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).