Wilamowski B.M., Irwin J.D. The Industrial Electronics Handbook. Second Edition: Industrial Communication Systems

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48-6 Industrial Communication Systems

 e.PCF.uses.a.virtual.carrier-sense.mechanism.aided.by.an.access.priority.mechanism.. e.PCF.

distributes.information.using.Beacon.management.frames.to.gain.control.of.the.medium.by.setting.the.

NAV.in.the.stations..In.addition,.all.frame.transmissions.under.the.PCF.may.use.a.Point.Interframe.

Space.(PIFS).that.is.smaller.than.the.DIFS.for.frames.transmitted.via.the.DCF.. is.means.that.point-

coordinated

.trac.has.priority.in.accessing.the.medium.over.stations.in.overlapping.networks.operat-

ing

.in.the.DCF.mode..Such.an.access.priority.may.be.utilized.to.realize.a.contention-free.(CF).access.

method.. e.PC.controls.the.frame.transmissions.of.the.stations,.so.as.to.eliminate.contention.for.a.

limited.period.of.time..Although.the.ability.of.providing.support.for.collision-free.transmissions.would.

be.very.benecial.to.industrial.communication,.especially.when.handling.time-constrained.trac,.the.

PCF.is.implemented.only.in.very.few.hardware.devices,.as.it.is.not.included.in.the.Wi-Fi.Alliance’s.

[Wi09].interoperability.standard.

48.4.3 Enhanced Distributed Channel access

 e.EDCA.is.an.extension.of.the.DCF.and.denes.eight.dierent.priority.levels.. e.priorities. are.

mapped.into.four.access.categories.(AC).in.compliance.with.the.IEEE.802.1D.standard.[IEE04],.thereby.

providing.dierentiated.and.distributed.channel.access..Within.a.wireless.station.with.QoS.support.

(QSTA).and.the.Access.Point.(AP).with.QoS.support.(QAP),.every.AC.is.represented.as.an.independent.

transmission.queue..Every.single.queue.contends.for.the.medium.separately.and.has.dierent.parameter.

sets.for.accessing.the.channel.

.parameter.set.consists.of.the.arbitration.interframe.space.number.(AIFSN),.the.two.bounding.

values.for.the.contention.window.CWmin[AC].and.CWmax[AC],.and.the.maximum.allowed.transmis-

sion

.time.for.one.station.TXOP

limit

.. e.AIFSN.depends.on.the.AC.and.is.used.to.derive.the.arbitration.

interframe.space.(AIFS).with.Equation.48.1,.where.aSlotTime.and.SIFS.are.determined.by.the.used.PHY.

layer.(e.g.,.9.and.16.μs.for.802.11g).

AIFS AC AIFSN[AC aSlotTime SIFS[ ] ]*

= +

(48.1)

Similar

.to.the.DCF,.a.station.always.has.to.wait.an.AIFS.before.it.can.contend.for.the.medium..

 e.backo.procedure.is.also.similar.to.the.DCF,.except.for.dierent.values.for.CWmin.and.CWmax..

 e.contention.for.the.medium.with.dierent.priorities.is.shown.in.Figure.48.2..As.a.result,.the.EDCA.

parameter.sets.of.the.four.ACs.cause.dierent.waiting.times,.i.e.,.a.decreased.waiting.time.for.high.

priority.frames.and.a.longer.waiting.time.for.low.priority.frames.. erefore,.the.probability.of.the.suc-

cessful

.data.transmission.of.high.priority.trac.is.increased.

Data

QSTA 1

QSTA 2

Defer Access

SIFS

Ack

SIFS

Slot time

PIFS

AIFS

[VO_AC]

AIFS

[VI_AC]

AIFS [BE_AC]

AIFS [BK_AC]

Contention

window

Contention window

802.11g

aSlotTime =

SIFS =

PIFS =

e.g. AIFS [VO_AC] =

9 μs

16 μs

25 μs

34 μs

QSTA2 starts to transmit

FIGURE 48.2 Channel.access.with.dierent.priorities.

Wireless Local Area Networks 48-7

48.4.4 HCF Controlled Channel access

Contention-free.medium.access.in.802.11e.[IEE05e].is.realized.with.HCF.Controlled.Channel.Access.

(HCCA)..HCCA.is.the.replacement.of.the.previously.dened.PCF.and.used.for.controlled.channel.

access.. e.time.between.two.consecutive.beacon.frames.is.called.a.superframe..It.is.divided.into.an.

optional.contention-free.period.(CFP).and.a.contention.period.(CP)..During.the.CFP,.the.hybrid.coor-

dinator

.(HC).controls.the.access.to.the.channel.by.polling.its.associated.stations.with.QoS.requirements..

However,.the.HC.is.also.allowed.to.initiate.a.controlled.access.phase.(CAP).during.the.CP.aer.detecting.

that.the.channel.is.idle.for.a.time.interval.longer.than.a.PIFS.(PIFS.=.SIFS.+.aSlotTime),.and.whenever.

there.is.a.need.to.transfer.time-critical.data..An.example.for.a.superframe.is.shown.in.Figure.48.3..

Apolled.station.is.granted.a.transmission.opportunity.(TXOP).allowing.the.station.to.occupy.the.channel.

for.a.time.period.equal.to.the.TXOP.value.. is.concept.elevates.HCCA.with.greater.exibility.than.its.

predecessor,.although.the.time.for.generating.CAPs.is.limited.to.a.maximum.duration.in.order.to.leave.

space.for.stations.operating.under.EDCA.

.very.important.concept.for.QoS.support.in.802.11e.is.the.admission control..Whenever.a.station.

wants.to.associate.with.a.certain.BSS,.it.has.to.specify.its.requirements.during.a.TSPEC.negotiation.

as.was.introduced.in.the.integrated.services.architecture.[IET97].. e.negotiation.is.done.with.a.traf-

c

.specication.element.(TSPEC).that.may.contain.parameters.related.to.the.time-critical.trac.ow,.

such.as.the.mean.data.rate.or.the.delay.bound:. ey.are.exchanged.between.the.QAP.and.the.QSTAs.to.

establish.a.trac.stream.(TS).. e.admission.or.the.rejection.of.the.new.TS.depends.on.the.adherence.

of.its.requirements..Every.station.can.have.up.to.eight.dierent.TSs.with.dierent.QoS.requirements.

Aer

.the.negotiation,.the.polling.schedule.for.the.stations.is.calculated.by.the.HC.based.on.the.previ-

ously

.dened.requirements.. e.ability.of.the.HC.to.perform.the.scheduling.depends.on.several.manda-

tory

.parameters,.such.as.the.Nominal MSDU Size,.the.Mean Data Rate,.the.delay bound,.etc..Although.

the.applied.algorithm.for.scheduling.and.admission.control.has.been.completely.le.open.to.the.imple-

menter,

.i.e.,.it.can.be.adapted.to.the.needs.of.specic.applications.and.kinds.of.trac.ows,.a.sample.

scheduler.can.be.found.in.Annex.K.of.the.802.11e.[IEE05e].

48.4.5 Direct Link Protocol and Block aCK

In.order.to.decrease.the.protocol.overhead,.the.802.11e.[IEE05e].also.denes.a.way.to.directly.communi-

cate

.with.other.clients.in.infrastructure.networks.and.to.acknowledge.more.than.one.frame.with.a.block.

acknowledgment.. e.direct.link.setup.(DLS).enables.two.stations.belonging.to.the.same.BSS.to.commu-

nicate

.directly.to.each.other.without.directing.the.frames.through.the.AP..Before.the.transmission.starts,.

the.direct.link.has.to.be.set.up.via.a.request.to.the.AP.that.is.forwarded.to.the.intended.other.station.

Contention free period (CFP)

IEEE 802.11e superframe

Contention period (CP)

Controlled access phase (CAP)

QAP

QSTA 1...n

Data

STA

PIFS SIFS SIFS SIFS SIFS SIFS PIFS SIFS SIFS SIFSAIFS[AC]

+Backoff

Data

STA

Data

STA

Data

STA

ACK

EDCA

Data to

STA 9

EDCA

Data

STA 7

Poll

Data

Poll

Data

STA

ACK

EDCA

Data

STA 8

FIGURE 48.3 Example.of.an.802.11e.superframe.

48-8 Industrial Communication Systems

 e.block acknowledgment.is.also.an.optional.feature.that.increases.the.throughput.eciency..With.

this.optio

.enab

led,

.a.stat

ion

.is.allo

wed

.to.tran

smit

.seve

ral

.fram

.with

.one.TXOP

.All.tran

smitted

fram

.form.a.singl

.bloc

.that.is.ackn

owledged

.by.only.one.bloc

.ackn

owledgment

.fram

.in.the.end,.

lead

ing

.to.a.red

uction

.of.the.nec

essary

.con

trol

.mes

sage

.exc

hanges.

48.5 Limitations of DCF and HCF for QoSSupport

in Industrial Environments

 e.DCF.mechanism.suers.from.various.limitations.from.the.point.of.view.of.supporting.the.trac.ows.

typi

cally

.foun

.in.indu

strial

.envi

ronments,

.for.seve

ral

.reas

ons.

.Firs

.as.coll

isions

.may.occu

.the.avai

lable

band

width

.is.lowe

red

.and.the.medi

.acce

.time.is.nonp

redictable.

. e.lack.of.pred

ictability

.repr

esents

a.majo

.prob

lem

.when.time

-constrained

.tra

.ows.have.to.be.hand

led,

.as.ther

.is.no.way.to.prov

ide

guar

antees

.on.dead

line

.meet

ing,

.even.in.stat

istical

.term

.More

over,

.ther

.is.a.pote

ntial

.for.capt

ure eect,

as.once.a.stat

ion

.gain

.acce

.to.the.chann

el,

.it.may.keep.the.chann

.busy.for.as.long.as.it.choos

es.

.A.way.

to.prev

ent

.a.stat

ion

.with.heav

.non-

real-time

.tra

.to.mono

polize

.the.chann

el,

.thus.sign

icantly

.redu

ing

.the.prob

ability

.that.real

-time

.tra

.will.sue

.from.heav

.cont

ention

.and.be.sign

icantly

.dela

yed

due.to.non

-real-time

.tra

c,

.is.wir

eless

.tra

c

.smo

othing.

. e.tra

c

.smo

other

.is.at.the.mid

dleware

.lev

el,

loca

ted

.betw

een

.the.netw

ork

.laye

.(IP).and.the.wire

less

.MAC.that.hand

les

.RT.and.NRT.tra

.die

ently,

.inje

cting

.them.in.the.MAC.laye

.at.a.die

rent

.rate

.An.adap

tive

.tra

.smoo

ther

.that.impl

ements

the.harm

onic

.incr

ease

.mult

iplicative

.decr

ease

.(HIM

.algo

rithm

.to.regu

late

.non-

real-time

.tra

.burs

befo

.they.are.sent.over.the.netw

ork,

.thus.priv

ileging

.real

-time

.ows

.is.prop

osed

.in.[Jai

03].

.In.[LoB

06],

.a.

Wire

less

.Tra

.Smoo

ther

.(WTS

)

.for.indu

strial

.WLAN

.is.pres

ented

.and.eval

uated.

. e.WTS,.base

.on.a.

fuzz

.cont

roller,

.is.able.to.prov

ide

.end-

to-end

.so.real

-time

.comm

unications

.with.low.roun

d-trip

.time

Both.appr

oaches,

.[Jai

03]

.and.[LoB

06],

.do.not.enta

.any.modi

cation

.in.the.802.

.prot

ocol.

Many

.work

.have.addr

essed

.the.limi

tations

.of.the.DCF.for.real

-time

.tra

.in.indu

strial

.and.robo

tic

appl

ications.

.For.exam

ple,

.in.[San

05],

.the.perf

ormance

.of.the.802.

11b

.proto

col

.using.broa

dcast

.and.

unic

ast

.tran

smissions

.in.die

rent

.unco

ntrolled

.load.scen

arios

.was.anal

yzed

.in.the.cont

ext

.of.real

-time

communication.between.mobile.robots.. e.paper.concludes.that.as.long.as.the.non-real-time.trac.

shar

ing

.the.chan

nel

.with.the.real

-time

.tra

.is.not.exce

ssively

.burs

ty,

.broa

dcast

.tran

smissions

.outp

er-

form

.unic

ast

.ones.in.term

.of.pack

.loss

es.

.Howe

ver,

.when.the.non-

real-time

.tra

.feat

ures

.very.burs

patt

erns,

.the.bro

adcast

.rel

iability

.sign

icantly

.deg

rades.

.lack.of.mech

anisms

.to.prov

ide

.QoS.guar

antees

.is.anot

her

.limi

tation

.of.the.IEEE.802.

.stan

dard.

.To.solv

.this.issu

.IEEE.(Tas

.Grou

.E).publ

ished

.the.IEEE.802.

11e

.stan

dard

.[IEE

05e]

.as.an.

amen

dment

.to.the.orig

inal

.802.

.stan

dard

.inte

nded

.to.enha

nce

.the.MAC.supp

ort

.for.appl

ications

with.QoS.requ

irements.

. e.prop

osed

.mech

anisms

.of.this.stan

dard

.were.disc

ussed

.in.Sect

ion

.48.4

and.in.Sect

ion

.48.4

.4.

However,

.rece

.lite

rature

.outl

ined

.some.limi

tations

.of.the.802.

11e

.prot

ocol

.when.die

rent

.kind

.of.traf

c

.are.supp

orted

.on.the.same.chan

nel,

.and.the.tota

.oer

.work

load

.is.high

.Some.work

.deal

.with.the.

issu

.thro

ugh

.simu

lation-based

.asse

ssments,

.othe

.thro

ugh

.anal

ytical

.cons

iderations.

. e.work.[Mor

06]

show

.thro

ugh

.simu

lations

.that.the.defa

ult

.para

meter

.valu

.of.the.EDCA.mode.are.not.able.to.guar

antee

indu

strial

.comm

unication

.timi

.requ

irements,

.when.the.high

est

.prio

rity

.clas

.(AC_

VO)

.is.used.to.sup-

ort

.real

-time

.tra

.in.shar

.medi

.envi

ronments

.wher

.othe

.type

.of.tra

.are.pres

ent.

. e.pape

conc

ludes

.stat

ing

.that.new.comm

unication

.appr

oaches

.must.be.devis

.in.orde

.to.adop

.IEEE.802.

11e

netw

orks

.on.the.fact

ory

.oor

.In.[Vit

07],

.it.was.show

.by.simu

lation

.that.it.is.bene

cial

.to.adap

.CWmi

.and.

CWma

.for.the.AC_V

.clas

.to.allo

.for.a.larg

.spec

trum

.of.back

o

.valu

es,

.thus.redu

cing

.the.numb

.of.

coll

isions

.insi

.that.clas

. e.reas

.for.thes

.resu

lts

.is.that.the.CWmi

.and.CWma

.sett

ings

.prov

ided

.by.

the.stan

dard

.for.the.AC_V

.clas

.dete

rmine

.a.narr

.rang

.of.back

o

.valu

.for.the.pack

ets

.in.the.clas

Among

.the.work

.addr

essing

.the.sensi

tivity

.of.IEEE.802.

11e

.perf

ormance

.to.chan

ges

.in.the.CWs.

depe

nding

.on.the.netw

ork

.load

.ther

.is.the.one.in.[Xia

04]

.whic

.exte

nding

.the.appr

oach

.in.[Bia

00],

mode

.the.EDCA.proto

col

.by.mean

.of.thre

e-dimensional

.Marko

.chai

.and.anal

yzes

.the.netw

ork

Wireless Local Area Networks 48-9

performance.with.a.varying.CW.size..Another.relevant.work.is.[Kon04],.which.uses.three-dimensional.

Mark

.chai

.to.anal

yze

.the.beha

vior

.of.the.die

rent

.ACs.when.both.the.CWs.and.the.AIFS.are.vari

ed.

Amon

.the.appr

oaches

.prop

osed

.in.the.lite

rature

.to.tune.the.CW,.ther

.are.the.Adapt

ive

.EDCF.(AED

CF)

prop

osed

.in.[Nao

05],

.the.Adapt

ive

.EDCA.(AED

CA)

.prop

osed

.in.[Rom

03],

.and.the.adapt

ive

.tech

nique

pres

ented

.in.[Vit

08].

.Whil

.the.AEDC

.and.AEDC

.appr

oaches

.do.not.prov

ide

.for.chan

ging

.the.valu

of.CWmi

.and.CWma

.but.simpl

.choo

.the.best.one.in.a.suit

able

.calc

ulated

.rang

.the.work.[Vit

08]

prop

oses

.an.adapt

ive

.tech

nique

.to.incr

ease

.the.chan

nel-access

.prob

ability

.of.the.high

est

.prio

rity

.AC.

in.a.gene

ral

.indu

strial

.scen

ario,

.using.a.fuzz

.cont

roller

.to.dyna

mically

.nd.the.most.appr

opriate

.CW.

rang

.on.the.basi

.of.the.obs

erved

.net

work

.con

ditions.

.[TJK

06],

.the.perf

ormance

.of.the.802.

11e

.chan

nel

.acce

.mech

anisms

.HCCA

.using.the.prop

osed

simpl

.sche

duler,

.and.EDCA.in.indu

strial

.autom

ation

.syst

ems

.were.comp

ared

.and.eval

uated.

.Even.

thou

.it.was.foun

.that.HCCA.is.supe

rior

.to.EDCA.in.scen

arios

.with.a.larg

.numbe

.of.stat

ions,

impr

oving

.and.adapt

ing

.the.HCCA.sche

duling

.algo

rithm

.woul

.lead.to.much.bett

.resu

lts,

.whic

.has.

also.bee

.pro

ven

.in.sev

eral

.wor

ks,

.[CL

M07],

.[GM

N03].

48.6 Security Mechanisms

Although.advantageous.to.local.area.networks.(LANs),.WLANs.in.industrial.environments.introduce.

addi

tional

.secu

rity

.chal

lenges.

.Comp

romising

.of.indu

strial

.WLAN

.can.vary.from.cost

.down

times

and.decr

eased

.syst

.perf

ormance,

.to.more.seri

ous

.cons

equences,

.such.as.indu

strial

.espi

onage,

.physi

cal

.inf

rastructure

.dam

age,

.and.eve

.los

.of.hum

.liv

es.

Some

.of.the.typi

cal

.WLAN.secu

rity

.issu

.enta

.auth

entication,

.acce

.cont

rol,

.encr

yption,

.jam-

ing,

.inte

rception,

.and.hija

cking.

.Secu

rity

.mech

anisms

.incl

ude

.vari

ous

.encr

yption

.proto

cols,

.such.are.

Wired.Equi

valent

.Priv

acy

.(WEP

.WiFi.Prot

ected

.Acce

.(WPA.and.WPA2

.Temp

oral

.Key.Inte

grity

Proto

col

.(TKI

P),

.Coun

ter

.Mode

.with.CBC-

MAC

.Proto

col

.(CCM

P),

.and.WLAN.Auth

entication

.and.

Priv

acy

.Inf

rastructure

.(WA

PI).

Although

.depr

ecated,

.WEP.(bas

.on.Rive

.Ciph

.4.[RC4

]

.encr

yption

.algo

rithm)

.is.stil

.in.wide.

use..WPA.and.WPA2.proto

cols

.intr

oduced

.impr

oved

.secu

rity

.rela

tive

.to.the.TKIP

-based

.WEP.appr

oach

by.intr

oducing

.a.larg

.key.leng

.and.a.new.Adva

nced

.Encr

yption

.Stand

ard

.(AES

)

.base

.algo

rithm

know

. as. the. Coun

ter

. Mode. with. Ciph

. Bloc

. Chai

ning

. Mess

age

. Auth

entication

. Code. Proto

col

(CCM

P).

.WEP2.also.intr

oduced

.TKIP

.TKIP.was.desig

ned

.with.a.goal.of.repl

acing

.the.WEP.proto

col

allo

wing

.lega

.hard

ware

.to.rema

.in.use..TKIP.intr

oduced

.mult

iple

.mast

.keys

.a.uniq

.RC4.for.

each.fram

.gene

rated

.by.a.mase

.key,.a.new.inte

grity

.chec

.hash

ing

.algo

rithm,

.etc..CCMP.was.desig

ned

with.the.goa

.of.rep

lacing

.bot

.TKI

.and.WEP

WLAN

.Auth

entication

.and.Priv

acy

.Infr

astructure

.(WAP

.is.the.Chin

ese

.Nati

onal

.Stand

ard

.for.the.

Wirel

ess

.LAN.bas

.on.the.Aut

hentication

.Ser

vice

.Uni

.(AS

U).

Following

.the.guidelines.for.a.secure.WLAN.deployment,.common.security.measures.(e.g.,.signal.strength.

limit

ation,

.MAC.addr

ess

.lte

ring,

.SSID.broa

dcast

.disa

bling,

.and.usin

.the.most.rece

.encr

yption

.prot

ocols)

are.highl

.reco

mmended

.and.shou

.not.be.igno

red.

Similarly

.to.WLAN

.the.ubiq

uitous

.wire

less

.pers

onal

.area.netw

orks

.(WPA

.form

.of.Blue

tooth,

Zigb

ee,

.and.mesh.netw

orks

.sue

.from.cert

ain

.secu

rity

.issu

es.

.Whil

.thes

.issu

.incl

ude

.thos

.of.

encr

yption

.and.auth

entication,

.they.also.rela

.to.conc

erns

.rela

tive

.to.the.“dis

covery

.mode

,”

.“pai

ring,”

and.ele

ments

.of.eav

esdropping

.and.loc

ation

.tra

cking.

48.7 Fast Handover

Especially.when.it.comes.to.widely.distributed.industrial.systems,.a.WLAN.has.to.consist.of.more.than.

one.AP.to.cove

.the.whol

.area

.Henc

.spec

ial

.atte

ntion

.has.to.be.paid.to.the.hand

over

.proc

edure

betw

een

.APs,.beca

use

.it.caus

.a.conn

ection

.disru

ption

.that.migh

.not.be.toler

able

.for.spec

ic

.indu

trial

.real

-time

.appl

ications.

.Usua

lly,

.the.hand

over

.consi

sts

.of.four.die

rent

.phas

es:

.the.sear

.phas

.the.

48-10 Industrial Communication Systems

open.authentication.phase,.the.association.phase,.and.the.robust security network association.(RSNA).

phase.as.shown.in.Figure.48.4..First,.the.connection.loss.will.be.detected.and.the.search.phase.starts.by.

means.of.scanning.all.channels.for.available.APs..Whenever.a.suitable.new.AP.is.found,.the.client.starts.

the.authentication.frame.exchange.followed.by.the.association..Finally,.RSNA.is.established.and.data.

can.be.transmitted.again.using.a.secure.connection.

.order.to.minimize.the.overall.handover.duration,.either.the.search.phase.or.RSNA.can.be.optimized..

RSNA.depends.mainly.on.the.AP.side,.whereas.the.search.phase.is.determined.by.the.client.side..In.[PCK07],.

a.good.survey.of.recent.works.in.the.area.of.fast.handover.and.currently.achievable.times.is.provided.

48.7.1 Mechanisms on the aP Side

 e.mechanisms.on.the.AP.side.mainly.address.a.reduction.of.RSNA..In.order.to.reduce.time-consuming.

authentication.against.an.authentication.server,.the.IEEE.802.11i.[IEE04i].standard.amendment.speci-

es

.a.preauthentication.mechanism.and.allows.a.caching.of.the.corresponding.pair-wise.master.keys.

(PMKs)..Preauthentication.provides.an.option.for.the.client.to.perform.a.full.IEEE.802.1X.authentica-

tion

.with.other.APs.in.range,.while.it.is.still.associated.to.its.current.AP.. e.PMK.caching.feature.allows.

both.AP.and.the.client.to.store.the.results.of.a.rst.full.802.1X.authentication..In.other.words,.whenever.

the.client.roams.back.to.an.AP.it.had.been.previously.associated.to,.only.a.four-way.handshake.is.neces-

sary

.to.establish.the.temporal.keys.for.encryption.

.further.improvement.is.achieved.by.methods.specied.in.the.802.11r.standard.amendment.[IEE08r].

for.a.fast.BSS.transition..Once.a.station.joins.the.wireless.network,.a.full.802.1X.authentication.is.done.

with.the.result.of.a.generated.PMK.that.is.then.distributed.to.all.APs.within.the.same.mobility.domain.

(MD)..Hence,.when.a.station.decides.to.handover.to.a.new.AP,.PMK.can.be.assumed.to.be.already.present..

However,.the.important.question.of.a.feasible.key.distribution.has.been.le.open.by.the.amendment..Aer.

this.the.four-way.handshake.and.the.resource.reservation.for.QoS.are.embedded.into.the.mandatory.

reassociation.procedure..To.sum.up,.three.enhancements.can.be.identied.in.the.802.11r.amendment..

Client

(mobile station)

Auth

Asso

SecAsso

Old AP New AP

Authentication

server (e.g., radius)

Secure association and data exchange

Probe request Ch 1/probe response Ch 1

Probe request Ch n/probe response Ch n

802.11 Authentication request/response

(Re) Association request/response

Key negotiation (4-Way-handshake)

Secure authentication

Secure association and data exchange

Loss of connection

Roaming-trigger/

search phase

Open systems

authentication

Association

Robust security

network association

FIGURE 48.4 Handover.procedure.in.802.11.WLANs.

Wireless Local Area Networks 48-11

Firstof.all,.an.elimination.of.the.802.1x.key.exchange.as.described.previously..Second,.the.four-way.hand-

shake

.for.sess

ion

.key.estab

lishment

.is.inte

grated

.into.the.mand

atory

.802.

.open.syst

ems

.auth

entication.

And.thir

.QoS.reso

urce

.requ

ests

.are.also.excha

nged

.befo

.the.reas

sociation

.with.the.new.AP.star

ts.

48.7.2 Mechanisms on the Client Side

 e.client-side.mechanisms.mostly.optimize.the.search.phase..It.is.desirable.to.know.the.set.of.possible.new.

APs.a.prio

.to.get.rid.of.the.time

-consuming

.scan

ning

.proce

.duri

.the.hand

over.

.Back

ground

.scan

ning

is.a.very.prom

ising

.solu

tion

.to.this.prob

lem.

.It.elim

inates

.the.chan

nel

.scan

ning

.dela

.comp

letely

.beca

use

.a.

stat

ion

.acti

vely

.prob

.avai

lable

.chan

nels

.duri

.the.norm

.data.exch

ange.

. at.is,.as.long.as.no.data.has.

to.be.tran

sferred,

.the.clie

.cont

inuously

.prob

.new.chan

nels

.for.pote

ntial

.APs.and.gets.back.imme

diately

to.the.curr

ent

.one..If.a.hand

over

.is.neces

sary,

.all.info

rmation

.abou

.neig

hboring

.cells.is.alre

ady

.pres

ent.

Moreover,

.an.addi

tional

.radi

.inte

rface

.can.also.be.used.on.the.clie

.side.to.both.passi

vely

.moni

tor

the.chan

nels

.and.to.gath

.info

rmation

.abou

.neig

hboring

.cell

. is.appr

oach

.is.call

.the.dual.radi

clie

.and.has.a.seco

.adva

ntage.

.It.also.allo

.a.seam

less

.hand

over

.using.both.radi

.inte

rfaces

.for.

data.comm

unication.

. e.data.tran

sfer

.is.init

iated

.with.radi

.inte

rface

.A.in.the.rst.BSS..When

ever

.the.

signa

.qual

ity

.of.radi

.inte

rface

.A.decr

eases,

.the.seco

.radi

.inte

rface

.B.star

.to.nd.a.new.AP.and.

gets.asso

ciated

.to.it..As.soon.as.the.signa

.qual

ity

.of.radi

.inte

rface

.A.is.belo

.a.cert

ain

.thre

shold,

.the.

data.comm

unication

.will.be.dire

cted

.to.radi

.inte

rface

.B,.whic

.is.alre

ady

.conn

ected

.to.a.new.AP,.and.

no.ser

vice

.int

erruption

.occ

urs.

48.8 Future Enhancements

Some.of.the.latest.additions.to.802.11.is.the.IEEE.802.11n.amendment.[IEE08n],.which.aims.at.increas-

ing

.the.thro

ughput

.(fro

.20.Mbps.up.to.appr

ox.

.200.Mbps.data.thro

ughput),

.as.well.as.exte

nding

.the.

rang

.of.rece

ption

.(thr

ough

.redu

cing

.signa

.fadi

ng)

.in.comp

arison

.to.the.lega

.802.

11a/g

.stan

dards.

One.of.the.most.impo

rtant

.conc

epts

.to.obta

.thes

.adva

ntages

.is.MIMO

.Seve

ral

.MIMO.feat

ures

.are.

supp

orted

.by.the.802.

11n

.amen

dment,

.incl

uding

.tran

smitter

.beam

forming,

.spat

ial

.divi

sion

.mult

iplex-

ing

.(SDM

.and.spac

.time.bloc

.codi

.(STB

C).

.Furt

hermore,

.using.an.adva

nced

.codi

.with.low.den-

.pari

.chec

.code

.(LDP

.and.appl

ying

.a.chan

nel

.bond

ing

.to.incr

ease

.the.chan

nel

.band

width

.to.

40.MHz.is.possi

ble.

.All.char

acteristics

.ment

ioned

.abov

.allo

.data.rate

.up.to.600.Mbps.to.be.spec

ied

in.802

.11n,

.whi

.is.rou

ghly

.10.tim

.mor

.as.com

pared

.to.802

.11a/g.

Moreover,

.the.Task.Grou

.v.is.curr

ently

.work

ing

.on.a.prop

osal

.for.a.wire

less

.netw

ork

.mana

gement

fram

ework,

.whic

.is.cont

ained

.in.the.802.

11v

.dra.[IEE

08v].

.Wirel

ess

.netw

ork

.mana

gement

.main

deal

.with.impl

ementing

.syst

em-wide

.func

tionalities,

.such.as.load.mana

gement

.amon

.die

rent

.cell

and.coor

dinating

.radi

.prop

erties

.betw

een

.neig

hboring

.APs.. e.load.mana

gement

.algo

rithms

.basi-

ally

.comp

rise

.load.bala

ncing

.and.admi

ssion

.cont

rol

.appr

oaches.

. e.mana

gement

.can.be.cent

ralized,

dece

ntralized,

.or.hybr

.depe

nding

.on.the.targ

eted

.arch

itecture

.of.the.netw

ork.

.Howe

ver,

.the.cent

ral-

ized

.arch

itecture

.is.most.comm

only

.depl

oyed

.and.also.addr

essed

.by.an.Inte

rnet

.Engi

neering

.Task.Forc

(IET

.work

ing

.grou

. e.work

ing

.grou

.spec

ies

.an.inte

roperable

.proto

col

.call

.cont

rol

.and.prov

sioning

.of.wire

less

.acce

.poin

.(CAP

WAP)

.[IET

06].

.It.aims.at.redu

cing

.the.comp

lexity

.of.mana

ging

.a.

larg

.numbe

.of.APs.and.main

.enco

mpasses

.admi

nistrational

.task

.to.ease.oper

ation,

.main

tenance,

and.conguration,.and.for.centralizing.client.management.

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[CLM07]

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.Tec

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.and.infor

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.exch

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. 11:.

Wire

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[IEE04i]

.IEEE.Sta

ndard

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.Tec

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.exch

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betw

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. system

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. and. metr

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. are

. netw

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. req

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. 11:.

Wire

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.LAN.medi

.access.cont

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.(MAC).and.physic

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.(PHY).spe

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.amen

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.802.11,.pp

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a

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[IEE05]

.IEEE.sta

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.Tec

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.and.infor

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.exch

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.system

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.IEEE.St

.802.3,.Jun

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[IEE05a]

.IEEE.Sta

ndard

.for.Info

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.Tec

hnology—Telecommunications

.and.infor

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.exch

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betw

een

. system

s—Local

. and. metr

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. are

. netw

orks—Specic

. req

uirements—Part

. 15.1:.

Wire

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.medi

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.(MAC).and.physic

.lay

.(PHY).spe

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[IEE05e]

.IEEE.Sta

ndard

.for.Info

rmation

.Tec

hnology—Telecommunications

.and.infor

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.exch

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.system

s—Local

.and.metr

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.are

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.Par

.11:.Wire

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LAN.medi

.access.cont

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.(MAC).and.physic

.lay

.(PHY).spe

cications

.amen

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.8:.Medi

access.cont

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.(MAC).qua

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.of.serv

ice

.enha

ncements,

.IEEE.Std

.802.11e-2005.(Amen

dment

.to.

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.802.11,.1999.Edi

tion

.(Re

a

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[IEE06]

.IEEE.Sta

ndard

.for.Info

rmation

.Tec

hnology—Telecommunications

.and.infor

mation

.exch

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betw

een

. system

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. and. metr

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. are

. netw

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. req

uirements—Part

. 15.4:.

Wire

less

. medi

. access. cont

rol

. (MAC). and. physic

. lay

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cications

. for. low-rat

WPANs,.IEEE.St

.802.15.4-2006,.Sep

tember

.2006.

[IEE07]

.IEEE.Sta

ndard

.for.Info

rmation

.Tec

hnology—Telecommunications

.and.infor

mation

.exch

ange

betw

een

. system

s—Local

. and. metr

opolitan

. are

. netw

orks—Specic

. req

uirements—Part

. 11:.

Wire

less

.LAN.medi

.access.cont

rol

.(MAC).and.physic

.lay

.(PHY).spe

cications,

.IEEE.Std

802.11-2007,.C1–1184,.Jun

.2007.

EE08k]

.IEE

.Stan

dard

.for.Inf

ormation

.Tec

hnology—Telecommunications

.and.inf

ormation

.exc

hange

bet

ween

. sys

tems—Local

. and. met

ropolitan

. are

. net

works—Specic

. req

uirements—Part

. 11:.

Wir

eless

.LAN.med

ium

.acc

ess

.con

trol

.(MA

.and.phy

sical

.lay

.(PH

.spe

cications

.ame

ndment

.1:.

Rad

.res

ource

.mea

surement

.of.wir

eless

.LAN

.IEE

.Std..802

.11k-2008

.(Am

endment

.to.IEE

.Std..

802

.11,

.20

07).

[IEE08n]

. IEE

. Dra



. Ame

ndment

. for. Sta

ndard

. for. Inf

ormation

. Tec

hnology—Telecommunications

and

information

.exc

hange

.bet

ween

.sys

tems—Local

.and.met

ropolitan

.are

.net

works—Specic

.req

uire-

ments—Part

.11:.Wir

eless

.LAN.med

ium

.acc

ess

.con

trol

.(MA

.and.phy

sical

.lay

.(PH

.spe

cications

ame

ndment

.4:.Enh

ancements

.for.hig

her

.thr

oughput.

.IEE

.Std

.802

.11n/D7.0,

.Dec

ember

.200

Wireless Local Area Networks 48-13

[IEE08r].IEEE.Standard.for.Information.Technology—Telecommunications.and.information.exchange.

bet

ween

.sys

tems—Local

.and.metr

opolitan

.are

.net

works—Specic

.requ

irements—Part

.11:.Wir

eless

LAN.medi

.acc

ess

.con

trol

.(MA

.and.phy

sical

.lay

.(PH

.spec

ications

.ame

ndment

.2:.Fas

.basi

ser

vice

.set.(BS

.Tra

nsition,

.IEE

.Std

.802

.11r-2008

.(Am

endment

.to.IEE

.Std

.802

.11,

.200

7),

.200

[IEE08v]

. IEE

. Dra



. Ame

ndment

. Sta

ndard

. for. Inf

ormation

. tec

hnology—Telecommunications

. and.

inf

ormation

. exch

ange

. bet

ween

. sys

tems—Local

. and. met

ropolitan

. are

. net

works—Specic

req

uirements—Part

.11:.Wir

eless

.LAN.med

ium

.acc

ess

.con

trol

.(MA

.and.phy

sical

.laye

.(PH

spe

cications

.wir

eless

.net

work

.man

agement,

.IEE

.Std

.802

.11v/D3.0,

.Jun

.200

[IET97]

.IETF.St

andard,

.Sp

ecication

.of.gua

ranteed

.qu

ality

.of.ser

vice,

.IETF.RFC.2212,.1997.

[IET06]

.IETF.Netw

ork

.Wor

king

.Gro

up,

.RFC.4564,.Obj

ectives

.for.cont

rol

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visioning

.of.wire

less

access.po

ints

.(CAPWAP),.IETF

.ht

tp://tools.ietf.org/html/rfc4564,

.Ju

.2006.

[ITU09a]

.Int

ernational

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49-1

49.1 Introduction

Bluetooth.is.the.widely.spread.short-range.wireless.technology.that.has.replaced.existing.cables.in.many.

xed.and.mobi

.appl

ication

.scen

arios

.with.high.meas

ures

.of.secu

rity

.and.an.enha

nced

.data.rate

.Its.

key.feat

ures

.are.robu

stness,

.low.powe

.smal

.size,.and.low.cost

.Blue

tooth

.tech

nology

.is.wide

.acce

pted

now.as.it.can.be.foun

.in.many.cell.phon

.and.comp

uter

.peri

pherals

.that.can.conn

ect

.with.any.othe

such.dev

ice

.resi

ding

.in.pro

ximity.

Bluetooth

.spec

ications

.were.deve

loped

.by.the.Blue

tooth

.Speci

.Inte

rest

.Grou

.(SIG

. e.Blue

tooth

SIG.consi

sts

.of.comp

anies

.in.the.area

.of.tele

communication,

.comp

uting,

.netw

orking,

.and.cons

umer

elec

tronics,

.which.try.to.den

.new.appl

ication

.pro

les

.and.enha

ncements

.to.the.comm

unication

.proto

cols

as.new.dem

ands

.ari

se.

Interoperability

.betw

een

.devi

ces

.supp

orting

.the.same

.so-c

alled

.Blue

tooth

.pro

le,

.is.guar

anteed

.by.

acert

ication

.pro

cess

.of.man

ufacturer

.dev

ices

.fun

ctionality.

.basic.stre

ngth

.of.Blue

tooth

.tech

nology

.is.to.hand

.both.voic

.and.data.tran

smissions,

.simul

ta-

neously.

. is.help

.the.user.to.carr

.out.vari

ous

.pers

onal

.acti

vities

.inno

vatively.

.For.exam

ple,

.the.user.

can.be.hand

s-free

.when.list

ening

.to.voic

.call

.and.at.the.same.time.prin

.shar

.data.amon

.peer

sync

hronize

.the.PDA

.the.lapto

.the.cam

era,

.and.oth

.Blu

etooth-enabled

.dev

ices.

49.1.1 History and technical Background

In.1994,.Ericsson.Mobile.Communications.was.the.rst.company.to.realize.the.need.to.cut.o.the.

cabl

.betw

een

.cell

ular

.phon

.and.thei

.acce

ssories.

. e.name.Blue

tooth

.come

.from.Hara

ld Blåtand,

the.King.of.Denm

ark

.(and.late

.the.King.of.Norw

ay),

.know

.for.tryi

.to.unit

.and.Chri

stianize

.his.

domi

nions.

.A.Scan

dinavian

.name.was.chos

.beca

use

.of.Eric

sson’s

.larg

.cont

ribution

.to.the.deve

lop-

ment

.of.Blu

etooth.

Bluetooth

49.1. Introduction.....................................................................................49-1

History.and.Technical.Background. •. Bluetooth.Specications

49.2. Bluetooth.Core.Architecture.Blocks.............................................49-3

Channel.Manager. •. L2CAP.Resource.Manager. •. Device.

Manager. •. Link.Manager. •. Baseband.Resource.Manager. •. Link.

Controller. •. Radio.Frequency. •. Bluetooth.Networks. •. Bluetooth.

Security

49.3. Bluetooth.Protocol.Stack................................................................49-6

49.4

. Blue

tooth

.Pro

les............................................................................49-7

Four.Bluetooth.General.Proles. •. Bluetooth.General.Proles

49.5. Competitive.Technologies..............................................................49-9

49.6

. Futu

.of.the.Blu

etooth

.Tec

hnology:

.Cha

llenges.....................49-10

References

...................................................................................................49-11

Stefan Mahlknecht

Vienna University

of Tec

hnology

Milos Manic

University of Idaho

Idah

Fal

Sajjad Ahmad

Madani

COMSATS Institute of

Info

rmation

Tec

hnology

49-2 Industrial Communication Systems

In.1998,.Ericsson,.Nokia,.IBM,.Toshiba,.and.Intel.founded.the.Bluetooth.Special.Interest.Group.(SIG).

to.wo

.ou

.a.st

andard

.an

.to.pr

omote

.th

.te

chnology.

. e.r

.sta

ndard

.was.pu

blished

.as.Ve

rsion

.1.

in.Jul

.199

.Ver

sion

.1.0

.fol

lowed

.in.Dec

ember

.of.the.sam

.yea

.Onl

.in.Feb

ruary

.200

.was.the.sta

dard

.of.Ver

sion

.V1.

.pre

sented,

.whi

.was.con

sidered

.the.rs

.rel

iable

.sta

ndard

.on.whi

.com

panies

cou

.bui

.pro

ducts

.in.lin

.wit

.the.mar

ket,

.as.the.pre

vious

.sta

ndards

.had.sign

icant

.aw

.and.ina

curacies.

.Of.lat

.the.sta

ndard

.ha

.com

.to.be.kno

.as.the.IEE

.802

.15.1

.sho

rt-range

.com

munication.

Bluetooth

.dev

ices

.com

municate

.as.sho

rt-range

.dev

ices

.(1–

100

.m).in.the.lic

ense-free

.ISM.ban

.at.

2.4

–2.4835

.GHz

.It.use

.a.rad

.tec

hnology

.cal

led

.the.fre

quency-hopping

.spr

ead

.spe

ctrum.

. e.ini

tial

dat

.rat

.was.spe

cied

.at.1.Mbp

.but.the.new

est

.enh

anced

.dat

.rat

.spe

cications

.ach

ieve

.up.to.3.Mbp

Blu

etooth

.de

nes

.not.onl

.a.rad

.but.als

.a.pro

tocol

.sta

.wit

.pro

les.

.Pro

les

.de

.the.cap

abili-

ties

.and.the.usa

.sce

narios

.dev

ices

.hav

.to.imp

lement

.in.ord

.to.be.int

eroperable

.wit

.oth

.dev

ices

sup

porting

.the.sam

.pro

le.

.With.cer

tication

.req

uired

.for.any.Blu

etooth

.dev

ice,

.int

eroperability

.sha

be.gua

ranteed.

.How

ever,

.as.it.has.bee

.sho

.in.pra

ctice,

.con

sumers

.hav

.als

.exp

erienced

.man

.pro

lems

.wi

.ce

rtied

.de

vices

.in.th

.pa

st.

49.1.2 Bluetooth Specications

 e.specication.process.is.an.ongoing.process.where.features.are.improved.while.continuing.to.maintain.

bac

kward

.comp

atibility

.wit

.pre

vious

.spe

cications.

49.1.2.1

Blu

etooth 1.0 and 1.0B

 ese

.ini

tial

.ver

sions

.nev

.got.out.into.the.mar

ket

.in.sign

icant

.numb

ers

.as.the.rel

eases

.had.sev

eral

pro

blems

.for.ven

dors

.in.dev

eloping

.int

eroperable

.dev

ices.

.A.man

datory

.Blu

etooth

.dev

ice

.har

dware

add

ress

.(BD

_ADDR)

.was.inc

luded

.whi

.con

necting

.the.dev

ices,

.whi

.pro

ved

.to.be.a.set.bac

.for.

var

ious

.Bl

uetooth

.pl

anned

.se

rvices.

49.1.2.2

Blu

etooth 1.1

Various

.err

ors

.wer

.rem

oved

.fro

.the.pre

vious

.rel

ease.

. e.Blu

etooth

.1.1.sho

rt-range

.tec

hnology

.was.

sta

ndardized

.as.the.IEE

.802

.15.1-2002.

.Add

itionally,

.fea

tures

.of.sup

port

.for.the.non

encrypted

.cha

nels

.an

.th

.Re

ceived

.Si

gnal

.Str

ength

.In

dicator

.(R

SSI)

.we

.ad

ded.

49.1.2.3

Blu

etooth 1.2

Users

.of.Blu

etooth

.1.1.wer

.con

fronted

.wit

.int

erference

.prob

lems

.wit

.Wir

eless

.LAN.dev

ices

.and.exp

rienced

.lon

.con

nection

.set

-up

.tim

.tha

.had.to.be.red

uced.

. e.key.fea

tures

.of.the.rel

ease

.are.as.fol

lows:

•

. An.ad

aptive

.fr

equency-hopping

.sp

read

.sp

ectrum,

.to.av

oid

.usi

.oc

cupied

.fr

equency

.ch

annels

•

. A.hi

gher

.e

ective

.da

.th

roughput,

.up.to.72

.kbp

•

. Ext

ended

. Syn

chronous

. Con

nections

. (eS

CO)

. tha

. inc

rease

. lat

ency

. for. con

current

. aud

. dat

tra

nsfer,

.imp

rove

.the.voi

.qua

lity

.of.aud

.lin

ks,

.and.all

.ret

ransmissions

.of.cor

rupted

.pac

kets

•

. e.pr

evious

.st

andard

.wa

.up

graded

.as.th

.IE

.80

2.15.1-2005

49.1.2.4

Blu

etooth 2.0 + ED

Besi

des

.som

.mod

ications

.and.xi

.of.err

ors

.in.the.pre

vious

.rel

ease,

.thi

.spe

cication

.int

roduced

the.opti

onal

.enh

anced

.dat

.rat

.(ED

.for.fas

ter

.dat

.tra

nsfer,

.whi

.was.3.Mbp

. e.EDR.pro

vides

.the.

fol

lowing

.fe

atures:

•

. re

.tim

.fas

ter

.tra

nsmission

.spe

ed,

.up.to.(2.

.Mbp

s);

.hen

ce,

.hig

.qua

lity

.aud

.lin

.wer

pos

sible

•

. Bac

kward

.com

patibility

.to.the.V1.

.spe

cications

.by.all

owing

.simu

ltaneous

.EDR.and.non

-EDR

con

nections

•

. Low

.po

wer

.co

nsumption

.du

.to.a.re

duced

.du

ty-cycle

.ca

pability