Introduction to IEEE 802 11 IEEE 802 11

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Introduction to IEEE 802. 11

Introduction to IEEE 802. 11

IEEE 802. 11 l A standard for wireless LANs l An excellent book: –

IEEE 802. 11 l A standard for wireless LANs l An excellent book: – Matthew S. Gast, Mike Loukides, 802. 11 Wireless Networks: The Definitive Guide , O’Reilly & Associates, Inc.

History of IEEE 802. 11 l 802. 11 standard first ratified in 1997 –

History of IEEE 802. 11 l 802. 11 standard first ratified in 1997 – – l 802. 3 LAN emulation 1 & 2 Mbps in the 2. 4 GHz band Two high rate PHY’s ratified in 1999 – – 802. 11 a: 6 to 54 Mbps in the 5 GHz band 802. 11 b: 5. 5 and 11 Mbps in the 2. 4 GHz band

The Beat Goes On l l l l 802. 11 c: support for 802.

The Beat Goes On l l l l 802. 11 c: support for 802. 11 frames 802. 11 d: new support for 802. 11 frames 802. 11 e: Qo. S enhancement in MAC 802. 11 f: Inter Access Point Protocol 802. 11 g: 2. 4 GHz extension to 22 Mbps 802. 11 h: channel selection and power control 802. 11 i: security enhancement in MAC 802. 11 j: 5 GHz globalization

IEEE 802 Standards 802. 1 MANAGEMENT 802. 2 LOGICAL LINK CONTROL DATA LINK LAYER

IEEE 802 Standards 802. 1 MANAGEMENT 802. 2 LOGICAL LINK CONTROL DATA LINK LAYER 802. 1 BRIDGING 802. 3 802. 4 802. 5 802. 11 802. 12 MEDIUM ACCESS MEDIUM ACCESS (WLAN) (Gigabit LAN) PHYSICAL (Ethernet) (token bus) (token ring) PHYSICAL . . . PHYSICAL LAYER

802. 11 MAC 802. 11 a 802. 11 b FHSS DSSS OFDM DSSS

802. 11 MAC 802. 11 a 802. 11 b FHSS DSSS OFDM DSSS

802. 11 BSS Basic Service Set (BSS) --- a basic LAN l Infrastructure BSS

802. 11 BSS Basic Service Set (BSS) --- a basic LAN l Infrastructure BSS l Independent BSS (Ad Hoc LAN) Access point

802. 11 ESS l Extended Service Set (ESS) Distributed System

802. 11 ESS l Extended Service Set (ESS) Distributed System

Major Protocols l l MAC Management Operations – – – Scanning Authentication Association Power

Major Protocols l l MAC Management Operations – – – Scanning Authentication Association Power Saving Timing Synchronization

Power Saving Beacon interval sleep Beacon window ATIM window time

Power Saving Beacon interval sleep Beacon window ATIM window time

When to stay awake? l ATIM: Announcement traffic indication map. l IBSS: If a

When to stay awake? l ATIM: Announcement traffic indication map. l IBSS: If a node has an outgoing data frame for B, it sends B a traffic announcement in the ATIM window. l A node stays awake for an entire beacon interval if it has incoming and/or outgoing traffic.

Beacons l Beacons carry information about the BSS. – – l l l To

Beacons l Beacons carry information about the BSS. – – l l l 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.

Beacon Contention/Generation l Each station: – – – l determines a random number k;

Beacon Contention/Generation l Each station: – – – l 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

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

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

Timing Sync Needed for Frequency Hopping f 1 f 2 f 3 f 4

Timing Sync Needed for Frequency Hopping f 1 f 2 f 3 f 4 f 5

802. 11 Timers (Clocks) l l l Timer: 64 bits, ticking in microseconds. Accuracy:

802. 11 Timers (Clocks) l l l Timer: 64 bits, ticking in microseconds. Accuracy: within + 0. 01%, or +100 ppm. Time synchronization needed for: – – l Frequency hopping Power management ∆ = max tolerable difference between clocks.

802. 11’s Time Sync Function l l l Beacon contains a timestamp. On receiving

802. 11’s Time Sync Function l l l 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: 00 12: 01 12: 02 faster adopts slower not adopts

Is IEEE 802. 11 TSF Scalable? Why or Why Not?

Is IEEE 802. 11 TSF Scalable? Why or Why Not?

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