IEEE Standards
Dr. R.Radha,
VIT Chennai

Outline
▪ Wireless
▪ IEEE 802.11
▪ IEEE 802.15.1
Dr. R. Radha, VIT Chennai

Basics
▪ Standardfor Wireless Local Area Network (WLAN)
▪ Commonly known as WiFi
▪ Data transmission using Electromagnetic Spectrum:
▪ Radio Waves, Infrarred
▪ License free –ISM band 2.4GHz
▪ Only a support to wired network – not a replacement
Dr. R. Radha, VIT Chennai
IEEE 802.11

Infrastructure Ad-hoc
Architecture – Basic Service Set (BSS)
Access Point(AP)
Station
Dr. R. Radha, VIT Chennai

Architecture – Extended Service Set (ESS)
Distribution System
Source: Behrouz A Forouzan, “Data Communications and Networking”, 4th Edition Dr. R. Radha, VIT Chennai

Station types
▪ Based on the mobility
▪ No transitionstation
▪ BSStransition station
▪ ESS transitionstation
Connection not guaranteed during movement
Dr. R. Radha, VIT Chennai

Active Scanning Passive Scanning
Association
Probe request
frame
Probe request
frame
Probe response
frame
Probe response
frame
Association request
frame
Association response
frame
Beacon
frame
Beacon
frame
Association request
frame
Association response
frame
Dr. R.Radha VIT Chennai

IEEE 802.11
▪ Physical Layer – various amendments available based on
▪ Bandwidth
▪ Encoding scheme
▪ Frequency Hopping Spread Spectrum (FHSS)
▪ Direct Sequence Spread Spectrum (DSSS)
▪ Orthogonal Frequency Division Multiplexing(OFDM)
▪ Speed : 1 , 2, 5.5,11, 54 Mbps
▪ Range 250 METERS
Dr. R.Radha VIT Chennai

IEEE 802.11 (contd.)
▪ Data Linked Layer
▪ MAC sublayer
▪ Distributed Coordination Function(DCF)
▪ Contention-based service
▪ Mandatory
▪ Point Coordination Function(PCF)
▪ Contention-free service
▪ Optional
Dr. R.Radha VIT Chennai

Distributed Coordination Function (DCF)
▪ Multiple stationscontend with each other to access carrier
▪ CSMA/CA (Carrier Sense Multiple Access Collision Avoidance)
▪ Reasons for not using Collision Detection:
▪ Stationsare half duplex
▪ Signal strengthis very low
▪ Hidden station problem
Dr. R.Radha VIT Chennai

CSMA/CA Carrier
Sender Receiver Other Station Other Station
Wait for DIFS
Check if free
Request to Send (RTS)
Wait for SIFS
Clearto Send (CTS)
Wait for SIFS
Data
Wait for SIFS
Acknowledgement
Wait for NAV (Network Allocation Vector)
DIFS – Distributed Interframe space
SIFS – Short Interframe space
Source: Behrouz A Forouzan, “TCP/IP Protocol Suite”, 4th Edition Dr. R.Radha VIT Chennai

Hidden Station Problem Exposed Station Problem
Problems Solved by CSMA/CA
Currently sending data Waiting to send data
R1 S1 S2 R2
R1
S1
S2
R2
S1 R1 S2
S1
R1
Send data Send data
S2
Dr. R.Radha VIT Chennai

Point Coordination Function (PCF)
Stationrequiring
contentionfree service
Access
Point
Wait for NAV (Network Allocation Vector)
Other
Station
Other
Station
Wait for PIFS
Beacon Frame
Wait for SIFS Poll Frame
Wait for SIFS
Acknowledgement
Data
Wait for SIFS
Acknowledgement
Contention free frame Dr. R.Radha VIT Chennai

IEEE 802.15
Dr. S. Kirthica,VITChennai

IEEE 802.15.1 - Bluetooth
▪ WLAN technology to connect devices of different functions
▪ Ad-hoc network
▪ License free band of 2.45 Ghz
▪ Bandwidth: 1-3 Mbps
▪ Range: ~10 metres
▪ Low power consumption
Dr. S. Kirthica,VITChennai

Architecture
Piconet
▪ 1 master & upto 7 slaves
▪ Communication only between
master and slave
▪ Stateof a slave:
▪ Active
▪ Parked
Scatternet
Dr. R.Radha VIT Chennai