1. Wireless Ad Hoc/Sensor Networks: From IEEE 802
Wireless Ad Hoc/Sensor Networks: From IEEE to Berkeley Motes and Beyond
Ten-Hwang Lai, OSU

2. Ten-Hwang Lai Ohio State University
Introduction to IEEE
Ten-Hwang Lai
Ohio State University

3. Standards for Wireless LANs
IEEE
Bluetooth
HiperLan (Europe)

6. 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

7. 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

8. 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

9. 802.11
MAC
802.11
FHSS
802.11
DSSS
802.11a
OFDM
802.11b
DSSS

10. 802.11 BSS Basic Service Set (BSS) --- a basic LAN Infrastructure BSS
Independent BSS (Ad Hoc LAN)
Access point

11. ESS
Extended Service Set (ESS)
Distributed System

12. Major Protocols MAC Management Operations
Scanning
Authentication
Association
Power Saving
Timing Synchronization
WEP (wired equivalent privacy)
Physical Layer

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

14. 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.

15. Beacons Beacons carry information about the BSS.
To allow new stations to join in
Timing synchronization
Every station must listen to Beacons.
Infrastructured BSS: AP sends beacons.
IBSS: every station contends for beacon generation in the beacon window.

16. 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

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

18. Timing Sync Needed for Frequency Hopping

19. 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.

20. 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

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