Electronic and photonic switching in the atm era

129 ELECTRONIC AND PHOTONIC SWITCHING IN THE ATM ERA‘ J. Masip- To &, J. Sole-Pa e a and G. Junyen -Gi al Uni e si a Poli scnica de Ca alunya, Spain ABSTRACT B oadband ne wo ks equi e high-capaci y swi ches in o de o p ope ly manage la ge amoun s o a ic luxes. Elec onic and pho onic echnologies a e being used o achie e his objec i e bo h allowing di e en mul iplexing and swi ching echniques. Focusing on he Asynch onous T ans e Mode (ATM), he inhe en di e en cha ac e is ics o elec onics and pho onics makes di e en a chi ec u es easible. In his pape , di e en swi ching s uc u es a e desc ibed, se e al ATM swi ching a chi ec u es which ha e been ecen ly implemen ed a e p esen ed and he implemen a ion cha ac e is ics discussed. Th ee di e se poin s o iew a e gi en om he elec onic esea ch, he pho onic esea ch and he comme cial swi ches. Al hough all he a chi ec u es whe e success ully es ed, hey should also ollow di e en ma ke equi emen s in o de o be comme cialised. This cha ac e is ics a e p esen ed and he a chi ec u es p ojec ed o e hem o e alua e hei comme cial capabili ies. INTRODUCTION Mul imedia communica ions a e expec ed o eplace elephony as he p edominan communica ions se ice. The cu en needs o 6.4 Gb/s o elephony o se e one million people may g ow o 600 Gb/s when high de ini ion MPEG ideo se ices (6 Mb/s) a e deployed. Thus, e y high-capaci y (Tb/s) swi ching will be equi ed in he u u e. ATM is he as packe swi ch echnique eme ged wi h he aim o se ice in eg a ion and bandwid h gain. The e is no doub abou he leade ship o pho onics o he anspo unc ions o Tb/s bandwid hs. This is possible due o he unique p ope ies o pho onics: 25 THz bandwid h, low c oss alk be ween he pho onic channels and s ong in e ac ion be ween ligh and semiconduc o s. Ins ead, swi ching unc ions a e solidly based on elec onics -high- speed elec onic ATM swi ches a e al eady comme cially ma u e hanks o an ex ensi e e o in unc ion implemen a ion (ha dwa e-so wa e codesign and VHDL au oma ic syn hesis) and high densi y ga e and in e connec ion capabili ies (mul i- chip modules). Ne e heless, a signi ican esea ch e o in pho onic swi ching implemen a ion has been done in spi e o he cu en poo p ocessing capaci y o he pho onic echnology. The scope is o su pass he speed limi o elec onics (abou 10 Gb/s) a a easonable cos and o a oid he elec o-op ic 1 This wo k has been possible hanks o a ellowship o he “Comisiona pe a la Uni e si a i Rece ca de la Gene ali a de Ca alunya” (1997Fl 00725) inside he CICYT p ojec “Field T ial o CMC and ATM” (TlC96-1127). con e sion bo le-neck owa ds an all op ical ne wo k. An ATM op ical swi ch wi h elec onic con ol is a i s s ep. The eme ging consensus is ha swi ching a o abo e ATM should be done elec onically, so pho onics may s ill ha e a ole in ATM swi ching. In (1 ), complexi y ac o s o elec onic swi ching, a ic demands and op ical unk swi ching a e discussed o b oadband ne wo ks. Ou pu pose is o ex end (1) p o iding a e iew o he ATM pano ama, gi ing compa isons o u u e esea ch de elopmen s ocusing on a chi ec u al and comme cial issues. This pape is o ganised as ollows: Sec ion 2 iden i ies he gene ic swi ching unc ions. Sec ion 3 p ojec s hem o e bo h he elec onic and pho onic echnologies. Sec ion 4 desc ibes he gene ic swi ch a chi ec u es. Sec ion 5 p esen s he mos ecen implemen a ions om he esea ch and he comme cial communi ies. Sec ion 6 e alua es hese implemen a ions om di e en poin s o iew. Finally, Sec ion 7 concludes his pape . GENERIC SWITCHING FUNCTIONS Mul iplexing. In o de o p ope ly manage la ge in o ma ion lows, a ic concen a ion in di e en mul iplexing laye s is equi ed a p esen , al hough he numbe o laye s may be educed. The in e change o in o ma ion be ween di e en channels o he same laye is ca ied ou by di e en swi ching unc ions acco ding o he mul iplexing In e na ional B oadcas ing Con en ion, 12-16 Sep embe 1997 Con e ence Publica ion No. 447, D IEE, 1997 s a egy. The e is a di e en echnology and p o ocol o e e y laye which gi es di e en cha ac e is ics o each one. A possible mul iplexing hie a chy is shown in Figu e 1. In his example, he mul iplexing s a egies a e WDM (Wa eleng h Di ision Mul iplexing), TDM (Time Di ision Mul iplexing) and ATDM (Asynch onous TDM). WDM, uses he op ical bandwid h spli in o ixed, non-o e lapping spec al bands ha a e anspa en o he bi - a e and code o ma . Con e sely TDM di ides he ansmission ime in o ames, which in u n a e spli in o slo s and hen one o mo e slo s a e assigned o a channel. TDM o e mul i-channel WDM will be based on he ITU (In e na ional Telecommunica ions Union) wa eleng hs s anda ds. Speci ica ions s a ed in ea ly 1997 and a e no s ill inished, bu a clea pic u e o he wa eleng h g id has eme ged wi h a channel spacing ixed o mul iples o 100 GHz wi hin he 1.5 ym wa eleng h window. As can be seen, TDM o e WDM has a ixed capaci y pe channel and he alloca ed esou ces canno be exceeded when necessa y and a e was ed when no used. ATDM sol es his p oblem by using a s a is ical alloca ion o he ansmission capaci y o a channel whe e in o ma ion packe s a e mul iplexed. Vi ual Ci cui S . Ci cui G3- Se ice Op ic WDM Figu e 1. Mul iplexing hie a chy. Swi ching. The undamen al pu pose o swi ching is he econ igu a ion o ou es and hei capaci ies as he a ic demands ac oss a ne wo k change o e ime. Any swi ch has o pe o m wo basic unc ions i espec i e o ans e mode: demul iplexing incoming channels acco ding o a gi en ou ing pa e n and mul iplexing he channels on o he ou going link. The swi ch is hus buil o a pa icula mul iplexing and ou ing s a egy. The ne wo ks can be ca ego ised acco ding o he combina ion o hese unc ions in ci cui -swi ching ( ixed capaci y and ou e), i ual ci cui -swi ching (s a is ical capaci y and ixed ou e) and da ag am-swi ching ne wo ks (s a is ical capaci y and ou e). This pape is ocused on ATM i ual ci cui -swi ching. Two di e en swi ching s uc u es a e possible, namely space-di ision and sha ed medium. Space- di ision in e connec ion s uc u e whe e an inpu has dedica ed links o all ou pu s and hus equi es demul iplexing be o e mul iplexing. Sha ed medium s uc u e whe e all inpu s sha e a common link o all 130 ou pu s and hus mul iplexing comes be o e demul iplexing. Basic swi ching elemen s a e based on hese s uc u es and can be in e connec ed in o a la ge swi ching ab ic. Besides muddemux, bo h s uc u es equi e ou ing unc ions. The ou ing unc ions a e s a ic o WDM and TDM once he connec ion is made, bu i is no s a ic o ATDM since packe s do no ollow any o de . Muddemux o WDM channels equi e combina o s and selec o s o he di e en wa eleng hs, while TDM equi es synch onisa ion o a oid channel o e lapping and ATDM equi es bu e ing o sol e packe con en ion. Elec onic and Pho onic Technologies S a e O The A F om abo e, o a gene al swi ching sys em, h ee main unc ions can be iden i ied: 1. Tempo al muddemux wi h bu e ing and 2. Wa eleng h muddemux wi h wa eleng h 3. Space-di ision swi ching. synch onisa ion. con e sion ( o imp o e ou ing). The ATM swi ch a chi ec u es use hese unc ions when hey a e a ailable o as packe swi ching (2). TABLE 1 summa ises he s a e o he a o bo h elec onic and pho onic echnologies when implemen ing he p e ious unc ions. Ma u e elec onic echnologies a e cu en ly a ailable a e decades o e olu ion. Elec onic swi ching has mos ly adop ed CMOS echnology, which allows o high ha dwa e complexi y, al hough wi h a line speed limi ed o 155 Mb/s (STM-1) in p ac ice. Highe line speeds a e achie ed by ei he using pa allel buses o mo e powe consuming elec onics han CMOS like GAS. These echnologies can implemen all p e ious unc ions excep o he wa eleng h domain. High-le el in eg a ion is possible o space- di ision swi ching, which is only limi ed by cu en ly a ailable chip packages. Time di ision swi ching is limi ed by he elec onic bandwid h, which is abou 10 Gb/s. One o he easons o he slow p og ess o pho onic pene a ion in swi ching is he imma u i y o he pho onic de ice echnology, compa able o he s a e o elec onics in he ‘60s. Howe e , apid p og ess in his ield is being made specially in he de elopmen o in eg a ed pho onics. Op ical TDM has con ibu ed he las ad ances in empo al mul iplexing and demul iplexing unc ions while bu e ing is sol ed using simple ibe delay lines. Synch onisa ion is no a comple ely sol ed p oblem ye . WDM and spa ial swi ching echnologies ha e e ol ed quickly and seem o be eady o be in oduced in comme cial de ices. Thei componen s can al eady ope a e a 131 ATM cell le elbas demons a ed in Sec ion 4. Fo u he in o ma ion abou he subjec s o his sec ion e e o (1) and (2). II II I A- Rea& o sys em 6- Good pe "? C- Rudimen a y D- Femible E- Nd eadble. TABLE 1 - Elec onic and pho onic s a e o he a o swi ching unc ions. RECENT SWITCHING IMPLEMENTATIONS Nex , a e e iewing he main high capaci y swi ching a chi ec u es, di e en ATM swi ching implemen a ion a chi ec u es a e desc ibed om h ee poin s o iew: elec onic esea ch, pho onic esea ch and comme cial swi ches. Implemen a ion de ails a e gi en in TABLE 2. High Capaci y Swi ching A chi ec u es Re iew Bu e ing in any packe swi ch is una oidable. The need o con en ion esolu ion has gene a ed di e en bu e ing s a egies. Inpu bu e s hold incoming packe s (cells) while he e is no possible pa h h ough he swi ch. In con as , ou pu bu e s hold con ending cells when he e a e mul iple cell a i als a he ou pu po s. Ou pu bu e is supe io since inpu bu e su e s om head o line blocking, ha is, cells wi h a ailable pa hs can no be swi ched because o he FIFO discipline ha holds one unswi chable cell on he head. Howe e , inpu bu e is easie o implemen because i does no equi e he speed necessa y o suppo ou pu bu e s. Di e en high capaci y swi ching a chi ec u es (Figu e 2) a e now p esen ed acco ding o hei basic swi ching s uc u e as p esen ed in he p e ious sec ion. Fu he in o ma ion can be ound in (3). a) ~~~ Sha ed Medium b) C ossba c) Banyan Based Figu e 2. Swi ch ab ics. mul iplexed among se e al inpu ou pu connec ions, based on disc e e ime slo s. A bus is an example o a physical conduc ing medium ha can accommoda e ime-di ision mul iplexing. A memo y module can also implemen connec ions based on ime di ision since i holds cells supplied by inpu po s ha a e emo ed by ou pu po s. This kind o swi ches a e limi ed by bandwid h and he e in scale. Mul icas ing and b oadcas ing a e easy o accommoda e since all ou pu s ha e access o all inpu da a. C ossba Swi ches. This single s age, single pa h nonblocking swi ches we e i s de eloped o ci cui swi ching and la e used o connec mul ip ocesso s. Many ATM swi ches a e based on c ossba swi ches o use i as a basic building block. C ossba swi ches a e a ac i e because hey a e non-blocking, simple, modula and wi h minimal delays. La ge ull c ossba s can be made wi h a ew VLSl chips, whose in eg a ion is only limi ed by he a ailable chip packages. Howe e , hey su e om squa e complexi y and as con ol mechanisms o a c ossba swi ch a e di icul . Many ou pu s selec ing one inpu easily pe o m he b oadcas unc ions. In o de o imp o e he c ossba pe o mance any o he bu e s a egies explained in he i s pa ag aph can be applied. Banyan Based Swi ches. The mul is age concep i s appea ed in he ci cui swi ching a ea. This kind o swi ches we e de eloped wi h he objec i e o a non blocking swi ch wi h lowe complexi y han c ossba swi ches. Fo ins ance, del a class ne wo ks ha e been p oposed o mul ip ocesso sys ems. This ne wo ks ha e a single sel - ou ing inlou pa h bu su e om in e nal blocking. These swi ches, which a e usually e e enced as Banyan based swi ches, a e modula , ha e he same la ency o all pa hs, suppo synch onous and asynch onous a ic and a e sui able o VLSl implemen a ion. The in e nal blocking makes he h oughpu dec ease wi h a highe ab ic dimension and inc ease wi h a highe swi ching elemen dimension. Thei main d awbacks a e he di icul y in dealing wi h conges ion due o he ex ensi e pipeline and bu e ing h ough he swi ch and also he di icul y o implemen b oadcas ing and mul icas ing. Sha ed Medium Swi ches. The physical connec ion be ween inpu and ou pu po s is implemen ed using a single high speed physical esou ce which can be a conduc ing medium o a memo y. This esou ce is ou di e en w&Ilengh s each. ' One delay S& wi h ou &m &elen&@. Fou ou & wi h ou di e en wd elengh s each. TABLE 2 - Implemen a ion de ails. 132 Elec onic Swi ching P o o ypes The e a e many di e en app oaches o he elec onic swi ching. As Banyan based swi ches had VLSl implemen a ion acili ies se e al swi ches we e de eloped. One o his muil i-s age swi ches, oge he wi h a single s age swi lch ope a ing on he elec onic limi s, a e now p esen ed. A Banyan based swi ch. Figu e 3 p esen s he UTXC a chi ec u e. I is o ganised in pe iphe al and cen al planes. The pe iphe al planes include he exchange e mina ion pe o ming heade ansla ion and policing. The cen al planes con ain he ATM swi ching ab ic whe e he BASE8 swi ching elemen s o m a del a class ne wo k. The global h oughpu depends on he numbe o s ages and planes. The BASE8 also se es as an in e ace be ween he pe iphe al and cen inl planes. Figu e 3. Elec onic Banyan based swi ch (4). The elec onic limi swi ch. A simple a chi ec u e has been used o ca y elec onic echnology owa ds i s limi s. As can be seen in Figu e 4, cells a i ing on each se ial link a e demul iplexed o 424 bi s (cell wid h), ou ed o dedica ed ou pul -side FIFO s o age acco ding o he con en s o he i ual channel and i ual pa h ields in he ATM cell heade , hen mul iplexed back o se ial o m and ansmi ed o des ina ion. The e is a high,-speed pa h wi h dedica ed FIFO bu e om each incoming link o each o he o he ou going links. I TolF om O he Links] while op ical in e aces a e a longe e m objec i e. Follows a desc ip ion o each concep and a mixed elec o-pho onic a chi ec u e in he las pa ag aph. Figu e 5. Fibe delay line swi ching ma ix (6). Fibe delay line swi ch concep . Signals a e ou ed on he basis o hei assigned wa eleng h and he con en ion is sol ed by op ical ibe delay lines adjus ed o mul iples o he cell du a ion. As shown in Figu e 5, a as uneable OWC (Op ical Wa eleng h Con e e ) assigns o each ATM cell he wa eleng h co esponding o i s a ge ou pu . Then, he wa e-space ma ix p o ides access o he ibe delay lines o inc easing leng h. Finally he ou pu il e s a e uned o a di e en wa eleng h de ining he ou pu add ess o he cell. The elec onic con ol d i es he OWCs and manages he wa e-space ma ix and delay lines as a FIFO. Figu e 6. Fibe loop swi ching ma ix (6). Fibe loop memo y swi ch concep . I is based on a ibe loop memo y o one cell du a ion. The di e en wa eleng hs o he loop a e used as di e en memo y posi ions. In case o con en ion he cell is con e ed o one a ailable wa eleng h in he loop and s o ed by uning on he ela ed op ical ga e in he loop. When con en ion is sol ed, he cell is ou ed o he des ina ion link uning he co esponding ou pu uneable il e and dele ed om he loop uning o he op ical ga e. The elec onic con ol, on he basis o he a ached ag, manages he memo y posi ions as a sha ed bu e . Figu e 4. A as elec onic a chi ec u e (5). Pho onic Swi ching P o o ypes Based on ealis ic analysis o he po en ial capabili ies and pe o mance achie able by he pho onic echnology, h ee di e en app oaches o ATM bu e ing and hei in eg a ion in ou di e en sys em concep s o he swi ching ma ix a e p esen ed in (6). They a e all composed o an all- Mul idimensional swi ch concep . I exploi s he op ical high-speed ou ing ne wo k elec onically wa eleng h domain o minimise he amoun o con olled. Incoming ATM cells a i e in phase, op ical bu e s equi ed in a mul is age swi ch. In accomplished by elec ical in e aces in a i s s ep case o con en ion he cell is con e ed o a di e en Figu e 7. Mul idimensional swi ching ma ix (6). 133 wa eleng h and ansmi ed a he same ime slo . The con ending cells a e no delayed in a bu e , hen bu e s can be elimina ed excep a he las s age o he swi ch. he ASX-200. The cells d ain om he swi ching ab ic memo y o he second- ie sha ed memo y swi ching/bu e ing modules, and om he e, a e ansmi ed o he ne wo k. 155 MWs ATM in e 1.25 GWs Op ical bus Figu e 8. Co po a e op ical ATM ne wo k (6). Co po a e op ical ATM ne wo k concep . Sui able o bo h access and p i a e ne wo ks. In his case, elec onic swi ches a e in e connec ed wi h an op ical double ibe ing h ough dedica ed op ical access nodes. Cells a e inse ed and d opped a he bi le el using mul i- unc ional high speed swi ches wi h dedica ed hyb id d i e s. Elec o-op ic swi ch An a chi ec u e ha also in e connec s elec onic swi ches h ough an op ical co e is p esen ed in (7). The ibe ing is subs i u ed by an op ical c ossba . Then, a complex con ol managemen p o ocol es ablishes op ical connec ions acco ding o he bu e occupancy, he p edic ed loads and he connec ion se -up ime. Comme cial Swi ches Mos comme cial ATM swi ches use single-s age echnologies o he sake o simple con ol and a ic managemen . They ypically ha e a o al swi ch h oughpu om 1 Gb/s o 10 Gb/s. La ge swi ches achie ing a capaci y close o 100 Gb/s ei he use mul is age swi ching ab ics o in e connec smalle swi ches o se e al gigabi pe second. In (8) a ious comme cial swi ches a e es ed; he one wi h he bes pe o mance was ASXQOO. This swi ch also has a good ma ke pene a ion ac o . So we ha e conside ed i as a good comme cial example. I s a chi ec u e is explained now oge he wi h he nex gene a ion swi ch ASX-1000. In he ASX-200 a chi ec u e (Figu e 9.a), cells a e p ocessed in h ee s eps. A he inpu , cells en e an ing ess po , a e sen h ough wo s ages o VPlNCl ansla ion and a e checked o compliance wi h hei a ic con ac . Cells a e hen dis ibu ed, using TDM, o mul iple sha ed memo y swi ching ou pu s. In he ASX-1000 a chi ec u e (Figu e 9.b), cells pass h ough he inpu unc ions in he same h ee-s ep o de as in he ASX-200. The majo ou pu -side di e ence is he p esence o a wo- ie hie a chical swi ching/bu e ing sys em. T a ic is dis ibu ed om he inpu s o he app op ia e i s - ie sha ed memo y ia as many as ou indi idual 2.56 Gb/s unidi ec ional TDM dis ibu ion ab ics. These dis ibu ion buses use he same TDM echnology as a) Comme cial a chi ec u e. b) A chi ec u e expansion. Figu e 9. Comme cial swi ch (9). EVALUATION ISSUES F om he implemen a ion poin o iew, op imum cos o a la ge swi ch is achie ed by selec ing a simple opology and using he highes -speed componen s a ailable a a easonable cos . Figu e 10.a illus a es his idea: o cons uc a swi ch o a gi en capaci y, ewe pa s o a highe -speed echnology can be used. The exac shapes o he cu es depend on he a chi ec u e, and hey can also shi wi h ime. So low speed elec onics equi e a la ge numbe o pa s. I op ical pa s a e in oduced a a easonable cos , he numbe o pa s can be conside ably educed as he elec o-pho onic a chi ec u es do. Finally, i e y high speed op ics a e used, he o al cos inc eases a he momen bu as men ioned ea lie , cos s could shi (7). F om he comme cial poin o iew, acquisi ion and main enance cos s a e no he only economics su ounding ATM due o he as echnological changes o i s componen s. Many ac o s o he han complexi y and pe o mance mus be used o e alua e he p e ious a chi ec u es. They a e enume a ed and discussed now ollowing he same s uc u e used in (10). Coexis ence. Comme cial ma ke s equi e a high le el o ATM in eg a ion in o de o coexis wi h o he LANNVAN echnologies. LAN emula ion is he solu ion o e ed by he ATM Fo um (11). In (12) di e en comme cial ATM elec onic swi ches whe e es ed and esul s demons a ed a good pe o mance in LAN emula ion. Bes pe o mances whe e ob ained wi h elec onic con e sion o ATM lows e en o local swi ching. Op ical swi ches wi h hei highe capaci y could be a desi able backbone i he educed p o ocol unc ionali ies did no became a d awback o LAN emula ion. Coexis ence o elec onic and pho onic echnologies is also equi ed. Exis ing elec onic swi ches can bene i om pho onic swi ching speed while e ol ing owa ds all-op ical ne wo ks. 134 Eiec o.op lc a ch. a) Technology cos s (7). b) Hie a chical clus e ing (10). Figu e 10. A chi ec u e cos s and scalabili y. Complexi y and scalabili y* Scalabili y e e s o a sys em capabili y o e ol ing o expanding in esponse o inc eased demands. This equi emen is c i ical, since ATM echnology is in i s in ancy s age and i s comme cial success depends on inc emen al deploymen and a mig a able s a egy. Two aspec s o he a chi ec u e mus be scalable: he numbe o po s and he speed o e mina ing po s. They a e somehow equi alen . Po scalabili y is closely ela ed o he complexi y measu es o he a chi ec u es. They a e summa ised in TABLE 3, whe e he i ial conclusion is ha he linea o de o he sha ed medium a chi ec u e is p e e ed. Howe e , he limi ed sha ed medium bandwid h limi s i s maximum scalabili y. A possible solu ion is o inc ease he le el o pa allelism wi hin he swi ch ab ic, ha is, o ou e a ic lows h ough mul iple and pa allel pa hs like mul iple buses wi hin he swi ch. This was he solu ion adop ed o he SX- 1000. Fo hose a chi ec u es wi h swi ching ne wo ks he solu ion would be o accommoda e pa allel ne wo k planes as he p esen ed Banyan based a chi ec u e does. Finally, a clus e a chi ec u e wi h mul iple swi ch ab ics in e connec ed ia an in e clus e swi ch (Figu e 10.b) seems a good solu ion o elec o-op ical swi ches like he ones p esen ed ea lie . Upwa d scalabili y o he a chi ec u e ela i e o po da a a es has a d as ic implica ion o he in e nal esou ces o he swi ch ab ic. Thus, scalabili y ela ed o po da a a es is mo e di icul o assess. 1 Ma ix TABLE 3 - Po scalabili y (10). I O de o F E icien use o bandwid h. The comme cial ma ke iews bandwid h in e ms o cos . ATM is a ac i e hanks o he capabili y o dynamic bandwid h alloca ion. Swi ching a chi ec u es ha employ a complex p o ocol o es ablishing connec ion and ou ing decisions do no use he in e nal bandwid h e icien ly. Con en ion esolu ion phases and cell duplica ion o b oadcas ing a e some examples. a e elec onically con olled. Thus, ha dwa e o so wa e bandwid h managemen p o ocols seem o easible in all cases. Reliabili y and aul ole ance. ATM as a LAN wi h a s a opology equi es a high le el o eliabili y and aul ole ance om he swi ch. Mul iple edundan swi ches ha ope a e in p ima y and backup modes a e a mus since chip ailu es would mos likely disman le se e al (i no all) pa hs. Elec o-op ical swi ches can p o ide qui obus pe o mance depending on he eliabili y o he op ical co e. CONCLUSION As o oday, he mos immedia e e olu ion owa ds he comme cial a ea seems o be domina ed by pho onics as a highe le el swi ching, while elec onics keep hei in e ace posi ion dealing wi h i s limi ed bandwid h. Rega ding he in e ace, elec onic TDM a chi ec u es can suppo expandabili y, nonuni o mi y o po da a a es and bandwid h managemen p o ocols. Inside he swi ch, pho onic a chi ec u es can p o ide o concu ency and speed. Thus, he imp o emen s in bo h elec onic and pho onic a chi ec u es should be in eg a ed in o de o comme cial implemen a ions o inc ease hei cos -e ec i eness. REFERENCES 1. Hui, J. Y. and Cheung, K. W., 1996. Op ical Ve sus Elec onic Swi ching o B oadband Ne wo ks. IEEE Ne wo k, No embeVDecembe 1996. pp. 21 o 25. 2. Thylen, L., Ka lsson, G. and Nilsson, O., 1988. Swi ching Technologies o Fu u e Guided Wa e Op ical Ne wo ks. Communica ions Maaazine, Feb ua y 1996. pp. 106 o 113. 3. Awdeh, R. Y. and Mou ah, H.T., 1994. Su ey o ATM Swi ch A chi ec u es. Comw e Ne wo ks and ISDN -S s ems, ol. 27. 1995. DD. 1567 o 1613. I, 4. Cla e o, S., Fassino, M., Liccia di, L. and Tu olla, M., 1994. La Realizzazione del Ci cui 0 BASE8. RapDo o Tecnico CSELT, Sep embe 1994. 5. Bu ne , S. E. and Chi ukula, R., 1996. On he Limi s o Elec onic ATM Swi ching. IEEE Ne wo k, No embedDecembe 1996. pp. 26 o 31. 6. Mase i, F. and o he s, 1996. High Speed, High Capaci y ATM Op ical Swi ches o Fu u e Telecom. T anspo Ne wo ks. IEEE J-SA in Communica ions, June 1996. pp. 979 o 998. 7. Mun e , E. and o he s, 1995. A High-Capaci y ATM Swi ch Based on Ad anced Elec onic and Op ical Technologies. lEEE Communica ions Maqazine, No embe 1995. pp. 64 o 71. 8. Mande ille, R., 1995. The ATM S ess Tes . Da a Communica ions, Ma ch 1995. pp. 68 o 82. 9. Fo eRunne ATM Swi ch A chi ec u e, Ap il 1996. 10. Rooholamini and o he s, 1994. Finding he Righ ATM Swi ch o he Ma ke . IEEE ComDu e , Ap il 1994. pp. 16 o 28. 11. ATM Fo um Technical Commi ee. LAN Emula ion o e ATM. Ve sion .1.0, Janua y 1995. 12. Mande ille, R. and Johnson, J. T., 1996. Fo ge he Fo kli . Da a Communica ions, Sep embe 1996. pp. 121 o 134. ACKNOWLEDGEMENTS ATM po en ials a e due o i s ha dwa e We hank P o esso Guido Albe engo om he Poli ecnico di implemen a ion capabili ies; hus, complex so wa e To ino o sugges ing us his opic, as well as P o esso Jose A. p o ocols used o p o ide op imal bandwid h Delgado Penin om he Uni e si a Poli ecnica de Ca alunya o managemen do no con ibu e o achie e a good encou aging ou co-ope a ion. We also hank Joan Vila Sallen o pe o mance on ATM. All p esen ed a chi ec u es his