A Novel Fault-Tolerant Multi-EPON System with Sharing Protection through Bridge ONUs

Transcription

1 Proeedgs of the Iteratoal MultCoferee of Egeers ad Computer Setsts 8 Vol I IMECS 8, 9- Marh, 8, Hog Kog A Novel Fault-Tolerat Mult-EPON System wth Sharg Proteto through Brdge ONUs I-Shya Hwag, Ze-Der Shyu ad Lag-Yu Ke Abstrat I the EPON, may prevous studes proposed dedated proteto arhtetures to protet the rtal ompoets whh results hgh ost for deploymet. To aheve hgh relablty ad low-ost for deploymet, ths artle proposes a ovel fault-tolerat Mult-EPON system wth ost-effetve shared proteto through Brdge ONUs. Uder the falures, the Brdge ONU otrols the faulty EPON, plays the role of OLT ad the trasmsso of faulty EPONs s restored by relayg to other teroeted adjaet EPONs. The mmum hop out relay algorthm ad the relay wdow mehasm are also proposed ths artle to help the data for relayg effetly. Furthermore, the Oe-Wat DBA eables the otroller of affeted PONs to obta more up-to-date buffer formato from eah ONU order to ehae overall system performae. The smulato results show that the proposed Mult-EPON system a provde hgh system performae for dfferet faled stuatos terms of average delay, MAX delay ad jtter, espeally hgh traff loads. Idex Terms Brdge ONU, DBA, EPON, fault-tolerat, proteto. I. INTRODUCTION I the EPON, all ONUs are served by the OLT usg a dsovery hadshake Mult-Pot Cotrol Protool ad share a ommo trasmsso hael towards the OLT by tme-dvso multple aess shemes. Oly a sgle ONU may trasmt data oe tmeslot to avod sgal ollsos. After the ONU s regstered by dsovery proess, the OLT otrols PON ad oordates the trasmsso wdow of ONUs wth grated GATE messages, whh ota the trasmsso start tme ad trasmsso legth of the orrespodg ONU. To avod sgals ollsos ad alloate badwdth farly the upstream dreto, shedule algorthms whh have bee extesvely researhed. There are two ategores of badwdth alloato shemes o EPONs: fxed badwdth alloato (FBA ad dyam badwdth alloato (DBA. I the FBA sheme, eah ONU s assged fxed tmeslots data trasmsso from the ONUs to the OLT at full lk apaty. I otrast to the FBA, the DBA further mproves the system a more effet way; the OLT alloates a varable tmeslot to eah ONU dyamally based o the badwdth request ad esures the I-Shya Hwag s wth the Departmet of Computer Egeerg ad See, Uversty of Yua-Ze, Chug-L, Tawa, 36 (phoe: ; fax: ; e-mal: shwag@satur.yzu.edu.tw. Ze-Der Shyu s wth the Departmet of Geeral Studes, Army Aademy, Chug-L, Tawa, 39 (e-mal: s949@mal.yzu.edu.tw. Lag-Yu Ke s wth the Departmet of Computer Egeerg ad See, Uversty of Yua-Ze, Chug-L, Tawa, 36 (e-mal: s9466@mal.yzu.edu.tw. Qualty-of-Serve (QoS by guarateed serve level agreemet (SLA. Furthermore, fault tolerae s also a mportat ssue PONs. There are two ategores of etwork falures EPON, oe s lk falure ad the other s ode falure. I lk falure, the falure of feeder fber wll halt the whole PON system, but the falure of a brah wll halt just oe ONU. I the ode falure, the falures of OLT or spltter wll ause the whole PON system to fault. Therefore, the OLT, feeder fber ad spltter are the most rtal ompoets the PON system. I order to protet PONs agast these serous falures, may researhers proposed dedated proteto arhtetures, however, they are ot ost-effetve, as they requre may redudat ompoets. Sharg badwdth to protet the eghborg PONs s a effet way to redue the ost of proteto. To aheve hgh relablty ad low-ost for deploymet, a ovel fault-tolerat Mult-EPON system wth shared proteto s proposed ths artle to provde proteto agast OLT falure ad feeder fber falure. The rest of ths paper s orgazed as follows. Seto deres the related work. Seto 3 proposes a ovel Fault-Tolerat Mult-EPON System whh s provded a robust fault-tolerat mehasm based o the oept of shared proteto. Seto 4 shows the smulato results terms of the average paket delay, MAX paket delay ad jtter performae. Fally, Seto 5 draws olusos ad offers further suggestos. II. LITERATURE REVIEW A. Fault-Tolerat Arhtetures Four proteto arhtetures are dsussed o PON the ITU-T Reommedato G.983. []. However, those arhtetures have a lot of reduday, ad they are ot eoomal solutos. Moreover, the proteto sheme wth oe old stadby OLT s proposed [] ad the stadby OLT utlzed to protet multple PONs. The sheme stll eeds old stadby equpmet ad supports oly oe OLT falure. A reslet fast proteto swthg sheme [3], whe a feeder fber break or equpmet falure ours etral offe (CO, ad the swthg s performed at the CO. Beause of the swth, t s more omplex ad the sheme stll eeds a redudat feeder fber to protet the feeder fber. I [4], a automat-proteto-swthg mehasm s proposed the ONU to fght agast dstrbuto fber breaks. The trasmsso of affeted ONU s restored by other teroeted ONUs whe brahes are dow. However, t aot provde ay proteto for OLT ad feeder fber whh are the most rtal ompoets of PON. I the rg topologes, the proteto sheme [5] has a large ISBN: IMECS 8

2 Proeedgs of the Iteratoal MultCoferee of Egeers ad Computer Setsts 8 Vol I IMECS 8, 9- Marh, 8, Hog Kog ovetoal rg ad a old bakup trasever ad reever to protet oe pot falure. The drawbaks of the rg topologes are more fber usage, hgher sgal atteuato ad serous ear-far problems. To address those problems, the double feeder fbers wth a hybrd small rg are trodued [6]. The sheme mmzes the fber usage ad assures o paket loss by usg hot stadby ompoets. However, the ONU s more omplex the sheme ad + proteto shemes have a low market peetrato due to ts hgh ost. Therefore, ths paper proposed a shared proteto sheme wth teroeted adjaet PONs by Brdge ONUs to avod reduday the EPON. B. ONU Prorty Shedulg To support dfferetated serve lasses, a prorty queug sheme, suh as DffServ, ad the queue maagemet tasks are arred out by eah ONU. The trasmsso of queued pakets s deded by a spef shedulg sheme. The strt prorty shedulg serves the buffered hgher-prorty pakets frst as defed IEEE 8.D. Lower-prorty pakets a oly be trasmtted whe the hgher-prorty queues are empty. Therefore, the lower-prorty pakets suffer exessve delays ad ufar reased paket loss. However, a shedulg sheme s also eessary to otrol the hgh-prorty traff f t exeeds the otrat of serve level agreemet (SLA. I [7], prorty-based shedulg s proposed to deal wth the problems by employg strt prorty shedulg wth a spef tme terval. Ths sheme provdes a bouded delay for low-prorty pakets ad esures faress by trasmttg pakets of all traff lasses. C. Dyam Badwdth Alloato The dyam badwdth alloato (DBA, suh as lmted badwdth alloato (LBA, has bee studed [8]. I the LBA, the tmeslots legth of eah ONU s upper bouded by the maxmum tmeslots legth, B max, whh ould be spefed by SLA. The drawbak of LBA s the poor utlzato for the upstream badwdth ad t restrts aggressve ompetto for the upstream badwdth, espeally uder o-uform traff. I order to better utlze the leftover badwdth from ONUs wth some traff baklogs, the authors [7] proposed a DBA sheme alled Exessve Badwdth Realloato (EBR whh ONUs were dvded to two ategores, lghtly-loaded ad heavly-loaded, aordg to ther guarateed badwdth B max. exessve badwdth, B exess, saved from lghtly-loaded group s redstrbuted to heavly-loaded ONUs to mprove effey. Ufortuately, the drawbaks of EBR are ufaress, dle perod problem ad alloatg more tha the requested badwdth to ONUs [9], whh was redefed as redudat badwdth problem our prevous researh []. To mprove badwdth utlzato, a early alloato mehasm was proposed [7], whh grats the badwdth of lghtly-loaded ONUs mmedately wthout ay delay whe t reeves the REPORT message. Moreover, the effet badwdth alloato algorthm ( wth a tme traker s proposed to address the dle perod problem []. It fores the OLT to grat the badwdth to a heavly-loaded ONU wthout watg realloato whe the upstream hael s gog to dle. However, the drawbak of [7], [] s that the serve order of ONUs hages eah serve yle, therefore, the estmato of the omg hgh prorty traff s severely mpared beause the watg tme eah ONU may hage drastally. I [], Xaofeg et al. proposed aother DBA sheme that matas faress mehasm of the exessve badwdth realloato operato well for heavly-loaded ONUs, but gores the faress of lghtly-loaded ONUs. The reaso s that the request by the lghtly-loaded ONU does ot osder the possble pakets arrvg durg the watg tme. Jtter performae studed [3] s aother mportat oer EPON, espeally for the hgh prorty serve whh s delay-varato sestve traff (e.g. voe trasmssos. I ths sheme, hgh prorty serve s proteted a separate sub-yle, therefore, the jtter performae s osderably mproved. III. THE PROPOSED NOVEL FAULT-TOLERANT MULTI-EPON SYSTEM A ovel fault-tolerat Mult-EPON system s preseted ths seto. I seto 3., we propose a fault-tolerat arhteture Mult-EPON, whh provdes proteto by sharg the badwdth wth the eghborg PONs. I seto 3., the mmum hop out relay path ma algorthm s proposed to address the shortest path to relay data ad alulates the avalable badwdth to eah PON uder falure. I seto 3.3, the Relay Wdow Mehasm s proposed to relay data betwee PONs ad ooperates wth two DBA shemes that are proposed to help the data relay ad mprove the system performae. A. Fault-Tolerat Arhteture To aheve hgh relablty ad low-ost for deploymet, eah EPON system s oeted the earest EPON by a Brdge ONU order to mmze fber usage, show Fg.. Whe the feeder fber s ut or OLT s dow, the Brdge ONU otrols the PON, plays the role of OLT ad reeves the data omg from the ONUs. The, the Brdge ONU relays the data to the OLT of the adjaet PON. I ormal stuatos, the Brdge ONU gores the upstream sgal of ONUs ad motors the sgal of dowstream hael to detet the falures. I [4], the passve optal spltter/omber (PSC broadastg the upstream sgal to all ONUs may ause potetal seurty problems ad hgher sgal power atteuato. To allevate those problems, the PSC, ostruted by a N PSC ad a PSC, s osdered the proposed arhteture, show Fg.. I the PSC, the upstream optal sgal power s oly trasmtted to OLT ad Brdge ONUs ad the dowstream optal sgal trasmtted by the Brdge ONU s broadasted to all ONUs as the dowstream sgal of OLT. I the Brdge ONU, both terfaes oet wth two adjaet EPON. Note that addto to the ovetoal trasever (a 3m trasmtter ad a 49m reever of ormal ONU mataed at the Brdge ONU, the Brdge ONU requres a extra 3m reever, a extra 49m trasmtter ad a swth. The advatages of the proposed arhteture are that o bakup feeder fbers ad bakup OLT modules are eeded ad the fber usage s lose to stadard EPON whh s wthout ay proteto mehasm. ISBN: IMECS 8

3 Proeedgs of the Iteratoal MultCoferee of Egeers ad Computer Setsts 8 Vol I IMECS 8, 9- Marh, 8, Hog Kog Fg. The Brdge ONU oets two adjaet PONs Fg. 4 The Fault Iformato Message Fg. Arhteture of the PSC Fg. 3 Cost-effetve Shared Proteto System B. Mmum Hop Cout Relay Path Ma Algorthm Whe faults our, order to let the affeted PONs determe the system stuato ad dede the relay path wth mmum hop out, the Brdge ONUs wll exeute four phases the Mmum Hop Cout Relay Path Ma Algorthm, ad they are desrbed the followg subseto. Note that there are two deftos of the Brdge ONU the boudary of fault area, oe s that the Brdge ONU has a faled PON o oly oe sde (.e. Brdge ONU BC Fg. 3, the other oe s the Brdge ONU has two faled PONs o both sdes ad a faled PON of the two has oly oe Brdge ONU (.e. Brdge ONU Fg. 3. Iformato Sedg Phase Whe the fault ours, the Brdge ONUs the boudary of fault area sed the Fault Iformato Message, show Fg. 4, to the Brdge ONU sde the fault area order to let other Brdge ONUs ad affeted OLTs get the Mult-EPON system stuato, suh as the umber of hop out ad guarateed tmeslots the left ad rght paths, to dede the relay path wth mmum hop out. After sedg the Fault Iformato Message, the seder wats for the ACK Message reply by the reever. If the watg reahes tmeout, the Fault Iformato Message wll be reset after radom delay. Watg Iformato Phase Whe the Brdge ONU reeved the Fault Iformato Message, t repled a ACK Message to the seder. The, t adds oe to the Number of hop out feld ad reords the formato of the urret PON, suh as the hop out ad guarateed tmeslots felds the Fault Iformato Message, ad seds t to the ext Brdge ONU or OLT. 3 Dedg Relay Path Phase After gettg all formato of the affeted PONs, the Brdge ONU dedes the relay paths. I order to redue the paket delay durg the falure tme, eah PON hooses the relay path wth mmal hop out. 4 Calulatg Avalable Badwdth Phase The otroller of affeted PONs alulates the avalable badwdth of eah PON as follows: PON _ BW = ( T MAX yle Ng ( S k k PON / j ALL _ PON, where S k / S j ALL _ PON j s the proporto of PON a k PON get mmum guarateed badwdth from the avalable MAX badwdth, T yle s the maxmum yle tme, g s the guard tme, N s the umber of ONUs the PON provdg the badwdth to Faulty PON, S k s the sum of S k, the mmum guarateed tmeslots for the, AF ad BE traff determed by SLA of ONU k whh s the PON. Ad S j s the sum of S j, the mmum guarateed tmeslots for the, AF ad BE traff determed by SLA of ONU j whh s the relay path that ludg PON. The S j ad S k a be S = expressed as k S k S = ad j S j, {, AF, BE}. C. Relay Mehasm ad Loal DBA The PON wth fault s referred to as Faulty PON ad the PON, whh provdes proteto by sharg badwdth to the Faulty PONs, s referred to as Proteto PON. After alulatg the avalable tmeslots of the PONs, the Brdge ONUs start to otrol the adjaet PON of the dowstream relay path. The Brdge ONUs, the Faulty PON, exeute the Oe-Wat DBA for loal ONUs ad the OLT the Proteto PON exeutes the Proteto DBA for loal ONUs. The both DBA shemes ooperate wth the Relay Wdow Mehasm to help relay the data hop-by-hop the Faulty PONs. For example, the Brdge ONU otrols the PON F ad the Brdge ONU DE otrols the PON E, show Fg. 3. The Brdge ONU relays the data queug ts buffer to the Brdge ONU DE. The, the Brdge ONU DE has two kds of data ts buffer; oe s PON E omg from loal ONU; the other s PON F omg from Brdge ONU. The Brdge ONU DE relays the data queug ts buffer to the S j ISBN: IMECS 8

4 Proeedgs of the Iteratoal MultCoferee of Egeers ad Computer Setsts 8 Vol I IMECS 8, 9- Marh, 8, Hog Kog otroller of PON D that s the Brdge ONU CD ad the Brdge ONU CD relays queug data to the Brdge ONU BC. Fally, the Brdge ONU BC relays all queug data to the otroller of PON B. The proposed Relay Wdow Mehasm ad two DBA shemes are desrbed the followg subseto. Relay Wdow Mehasm There are two trasmsso wdows eah PON of the relay path. Oe s the loal DBA wdow trasmtted by loal ONUs ad the other oe s the relay wdow trasmtted by the adjaet Brdge ONU the dowstream relay path, show Fg. 5. The OLT or the Brdge ONU spefes the start tme of the relay wdow the GATE message ad trasmts t to the adjaet Brdge ONU the dowstream relay path. Whe the relay wdow begs, the Brdge ONU spefes trasmsso legth a REPORT message ad seds t to the otroller of upstream PON. After the otroller gets the REPORT message, t a kow whe the ed of relay wdow s ad the start to exeute the loal DBA. Whe a Brdge ONU trasmts a upstream paket the relay wdow, the pakets from loal ONUs or the adjaet Brdge ONU the dowstream relay path are stll arrvg. The traff lass wth the hghest prorty for strtly delay sestve serves s typally a ostat bt rate (CBR. To further redue the paket delay tme, the Brdge ONU predts the badwdth requremet durg the relay wdow by the traff rate wth the rate-based predto sheme preseted [5]. The, the Brdge ONU reports the total legth trasmttg tmeslots of ths relay yle wth upper bouded by guarateed badwdth the dowsde relay path, ad t a be expressed as = G, + m( R,, PON_ BWk k dowstreampontherelaypath (, where R, s the sum of request tmeslots for dfferetated traffs the queues of the Brdge ONU the AF BE th yle,.e. R, = R, + R, + R, + P,, the P, s the predted tmeslots of traff omg durg the relay wdow, ad PON_ BW k s the sum of avalable k dowstreampontherelaypath badwdth of Faulty PONs the dowsde of the relay path. Two DBA Shemes for Loal ONUs I the Faulty PONs, the lk utlzato s mpossble to use fully. The reaso s that the avalable badwdth s provded by the OLT Proteto PON ad s shared wth the affeted PONs. The paket delay s more mportat tha lk utlzato the Faulty PONs. However, the lk utlzato ad the paket delay are of the same mportae Proteto PON. Therefore, the two DBA are proposed to deal wth the dfferet etwork haratersts for mprovg the whole Mult-EPON system performae. Frst, the Oe-Wat DBA s proposed to redue the paket delay the Faulty PON. Seod, the Proteto DBA s proposed to mprove the hael utlzato ad redue the paket delay the Proteto PON. Oe-Wat DBA Sheme the Faulty PON The operato of tradtoal DBA shemes are that the REPORT messages pggybak data tmeslots ad report the queue legth of the ONU, but wthout osderg the paket arrvg durg the watg tme. It s observed that the paket delay those DBA shemes s lose to.5 trasmsso yle tme. Therefore, the pakets arrvg the watg tme aot be trasmtted the urret yle eve f the ONU s lghtly-loaded. Ths wll result loger paket relayed delay ad s ufar to the lghtly-loaded ONU. To mprove the drawbaks ad offer better QoS the Mult-EPON system, the proposed Oe-Wat DBA shfts the report tme of ONUs purposely order to eable the Brdge ONU to obta more up-to-date buffer oupay formato from eah ONU. Ths pot s further llustrated Fg. 6. The ONU uploads ts REPORT message betwee the (-th ad (-th ONU. Whe the Brdge ONU reeves the REPORT message of ONU, t starts to alulate avalable badwdth of ONU ad grat the avalable badwdth the GATE message to ONU mmedately. After the ed of trasmsso wdow of ONU -, the REPORT message s uploaded by (+th ONU, ad the, the ONU starts to upload the queug data grated tmeslots. Although the amout of ost guard tme the Oe-Wat DBA s twe as muh as the umber of the DBA shemes pggybakg ther REPORT messages data tmeslots. However, the average pakets delay s smaller tha oe yle tme ad lose to half of a yle tme. Therefore, the Oe-Wat DBA a redue to almost oe yle tme the average paket delay. Whe t reeves a REPORT message from a loal ONU, the Oe-Wat DBA assgs the tmeslots to the ONU based o the guarateed tmeslots mmedately ad a be expressed as G = m( R, PON_ BW ( S / S, where k k PON R s the sum of requested BW for dfferetated traffs of ONU, ad S / Fg. 5 The Relay Wdow Fg. 6 Oe-Wat DBA S k k PON s the proporto of ONU a get grated badwdth from the avalable badwdth of ths PON deoted as PON _ BW. After fshg gratg badwdth to the ONU by sedg GATE message, the Oe-Wat DBA spefes the REPORT sedg tme of ONU + at the ed of uploaded tmeslots ONU. Moreover, after gratg the last ONU loal yle, the otroller of the PON vokes the Relay Mehasm. Whe the otroller reeved the REPORT message of the adjaet Brdge ONU of the PON, t exeutes the Oe-Wat DBA aga. ISBN: IMECS 8

5 Proeedgs of the Iteratoal MultCoferee of Egeers ad Computer Setsts 8 Vol I IMECS 8, 9- Marh, 8, Hog Kog Proteto DBA Sheme the Proteto PON The Proteto PON s the fal hop the relay path, the performae of paket delay relay data ad lk utlzato are the key fators o the system performae. To further mprove badwdth utlzato ad paket delay of relay data, there are two trasmsso wdows the Proteto DBA. Oe s the relay wdow for Brdge ONUs to relay data; the other s loal trasmsso wdow for loal ONUs, show Fg. 7. Furthermore, to address the jtter performae of traff, the proposed Proteto DBA fxed the serve order of all loal ONUs ad the Brdge ONU the PON. Frstly, at the begg of Nth Relay Wdow to trasmt the data, the Brdge ONU lmted the trasmttg tmeslots by equato ( ad broadasts the REPORT message to the OLT order to spefy ts trasmsso legth. The, the Brdge ONU starts to relay the data queue ts buffer to OLT, show Fg. 7. Seodly, after reevg the REPORT message of the Brdge ONU, the OLT exeutes the Proteto DBA sheme to alloate badwdth to loal ONUs for (N+th trasmsso yle ad seds all GATE messages to loal ONUs. Thrdly, the OLT spefes the begg tmeslots of (N+th Relay Wdow by sedg a GATE message to the Brdge ONU. Note that the trasmssos of dfferet odes are separated by a guard tme. The detal of alloatg tmeslots for loal ONUs the proposed Proteto DBA s desrbed as follows. Frst, alulate R, of all ONUs ad talze the avalable badwdth, B avalable, whh s expressed as B avalable = PON _ BW. The, the proposed Proteto DBA wll selet the ONU wth the maxmal resdue badwdth,.e. max( S R,, from uassged ONUs. The grated badwdth for ONU, G, +, the ext yle s gve as follows G, + = m Bavalable ( S/ Sk, R., k uassged, where R s the sum of requested BW for dfferetated traffs of ONU the th yle,.e. AF BE R, = R, + R, + R, + P,, where P, s the predted tmeslots of traff wth the rate-based predto sheme preseted [5] ad S / S k s the proporto of k uassged ONU a get grated badwdth from the avalable badwdth, B avalable. Furthermore, the grated badwdth for, AF ad BE lasses are as follows: G, + = m( G, +, R, + P, AF AF. G, + = m( G, + G, +, R, BE AF G, + = G, + G, + G, + I the fal, the avalable badwdth beomes Bavalable = Bavalable G, +. The whole proess otues utl all loal ONUs have bee assged, ad the Proteto DBA fxes the trasmsso order of ONUs to mprove the jtter performae. The, the OLT seds the GATE message to all loal ONUs ad spefes the start tme of (N+th Relay Wdow by sedg a GATE message to the Brdge ONU. Fg. 7 The operato of Proteto DBA wth a Relay Wdow (a Searo (b Searo ( Searo 3 (d Searo 4 Fg. 8 Four Sgfat Searos IV. PERFORMANCE EVALUATION The system performae s aalyzed by smulatg the four sgfat searos, show Fg. 8, ad ompared wth [] terms of average paket delay, MAX paket delay ad jtter. The performae evaluato s studed usg the OPNET smulator wth oe OLT ad 3 ONUs a PON. The dowstream ad upstream apates are both Gb/s. The dstae from a ONU to the OLT s assumed km ad the dstae betwee eah PON s assumed km. Eah ONU has fte buffer ad the serve poly s frst- frst-out dsple. The traff model s haraterzed by self-smlarty ad log-rage depedee (LRD [6]. Ths model s used to geerate hghly bursty AF ad BE traff lasses wth a Hurst parameter of.7, ad paket szes are uformly dstrbuted betwee 64 ad 58 bytes. Furthermore, hgh-prorty traff s modeled usg a Posso dstrbuto ad paket sze s fxed to 7 bytes. The traff profle s as follows: % of the total geerated traff s osdered hgh prorty, ad the remag 8% equally dstrbuted betwee low- ad medum-prorty traff [7]. For smplty, the total etwork load s evely dstrbuted amogst all ONUs the same relay path ad the ONUs are equally guarateed badwdth weghted [7], [8]. A. Average Ed-to-Ed Delay Fg. 9 ompares the average paket delay from ONUs to etral offe amog the four searos ad for, AF, BE, ad total traff, respetvely. Fg. 9(a shows the proposed Mult-EPON system uder falures has better performae tha whe the traff load s greater tha 4%. The delay tme of Mult-EPON reahes ms whe the traff load s heavy, but stll s less tha.5 ms, whh s spefed by ITU-T Reommedato G.4. Fg. 9(b shows the delay tme of Mult-EPON searos for AF traff are stll shorter tha the whe traff load exeeds 7%. Fg. 9( shows that Mult-EPON yelds otable mprovemets of ad AF serves wthout degradg the BE serves. ISBN: IMECS 8

6 Proeedgs of the Iteratoal MultCoferee of Egeers ad Computer Setsts 8 Vol I IMECS 8, 9- Marh, 8, Hog Kog searo searo searo3 searo4 Avg. Delay (a BE Avg. Delay searo searo searo3 searo searo searo searo3 searo4 AF Avg. Delay searo searo searo3 searo4 B. MAX Ed-to-Ed Delay Fg. ompares the maxmum paket delay amog the four searos ad for all traff lasses. Fg. (a shows the proposed Mult-EPON system has better performae tha the whe traff load exeeds 6% the traff. I Mult-EPON searos, the MAX delay for traff reases smoothly wth traff loads ad mples the otrol ablty the Mult-EPON. The MAX delay for traff at full traff load s less tha 9%. The reaso s that the trasmsso yle reahes T MAX yle results the rate-based predto of traff more aurately. I Fg. (b, the MAX delay performae of for AF traff s better tha the Mult-EPON searos, beause the AF paket eouters log relay tme the relay path. However, whle the traff s betwee 6%-8%, the has the logest MAX delay beause of the trasmsso order of ONUs hagg drastally. I Fg. (, the MAX delay for BE traff reases rapdly whe the traff load exeeds 9% beause the system s full load. C. Jtter Performae The delay varae s alulated as N - σ = d d ( N, where the d s the delay tme of = paket ad N s the total umber of reeved pakets. As Fg. shows, the delay varaes of Mult-EPON are hgher tha the whe traff load s below 7%. The reaso s that the pakets omg from PONs wth falures may be relayed by other Brdge ONUs. However, the delay varae of sheme reases drastally whe traff load exeeds 8%. The reaso s that the serve yle order every yle of the s haged drastally ad the order of Mult-EPON s always fxed (b Avg. Delay searo searo searo3 searo ( (d Fg. 9 Average Ed-to-Ed Delay MAX Delay Fg. (a MAX Delay BE MAX Delay searo searo searo3 searo Fg. ( BE MAX Delay Delay Varae (ms.... searo searo searo3 searo4 AF MAX Delay Fg. (b AF MAX Delay searo searo searo3 searo4 Jtter Fg. Jtter for traff V. CONCLUSION I ths artle, a ovel fault-tolerat Mult-EPON system s proposed to protet the rtal PON elemet falure, suh as OLT falure or feeder fber ut. Beause of o lmted umber of teroeted EPONs ad wthout ay redudat ompoets, the proposed system s very flexble, ost-effetve ad uses smple shared proteto arhteture o EPON. Overall, the smulato results ofrm that the fault-tolerat Mult-EPON system yelds otable mprovemets average paket delay, MAX paket delay ad delay varato for traff uder dfferet falures. RERENCES [] ITU-T, Study Group 5. G.983: Hgh Speed Optal Aess Systems based o Passve Optal Network (PON tehques,. [] Y.M. Km, J.Y. Cho, J.H. Ryou, H.M. Baek, O.S. Lee, H.S. Park, M. Kag, ad J.H. Yoo, Cost effetve proteto arhteture to provde dverse proteto demads Etheret passve optal etwork, Iteratoal Coferee o Commuato Tehology, Vol., pp. 7 74, 3. [3] M.K. Abdullah, W.T. P g, P.W. Lau, ad E.R. Tee, FTTH aess etwork proteto usg a swth, The 9 th Asa-Paf Coferee o Commuatos, Vol. 3, pp. 9, Sept. 4, 3. [4] N. Nadarajah, E. Wog, M. Attygalle, ad A. Nrmalathas, Proteto swthg ad loal area etwork emulato passve optal etworks, Joural of Lghtwave Tehology, Vol. 4, Issue 5, pp , May 6. [5] X. Zhao, X. Che, ad X. Fu, A ovel proteto swthg sheme for PONs wth rg plus tree topology, Proeedgs of the SPIE, Vol. 6, pp , Nov. 5. [6] D. Hossa, H. Erka, R. Dorsvlle, M. Al, S. Sham, ad C. Ass, Proteto for a Rg-Based EPON Arhteture, d Iteratoal Coferee o Broadbad Networks, Vol., pp , Ot. 3 7, 5. [7] C. Ass, Y. Ye, S. Dxt, ad M.A. Al, Dyam badwdth alloato for Qualty-of-Serve over Etheret PONs, IEEE Joural o Seleted Areas Commuatos, Vol., o. 9, pp , Nov. 3. [8] G. Kramer, B. Mukherjee, ad G. Pesaveto, Iterleaved pollg wth adaptve yle tme (IPACT: A dyam badwdth dstrbuto sheme a optal aess etwork, Photo Network Commuatos, Vol. 4, o., pp. 89 7, Ja.. [9] B. Che, J. Che, ad S. He, Effet ad fe shedulg algorthm for badwdth alloato Etheret passve optal etworks, IEEE Joural of Seleted Tops Quatum Eletros, Vol., o. 4, pp , July Aug. 6. [] I.S. Hwag, Z.D. Shyu, L.Y. Ke, ad C.C. Chag, A Novel Early DBA Mehasm wth Predto-based Far Exessve Badwdth Realloato Sheme EPON, The 6 th Iteratoal Coferee o Networkg (ICN 7, Sate Lue, Martque, Aprl -8, 7. [] J. Zheg, Effet badwdth alloato algorthm for Etheret passve optal etworks, IEE Proeedgs Commuatos, Vol. 53, Issue 3, pp , Jue 6. [] X. Ba, A. Sham, ad C. Ass, O the faress of dyam badwdth alloato shemes Etheret passve optal etworks, Computer Commuatos, Vol. 9, o., pp. 3 35, July 6. [3] A. Sham, B. Xaofeg, C.M. Ass, ad N. Gha, Jtter performae Etheret passve optal etworks, Joural of Lghtwave Tehology, Vol.3, Issue 4, pp , Apr. 5. [4] S.R. Sherf, A. Hadjatos, G. Ellas, C. Ass, ad M.A. Al, A ovel deetralzed Etheret-based PON aess arhteture for provsog dfferetated QoS, Joural of Lghtwave Tehology, Vol., Issue, pp , Nov. 4. [5] G. Kramer, B. Mukherjee, S. Dxt, Y. Ye, ad R. Hrth, O supportg dfferetated lasses of serve EPON-based aess etworks, Joural of Optal Networkg, Vol., o. 8/9, pp., Aug.. [6] W. Wllger, M.S. Taqqu, ad A. Erramll, A bblographal gude to self-smlar traff ad performae modelg for moder hgh-speed etworks, Stohast Networks, 996. Avalable: ISBN: IMECS 8