duplex structure for high reliability; related technology has been developed that ... Broadband ISDN (B-ISDN) has become recognized as a ... system architecture.
ATMSwITCHmGNODESYSTEMTECHNOLOGYFOR EFFECTIVE
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Reprintedfrom正EEGIobalTblecommunicationsConference, GLOBEC OO MM '' 9 5 , N o v mb be er r ]C 9 5 , N o ve em l3-17Novemberl995,Singapore,@1995正EE
ATMswitchingnodesystemtechnologyfOreffectivemamtainabinty NoriharuMiyaho,ArataItoh,andKazukuniKoyama NrrNetworkServiceSystemsLaboratories -9-11Midori-cho,Musashmo-shi,Tokyol80,JaPan T℃1.:+81-422-59-2258 Fax:+81-422-59-4549
E M a i l : m i y a h o @ n t t s s l . n s l a b . n t t j p ABSTRACT
AlthoughATMswitchingnodesarebemgdeployed,much workisstillneededtoresolveproblemswiththeir mamtamabnity. T h i s p a p e r d i s c u s s e s t h e c u r r c n t r e s e a r c h a n d e x p e r i e n c e concerningthedevelopmentofATMnodeshomtheviewpomt ofmaintainabilityandclarifiestheconceptsofhardware maintainabilitybyintroducingefficientconnectiontest methodsusinganOAMcell-handlingmechanism,anATM t r a f f i c m o n i t o r i n g m e c h a n i s m w i t h Q o S c o n t r o l , a n d a t e s t c e l l generation/checkingmechanismfOrin-scrviceconnection t e s t i n g . T o m c r e a s e m a i n t a m a b i l i t y , h a r d w a r e f a n u r e d e t e c t i o n / indicationmethods,alayeredmanagementschemeupon detcctionofalinefailure,andautomaticlineswitchingtoa stand-bysystemareproposed. 1.In位odUnctmn
BroadbandlSDNG-ISDN)hasbecomerecognizedasa keytoimprovmgthetelecommunicationworld;ithasbeen adoptedasthevehicleforprovidingawidevarictyof communicationservices.AsynchronousTransferMode (ATMtechnologyhasbeenwidelystudiedandwillbeusedto mplementtheB-ISDN. Inparticular,SDHtransmissionsystems,already
managementschemeandthetechnologyneededfOrautomatic m e s w i t c h i n g u p o n f a i l u r e d e t e c t i o n . 2．AⅡMnodesystemrequirementsfromtheviewpomtof maintainabinty
ForimplementmgpracticalATMnodesystemsfOrpublic networks,therequirementsshowninTablelshould,asa minimum,betakenintoconsiderationfromtheviewpointof maintainability.TheATMnodesystembasicallyusesafUll d u p l e x s t r u c t u r e f O r h i g h r e l i a b i l i t y ; r e l a t e d t e c h n o l o g y h a s beendevelopedthatcanestablishbothemcientmaintenance andoperationatreasonablecost.WhileATMswitching systemsfbrLANsandPBXshaverecenUybeendevelo"d,the requirementsanddesignprinciplesthantheviewpointof mamtamabintyaremuchdifferentfromtheATMnodesystem thatwnlbeusedtosupportpublicnetworks,asshownmTablc 1.Fbrexample,hotstand-byredundantsystemoperationfOr 9uickrecoveryuponfanure,ATMlevellinemomtoring,and automaticconnectiontestingwiminanodeareindispensable mranATMnode.
BoththeATMnodesystemandtheATMLAN/PBX shouldsupportbasiccallcontrolandVC/VPswitching nmctions.SincethefOnnershouldbemuchmorereliable,m-
servicemaintenancebythecarriershouldbepossible・For
establishedfOrcommercialuseasauniversalstandardized
v e h i c l e f O r c a n y i n g m u l t i m e d i a s i g n a l s , h a v e b e e n a p p l i e d t o ATMbackbonenetworks.ATMswitchingsystemsand c o r r e s p o n d i n g h i g h s p c e d A T M t r a n s m i s s i o n s y s t e m s , s u c h a s ATMcrossconnectsystemsusmgSDHtechnology,havebeen b u i l t a n d t e s t e d [ 1 ] [ 5 ] . CommerciallyviableATMnodesystemsmustaddressthe issuesofmaintainabili[yandreliability.Thispapermainly discussestheconceptofaself-testmechanismfor commerciallyavailableATMswitchingnodesystemsfromme v i e w p o i n t o f h a r d w a r c m a i n t a i n a b i l i t y . ThispaperisorganizedasfOllows.Chapter2discusses ATMnodesystemrequirementsfromtheviewpointof maintainability.Chapter3introducesapracticalATM s w i t c h i n g n o d e s y s t e m c o n f i g u r a t i o n w i t h v a r i o u s t r a n s m i s s i o n l i n e i n t e r f a c e s . C h a p t e r 4 a d d r e s s e s h a r d w a r e f a i l u r e d e t e c t i o n andfailureindicationme[hods,andATMtrafficmonitoring
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c o n c e p t s w i t h O o S c o n t r o l . C h a p t e r 5 d e s c r i b e s a c o n n e c t i o n testconceptusmgTCUandanOAMhandlmgmechanismand c l a r i n e s i t s p e r f O r m a n c e . C h a p t e r 6 d i s c u s s e s a l a y e r e d f a i l u r e
TablelATMnodesystemrequirements homtheviewpomtofmaintamability.
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ra廿on
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thesercasons,theATMnodesystcmmustsurpasstheATM LAN/PBXsystemintermsofreliability,maintainability, expandabmty,andmtegnty.
s o f t w a r e p r o c e s s m g o r t h e s e l f L c h e c k i n g h a r d w a r e m e c h a n i s m . TheRMrcanhandlcrcmotePL,remotepower-on,remote d i a g n o s t i c s , a n d s o o n v i a t h e O P I .
3.PIacticalATMswitchmgnodesystem -AHMconnguration. WedevelopedtheATMcircuithandlmgmoduleAIMfOr useasanATMbackbonenmesysteminapublicnetworkfOr hamerelayandcellrelayservices.Theconfigurationofan AHMwith皿gh-speeddatacommumcationservicemterfaces, mtroducedasthenrststeptoB-ISDN,isshownmFigurel. IneachSDHtermmationunit,afterthecorresponding OAMcenshave"enprocesscd,theATMcenheadermeach VCisconvertedmtomcominglmeumtsCJUS,suchasHLUs andTLUs)byreferringtoaheaderconversiontable.To
4．ConceptofhardwaremaintainabilityinATMnode
establishachannelfOreachcall,theccllheaderinfOrmation
TodesignanATMnodesystemthatoffersquickrecovery upondetectionofhardwarefailure,twotypesoffailure
system
IntheAIM,themamsignalandclocksiglallmespassmg througheachfUnctionblockhaveaduplexconngurationto minimizeservicemterruptionuponfailurc・MostfUnction blocksareoperatedmtheactive/hotstand-bymodesoasto e f f c t q u i c k r e c o v e r y u p o n f a i l u r e . T h i s m e a n s t h a t e a c h s t a n d bysystemisactivatedbycallprocessingsoftware a u t o m a t i c a l l y w i t h o u t c o n s i d e r a b l e d e l a y . 4.1Hardwaremiluredetectionandm髄四,n⑪nmetmds
thatwnlbewrittenmtoeacharrivingcell,suchastheVPI, VCI*outingtag,andQoSclassidentifier,aresetbythe processorandcontrolunitCCU)mtheAHMduringthecall set-upphase.EachLUconnectedtoasubscriberlmehasa UsageParameterControl(UPC)fUnctiononitsmcommg s w i t c h i n g n e t w o r k s i d e . A 6 M b i t / S c e l l r e l a y s u b s c r i b e r l i n e isaccommodatedmthelow-speedlmetermmation(LLI)and hamerclaytermmals(FRTs)areaccommodatedmthelowspeedlmetenninationfbrhamerelayservice(FRI)viathe
indicationmethodsshouldbeusedfOreHectiveATMnode
maintenance.OneusesinterruptcontrolsignalsfOrquick processing,suchasimmediatelyswitchmgtotheredundant systembysoftwarecontrol.Theothertypetransmitsstatus mfOrmationtothecontrolprocessorasynchronouslybyDMA control.StatusinfOrmationisusuallyhandledbyperiodic softwarecontrolprocessmgwithal6-to32-mspedod・This t a s k b a s i c a l l y d o e s n o t r e q u i r e t h e h i g h e s t e x e c u t i o n p r i o r i t y . AnyfailuredetectedintheATMswitchfUnctionblockis h a n d l e d b y t h e m i c r o p r o c e s s o r . W h e n a f a i l u r e i s r e c o g n i z e d asapermanentmalfimction,afailureoccurrencemessageis senttothePCUasynchronouslyoraninterruptsignalis
hamerelayswitch(FRS). ThePCUincludescallcontrolsoftwareandexecutesboth
PVCanddemandVCconnectioncontrolsaccordingtothe
Q.2931protocolmtheuser-networkmterface(UNI)andtheBISUPprotocdinthenetwork-networkmterfacemNI). Localmaintenanceworkstations(MWSs)andtheremote maintenancetennmal(RMT)areimmediatelyinformedviathe operationsystemmterface(OPI)ofanyfamtsdetectedbythe
Theconditionsdetcrminingwhichmethodshouldbe
appliedareshownmTable2.Forfailuresmthetransmission s y s t e m , t h e a p p r o p r i a t e m a l h l n c t i o n m e s s a g e s h o u l d b e s e n t t o
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l o c a l i z e t h e Q o S d e t e r i o r a t i o n t o t h e o u t p u t b u " r s t o s i m p l i W mtemallinktrafficmanagement.Smceccllsarequeuedmthe outputbufferinafirst-infirst-out(FIFO)manncr,the d i S t r i b u t i o n o f t h e c e l l d e l a y a n d a v a r i e t y o f r e l a t e d t r a f f i c characteristicscanbeapproximatedbymeasuringthequeue behavior[6]・TheATMtrafncmeasurcmenthmctionshould
Thble2ATMn"chardwaremnureindicationclassification. F画IureIndに唾i⑥、 meth因
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F o r e f f e c t i v e p r o c e s s i n g o f c o n n e c t i o n a d m i s s i o n c o n t r o l anddetectionoftheonsetofcongestion,thehardware automaticallymeasures(a)thenumberofarrivingand discardedcellsperVPovertimemtervalT1orT2and(Uthe maximumnumberofarrivingcellsovertimepedodT3,as shownmFigure2・Thevaluesarestatisticallyprocessedto e s t m a t e t h e a n t i c i p a t e d c e l l l o s s r a t e , l i n e e f f i c i e n c y , a n d c o n g e s t i o n c o n d i t i o n . T h e n u m b e r o f d i s c a r d e d c c l l s p e r V P bufferisusedtotriggercongestioncontrolbysettingan a p p r o p r i a t e t h r e s h o l d . I n p a r t i c u l a r , s e l e c t i v e c e l l d i s c a r d hmctionsmustbeusedwhenthequeuebufferlengthexceedsa pre-determinedthreshold,Q2・Here,T1,T2,andT3are approximatelyseveralhundredsofms,1s,andseveraltensof s e c o n d s , r e s p e c t i v e l y . Basedontheabovediscussion,otherATMtraffic c h a r a c t e r i s t i c s , s u c h a s t h e m i s i n s e r t e d c c l l r a t e , t h e t e q u e n c y ofexceedingthepre-determmedthresholdfOreachVPbuHer, andsoonaremeasuredwithanappropdatesoftwareoperation
redu"antSyStem isnotgx且c哩學苞
SⅧtchI咽也 『edurmantSyStem Isnotex壁in璽
tbcPCUmthefbrmofastatusindicationbyDMAcontrol. Thisisbecausetheactive-lineterminationunitis
a u t o m a t i c a l l y s w i t c h e d t o t h e h o t s t a n d b y r e d u n d a n t s y s t e m byhardware,sosoftwarecontrolisnotneeded.Forabnormal events,suchasbufferovernoworUPCviolationintheline
t e r m i n a t i o n u n i t , t h c a p p r o p r i a t e e r r o r m e s s a g e s a r e s e n t t o t h e PCUmthefOrmofastatusmdicationbecausethoseeventsdo
notconstitutesedousfanuresthatdemandswitchingtothe redundantsystem;theoperatorsare,however,infOrmedbythe MWS.
Ontbeotherhand,interruptcontrolsignalsarenotused whentbereceptionofbasicclocksignalsfromthe transmissionsystembecomesintermittentbecauscthis conditionisinstantlydetectedbyhardwareandtheredundant systemisautomaticallyactivated.Thus,bydennmgandusmg thesetwomnure-mdicationmethods,eHectivemaintamability mron-lmesoftwarecontrolcan"easnyattained.
mterface.
5.Erectiveconnectiontestconcepts 5､1ClassifncationofconnectiontestusingTCUandOAM cen-handlingmechamsm
ATMnodemaintainabnitycanbeincreasedbyusingthe mllowmgtwoperfonnancemomtoringactions. ( 1 ) D e p l o y m g a t e s t c e l l g e n e r a t i o n / c h e c k i n g u n i t ( r C U ) i n s i d e
4.2ATMtraricmomtoringconceptsandinterfacewith sonwarecontrol
TheselfbroutmgATMswitchfabricshould"designedto
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5.2Pe㎡OrmanceandtestingconditionsofTCU ThesimultancouscheckingofseveralVP/VCconnection p a t h s s h o u l d b e a v a i l a b l e f O r T C U p c r f o r m a n c e . TheATMswitchisbestimplcmcntedasanincoming/ outgomgselftroutingone-wayswitchtoensurenembnityin processingmcommgandoutgoingtramcmdependenUy. T℃stcellsaredismbutedtoeachlmeumtthroughanATM switch,andloopedbackmthelmeunitbytheuseofatest-cell fOlding-backmechanismconsistingofacellextraction h'nctionandacellinsertionhmction・NotethattheVPI/VCI
numberoftheestccnischan"deverytimeitpassesthrougha
mechanismmeachLUfbrbothVP-andVC-levelconncctions
headerconversionfIqtable,soeverychannelcanbechec"d mthesametest.TherefOre,bymtroducmgthistestmethod,we c a n d r a s t i c a l l y r e d u c e t h e n u m b e r o f t e s t s a n d t h e t e s t m g t i m e [7].Here,considedngthepossibleusageofanVCsidentined bytheHCtableandthemaximummultiplexingdegreconeach route,cel1transferspcedRfromtheTCUsatismesthefOnnula ( 1 ) R≦RmaXm.(1) whereNisthemammumVCcapacityintheHCtable,and RmaxisthemaximumtransferspeedatpointSatwhichthe V C s o f t e s t c e l l s a r e m u l t i p l e x e d , a s s h o w n m F i g u r e 4 .
m r r e a l t i m e c e l l m o w p e r f o r m a n c e m o m t o r i n g . Figure3nlustratestheaboveconceptandtheoverall connectiontestschemeinanodeand"tweenadjacentAIWs usmgTCUastheATMcellgenerationandcheckingtool.As
TheshadedareaoftheHCtablemdicatestheVPI/VCI numberbemreconversion,otherwiseitistheVPUVCInumber afterconverSion.Thus,theVCIofeachemittedcellis convertedNtimes;Ncellsofadi丘erentnum"rofVqscanbe
shown,theTCUcanalsobeusedfbrmter-omcecelltransfer
multiplexeduptothemaximumtransferspeedatpointSby makinguseofbothHCTbblelandHCTable2.Theyareboth loopedbacktotheTCUduetothetest-cellfOlding-back
TCU
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e a c h n o d e f O r c o n s t a n t l y m o n i t o r i n g t h e p c r f o r m a n c e o f a l l s w i t c h i n g r o u t e s m t h e n o d e a n d b e t w e e n a d j a c e n t n o d e s . ②DeploymganOAMcell(monitoringcell:Mqhandling
q u a l i t y v e r i n c a t i o n . W h e n t h e T C U g e n e r a t e s p s e u d o u s e r c e l l s fOrmter-nodeVPormtra-nodeVCtesting,MCsareinserted m t o t h e u s e r c e l l s t r e a m a t t h e L U S . F a u l t s a r e t h u s l o c a t e d b y
mechanismmthelineterminationunit_
usmgtheLUmonitoringcellmechaniSm.
Byusingthistestcellmultiplexingmechanism,evenifthe
F b r c o n t m u i t y c h e c k i n g , t e s t i n g s h o u l d b e p o s s i b l e f b r
② a r b i t r a r y c e l l t r a n s m i s s i o n s p e e d s u p t o t h e m a x i m u m r a t e o f thesubscriber/trunklmesand
C ) s i m u l t a n e o u s c h e c k i n g o f m u l t i p l e c o n n e c t i o n p a t h s . F u r t h e r m o r e , t e s t i n g s h o u l d b e p o s s i b l e w h e t h e r t h e V P I /
承ｌｌｌＮｌｌｌ定
(1)arbitrarycombinationsofVP/VCconnections
Vqconnecdonisinuseornot.
F r o m t h e v i e w p o i n t o f m a m t e n a n c e , t h e f b 】 l o w m g t w o t y p e s o f c o n n e c t i o n t e s t m g a r e n e e d e d .
Typel:Testmgbyusingpseudousercell(withuserVCI)+
Rm
MC.
ThistestisfOrtestingspecificVP/VCconnectionsorwhen u s e r s r e q u i r e p r e c i s e c o m m u n i c a t i o n q u a l i t y c h e c k i n g ・ I n t h i s
c a s e , t h e O A M i d e n t i f i e r i s i n c l u d e d i n t h e c o r r e s p o n d i n g p a y l o a d f O r d i s t i n g u i s h i n g t h e t e s t c e l l f r o m t h e a c t u a l u s e r cens.
Type2:TestingbyusingonlyOAMcellwithspecificVC1. Tbistypeofcomectiontestiss"cinedbyitsVq(=003).Itis executedwhenconstructingaswitchingnodeorassessing
table
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B y a n a l y z i n g t h e r e t u r n e d t e s t c e l l s i n t h e T C U , s w i t c h m g p e r f b r m a n c c a t t r i b u t e s , s u c h a s t h e b i t e r r o r r a t e , t h e c e l l l o s s ratio,andthemis-insertionratio,canbcdeterminedfbreach route,enablingcontinuousperfOrmancecheckingofeach s w i t c h i n g r o u t e .
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ontent
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Fig.4ATMswitcbcontinuoustestcenmechanism.
I
TCUcannotgcneratetestcellsatthemaximumdefinedlmeunitcelltransferspeed,wecanachieveamaxmumloadtestof
P『ﾛ促回且sS回伽arefp『日日u日碓回
thelmeunitbecausetestcellstransferrcdnomtheTCUcanbe
accumulateduptothemaxmumcelltransferspcedatpomtSin t h e l i n e u n i t ． Ⅱ T o i s t h e r o u n d t r i p t i m e o f a t e s t e l l l o o p b a c k homtheTCU,therequiredcontinuoustestcellemisSiontme のfromtheT℃UisgvenbythefOrmula(2). SmceT=NTo,
T≦(Rmax/R)To.
（ 2 ）
B y a d j u s m g c e l l e m i s s i o n t m e T t o s a t i s f y m r m u l a ( 2 ) , a n d b y executmgcellemissionfromtheTCUNtimes,amaximum
loadestontheATMswitchcanbeperformed. TheTCUgeneraesccnswhichloopbackattheLUOruser/ networkinterface・Considertherequiredbuffersizefor insertmgOAMcellsattheLUloop-backpoint・Afewcell
b u f f e r s a r e n e e d e d a t t h e c e l l i n s e r t i o n p o i n t . F o r e x a m p l e , a s s u m m g t h e o f f e r c d l o a d o n a l 5 0 M b i t / s i n p u t t r a n s m i s s i o n
l i n e i s O . 9 , a n d t h e c e l l a m v a l m o d e l h a s a P o i s s o n i n p u t , t h e requircdcellbuHersizeisaboutonecell,threecells,andten
c c l l s , c o r r e s p o n d m g t o i n s e r t c d c e l l t r a n s m i s s i o n s p e e d s o f 6 4 K,1.SM,and6MbiVSundertheconditionthatthecelllmsrate
islessthanlOE-11.ThisproWsedtestmechanismcanthusbe e c o n o m i c a l l y i m p l e m e n t e d .
Fig.5Layeredfanuremanagementscheme. 7.Concl皿sion
WchavedescribedtherequirementsfOranATMnode systeminapublicnetworkfromtheviewpointof m a i n t a i n a b i l i t y a n d h a v e c l a d n e d t h e c o n c e p t s o f h a r d w a r e m a i n t a i n a b i l i t y b y i n t r o d u c i n g e f f e c t i v e c o n n e c t i o n t e s t methodsimplementedbyacell-handlingmonitoring mechanismandatest-cellgeneration/Checkingmechamsm
6.Layeredmanagementschemeupondetectionofline
insidetheATMnode・Inparticular,weclarifiedatestcel1
mil叩正
m u l t i p l e x i n g m e c h a n i s m t h a t m a k e s i t p o s s i b l e t o p e r f O n n a maxmumloadtesteveniftheTCUcannotgeneratetestcens
F b r e f f e c t i v e l y m a n a g i n g a n d p r o c e s s i n g a d e t e c t e d l i n e mnurenomthesecdonleveltotheVPlevelmsteps,theAIW usesalayeredfanuremana"mentscheme,asshownmFigure 5 ・
T h e p r o c e s s o r c a n r e c o g n i z e a f a i l u r e o f a l l u p p e r l a y e r s
attbedefinedmaximumtransferspeedinthelineumt.We proposedaneHectivehardwarefailuredetection/mdication methodtofacilitatetheon-linesoftwarecontrol
m a i n t a i n a b i l i t y ・ W e e s t a b l i s h e d a n A T M t r a H i c m o n i t o r i n g
iomalowerlayerfailurenotincation,sowhenfailuresintwo
conceptwithQoScontrol,andalayeredmanagementscheme
o r m o r e l a y e r s a r e s i m u l t a n e o u s l y d e t e c t e d b y h a r d w a r e , o n l y t h e a l a r m s o f t h e l o w e s t l a y e r s h o u l d b e p a s s e d t o t h e p r o c e s s o r t o f a c n i t a t e s o f t w a r e p r o c e s s m g . T h u s , t h e s o f t w a r e r e c e i v e s
u p o n d e t e c t i o n o f l i n e f a i l u r e , t h a t t a k e s t h e c o r r e s p o n d i n g softwareactionintoaccount.Thesetechnologiesmake p o s s i b l e a n e c o n o m i c a l , f U l l y r e l i a b l e A T M n o d e s y s t e m .
o m y t h e s i m p n f i e d f a u l t m d i c a t i o n i n f o r m a t i o n , w h i c h c o n s i s t s
o f t h e f a u l t s t a t u s : A 1 , A 2 , o r B . A r e c o v e r y m e s s a g e s h o u l d b e issuedwhenallfanureshavebeenrectified.
Asmosttransmissionlinesotherthanlow-speed
Remrences
[ 1 ] I s h i k a w a , H ､ , ' ' E v o l u t i o n f r o m n a r r o w b a n d n e t w o r k s , 正 E E mm.MagazmeAug.,1992.
t r a n s m i s s i o n l m e s a r e d u p l i c a t e d , a n y a c t i v e l i n e t h a t f a i l s i s automaticallyswitchedtoitsstand-bybytheautomatic
[ 2 ] T o k i z a w a , 1 . , U e d a , H . , a n d K i k u c h i , K , " A T M t r a n s p o r t s y s t e m a r c h i t e c t u r e a n d f i e l d t r i a l ' ' , G l o b e c o m ' 9 3 4 0 . 1 , p p .
hardwareswitchingmechanismspccifiedinlTU-T R e c o m m e n d a t i o n G . 7 8 3 t o e n S u r e t h e a v a i l a b i l i t y o f t h e V P a n d / O r V C c o n n e c t i o n . F o r h i g h c o n n e c t i o n r e l i a b i l i t y , e a c h l i n e t e r m m a t i o n b l o c k s h o u l d h a v e t h i s s w i t c h i n g m e c h a n i s m .
[3]Miyaho,N.,Hirano,M,Takagi,Y､,Shiomoto,K.,and Takahashi,T.,@OAnATMSwitchmgSystemArchitecturefOr F i r s t G e n e r a t i o n o f B r o a d b a n d S e r v i c e s ' ' , I S S ' 9 2 , V o 1 . 1 , A 3 . 2 ,
1449-1453,Novem"rl993.
pp.285-289,Octoberl992.
T h e r e a r e t w o p r e r e q u i s i t e s f O r l m e s w i t c h i n g t o t h e s t a n d b y
[4]Miyaho,N.,Shiomoto,K.,andTakenaka,T.,
systcmtooccur.
@$DevelopmentofacommercialATMnodeasthebackbone nodefOrhighspeeddatacommunicationnetwork",ISS'95,
( 1 ) T h e l i n e t e n n i n a t i o n u m t i s o p e r a t m g m h o t s t a n d b y m o d e . (2)LineswitchingEdonebyonlythehardwarcmechanism andnosoftwareprocessingcontrolisrequiredfOrline s w i t c h i n g .
W h e n t h e S D H i n t e r f a c e d e t e c t s a f a i l u r e e v e n t , t h e a c t i v e
l i n e m t e r f a c e i s s w i t c h e d t o t h e r e d u n d a n t s y S t e m ・ T h e o n l i n e call-controlsonwareisnotifiedofthismodetransitionandthe
s o f t w a r e r e v i s e s t h e c o r r e s p o n d i n g l i n e m a n a g e m e n t t a b l e .
Vol.1,C4.1,1995.
[ 5 ] K o u , K . , A r u t a k i , A . , a n d l w a s a k i , S . , @ @ T h e a r c h i t e c t u r e andimplementationofATMswitchfOrbroadbandlSDN", Globecom'931.2,pp.8-13,Novemberl993. [61Miyaho,N.,Hirano,M.,Takenaka,T.,Koinuma,K,and
Ishikawa,H.,"ATMSwitchingSystemTechnologier,正EE DenshiTbkyo,No.31,1993.
[ 7 } I t o h , A . , a n d M i y a h o , N . , " F u n c t i o n t e s t m e t h o d s u s m g l e s t cellsfbrATMswitchingsystem'',ICC'95,27.6,Junel995.
