IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specifications for implementing wireless local area network (WLAN) computer communication in the 2.4, 3.6, 5, and 60 GHz frequency bands. The goal of 802.11 is to provide simple, robust, and affordable wireless connectivity along with time-bound and asynchronous services. It uses either spread spectrum or infrared signaling techniques. The standard defines the MAC sublayer and three physical layer types: infrared, frequency-hopping spread spectrum (FHSS), and direct-sequence spread spectrum (DSSS). It supports infrastructure-based and ad-hoc network configurations.

1. IEEE 802.11
Presented By:
Abhishek Pachisia
B.Tech – IT

2. Foreword - 1
• Belong to 802.x LAN standards.
• Primary goal
– Simple and Robust WLAN
– Time bound and Asynchronous services
• MAC Layer
– Should be able to operate with multiple
physical layers (different medium sense &
transmission characteristic.
• Physical layer.
– Infra red & Spread spectrum radio
transmission techniques.

3. Foreword - 2
• Additional features of WLAN
– Support of power management
– Handling of hidden nodes
– Ability to operate world wide.
• 2.4 GHz ISM band – original standard.
– 1 Mbits/s – Mandatory
– 2 Mbits/s – Optional.

4. System Architecture - 1
• Basic System Architecture
– Infrastructure based
– Ad-hoc.
• Components
– Station (STA)
– Access Points (AP)
– Basic Service Set (BSS)
– Extended Service Set (ESS)
– Portal

5. Architecture of an Infrastructure based IEEE
802.11

6. System Architecture - 2
• Stations
– Access mechanism to wireless medium
– Radio contact to the AP.
• BSS
– BSSi are connected via Distributed System.
• ESS
– Form Single network, extends wireless
coverage area.
– ESSID : Name of network; Separate different
network
• Portal
– Internetworking unit to other LANs.

7. System Architecture - 3
• AP’s support roaming.
• Distributed system – Transfer between
AP’s.
• Infrastructure based network allow ad-hoc
network between stations -> IBSS.
• IEEE 802.11 does not specify
– Routing
– Forwarding of data
– Exchange of topology Information

8. Architecture of IEEE 802.11 ad-hoc wireless
LANs

9. Protocol Architecture - 1
• 802.11 fits seamlessly into 802.x wired
networks.
• Most common scenario – 802.11 & 802.3
via bridge.
• Difference in bandwidth is noticed.
• Upper part of logical link layer and data
link control layer covers MAC differences.

10. IEEE 802.11 – Protocol architecture and
belonging

11. Protocol Architecture - 2
• Physical Layer(PHY)
– Physical Layer Convergence Protocol (PLCP)
– Physical Medium Dependent sublayer (PMD)
• Medium Access Control Layer (MAC)
– To access medium.
– To fragment user data.
– To encrypt.
• PLCP
– Carrier sense signal (CSS)
– Common Service Access Point(SAP)
• PMD
– Encoding/Decoding Signals.

12. Station Management
DLC LLC
MAC MAC Management
PLCP
PHY
PMD PHY Management
Detailed IEEE 802.11 protocol architecture
and management

13. Physical Layer
• Three Layers
– Infra red (1)
– Radio transmission (2)
• Clear Channel Assessment signal (CCA).
– MAC mechanism controlling medium access.
– Indicates state of medium.
• Service Access Point (SAP)
• Versions of PHY layer
– FHSS
– DSSS
– Infra red

14. FHSS
• Allows coexistence of multiple networks.
• Original Standard
– 79 hopping channel North America.
– 23 hopping channel Japan
• Pseudo random hoping pattern.
• Standard – GFSK as modulation for FHSS
PHY.
• 1Mbits/s is mandatory & 2Mbit/s is
optional.
• MAC data is scrambled using
s(z)=z7+z4+1

15. Bits 80 16 12 4 16 Variable
Synchronization SFD PLW PSF HEC Payload
PLCP Preamble PLCP Header
Format of an IEEE 802.11 PHY frames using
FHSS

16. DSSS - 1
• Separated by code.
• Achieved using 11-chip Barker sequence.
• Key characteristics
– Robustness against interference
– Insensitivity to multipath propagation.
• Implementation - Complex than FHSS.
• Uses
– Differential Binary Phase Shift Keying
(DBPSK)
– Differential Quadrature Phase Shift Keying
(DQPSK)

17. DSSS - 2
• Maximum transmit power
– US => 1W
– Europe => 100mW EIRP
– Japan => 10mW/MHz
• Bits are scrambled by
s(z)=z7+z4+1
• Two basic parts
– PLCP part (Preamble and header)
– Payload part.

18. Bits 128 16 8 8 16 16 Variable
Synchronization SFD Signal Service Length HEC Payload
PLCP Preamble PLCP Header
Format of an IEEE 802.11 PHY frame using
DSSS

19. Infra red
• Uses visible light => 850-950nm.
• No line of sight required.
• Maximum range =>10m (no interference).
• Today no product offer communication
based on infra red.
• Proprietary products offer up to 4Mbits/s
using diffuse infra red light.
• Directed infra red communication based
on IrDA can be used (IrDA,2002).