Overview of Wireless LANs Use wireless transmission medium Issues of high prices, low data rates, occupational safety concerns, & licensing requirements now addressed key application areas: LAN extension cross-building interconnect ad hoc networking
36
Embed
Overview of Wireless LANs Use wireless transmission medium Issues of high prices, low data rates, occupational safety concerns, & licensing requirements.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Overview of Wireless LANs
Use wireless transmission medium Issues of high prices, low data rates,
occupational safety concerns, & licensing requirements now addressed
key application areas: LAN extension cross-building interconnect ad hoc networking
Wireless LAN Requirements
Throughput - efficient use wireless medium No of nodes - hundreds of nodes across multiple cells Connection to backbone LAN - using control modules Service area - 100 to 300 m low power consumption - for long battery life on
mobiles Transmission robustness and security license-free operation handoff/roaming Dynamic configuration - addition, deletion, and
relocation of end systems without disruption to users
Wireless LAN at a glance
Wireless LAN
Medium
access
control
FDMA CS
MA
/CA
CDMA
Tran
smis
sion
med
ia
Infrared
Radio
Topologies
Ad hoc
Infrastructure
Applications
Sta
nd
ard
s
IEEE ETSI (Hipper LAN)
CDMA: Code Division Multiple Access ETSI: European Telecom. Standards InstituteCSMA/CD: CSMA with Collision Detection FDMA: Frequency Division Multiple AccessCSMA/CA: CSMA with Collision Avoidance TDMA: Time Division Multiple Access
CDMA: Code Division Multiple Access ETSI: European Telecom. Standards InstituteCSMA/CD: CSMA with Collision Detection FDMA: Frequency Division Multiple AccessCSMA/CA: CSMA with Collision Avoidance TDMA: Time Division Multiple Access
CSMA/CDT
DM
A
Pulse-position modulation
Direct modulation
Multi-subcarriermodulation
Single-carriermodulation
Transmission schemes
Carriermodulation
Spread spectrum
On-offkeying
Direct Sequence
Frequency hopping
AirportsWarehouses
Retail stores
Old buildings
Hospitals
Wireless LANs
IEEE 802.11 Basic service set (cell)
Set of stations using same MAC protocol Competing to access shared medium May be isolated May connect to backbone via access point
(bridge) Extended service set
Two or more BSS connected by distributed system
Appears as single logic LAN to LLC level
802.11 modes
Infrastructure mode All packets go through a base station Cards associate with a BSS (basic service set) Multiple BSSs can be linked into an Extended
Service Set (ESS) Handoff to new BSS in ESS is pretty quick Moving to new ESS is slower, may require
re-addressing Ad Hoc mode
Cards communicate directly. Perform some, but not all, of the AP functions
A BSS without an AP is called an ad hoc network;
a BSS with an AP is called an infrastructure network.
Note
Basic service sets (BSSs)
Wireless connections: Access Point as a Bridge
Extended service sets (ESSs)
Types of station
No transition Stationary or moves within direct
communication range of single BSS BSS transition
Moves between BSS within single ESS ESS transition
From a BSS in one ESS to a BSS in another ESS
MAC layers in IEEE 802.11 standard
Media Access Control
Distributed coordination function (DCF): CSMA/CA No collision detection After finding channel idle, the station waits for a time
period called distributed interframe space (DIFS). Then sends RTS (Request to send) & waits for time
period short interframe space (SIFS) Destination sends clear to send (CTS) to source station After time period of SIFS source sends data After successful transmission of data source waits for
acknowledgement Point coordination function (PCF): It can be implemented in Infrastructure network.
AP performs polling for all the stations.
CSMA/CA flowchart
CSMA/CA NAV (Network allocation vector)
Frame format
Duration of transmission
Sequence control
Subfields in FC field
Control frames
Addresses
Addressing mechanisms
Hidden station problem
The CTS frame in CSMA/CA handshake can prevent collision from
a hidden station.
Note
Use of handshaking to prevent hidden station problem
Exposed station problem
Use of handshaking in exposed station problem
WIRELESS LAN :Physical layers
Industrial, scientific, and medical (ISM) band
Physical layer of IEEE 802.11 FHSS
Physical layer of IEEE 802.11 DSSS
Physical layer of IEEE 802.11 infrared
BLUETOOTHBLUETOOTH
BluetoothBluetooth is a wireless LAN technology designed to is a wireless LAN technology designed to connect devices of different functions such as connect devices of different functions such as telephones, notebooks, computers, cameras, printers, telephones, notebooks, computers, cameras, printers, coffee makers, and so on. A Bluetooth LAN is an ad coffee makers, and so on. A Bluetooth LAN is an ad hoc network, which means that the network is formed hoc network, which means that the network is formed spontaneously. spontaneously.
Bluetooth basics
Short-range, high-data-rate wireless link for personal devices Originally intended to replace cables in
a range of applications e.g., Phone headsets synchronization, remote controls
Operates in 2.4 GHz ISM band Same as 802.11 Frequency Hopping Spread Spectrum
across ~ 80 channels
Protocol Architecture
Piconet Architecture
One master and up to 7 slave devices in each Piconet:
Master controls transmission schedule of all devices in the Piconet
Time Division Multiple Access (TDMA): Only one device transmits at a time
Frequency hopping used to avoid collisions with other Piconets 79 physical channels of 1 MHz each, hop between channels 1600
times a sec
Scatternets
Combine multiple Piconets into a larger Scatternet Device may act as master in one Piconet and slave in another Each Piconet using different FH schedule to avoid interference
Can extend the range of Bluetooth, can route across Piconets