1. Introduction to IEEE

2. IEEE 802.11 A standard for wireless LANs An excellent book:
Matthew S. Gast, Mike Loukides, Wireless Networks: The Definitive Guide , O’Reilly & Associates, Inc.

4. 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: and 11 Mbps in the 2.4 GHz band

5. The Beat Goes On 802.11c: support for 802.11 frames
802.11d: new support for 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

6. IEEE 802 Standards . . . 802.2 LOGICAL LINK CONTROL 802.1 BRIDGING
MEDIUM ACCESS
(Ethernet)
PHYSICAL
MEDIUM ACCESS
(token bus)
MEDIUM ACCESS
(token ring)
MEDIUM ACCESS
(WLAN)
MEDIUM ACCESS
(Gigabit
LAN)
. . .
802.1 BRIDGING
802.2 LOGICAL LINK CONTROL
LAYER
DATA
LINK
802.1 MANAGEMENT

7. 802.11
MAC
802.11
FHSS
802.11
DSSS
802.11a
OFDM
802.11b
DSSS

8. 802.11 BSS Basic Service Set (BSS) --- a basic LAN Infrastructure BSS
Independent BSS (Ad Hoc LAN)
Access point

9. ESS
Extended Service Set (ESS)
Distributed System

10. Major Protocols MAC Management Operations Scanning Authentication
Association
Power Saving
Timing Synchronization

11. Power Saving Beacon interval sleep sleep time
Beacon window ATIM window

12. 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.

13. 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.

14. 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.
beacon interval
window

15. Timing Sync Needed for Power Saving
Beacon interval
sleep
sleep
time
Beacon window ATIM window

16. Timing Sync Needed for Frequency Hopping

17. 802.11 Timers (Clocks) Timer: 64 bits, ticking in microseconds.
Accuracy: within %, or +100 ppm.
Time synchronization needed for:
Frequency hopping
Power management
∆ = max tolerable difference between clocks.

18. 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.
12:01
12:01
12:00
12:01
12:02
faster
adopts
slower
not adopts

19. Is IEEE TSF Scalable?
Why or Why Not?