Introduction to IEEE 802.11. IEEE 802.11 A standard for wireless LANs An excellent book: – Matthew...
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Transcript of Introduction to IEEE 802.11. IEEE 802.11 A standard for wireless LANs An excellent book: – Matthew...
![Page 1: Introduction to IEEE 802.11. IEEE 802.11 A standard for wireless LANs An excellent book: – Matthew S. Gast, Mike Loukides, 802.11 Wireless Networks: The.](https://reader036.fdocuments.us/reader036/viewer/2022081506/56649e2f5503460f94b1f749/html5/thumbnails/1.jpg)
Introduction to IEEE 802.11
![Page 2: Introduction to IEEE 802.11. IEEE 802.11 A standard for wireless LANs An excellent book: – Matthew S. Gast, Mike Loukides, 802.11 Wireless Networks: The.](https://reader036.fdocuments.us/reader036/viewer/2022081506/56649e2f5503460f94b1f749/html5/thumbnails/2.jpg)
IEEE 802.11
A standard for wireless LANs
An excellent book:– Matthew S. Gast, Mike Loukides,
802.11 Wireless Networks: The Definitive Guide , O’Reilly & Associates, Inc.
![Page 3: Introduction to IEEE 802.11. IEEE 802.11 A standard for wireless LANs An excellent book: – Matthew S. Gast, Mike Loukides, 802.11 Wireless Networks: The.](https://reader036.fdocuments.us/reader036/viewer/2022081506/56649e2f5503460f94b1f749/html5/thumbnails/3.jpg)
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History of IEEE 802.11
802.11 standard first ratified in 1997– 802.3 LAN emulation– 1 & 2 Mbps in the 2.4 GHz band
Two high rate PHY’s ratified in 1999– 802.11a: 6 to 54 Mbps in the 5 GHz band– 802.11b: 5.5 and 11 Mbps in the 2.4 GHz band
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The Beat Goes On
802.11c: support for 802.11 frames 802.11d: new support for 802.11 frames 802.11e: QoS enhancement in MAC 802.11f: Inter Access Point Protocol 802.11g: 2.4 GHz extension to 22 Mbps 802.11h: channel selection and power control 802.11i: security enhancement in MAC 802.11j: 5 GHz globalization
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IEEE 802 Standards
802.3 MEDIUMACCESS
(Ethernet)
PHYSICAL
802.4 MEDIUMACCESS
(token bus)
PHYSICAL
802.5 MEDIUMACCESS
(token ring)
PHYSICAL
802.11 MEDIUMACCESS
(WLAN)
PHYSICAL
802.12MEDIUMACCESS
(Gigabit
LAN)PHYSICAL
. . .
802.1 BRIDGING
802.2 LOGICAL LINK CONTROL
PHYSICAL
LAYER
DATA
LINK
LAYER
802.
1 M
AN
AG
EM
EN
T
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802.11
802.11 MAC
802.11FHSS
802.11DSSS
802.11aOFDM
802.11bDSSS
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802.11 BSS
Basic Service Set (BSS) --- a basic LAN Infrastructure BSS Independent BSS (Ad Hoc LAN)
Access point
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802.11 ESS
Extended Service Set (ESS)
Distributed System
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Major Protocols
MAC Management Operations
– Scanning– Authentication– Association– Power Saving– Timing Synchronization
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Power Saving
sleep
Beacon window ATIM window
Beacon interval
timesleep
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When to stay awake?
ATIM: Announcement traffic indication map.
IBSS: If a node has an outgoing data frame for B, it sends B a traffic announcement in the ATIM window.
A node stays awake for an entire beacon interval if it has incoming and/or outgoing traffic.
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Beacons
Beacons carry information about the BSS.– To allow new stations to join in– Timing synchronization
Every station must listen to Beacons. Infrastructure BSS: AP sends beacons. IBSS: every station contends for beacon
generation in the beacon window.
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Beacon Contention/Generation
Each station:– determines a random number k;– waits for exactly k idle slots to pass;– transmits a beacon (if no one else has done so).
Beacon: several slots in length.
window
beacon interval
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Timing Sync Needed for Power Saving
sleep
Beacon window ATIM window
Beacon interval
timesleep
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Timing Sync Needed for Frequency Hopping
f1
f2
f4
f3
f5
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802.11 Timers (Clocks)
Timer: 64 bits, ticking in microseconds. Accuracy: within + 0.01%, or +100 ppm. Time synchronization needed for:
– Frequency hopping– Power management
∆ = max tolerable difference between clocks.
– Desired value: 25 s
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802.11’s Time Sync Function
Beacon contains a timestamp. On receiving a beacon, STA adopts beacon’s
timing if T(beacon) > T(STA). Clocks move only forward.
faster adopts
12:01 12:00
slower not adopts
12:01 12:0212:01
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Is IEEE 802.11 TSF Scalable?
Why or Why Not?
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