operates during contention periods. HCCA can create contention-free periods under hybrid coordination, but in practice HCCA is less commonly implemented. :contentReference[oaicite:20]{index=20} .. panels:: :container: container pb-4 :column: col-lg‑12 p‑2 :card: shadow **How are beacon frames involved in 802.11e QoS / channel control?** Beacons advertise EDCA parameters and may include QoS information; they help stations know what AC parameters to use. :contentReference[oaicite:21]{index=21} .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Topics in this section, * :ref:`List of channels ` * :ref:`List of channel widths ` * :ref:`List of Bands ` * :ref:`Reference links ` .. _channels_e_step4: .. tab-set:: .. tab-item:: List of channels ===================== ======================= ====================== ============== Channel Number (MHz) Center Frequency (MHz) Frequency Range DFS Required ===================== ======================= ====================== ============== 36 5180 5170‑5190 No 40 5200 5190‑5210 No 44 5220 5210‑5230 No 48 5240 5230‑5250 No 52 5260 5250‑5270 Yes 56 5280 5270‑5290 Yes 60 5300 5290‑5310 Yes 64 5320 5310‑5330 Yes 100 5500 5490‑5510 Yes 104 5520 5510‑5530 Yes 108 5540 5530‑5550 Yes 112 5560 5550‑5570 Yes 116 5580 5570‑5590 Yes 120 5600 5590‑5610 Yes 124 5620 5610‑5630 Yes 128 5640 5630‑5650 Yes 132 5660 5650‑5670 Yes 136 5680 5670‑5690 Yes 140 5700 5690‑5710 Yes 144 5720 5710‑5730 Yes 149 5745 5735‑5755 No 153 5765 5755‑5775 No 157 5785 5775‑5795 No 161 5805 5795‑5815 No 165 5825 5815‑5835 No ===================== ======================= ====================== ============== .. _channels_e_step5: .. tab-set:: .. tab-item:: List of channel widths * channel widths .. _channels_e_step6: .. tab-set:: .. tab-item:: List of Bands ======================= ====================== ====================== ============================================================ Band Name Frequency Range (GHz) Frequency Range (MHz) Channels ======================= ====================== ====================== ============================================================ UNII-1 5.150 – 5.250 5150 – 5250 36, 40, 44, 48 UNII-2 (DFS) 5.250 – 5.350 5250 – 5350 52, 56, 60, 64 UNII-2 Extended (DFS) 5.470 – 5.725 5470 – 5725 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 144 UNII-3 5.725 – 5.825 5725 – 5825 149, 153, 157, 161, 165 ======================= ====================== ====================== ============================================================ .. _channels_e_step17: .. tab-set:: .. tab-item:: Reference links * Reference links