Definition and specification of "CANlike" protocols in the context of wireless networks

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Definition and specification of ”CANlike” protocols in the context of wireless networks

Guy Juanole, Gérard Mouney

To cite this version:

Guy Juanole, Gérard Mouney. Definition and specification of ”CANlike” protocols in the context of

wireless networks . [Research Report] LAAS/CNRS. 2015. �hal-01174850�

ontext of wireless networks

GuyJuanole

1,2

, GérardMouney

1,2 1

CNRS, LAAS, 7 avenuedu ColonelRohe, F-31400, Toulouse,Frane

2

Univ de Toulouse,UPS, INSA, INP, ISAE, LAAS,F-31400 Toulouse,Frane

juanolelaas.fr, mouneylaas.fr

Abstrat

Theimplementationofdistributedreal-timeappliationsonwirelessnetworksonstitute

todaya newimportanthallengeand,inthisontext,theMACprotools, whihimplement

theframeexhangesheduling,haveanessentialrole. Thispaperispreisely onernedby

thespeiationofsuhMACprotools. WespeifyMACprotoolsalled CANlikeproto-

ols beause theyareinspired by theMACprotool of thenetwork CAN whih is a wired

network. Thepresentationmadeinthispaper,afterareminderofbasiknowledges(wireless

networkphysiallayer,dierenttopologies,CANwirednetwork,MACprotoolharateris-

tis)showshowtointegratethesebasiknowledgesinordertospeifytheCANlikeprotools

forseveraltopologies(mono-hoptopology andthreedierentmulti-hoptopologies(hains)).

In the onlusion too, weprove (by onsidering a mono-hop topology) the interest of the

CANlikeprotoolsforimplementingappliationsin networkedontrolsystems (byompar-

isonwiththeWiFi-DCF protool).

1 Introdution

Wireless networks andmore partiularlyWireless LoalAreaNetworks(WLANs) aremoreand

more used today inthe industrial area where we have real-time distributed appliations whih

requireQualityofServie(QoS) guaranteesfortheir ommuniations. Inthis ontext,theMAC

protools, whih implement theframe sheduling, have anessential role. WLANsan be either

mono-hannelor multi-hannel. Hereweonsider themono-hannelase.

In the ontext of the wireless networks, the protools of the CSMA (Carrier Sense Multiple

Aess) type and, partiulary, with the attribute CA (Collision Avoidane) [1℄ are very often

onsidered and used. The attribute CA is based on a Bakoproedure whih allows, in om-

parison to the strit CSMA type, to redue the ollision ourrene but not to eliminate this

ourreneand thenwe annotgiveQoS guarantees fortheframe transfer.

Mastering the ollisions and giving QoS guarantees is possible by assoiating priorities to the

frames of the ows (the role of the priorities is to allow to implement a Collision Resolution

(CR)mehanismi.e. to transformwhatwouldbeaollision situation withaCSMAtypepro-

toolinto awinner-looser(s)situation whihresultsfrom atournament basedonthepriorities

omparison; the winner is the frame whih has the highest priority). The rst approah is to

use the BlakBurst tehnique [2℄. The idea is to let the ontending nodes send rst jamming

signals (alled BlakBurst (BB) messages)of length aordingto thepriority. The node whih

hasthelongestjammingsignal(i.e. thehighestpriority)winstheompetitionandthensendsits

frame. Thedrawbakofthis tehnique isthat, if we havea greatprioritynumber,thejamming

signals will be very long and give important delays [3℄. The seond approah is to adapt the

MACprotoolofthewiredCANbus(thepriorityoftheframeisexpressedbytheIDeldwhih

this paper(oneptof CANlike protool).

This paperinludes threeparts:

•

^{therstpart presentsbasi} knowledges,

•

^{theseond part onernsmainly the speiation of themain parametersof the CANlike}

protools for dierentwireless networktopologies; itpresentsalso solutionsfor aproblem

whih ours in a hain topology and whih is alled the intraow problem (onurrent

frame transferinaframe owgoingfrom asoure nodeto a destinationnode).

•

^{thethird partisa onlusion.}

2 Preliminaries: Basi knowledges

Three types of basi knowledges are neessary. The type 1 onerns the harateristis of the

wireless networks physial layer and some important onsequenes for the MAC layer with a

protool of the CSMA type (pure CSMA or CSMA-CA). The type 2 onerns dierent node

interonnetion strutures (i.e dierent topologies) in a wireless ontext. The type 3 onerns

thepriniplesthat underlietheCAN-like protools for thedierenttopologies whih havebeen

onsidered.

2.1 Type 1 of the basi knowledges

2.1.1 The wireless transeiver

Inawireless ontext(ontrarilyto thewiredontext),atranseiverannotsimultaneously send

and reeive on a hannel and has three states: transmitter, reeiver, sleeper. Here we do not

onsiderthestate sleeper whih isusedfor onsiderationsof energyeonomy.

Two time attributes haraterize the transeiver behavior: the hannel Sensing Time

τ ST

^and

theTurnaround Time

τ T T

^.

τ ST

^{allows thetranseiver(inthereeiverstate)to test thehannel}

state (busy oridle)dependingon whetherthedetetedEnergy on

τ _ST

^{ishigher or lowerthana}

prexedthreshold (noted

Ethr

^).

τ T T

^{is thetime to go from thereeiver}(transmitter) state to thetransmitter(reeiver)state.

Ifthehannelisdetetedidle,thetranseiverango(aftera

τ _{T T}

^)inthetransmitterstatewhih allowstheMACentitytosendaframe. Aftera frametransmission, thereeiveran(after

τ _{T T}

⁾

ome baktothereeiverstate.

Relativelyto aframetransmission(byonsideringframeswhereallthebitsuses thesame ode,

and thenhave,fromthepowerpoint ofview,identialtransmissiononstraints),thehannelis

denedbymeans of two parameters(bandwidth, signal reduing)and thenthe transmissionof

anodeisharaterized, interm ofthesignalreduing(withrespetto thepowerofthesignalof

theemitted frame)bytwo ranges: CarrierSenseRange(

R _CS

^{) and T}ransmissionRange(

R _T

^).

2.1.2 Carrier Sense Range (

R CS

⁾

The

R CS

^{,whihisassoiatedtoanode}

i

^(noted

R CS (i)

^),isrepresentedbyairleofenter

i

^and

ofradius noted

r CS (i)

^{. Theradius}

r CS (i)

^{is themaximal rangeinwhihthesending of aframe}

bythe node

i

^{indues for all node}

j

^{being inthe irle, thedetetion of a signal, the Powerof}

whih ishigher thanor equaltoa threshold noted

P (R CS (i))thr

^(theprodutof

P (R CS (i))thr

by

τ ST

^{gives the threshold}

Ethr

^{, i.e the limit of the detetion of a busy hannel state after a}

frametransmissionbythenode

i

^{). Notethat,thefatthatanode}

j

^,intheirle

R _CS (i)

^,detets

asignalresultingfromthesending ofa framebythenode

i

^{,doesnotmean neessarilythatthe}

node

j

^{isableto deodethis frame(thatdependsonthedistane}

d _ij

^{). Thisremark justiesthe}

neessityto introduetheonept ofTransmissionRange(

R T

^).

Thedenition ofthe

R CS (i)

^{requiresstillto preise thefollowingpoints:}

1. thenode

i

^{isalledexposednode to allthenodes}

j

^whihareinthe

R CS (i)

^{(beause the}

transmission of a frame by the node

i

^{induesthe busy hannel state whih prevents all}

thenodes

j

^{to usethehannelduring this}transmission duration),

2. thenodes

j

^{arethenodeswhih,intheframeworkof the}

R _CS (i)

^{,areinompetition with}

thenode

i

^{for thesending of aframe. Morepreisely:}

•

^{if onenode}

j

^startsa transmissionjustbeforean attemptofthenode

i

^,thisindues,

forthenode

i

^{,thesituationbusyhannel whihdelaysits}possibilityoftransmission,

•

^{if onenode}

j

^andthenode

i

^transmitssimultaneously,thisinduesasituation emis- sionollision.

We have tonote thatthese twosituations arenormalsituationsbydenitionof thestrit

ontext CSMA. We desribe,relativelyto thenode

i

^{,these two situationsasendogenous}

interferenes beause they resultfromations ofthenodes

j

^{whih areinthe}

R CS (i)

^.

3. nodesan be outsidethe

R _CS (i)

^{. Amongthesesnodes, some ofthem an have their}

R _CS

whihhave an intersetionwith

R _CS (i)

^{. Call}

k

^{suha node and}

R _CS (k)

^{itsCarrierSense}

Range, and rename

jj ^′

^{the nodes}

j

^{whih are at the} intersetion of

R CS (i)

^and

R CS (k)

^.

The nodes

jj ^′

^{an hear the attempts of the}transmission of the nodes

i

^and

k

^{whih an}

thenreate,inthesenodes

jj ^′

^,interferenesituationsthatweallexogenousinterferenes (beauseresultingofationsof thenodes

i

^and

k

^{,whiharenotinthesame CarrierSense}

Range). This harateristi willhelp us topresent thehiddennode problem.

2.1.3 Transmission Range (

R _T

⁾

Consideragainanode

i

^{and itsassoiated}

R CS (i)

^{. The}

R T

^{,whihisalsoassoiated tothenode}

i

^(noted

R _T (i)

^{), is}representedbya irleof entre

i

^{and ofradius}

r _T

^,noted

r _T (i)

^{. The radius}

r T (i)

^{is the maximal range in whih the sending of a frame by the node}

i

^{sets, for all nodes}

j

being in the irle,the detetion of a signal, thepowerof whih is higher thanor equalto the

power neessaryto deode theframe sent bythenode

i

^{i.e. a power higher thanor equal to a}

thresholdnoted

P(R T (i)thr)

^{. Obviously}

P (R T (i)thr) > P (R CS (i)thr)

^.

Remark: In pratie,generally, we have

r CS (i) > r T (i)

^{whih an still be expressed}

R CS (i) >

R _T (i)

^{. However, we an also onsider a partiularase whih an be expressed}

P (R _T (i)thr) = P (R CS (i)thr)

^{and then}

R CS (i) = R T (i)

^{(i.e. any node in theCarrierSense Rangeof thenode}

i

^{an deode thesignaloftheframe sent bythenode}

i

^{). Inshort,wean say}

R CS (i) ≥ R T (i)

^.

2.1.4 Transmission hop

A transmission hop is the basi element of a ommuniation path between omputers i.e. it

represents, in the framework of an implementation, the distane (noted

d

^{) between a node,}

transmitterof a frame, andthe next node, inthe path,whihreeivesdiretly and deode this

frame. Wehave :

d ≤ r T < 2d

^{i.e. we an havea pathof one hopin}

R T

^{and obviouslymore in}

R _CS

^when

r _CS ≥ 2d

^.

2.1.5 Hidden node

a)Consideragainthepresentationinthesubsetion2.1.2andonsidertheaseofatransmission

of a frame in one hop from thenode

i

^{to a node}

jj ^′

^{(then this frame will be well reeived and}

well deoded inthenode

jj ^′

^{if there isno kind of}interferene). A node hidden to thenode

i

^is

a node

k

^{[4℄, [5℄, beause the node}

k

^{is a node exposed to the node}

jj ^′

^{(i.e the node}

jj ^′

^{is in}

the

R CS (k)

^{), whih an lead, relatively to an attemptof a frametransfer bythe node}

i

^{,to two}

exogenous interferenesituations inthereeptionativityof thenode

jj ^′

^:

•

^{situation 1: asituation alledbusyhannel resultingfromthesending ofa framebythe}

node

k

^{before thesendingattempt bythenode}

i

^{(butthis one annotseethestate of the}

hannel asthenode

k

^{is notin its}

R CS

^{); the result will be the non} onsideration, by the node

jj ^′

^{,oftheframe omingfromthenode}

i

^{(thenits loss),}

•

^{situation 2: a situation alled ollision in reeption whih results from a} simultaneous

sending ofa framebythenodes

i

^and

k

^{,whih anlead, on theframesentbythenode}

i

^,

to thedeodingimpossibilitybythenode

jj ^′

^.

The ourrene of the situation 2 depends, at the node

jj ^′

^{, on the ratio Signal Power of the}

frame oming from the node

i

^(all

P i

^{this power) on Signal Power of the frame oming from}

thenode

k

^(all

P k

^{thispower). Byalling}

d

^{thelength ofthehop}

i, jj ^′

^and

l

^thedistane

k, jj ^′

we have:

P

_i

P

_k

= ( _d ^l ) ⁴

^{. The ondition for a orret deoding of the frame sent by the node}

i

^is

P

_i

P

_k

≥ 10

^{[6℄,whih denesthelimit valueof}

l

^alledInterferene Range etnoted

R I

^{. Wehave}

R I = 1.78d

^.

b) We an now give the quantitative onditions [6℄ whih express the behaviour of a node

k

hiddento thenode

i

^{. Asitis anode outsidethe}

R CS (i)

^,wehave

d + l > r CS ( i )

^.

•

^If

l ≤ 1.78d

^{,we an have thesituations1 and 2,}

•

^If

l > 1.78d

^{,wean onlyhavethesituation 1. Thesituation 1an alwayshappen beause}

thenode

jj ^′

^{is inthe}

R CS (k)

^.

2.2 Type 2 of the basi knowledges

Weonsidertopologieswherealwaystheframes,exhangedbetweenallthenodes,useforalltheir

bits the same ode (i.e. all the bits have, from thepowerpoint of view,identialtransmission

onstraints)andthenthetransmissionofall thenodesareharaterizedbythevalues

R CS

^,

R T

and

d

^{. This situation is the ase of the protools of the CSMA type (pure CSMA or CSMA-}

CA).We an have eithertopologies,alledmono-hop topologies,or topologies alledmulti-hop

topologies(important examplesarethehainsthat we onlyonsider here).

2.2.1 Mono-hop topologies

Mono-hop topologies aretopologies where eah node an ommuniate diretly(one hop) with

all the other nodes. In suh a topology, all the nodesare in theintersetionof their range

R T

(andobviouslytoo oftheir range

R CS

^as

R CS ≥ R T

^;herewetake

R CS = R T

^{). So wehave not}

thehidden node problem. Thisdenes full-meshed topologies. On thegure 1we represent an

exampleof suha topologywhihis madeupof

4

^nodes

1

^,

2

^,

3

^,

4

^{whereeahnodeis theenter}

of airle ofradius equalto

r T

^.

Inthis topology,we an only have endogenousinterferenes.

2.2.2 Chains (Multi-hop topologies)

Note that, for drawing size reasons, we only represent the

R CS

^{ranges and,} furthermore, their irles arerepresentedbyellipses.

We onsider nodeswhere theradius of the range

R CS

^{an inlude at themost}

h

^hops(

h ≥ 1

^).

We dene three types of hains. The rst one with

h > 1

^{(noted hain-1) is a hain where}

3 1

4 2

R

CS

(3) = R

T

(3) R

_CS

(1) = R

_T

(1)

R

CS

(2) = R

T

(2) R

CS

(4) = R

T

(4)

Figure1: Mono-hop topology(fullmeshedtopology)

all the nodes are in the intersetion of their range

R CS

^{and then we have not still the hidden}

nodeproblem (beausenone node isoutsidethe ranges

R CS

^{of theother nodes). Weonly have}

endogenous interferenes. Onthe gure2,we represent an example of suh atopology(hain

of3hops)whihismadeupof4nodes

1

^,

2

^,

3

^,

4

^{wheretheradiusoftheranges}

R CS

^ofthenodes

inludeat themaximum3hops(

h = 3

^{). Obviously}

R T (i) < R CS (i)

^.

1 2 3 4

d d d R

_CS

(3) R

_CS

(4)

R

_CS

(2) R

_CS

(1)

Figure2: hain-1 (4 nodes, 3hops)

Thetwoothertypes(notedhain-2andhain-3)havethehiddennodeproblembeausenodes

areoutsidetherange

R CS

^{ofothernodes. We}distinguishtwoases aordingtothevalueof

h

^:

h = 1

haraterizes a hain notedhain-2 where we onsider

R T = R CS

^;

h > 1

haraterizes a

hainnotedhain-3 whereobviously

R T < R CS

^.

We represent,on thegures 3 and4, respetivelyan example of thehain-2 and anexample of

thehain-3 with

h = 2

^{(the two hains have}

7

^{nodes numbered from}

1

^to

7

^{). We didnotdraw}

the

R CS

^{ofall thenodesfor reasonsofgure larity.}

d d d d d d

1 2

3

4

5

6 7

R

_CS

(7) = R

_T

(7) R

_CS

(2) = R

_T

(2)

R

_CS

(1) = R

_T

(1)

Figure3: hain-2

Wean easily see

•

^{on the gure3, the nodes (}

i + 2

^{) are thehidden nodesof the nodes}

i

⁽

i ∈ [1, 5]

^{) and the}

nodes(

i − 2

^{) arealsothehidden nodesof thenodes}

i

⁽

i ∈ [3, 7]

^),

•

^{on the gure4, the nodes (}

i + 3

^{) are thehidden nodesof the nodes}

i

⁽

i ∈ [1, 4]

^{) and the}

nodes(

i − 3

^{) arealsothehidden nodesof thenodes}

i

⁽

i ∈ [4, 7]

^).

d d d d d d

1 2 3 4

5

6

7

R

_CS

(1) > R

_T

(1) R

_CS

(4) > R

_T

(4) R

_CS

(7) > R

_T

(7)

Figure4: hain-3

It is important to note thedierene in the role of the hidden node depending on whether we

havea hain-2 ora hain-3 (see2.1.5)

•

^{hain-2: asthehiddennode}

i + 2

^(or

i − 2

^{) ofa node}

i

^{isat thedistane}

d

^(i.e.

< 1.78d

⁾

of the node

i + 1

^(or

i − 1

^{), we an have the two situations 1 and 2 of the exogenous}

interferenes,

•

^{hain-3: asthehiddennode}

i + 3

^(or

i − 3

^{)ofa node}

i

^{isat thedistane}

2d

^{( i.e.}

> 1.78d

ofthenode

i + 1

^(or

i − 1

^{),weonly have thesituation1 of theexogenous}interferenes.

We an nowextrapolate from this observation the general ase where we onsider a radius

of

R CS

^inluding

h

^{hops: thenodes(}

i + (h + 1)

^)and(

i − (h + 1)

^{) are thehidden nodes for the}

nodes

i

^{(anhidden node to anode}

i

^{istherstnode outsidethe}

R CS

^{assoiated to thenode}

i

^).

2.2.3 Conept of topology lasses

By looking at the onsequenes of the transmission of a frame by a node

i

^{, we an} distinguish two topologieslasses:

•

^{the lass 1 (mono-hop and hain-1), whih represents one broadast domain, i.e. the}

transmissionofaframegeneratesasignalwhihisheard byalltheothernodes(beause

allthe nodesareintheintersetionoftheir

R CS

^ranges),

•

^{the lass 2 (hain-2 and hain-3), whih represents multiple broadast domains, i.e. the}

transmissionof aframe generatesa signalwhih isonly heard bytheothernodeswhih

areintherange

R CS (i)

^{;all thenodes, whih areoutside}

R CS (i)

^{,donothearanysignal.}

Aboutthe word heard, we an distinguish two semantis (whih will allowto underline simi-

laritiesbetweentopologies ofthetwolasses): thestrong semantiwhih isthe signalwhihis

reeivedbya node,an be deodedbythis node;theweaksemantiwhihis thesignal,whih

isreeived bya node,induesonlya busyhannel state.

The topologies mono-hop (lass 1) and hain-2 (lass 2) are only haraterized by the strong

semanti(as

R CS = R T

^{). Thetopologieshain-1(lass1)andhain-3(lass2)are}haraterized bythetwo semantis (as

R CS > R T

^{): thestrong semantifor thenodes (}

i − 1

^{) and (}

i + 1

^{) i.e.}

thenodes whih arethe neighbours of thenode

i

^{(they areone hop distant of thenode}

i

^{); the}

weak semantifor thenodesdistant ofthenode

i

^from

2

^{hops till}

h

^hops.

2.3 Type 3 of the basi knowledges

ThesebasiknowledgesonernthemainpriniplesoftheCANlikeprotools. Astheseprotools

are inspired bythe CAN network MAC protool, we rst make a reminder of thepriniples of

thisMACprotool. Then,weshowhowweanadaptthesepriniplestothedierenttopologies.