ieee 802.11 architecture
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WIFI AND THE IEEE802.11 WIRELESS LAN
STANDARD
IEEE 802 ARCHITECTUR
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Protocol Architecture
•
What i !rotocol"Peer layers communicate by means of
formatted blocks of data that obey a set of or conventions.
•
Are dened specically for LAN and MAN.• LAN protocol is related to OSI architecturedeveloped by I!!! "#$ committee.
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IEEE 802 Protocol La#erCo$!are% to &SI 'o%el
I!!! "#$
%eferenceModel
Application
Netork
PresentationSession
&ata Link
'ransport
Physical mediumdependent
Physical
Medium access control
(pper)layerprotocols
Physical layerconver*ence procedure
Lo*ical link control
Medium
Medium
Scope ofI!!! "#$standards
LL+servicaccespointP-
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To u, la#er !h#ical la#
•Physical layer conver*ence procedure
&enes a method of mappin* "#$. MA+ layeprotocol data units ,MP&(s- into a framin* formatsuitable for sendin* and receivin* user data andmana*ement information beteen $ or more stat
• Physical medium dependent sub layer ,PM&-
&enes the characteristics of and method oftransmittin* and receivin* user data throu*h a i
medium beteen $ or more stations.
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&SI la#er 2• Provide an interfac
hi*her layers and /o and error con
&ata Link Mediumaccesscontrol
Lo*ical linkcontrol
• On transmission assemble data intaddress and errorelds.
• On reception0 disaframe and performreco*nition and erdetection.
• 1overn access to
OSI%eference
Model
I!!! "#$%eference
Model
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Separation of LL+ and MA+
•
%easons of separation are2. 'he lo*ic re3uired to mana*e access to a share
access medium is not found in traditional layerlink.
$. 4or the same LL+0 several MA+ options may beprovided.
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A
'AChea%e
r
LLChea%e
r
IPhea%er
A!!licatio(%ata
'A
tra
TCPhea%e
r
'AC +ra$e
LLC !rotocol %ata
u(it
IP %ata)ra$
TCP e)$e(t
IEEE 802Protocol i(Co(te3t
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MA+ 4rame 4ormat
•
4unction2- Performin* functions related to medium access
- 'ransmittin* the data
•4ields2
) MA+ control) &estination MA+ address
) Source MA+ address
) &ata
) +yclic %edundancy +heck
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4ields of the frame
•MA+ control2 contains any protocol controlinformation of the MA+ protocol
• &estination MA+ address2 the destinationphysical attachment point on the LAN
•
Source MA+ address2 the source physicalattachment point on the LAN
• &ata2 the body of the MA+ frame
• +%+2 An error)detectin* code
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LAN Protocol Architecture
• MA+ layer2 detectin* errors anddiscardin* any frames that are in error
• LL+ layer2 keeps track of hich frameshave been successfully received andretransmits unsuccessful frames
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Lo*ical Link +ontrol ,LL+-
•
'ransmission of link level P&(s beteen st• Must support multi)access0 shared medium
• %elieved of some details of link access by MA+ layer
•
Addressin* involves specifyin* source anddestination LL+ users
) referred to as service access points ,SAP
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LL+ Services
• (nacknoled*ed connectionlessservices
• +onnection)mode service
• Acknoled*e connectionlessservice
o Species the mechanism for addressin* stations across themedium and for controllin* the e5chan*e of data beteen
to userso Operation and format is based on 6i*h)level &ata Link
+ontrol ,6&L+-o 'hree alternatives services for attached devices2
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(nacknoled*ed connectionless service
A data*ram)style service
%e3uires minimum lo*ic(seful in 2)
. 6i*her layers of softare ill provide the necessarreliability and /o mechanism0 hich e7cient to avoduplication
$. Overhead of connection establishment and mainteun8ustied or even counter productive.
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+onnection)mode service
•Lo*ical connection is set up beteen to userse5chan*in* data0 and /o control and error contprovided.
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Acknoled*ed connectionless service
Provides data*ram that able to be acknoled*edprior lo*ical connection is set up.
+onnection)mode service2 the LL+ softare musmaintain some sort of table for each active connto keep track of the status of that connection
6andlin* of important and time critical alarm oremer*ency control si*nals in a factory
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LL+ Protocol
• Modeled after 6&L+ and has similar functions and formats
•
&i9erences beteen LL+ and 6&L+• LL+ make use of the asynchronous balanced mode of operation
,'ype $ Operation-
• LL+ supports an unacknoled*ed connectionless service ,'ype
• LL+ supports an acknoled*ed connectionless service ,'ype : O
• LL+ permits multiple5in*
•
&SAP and SSAP ; to specify the destination and source use• bit &SAP ) to indicate individual or *roup address
• bit SSAP ) to indicate P&( is a command or response
• 4ormat of LL+ control eld is the same to 6&L+
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• 'ype operation
(nnumbered information ,(I- P&( ; to transfer user d
No acknoled*ement0 /o control0 or error control.
<I& and '!S' P&( ; to support mana*ement functionassociated ith all three types of operation
<I& P&( ; to e5chan*ed to types of operation
'!S' P&( ; to conduct loopback test of the transmission pato LL+ entities
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• 'ype $ operation
A data link connection is established beteen to LL
prior to data e5chan*e.+onnection establishment is attempted by type $ pro
If the connection is accepted0 the destination LL+ entreturns an unnumbered acknoled*ement,(A- P&(.
Once the connection is established0 data are e5chan*information P&(s0 as in 6&L+.
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• 'ype : operation
!ach transmitted P&( is acknoled*ed.
A ne unnumbered P&(0 the acknoled*ed connect,A+- information P&(0 is dened.
(ser data are sent in A+ command P&(s and must backnoled*ed usin* an A+ response P&(.
Only one P&( in each direction may be outstandin* atime.
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'he =i)4Alliance
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I!!!"#$.TERMINOLOGY
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IEEE 802.11 ARCHITECTURE• ESS/ to or more
interconnected by•
A sin*le lo*ical LA
• SS/ stations e5esame MA+ protoco
• +ompetes for acc
• +onnected to a &
•
Statio(4tatio( SS/
• MA+ frame from oAP?destination s
• To re$ote SS/
• MA+ frame from l>SS?AP?&S?re
• &S can be a sitc
ired@ireless net
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• I(%e!e(%e(t SS ISS/• No connection to other >SS
• i.e mobile stations
• An ad hoc netork• Stations communicate directly
ithout AP
•
Portal/ used to inte*rate theI!!! "#$. architecture ith atraditional ired LAN
• Implemented in a device attachedto the &S
• e.* brid*e or router
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SS Co(5)uratio(
•
Si$!le• !ach station belon*s to a sin*le >SS
• =ithin ran*e only of other stations ithin the same >
• &-erla!!i() SS• Station could participate in more than one >SS
• &ynamic association beteen a station and a >S• Stations may turn o90 come in or out of ran*e
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I!!! "#$. S!%I+!S
•
I!!! "#$. &enes B service that need to be prby the ireless LAN to provide functionality e3uito that hich is inherent to ired LANs.
• 'o ays of cate*oriCin* them.• The er-ice !ro-i%er
•
The er-ice are ue% to u!!ort +or
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I!!! "#$. S!%I+!S
. 'he service providerD• 'he tatio( or the %itri,utio( #te$.
• Station services are implemented in every "#$. staincludin* access point0 AP.
• Ditri,utio( er-ice are provided beteen basic ssets ,>SSs-D services implemented in an AP or in anot
special purpose device attached to the distributed sy
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I!!! "#$. S!%I+!S
$. 'he services are used to support forD
• 'o control I!!! "#$. LAN access and condentiality
• 'o support delivery of MA+ service data unit ,MS&(s-stations.
EMS&(s is the block of data passed don from the MA+the MA+ layer.
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&istribution of Messa*es ithin
• Ser-ice involved are %itri,utio( and i(te)ratio(.
• Ditri,utio( is the primary service used by station to e5chframes hen the frame must transfer the distribution system*et from a station in one basic service set0 >SS to a station >SS.
• I(te)ratio( service enables transfer of data beteen a staI!!!"#$. LAN and a station on an inte*rated I!!!"#$.5 LA
• %efers to a ired LAN that is physically connected to the &Shose station maybe lo*ically connected to an I!!! "#$. inte*ration service.
• 'his service does any address translation and media convere3uired for the e5chan*e of data.
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Association)%elated Services
•
Primary purpose of MA+ layer is to transfer MS&beteen MA+ entitiesD usin* distribution service
• 4or distribution service to function0 it re3uiresinformation of the station ithin the e5tended seset0 !SS.
•
'he information is provide by the association)relservices.
• >efore the distribution service can deliver data taccept data from a station. 'he station must beassociated rst.
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: transition types based on mob
• No tra(itio(2 A station of this type is either stationarymoves only ithin the direct communication ran*e of a >SS.
• aic tra(itio(2 &ene as a station movement from oanother >SS ithin the same e5tended service sets0 !SS
• %e3uires the addressin* capability be able to reco*niCe the neof the ne station.
• ESS tra(itio(2 &ene as a station movement from a >!SS to a >SS ithin another !SS.
• Support only if the station can move. Maintenance of upper)laconnections supported by "#$. cannot be *uaranteed. &isruservice is likely to occur.
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Association)%elated Services
• 'o deliver a messa*e ithin a distribution system&istribution service needs to kno here thedestination station is located.
• &S needs to kno the identity of the APD to hich thmessa*e should be delivered in order for the messa*reach the destination station.
• Station must maintain association ith the AP ithin current >SS. Aociatio(6 reaociatio( and %iaociatio( services are related.
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Association)%elated Services
• Aociatio(2 !stablishes an initial association ba station and an AP.
• Reaociatio(2 !nable an established associatitransferred from one AP to another. Alloin* mostation to move from one >SS to another.
•
Diaociatio(2 Notication from either a statioAP that an e5istin* association is terminated. Stashould *ive notication before leavin* an !SS orshuttin* don.
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ACCE
SSP%IA+FS!%I+!S
A
'h di9 b t
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'he di9erence beteen
wired LA G wireless LA
Characteritic Wire% LAN Wirele LAN
'ransmission A station must bephysically connectedto the LAN
Any station ithinradio ran*e of theother devices on thLAN can transmit
%eceivin* 'he receivin* endmust be attached tothe ired LAN
Any station ithinradio ran*e canreceive
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3 Services that provides a
wireless LAN
d bli h
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• (sed to establish t
identity of the stat
to each other.
• I!!! "#$. re3uire
mutually acceptab
and successful
authentication bef
station can establisassociation ith an
Authentication
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2
&eauthentication 'his service is invoked heneve
an existing authentication is
to be terminated
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• (sed to !re-e(t the
co(te(t of messa*e
from ,ei() rea% byother than intendedrecipient.
• 'he standard
!ro-i%e for theoptional use of
e(cr#!tio( toassure privacy.
Privacy
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SU''AR7
• Protocol is needed to provide communication bet
peer layers• LLC provides an interface to hi*her layers and pe
/o and error control
• 'AC *overns access to LAN transmission medium
• I!!! "#$. architecture illustrates the buildin*
of a ireless LAN• 'here are NINE er-ice that need to be provide
ireless LAN to !ro-i%e +u(ctio(alit#
• 'here are THREE er-ice that provide a irelesith acce a(% !ri-ac#