1. Wireless LAN Advantages 1. Flexibility 2. Planning 3. Design
4. Robustness
5. Cost
WHERE ?? HOTELS,AIRPORT,LECTUREHALLS

2. WLAN Disadvantages 1. QoS (Lower Quality)
2. Restrictions –limited to low power senders
and certain frequency bands
3. Safety and Security
(Radio Transmission Interference Hospital Equipment)

3. DESIGN ISSUES FOR COMMERICAL SUCCESS
Global Operations
Low Power
License Free Operations
Robust Transmission Technology
Easy to use ( Plug –and-Play)

4. Infrared VS Radio Transmission

5. Infrastructure Vs Adhoc Networks

6. IEEE 802.11 Famous Family Of WLAN in which many products available
Time Bounded and Asynchronous Services

7. Architecture of an Infrastructure based on IEEE 802.11

8. Architecture of IEEE 802.11 Adhoc Wireless Lan

9. IEEE 802.11 Protocol Architecture and Bridging

10. Layers and Functions

11. Physical Layer 3 Different Variants
All Phy Variants have CCA(Clear Channel Assessment) Signal
FHSS
DSSS
PHY Layer, based on Infrared transmission uses near light at nm.

12. IEEE 802.11 Medium Access Control
MAC layer covers three functional areas:
–Reliable data delivery
–Access control
–Security

13. MAC LAYER 3 BASIC ACESS MECHANISM
(1) CSMA/CD by avoiding Hidden Terminal
Problem
(2) DCF (Distributed coordination Function)
(3) PCF (Point Coordination Function)
MAC MECHANISMS ARE ALSO CALLED
AS DISTRIBUTED FOUNDATION
WIRELESS MAC (DFWMAC)

14. Inter Frame Spacing
All access methods; controlling waiting time is important.

15. Reliable Data Delivery
More efficient to deal with errors at the MAC level than higher layer (such as TCP)
Frame exchange protocol
–Source station transmits data
–Destination responds with acknowledgment (ACK)
–If source doesn’t receive ACK, it retransmits frame
Four frame exchange
–Source issues request to send (RTS)
–Destination responds with clear to send (CTS)
–Source transmits data
–Destination responds with ACK

16. DFWMAC

17. FRAME FORMAT

18. FRAME FORMAT Contd..
Duration Id : Time in which medium is occupied
Checksum : To protect the frames
To DS & From DS
More Frag-> 1 (if another frames follows)
Retry ->1 (Earlier Frame retransmit)
Power Management -> 1-PS mode ,0 –Active
Wired Equivalent Privacy(WEP): Standard security mechanism applied
Order : Received Frames to be processed in the strict order

19. Interpretation of the MAC Address in an 802.11 MAC Frame

20. MAC Management Synchronization :
Finding WLAN, Synchronization of Internal Clocks, Generation of Beacon Signals Generation
Power Management :
Periodic Sleep,Buffering,without missing a Frame
Roaming :
Joining Network; Changing AP;Scanning for AP
Management Information Base :
Current state of Wireless station is stored for internal and external access

21. Synchronization Node of 802.11 network maintains INTERNAL CLOCK
Timing Synchronization Function
Within BSS,Periodic transmission of a BEACON FRAME
BEACON –Timestamp and MF(PM,Roaming)
From Time to Time Internal Clock to be adjusted.

22. Beacon Transmission in a Busy 802.11 Infrastructure Network
AP Performs Synchronization

23. Beacon Transmission in a Busy 802.11 Adhoc Network
NO AP;Each Node has its own timer & starts the transmission of a beacon signal after the beacon interval
Random Back off Algorithm –Beacon Frames & only one BEACON Wins.

24. POWER MANAGEMENT
Switch off the transceiver whenever it is not needed –Should support all applications
Sending device –Simple
Receiving device –Not aware-WakeUp Periodically
Longer off periods save battery life but reduces average throughput.

25. Power SAVING
Two States for a Station –SLEEP & AWAKE & Buffering of data in senders
Receivers awake periodically and stay awake for a certain time
Senders Announce the destinations of the buffered data
Destination wakes until the transmission takes place

26. Power Management –Adhoc Networks
•No AP to buffer data
•Nodes ability to buffer data frames
•Synchronization –All stations wake up at the same time
•All Stations will announce the list of Buffered Frames-AdhocTIM
•Announcement -ATIM Window
•ATIM Interval –wakes & goto sleep if no frame is buffered
•Others transmit and get the ACK

27. ROAMING 10-20m transmission quality User move from ap-ap
Station scans for NEW AP
Scanning defined in PHY Layer
PASSIVE & ACTIVE
Passive
-Simply Listens to Medium to find the other network.

28. ACTIVE SCANNING PROBE on each channel & wait for a response
Based on the response ;the station decides to join BSS
Station selects AP;Send the Association Request
Get the Association Response
After joining new AP ; DS will update and inform the old AP