Presentation on 802.11 WLAN talking about architecture, protocol stack, physical layer, services, mac sublayer and frame structure of 802.11

1. 802.11
WLAN
Group 6
Priyanshu Agrawal
Tushar Choudhary
Aditya Singh

2. Agenda
802.11
Architecture
and Protocol
Stack
01
802.11
Physical
Layer
02
802.11
MAC
Sublayer
03
802.11
Frame
Structure
04
802.11
Services
05

3. 802.11
Architecture and
Protocol Stack
1

4. TYPES OF ARCHITECTURE
1. AD HOC NETWORK
2. INFRASTRUCTURE NETWORK

5. Ad Hoc Network
• This mode is a collection of
computers that are
associated so that they
can directly send frames
to each other.
• There is no access point.

6. Infrastructure Network
• Each client is associated with
an Access Point that is in turn
connected to the other
network.
• The client sends and receives
its packets via the AP.
WHAT IS ACCESS POINT ?

7. Protocols

8. Data Link
Layer
MAC Sublayer
In 802.11, the MAC (Medium Access Control) sublayer determines
how the channel is allocated, that is, who gets to transmit next.
Logical Link Layer
Above it is the LLC (Logical Link Control) sublayer, whose job it is to
hide the differences between the different 802 variants and make
them indistinguishable as far as the network layer is concerned.

9. 802.11 Physical
Layer
2

10. Microwave Oven
Garage Door Openers
Cordless Phones
Baby Monitors
802.11 Physical Layer
Radio Spectrum
2.4
GHz
5
GHz
ISM

11. 802.11 Physical Layer
802.11b
• upto 11 Mbps
• Similar to CDMA
• 2.4 GHz
• Barker sequence is the spreading sequence used.

12. 802.11 Physical Layer
802.11a
• upto 54 Mbps
• OFDM (Orthogonal Frequency Division Multiplexing)
• 5 GHz
• Formed first but was approved later than 802.11b.

13. 802.11 Physical Layer
802.11
g
• upto 54 Mbps
• OFDM (Orthogonal Frequency Division Multiplexing)
• 2.4 GHz

14. 802.11 Physical Layer
802.11n
• upto 600 Mbps
• OFDM (Orthogonal Frequency Division Multiplexing)
• 2.4 GHz and 5 GHz
• MIMO (Multiple Input Multiple Output)
• Doubled channels from 20MHz to 40 MHz

15. 802.11 Physical Layer
802.11ac
• upto 6.8 Gbps
• OFDM (Orthogonal Frequency Division Multiplexing)
• 5 GHz
• Downlink MU-MIMO (Multi User - Multiple Input
Multiple Output)

16. • upto 10 Gbps
• OFDMA (Orthogonal frequency-division multiple
access)
• 2.4 GHz and 5 GHz
• Downlink and Uplink MU-MIMO (Multi User -
Multiple Input Multiple Output)
802.11 Physical Layer
802.11ax

17. 802.11 MAC
Sublayer
3

18. • IEEE 802.11 defines two MAC sublayers: 1) Distributed coordination function (DCF)
2) Point coordination function (PCF)
• 802.11 tries to avoid collisions with a protocol called CSMA/CA (CSMA with Collision Avoidance).
• This mode of operation is called DCF (Distributed Coordination Function) because each station
acts independently, without any kind of central control.

19. • Initially before sending station senses whether
channel is free or not.
• Otherwise, the station chooses a random backoff
value using binary exponential backoff.
• When the counter reaches zero the station transmits
the entire frame and then waits for an
acknowledgment.
• If an acknowledgment is received, the transmitting
station knows that its frame has been correctly
received at the destination station.
• If the acknowledgment isn’t received, the transmitting
station reenters the backoff phase in step 2, with the
random value chosen from a larger interval.

20. • PCF (Point Coordination Function) in which the access point controls all activity in its cell, just
like a cellular base station. However, PCF is not used in practice because there is normally no
way to prevent stations in another nearby network from transmitting competing traffic.
• There are two main reasons why 802.11 MAC does not implement collision detection:
⚬ Station must be able to send data and receive collision signals at the same time.
⚬ Hidden terminal problem

21. • From the perspective of node 1, node 2 is a
"hidden" node. If a simple transmit-and-pray
protocol was used, it would be easy for node 1
and node 3 to transmit simultaneously, thus
rendering AP unable to make sense of anything.
• An optional RTS/CTS mechanism uses the NAV to
prevent terminals from sending frames at the
same time as hidden terminals.
Hidden Terminal Problem
Img source:

22. • The network allocation vector is a virtual carrier-sensing mechanism used with wireless
network.
• While RTS/CTS sounds good in theory, it is one of those designs that has proved to be of little
value in practice.
• CSMA/CA with physical and virtual sensing is the core of the 802.11 protocol.

23. 802.11 Frame
Structure
4

24. 802.11 Frame Structure

25. 802.11 Frame Structure

26. 802.11 Frame Structure

27. 802.11 Frame Structure

28. 802.11 Frame Structure

29. 802.11
Services
5

30. • Association
• Re association
• Dissociation
• Authentication
• Distribution
• Integration
• Data Delivery
• Privacy
• QOS traffic scheduling
• Transmit power control
• Dynamic Frequency Selection
802.11 Services

31. Future Prospects & Conclusion
• IEEE 802.11ax™, or Wi-Fi 6, is the most recent standard in the
series, published in 2021.
• Next to take center stage will be Wi-Fi 7.
• Wi-Fi 7 is based on features defined in the IEEE P802.11be™
draft amendment.
• The evolution of IEEE 802.11-based Wi-Fi standards continues
today, providing much faster data transmission rates, longer
ranges, and more reliable and secure connections.

32. References
• 802.11 Wireles Networks The Definitive Guide; Matthew S. Gast;
ISBN:0-596-00183-5
• Tanenbaum, Andrew S., 1944-Computer networks / Andrew S.
Tanenbaum, David J. Wetherall. ISBN-13: 978-0-13-212695-3
(alk. paper)
• Computer networking: a top-down approach / James F. Kurose,
University of Massachusetts, Amherst, Keith W. Ross, NYU and
NYU Shanghai. ISBN 9780133594140
• Forouzan, Behrouz A. Data communications and networking I
Behrouz A Forouzan. ISBN 978-0-07-296775-3

33. Thank You