IEEE 802.11 Architecture

7/23/2019 IEEE 802.11 Architecture

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WIFI AND THE IEEE802.11 WIRELESS LAN

STANDARD

IEEE 802 ARCHITECTUR



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.



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-



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.



&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



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.



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



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



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





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



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



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



(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.



+onnection)mode service

•Lo*ical connection is set up beteen to userse5chan*in* data0 and /o control and error contprovided.



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



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+



• '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



• '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+.



• '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.



'he =i)4Alliance



I!!!"#$.TERMINOLOGY



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



• 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



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



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



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



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.



&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.



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.



: 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.




• '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.




• 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.



ACCE

SSP%IA+FS!%I+!S

A

'h di9 b t



'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



3 Services that provides a

wireless LAN

d bli h



• (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





2

&eauthentication 'his service is invoked heneve

an existing authentication is

to be terminated



• (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



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#

IEEE 802.11 Architecture

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