Chapter 4 - Wirelsess LAN Lec Concise (1).ppt

Chapter 4 - Wirelsess LAN

1. Chapter Four
Wireless Local Area Networks(WLANs)

2. Wireless LAN Overview
A wireless LAN or WLAN is a wireless local
area network that uses radio waves as its
carrier.
The last link with the users is wireless, to give a
network connection to all users in a building or
campus.
The backbone network usually uses cables
Most modern WLANs are based on IEEE 802.11
standards and are marketed under the Wi-Fi
brand name

3. Advantages of WLANs are:
Flexibility:Withinradiocoverage,nodescan
communicatewithoutfurtherrestriction.Radiowaves
canpenetratewalls,sendersandreceiverscanbe
placedanywhere
Planning:Onlywirelessad-hocnetworksallowfor
communicationwithoutpreviousplanning,anywired
networkneedswiringplans.
Design:Wirelessnetworksallowforthedesignof
small,independentdeviceswhichcanforexamplebe
putintoapocket.
Robustness:Wirelessnetworkscansurvive
disasters,e.g.,earthquake.

4. Disadvantages of WLANs
Quality of service: WLANs typically offer lower
quality than their wired.
Restrictions: All wireless products have to
comply with national regulations. Several
government and non-government institutions
worldwide regulate the operation and restrict
frequencies to minimize interference.
Safety and security: Using radio waves for data
transmission might interfere with other high-
tech equipment in, e.g., hospitals.

5. Cont..
Globaloperation:WLANproductsshouldsellin
allcountriesso,nationalandinternational
frequencyregulationshavetobeconsidered.In
contrasttotheinfrastructureofwirelessWANs,
LANequipmentmaybecarriedfromonecountry
intoanother–theoperationshouldstillbelegal
inthiscase.
Lowpower:DevicescommunicatingviaaWLAN
aretypicallyalsowirelessdevicesrunningon
batterypower.TheLANdesignshouldtakethis
intoaccountandimplementspecialpower-saving
modesandpowermanagementfunctions.

6. BASIC WLAN COMPONENTS
Foronetosetupawirelesslocalareanetwork,
twobasiccomponentsmustbeavailable:wireless
networkcardsandwirelessaccesspoint(s).
Thethirdbasiccomponent,wirelessbridge,is
usedtolinktwoormorebuildingstogether.The
wirelessnetworkcardsareattachedtomobile
computingdevices,andtheyconnecttoanaccess
point.Anaccesspointisessentiallyahubthat
giveswirelessclientstheabilitytoattachtothe
wiredLANbackbone.

7. WLAN TRANSMISSION TECHNOLOGIES
WirelessLANsaregenerallycategorized
accordingtothetransmissiontechniquein
use.AllavailablewirelessLANproductsfall
intooneofthecategoriesbelow:
Infrared(IR)LANs?
SpreadSpectrumLANs?
radiowave?

8. Common Topologies
The wireless LAN connects to a wired LAN
•There is a need of an access point that bridges wireless LAN
traffic into the wired LAN.
•The access point (AP) can also act as a repeater for wireless
nodes, effectively doubling the maximum possible distance
between nodes.

9. Classification of Wireless Networks
Base Station:: all communication through an
Access Point (AP){note hub topology}.Other
nodes can be fixed or mobile.
Infrastructure Wireless :: AP is connected to
the wiredInternet.
Ad Hoc Wireless:: wireless nodes communicate
directly with one another.
MANETs (Mobile Ad Hoc Networks) ::ad hoc
nodes are mobile.

10. Wireless LANs
(a) Wireless networking with a base station. (b) Ad hoc networking.

11. IEEE 802.11
IEEE802.11isasetofstandardsforawireless
localareanetwork(WLANn).Thestandardis
betterknownasWi-fi.IEEE802.11seefigure
2.4,Theoriginal802.11standardwaspublishedin
1997.
Thisstandardprovidedadataspeedof1or2
Mbit/s.Thestandardoperatesinthenearly
worldwideavailable2.4GHzbandrangingfrom
2400-2483.5MHz.Thestandarduseseither
frequencyhoppingorcoding(directsequence
spreadspectrum).

12. System architecture
Comparison: infrastructure vs. ad‐hoc
networks
Wireless networks can exhibit two
different basic system architectures
infrastructure-based or ad-hoc.

13. WLAN Architecture
Infrastructuredwireless LAN
Ad-Hoc LAN
Independent Basic Service Set Network

14. 802.11 Roaming
Noorbadconnection?Thenperform:
Scanning–scantheenvironment,i.e.,listeninto
themediumforbeaconsignalsorsendprobes
intothemediumandwaitforananswer
ReassociationRequest–stationsendsarequest
tooneorseveralAP(s)
ReassociationResponse–success:APhas
answered,stationcannowparticipate–failure:
continuescanning

15. Cont..
APacceptsReassociationRequest–signalthe
newstationtothedistributionsystem–the
distributionsystemupdatesitsdatabase(i.e.,
locationinformation)–typically,thedistribution
systemnowinformstheoldAPsoitcanrelease
resourcesI
Inter‐AccessPointProtocol(802.11f)–
CompatiblesolutionforRoamingbetween
differentvendors’APs–Load‐balancingbetween
AP

16. European standard developed by ETSI/BRAN
(European Telecommunications Standards
Institute/Broadband Radio Access Networks)
Physical Layer is very similar to 802.11a
Standard based on wireless ATM
(Asynchronous Transfer Mode)
It is a wireless standard derived from
traditional LAN environments and can support
multimedia and asynchronous data effectively
at high data rates of 23.5 Mbps.
What is HIPERLAN/2?
tseng:16

17. Cont..
ThemainideabehindHIPERLANisto
provideaninfrastructureorad-hoc
wirelesswithlowmobilityandasmall
radius.
HIPERLANsupportsisochronoustraffic
withlowlatency.TheHiperLANstandard
familyhasfourdifferentversions.
Thekeyfeatureofallfournetworksis
theirintegrationoftime-sensitivedata
transferservices
tseng:17

18. HIPERLAN requirements
tseng:18
Short range -50m
Low mobility -1.4m/s
Networks with and without infrastructure
Support isochronous traffic
audio 32kbps, 10ns latency
video 2Mbps, 100ns latency
Support asynchronous traffic
data 10Mbps, immediate access
HIPERLANaimstocreateanddemonstrateaEuropean
capabilityforhigh-performanceradionetworkingfor
portablecomputers

19. HIPERLAN PROTOCOL
tseng:19

20. Overview: original HIPERLAN protocol family
tseng:20

21. HiperLAN2
tseng:21

22. HiperLAN2
IEEE 802.11 is a widely accepted standard
in the United States for wireless LANs
Primarily a “cellular” random access scheme
with ad hoc networking and contention free
access
802.11b products are available now, but 802.11a
are better
HIPERLAN/2 is being pushed in Europe
Wireless ATM solution for real-time traffic
Standard reflects the network topology
There is an effort to agree on one world-
wide standard, keep your fingers crossed
tseng:22

23. Wireless Sensor Networks:
•sensor
–A transducer
–converts physical phenomenon e.g. heat, light, motion,
vibration, and sound into electrical signals
•sensor node
–basic unit in sensor network
–contains on-board sensors, processor, memory,
transceiver, and power supply
•sensor network
–consists of a large number of sensor nodes
–nodes deployed either inside or very close to the
sensed phenomenon

24. Thank You!