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

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)

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

Infrared VS Radio Transmission

Infrastructure Vs Adhoc Networks

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

Architecture of an Infrastructure based on IEEE 802.11

Architecture of IEEE 802.11 Adhoc Wireless Lan

IEEE 802.11 Protocol Architecture and Bridging

Layers and Functions

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 850-950nm.

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

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)

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

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

802.11 DFWMAC

802.11 FRAME FORMAT

802.11 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

Interpretation of the MAC Address in an 802.11 MAC Frame

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

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.

Beacon Transmission in a Busy 802.11 Infrastructure Network AP Performs Synchronization

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.

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.

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

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

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.

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