A etwork throughput compariso of optical metro rig architectures M. Veeraraghava, H. Lee, J. Aderso, K. Y. Eg This paper compares three differet metropolita-area etwork (MAN) architectures from a etwork throughput perspective. We compare etwork throughput both before ad after a fiber cut/restoratio because a critical compoet of a MAN architecture is its ability to restore service rapidly after a fiber cut or other failure. The three architectures cosidered i this work are:. A circuit-switched rig, such as a Sychroous Optical Network/Sychroous Digital Hierarchy (SONET/SDH) rig []. A esiliet Packet ig (P) such as that proposed i [] 3. Village Networks iopn solutio [3]. I Sectio, we describe the traffic patters assumed for the comparative aalysis. Sectio describes the circuit switched rig architectures ad aalyzes the etwork throughput of these rigs before ad after fiber cuts. Sectio 3 describes ad aalyzes the P rig.. Traffic patters assumed for aalysis Network throughput depeds upo the traffic patter. Three patters assumed commoly i existig literature [][] iclude cetralized, mesh ad cyclic patters. The cetralized traffic patter correspods to a access rig, where all odes sed/receive data to/from oe ode (for example, the ode that provides access to the Iteret). The mesh patter is more commo i iteroffice cofiguratios where traffic exists betwee ay two offices. The access patter occurs i access metro rigs, where data from/to differet customer eterprises flows to a telecommuicatios service provider ode. O the other had, the mesh patter is commo i core metro rigs, where data flows betwee ay two odes o the rig. The cyclic patter is icluded to allow us to compute maximum etwork throughput, i.e., the maximum traffic that ca be carried betwee all pairs of odes. We allow for demad to be both split o to multiple paths or ot split, i.e., all the demad betwee two odes is set o the same path. Furthermore, we assume that demad is uiformly the same betwee all ode pairs for which a o-zero demad exists. The traffic patter type determies whether. The shorthad otatio metro is used for metropolita-area etworks.
a ode pair has a o-zero demad or ot. With the mesh traffic patter, every ode seds traffic of o-zero value d to every other ode o the rig. Thus, ode i seds d Mbps to ode j, where j i, while simultaeously ode j seds d Mbps to ode i. I the cetralized patter, every ode i seds data to a cetral ode (hub), say ode, ad receives data from the hub. Thus, d j = d j = d, j, while d ij = 0, i, j. Fially, the cyclic patter is oe i which data oly flows betwee eighbor odes. If odes o a rig are umbered i sequece, + ad 0 otherwise, ode is the same as ode. I uidirectioal rigs, a simplex cyclic patter yields the maximum etwork throughput. For the iitial aalysis, we assume uiform loads, which meas the traffic is the same for all ode pairs that have a o-zero demad. But for subsequet aalysis, we assume time-varyig demads, which are ot uiform. This is required to show the advatage of usig packet-switched rigs over provisioed circuit-switched rigs. d ij = d j = i + i. Circuit-switched rig. Descriptio of four rig architectures eferece [] describes four architectures for Self-Healig igs (SH). These iclude Bidirectioal SH with four fibers (B-SH/), Bidirectioal SH with two fibers (B-SH/), Uidirectioal SH (U-SH) with two fibers i a folded architecture (U-SH/APS), ad USH i a path protected architecture (U-SH/PP). Drake [5] classifies these architectures as -fiber bidirectioal rig, -fiber bidirectioal rig, Uidirectioal Lie Switched ig (ULS), ad Uidirectioal Path Switched ig (UPS), respectively. The term Bidirectioal Lie Switched ig (BLS) is also commoly used for bidirectioal rigs. I this paper, we refer to these four rig architectures as -fiber BLS, -fiber BLS, ULS, ad UPS. A rig is bidirectioal if sigals i both directios of a duplex chael travel over the same path, while i a uidirectioal rig the sigals i the two directios of a duplex chael travel over opposite paths. The term fiber is used to represet oe directio of a duplex chael. For example, i a -fiber rig, fibers betwee two odes costitute a duplex chael. The secod fibers are used to provide a protectio duplex chael betwee the same two odes. A uidirectioal rig architecture is show i Fig.. I uidirectioal rigs, primary traffic is set o the workig rig (which i Fig. is the clockwise rig). There are two variats of uidirectioal
rigs: ULSs ad UPSs. I ULSs, traffic is oly set o the workig rig. Traffic from ode to ode traverses the fiber from ode to ode. Traffic from ode to will go roud the workig rig from ode to ode 3 to ode to ode. Each ode is a add/drop multiplexer, i.e., it adds some sigals to the rig ad removes others from the rig. The protectio rig is oly used whe there is a Workig Protectio Half the time slots are reserved o each rig for protectio 3 3 3 Uidirectioal rig -fiber bidirectioal rig -fiber bidirectioal rig Fig. SONET rig architectures fiber cut or failure ad the rigs are recofigured. I a UPS, to provide path protectio for all sigals, data from ode to ode is set both o the short path (fiber from ode to ode ) ad also o the log path from ode to odes, 3, o the protectio rig. The reaso for sedig the traffic o the secod rig is that if a failure/fiber cut occurs, the ode ca quickly select data set o the protectio rig. I a rig with odes, data from ode to ode is set o the workig rig o the log path,,, 3,..., -, as well as o the protectio rig o the short spa from ode to ode. The sigal received o the log path is the oe used uder ormal circumstaces. It is oly uder failure coditios that the sigal set o the path ode to ode is used eve though this path is shorter ad hece delays will be lower. Thus, i a UPS, traffic is set o both rigs uder ormal coditios, while i a ULS, traffic is oly set o the workig rig before a failure/fiber cut. Two bidirectioal rig architectures are show i Fig.. I the -fiber case, data from ode to ode is set o the fiber from ode to ode. Data i the opposite directio is set o a fiber from ode to ode. The secod pair of fibers are reserved for protectio. I the -fiber BLS, data from ode - is set o the direct spa from to ad data from ode to is set o the direct spa from to. But because there is o additioal pair of fibers to serve as a protectio rig, half the time slots o each fiber are reserved as protectio badwidth. This meas that the trasceivers o a -fiber BLS 3
should be capable of sedig ad receivig data at twice the badwidth of trasceivers o a -fiber BSL.. Computatio of etwork throughput before fiber cut/restoratio Let be the trasceiver rate used o each fiber (this rate is also referred to as the fiber trasmissio rate ). This is the rate at which data is set o each spa (part of the rig betwee two adjacet odes) i each directio (i.e., o a fiber). The total etwork throughput T is the demad betwee all pairs of odes that ca be carried o each type of rig with fiber trasmissio rates. This is the total of all traffic that eters the rig at a add/drop ode ad exits at aother add/drop ode. The uit of measuremet of both etwork throughput ad trasmissio rate is Mb/s. For the three traffic patters, the relatio betwee etwork throughput ad d, the o-zero demad, Table : Network throughput as a fuctio of the o-zero (uiform) demad d Traffic Patter Mesh Cetralized Cyclic defied i Sectio., is give i Table, where Network throughput T -------------------- ( ) d ( )d d is the umber of odes o the rig. For each traffic patter ad rig type, Table shows the demad d, which we determie by coutig the umber of o-zero demads routed o a fiber, ad makig the assumptio that all o-zero demads are equal. The etwork throughput is computed by addig all the o-zero demads. Effectively, this is doe by pluggig i d from Table ito the etries i the secod colum of Table that relate T to d. Explaatios for d are provided i the three sub-sectios..-..3. is idicated as E (Eve) or O (Odd), ad demad is idicated as NS (Not Split), S (Split), or D/C (Do t Care), which
meas the result is idepedet of whether the demad is split or ot split. Table : Network throughput for differet types of rigs ad differet traffic patters ig ULS/ UPS -fiber BLS Traffic patter Mesh Cyclic Simplex cyclic Mesh Cetralized Cetralized Cyclic d (each o-zero demad) -------------------------------- ( ( ) ) ------------ --- Network throughput T 8 -------------------- ( + ) : E; demad: NS 8 ( ) ( ----------------- + ) : E; demad: NS 8 - : E; demad: S 8 ( ---------------- ) : E; demad: S ------------------- 8 : O; demad: D/C 8 ( ( ----------------- + ) : O; demad: D/C ) - : E; demad: NS ( ---------------- ) : E; demad: NS ( ---------------- ) : E; demad: S : E; demad: S : O; demad: D/C ( ---------------- ) : O; demad: D/C 5
ig -fiber BLS Table : Network throughput for differet types of rigs ad differet traffic patters Traffic patter Mesh Cetralized Cyclic d (each o-zero demad) Uder the mesh traffic patter assumptio, for a uidirectioal rig, etwork throughput is twice the rate of the trasceiver. For bidirectioal rigs, for large, i the -fiber case, the etwork throughput approaches 8 times the trasceiver rate, while i the -fiber case, the etwork throughput approaches times the trasceiver rate. Also, as oted i Sectio., the etwork throughput remais uchaged after a fiber or cable cut for all four rigs... Uidirectioal rigs (UPS, ULS) Network throughput T -------------------- ( + ) : E; demad: NS ( ) ( ----------------- + ) : E; demad: NS - : E; demad: S ( ---------------- ) : E; demad: S ------------------- ( : O; demad: D/C ( ----------------- + ) : O; demad: D/C ) - :E; demad: NS -------------------- ( ) :E; demad: NS ------------ :E; demad:s :E; demad:s : O; demad: D/C ------------ : O; demad: D/C --- Fig. illustrates how the cetralized traffic patter is supported o a uidirectioal rig. Each fiber (-), (-3), (-),... (-) (-), (-3), (-),... (-) 3 6 5 (-), (3-), (-),... (-) Fig. Uidirectioal rig: cetralized demad 6
carries traffic from ( ) ode pairs. For example, the fiber from ode to 3 carries traffic from ode to odes 3,,...,, ad also traffic from ode to ode (because the rig is uidirectioal, this traffic is routed o the log path). Therefore, i a UPS or ULS, because each fiber supports traffic ode pairs, uder the uiform demad assumptio, the demad d betwee ay two odes is d = ------------ EQ() Fig. 3 illustrates how the mesh demad traffic patter is supported o a uidirectioal rig. The fiber from ode to carries traffic from all odes to ode, the traffic from all odes to ode 3 except from ode (which is carried o the short spa fiber from ode to ode 3), the traffic from all odes to ode except from odes ad 3, ad so o. The last term shows the traffic to ode ; this cosists of oly the traffic from ode because traffic from all other odes to ode is carried o other spas. No traffic to ode is carried o the fiber from ode to ode. The total umber of o-zero demads [(-), (-), ((-)-),... (3,)] + [(-3), (5-3)...(-3)] + [(5-), (6-),... (-)] +... [(-(-)), (,(-)] + [(-)] 3 [(-3), (-3), (5-), (6-5),... (,), (-)] 3 6 5 6 5 Mesh demad Cyclic demad Fig. 3 Uidirectioal rig: mesh ad cyclic demad patters carried o the fiber from ode to ode is ( ) + ( ) + + = ( ). Assumig that all o-zero demads are equal, we divide the fiber trasmissio rate equally amog all these demads. Therefore d = -------------------------------- ( ( ) ) EQ() Fig. 3 illustrates the cyclic patter o a uidirectioal rig. The fiber from ode to ode 3 carries the demad from to 3, from to 3, from 5 to, etc., because traffic is oly set betwee eighbors 7
with this cyclic patter. There are demads ad hece d = --- EQ(3) With the simplex cyclic patter [6], traffic demad from ode to ode is d, but the demad from ode to ode is 0. Therefore o ay fiber, oly oe demad d is carried. Therefore d =... -fiber BLS Next, cosider a -fiber BLS with the cetralized traffic patter. I this case demad d depeds upo whether, the umber of odes o the rig, is eve or odd, ad if it is eve, whether demad is split o two paths or ot. If is eve ad demad is ot split, the we cosider the worst case path to limit d so that a fiber with trasmissio rate ca support the total demad amog all ode pairs. As (-), (-3), (-),... (-/), (-(/+)) if is eve ad demad is ot split e.g., =0; the -, -3, -, -5, -6 If is eve ad demad is split the the 3 last (-(/+)) term will be split. 6 5 (-), (-3), (-),... (-((-)/)) if is odd e.g., =9; the -, -3, -, -5 i the opposite directio -9, -8, -7, -6 Fig. -fiber bidirectioal rig: cetralized traffic patter illustrated i Fig., the traffic from ode to ode 6 is carried o the clockwise rig. Thus, fibers i the couter-clockwise directio from ode to ode 0, 0 to 9,... 7 to 6, carry less load. If demad is split the the -6 demad is divided equally o the two rigs. d ( ) if is eve ad demad is ot split = (( ) ) if is eve ad demad is split equally (( ) ) if is odd EQ() 8
For the mesh case, see Fig. 5 for how the traffic demad is routed o the -fiber bidirectioal rig. 6 Fig. 5 5 [(-), (-), ((-)-),... (/+)-)] + [(-3), (-3),..., ((/+3)-3)] + [(-), (-),... ((/+)-)] +... [(-(/+))] if is eve [(-), (-), ((-)-),... ((+)/+)-)] +... [(-(/+))] if is odd 3 If =0, -, -3, -, -5, -6 goes i clockwise -0, -9, -8, -7 i couterclockwise - ot symmetric (demad o-splittig) but max. capacity reqmt. is i the clockwise directio. Same BW used for couter-clockwise rig though theoretically that could be of less BW. This problem does ot arise if is odd. -fiber bidirectioal rig: mesh traffic patter From Fig. 5, we ote that there are carried o the fiber from ode to ode, i.e., there are terms i the first [] term of the demad terms. The last [] term has term. Therefore, it adds to + ( ) + +, which is (( ) ( + ) ). A similar reasoig ca be applied for the case whe is odd. If we allow demad splittig, the istead of the asymmetric traffic distributio patter show i Fig. 5, the traffic distributio is symmetric. Half of the -6 traffic goes clockwise ad the remaiig couter-clockwise. Uder this assumptio, the traffic to ode will be [(-), (-), ((-)-),... (/+3)-) + 0.5((/+)-)] + [(-3), (-3),..., ((/+)-3), 0.5((/+3)-3)] +... + 0.5([(-(/+))]. There are + ( + 3) + terms i the first [] term, i.e., there are terms, without coutig the 0.5 term. The last [] term has term, which is a 0.5 term. Therefore, it adds to ( ) + (( ) ) + +, which is (( ) ( ) ) + 0.5 terms, which is equal to 8. Therefore, + ( + ) + d = - - + - if is eve ad demad is ot split ( ( 8) ) if is eve ad demad is split ------------ + + ------------ - if is odd EQ(5) For the cyclic patter, i a -fiber bidirectioal rig, the oly demad carried o a fiber is from oe ode to its eighbor. Hece, d = EQ(6) 9
..3 -fiber BLS As explaied i [7], a -fiber BLS is equivalet to a -fiber BLS with logical fibers. Oly half the slots i the two fibers are used to carry workig traffic ad the remaiig half the time slots are reserved for protectio reasos. Sice the rig is bidirectioal, both rigs carry workig traffic i opposite directios.therfore, the demad that ca be carried o a fiber i a -fiber BLS is always half the demad that ca be carried o a fiber i a -fiber BLS. As a illustratio, cosider the cetralized demad traffic as show i Fig. 6. If is eve ad demad is ot split, the the umber of demads 6 5 (-), (-3), (-),... (-/), (-(/+)) if is eve e.g., =0; the -, -3, -, -5, -6 Demad: ot split 3 (-), (-3), (-),... (-((-)/)) if is odd e.g., =9; the -, -3, -, -5 i the opposite directio -9, -8, -7, -6 Fig. 6 -fiber bidirectioal rig: cetralized demad carried o the - fiber is. Sice oly half the fiber trasmissio rate ca be used for these demads, with the remaiig half set aside for restoral, demad d is ( ) ( ), which is as show below. The remaiig two cases i EQ(7) ca be reasoed through similarly. d = if is eve ad demad is ot split - + 0.5 if is eve ad demad is split ( ) if is odd EQ(7) For the other two traffic patters, mesh ad cyclic, the result is the same, i.e., demad d betwee ay two odes is half the demad that ca be carried i a -fiber BLS. Table shows the values for d i a -fiber BLS for these traffic patters... Numerical results The etwork throughput for a OC-8 rig of all four architectures uder a mesh traffic patter assumptio is illustrated i Fig. 7. Give (trasceiver rate), maximum throughput will be achieved i -fiber BLS with demad splittig. Sice demads from fewer ode pairs share the fiber trasmissio 0
Fig. 7 Network throughput of rigs uder mesh traffic patters rate i bidirectioal rigs, each o-zero demad ca be higher ad hece the total etwork throughput is higher. As explaied i Sectio..3, oly half the demad ad hece etwork throughput of a - fiber BLS ca be supported o a -fiber BLS. The reaso etwork throughput is higher for the demad splittig case relative to the o-splittig case is that demad from some ode pairs is completely routed o oe path i the latter case, makig the per ode pair demad smaller. The differece i the two cases, demad splittig ad demad o-splittig is oly see whe is eve as is evidet from Sectio.. Figs. 8 ad 9 show similar plots but with differet traffic patters, i.e., the cetralized ad cyclic cases. I the cetralized case, there is o differece betwee a -fiber BLS ad a uidirectioal rig. Iterestigly, the total etwork throughput is more with the mesh traffic patter tha the cetralized eve though the per ode pair o-zero demad value d is smaller. The highest etwork throughput is achieved uder the cyclic patter assumptio; this is the maximum achievable for the bidirectioal rigs. Sice etwork throughput depeds o ad as show i Table, we vary for a fixed rig size = 8. I this case, we also plot the etwork throughput versus for all the architectures uder differet traffic patters. These are show from Fig. 0 to Fig.. The values of are OC3, OC9, OC, OC8, OC, OC36, OC8, OC9 as show i the SONET hierarchy [8]. Summig up the characteristics show i Fig. 0 to, -fiber BLS with demad splittig gives us best choice to get maximum
Fig. 8 Network throughput of rigs uder cetralized traffic patter Fig. 9 Network throughput of rigs uder cyclic traffic patter throughput. The umber of DS3s that ca be supported as icreases to OC9 is quite large relative to a OC8 rig.
Fig. 0 Network throughput of rigs vs. for mesh traffic patter (=8) Fig. Network throughput of rigs vs. for cetralized traffic patter (=8).3 ecovery procedures followig fiber cuts I this sectio, we describe how each rig performs restoratio after a fiber or cable cut. I a UPS, sice traffic is set o both fibers i two opposite directios, the receivig ode receives two idetical sigals with differet delays. Durig ormal operatio, oly the primary sigal is used, but both sigals are moitored for alarms ad maiteace sigals. After a cable cut, where both fibers o a spa are 3
Fig. Network throughput of rigs vs. for cyclic traffic patter (=8) lost, AIS sigals are set by the two odes o either eds of the cable cut o all the paths. Upo detectig a AIS, the : selector devices at all the odes receivig the path sigals make a switch to the protectio sigal if ecessary. AIS is set at the path level ad is hece ot examied by itermediate odes. eferece [] has a more detailed explaatio of path protectio restoratio. estoratio i ULSs ca be doe i oe of two ways. Both follow the automatic protectio switchig (APS) protocol usig the K ad K bytes of the LOH [9]. At the ed of the restoratio, the rig has loopbacks at the two eds of the failed lik. I a -fiber BLS, the APS procedure is used to recofigure the rig after a fiber cut. eferece [5] explais the APS procedure i detail. If oe fiber i a spa is cut, the short path spa protectio APS procedure ca be carried out. If both fibers i a cable (across a spa) are cut, the log path rig protectio APS procedure is carried out. The differece lies i how the K/K sigals are set. I a -fiber BLS, the recovery procedure also uses the APS scheme with two loopbacks occurrig at the two OADMs o either side of the cable cut. Followig restoratio after sigle fiber or cable cuts, the uidirectioal rigs ad -fiber bidirectioal rig cotiue supportig the same etwork throughput because a equal amout of protectio badwidth lies uused before the cut. A fiber cut is a cut of a sigle fiber, i.e., trasmissio i oe directio betwee odes is iterrupted. We assume a cable cut to be a cut of both fibers betwee two odes,
i.e., i both directios. ecovery mechaism for both these types of cuts leaves the etwork throughput uchaged with these SONET rigs. I the -fiber BLS case, the traffic carried before the cut has to be supported with differet routig after the cut. The architecture becomes that of a liear etwork. The worst case cut is if oe of the two spas coected to the hub fail. For example i Fig. 3, if ode is the hub, ad the fiber from ode (-), (-3), (-),... (-) if is eve or odd o questio of demad splittig or ot because there is oly oe path. 3 6 5 Fig. 3 -fiber bidirectioal rig after a cut: cetralized traffic patter to ode fails, the the rig will be wrapped aroud at odes ad. The lik with the heaviest load will be the lik from ode to ode, which carries demad pairs as show i Fig. 3. The lik from ode to 3 carries demad from oe less ode pair, lik 3 to carries demad from two less ode pairs ad so o because uder the cetralized traffic demad patter, each ode oly seds to ad receives from the hub. Thus, uder this cofiguratio, d ca be d = ----------------. EQ(8) ( ) Whe this demad is compared to the demad listed for the -fiber BLS i Table, we see that the total demad carried before the fiber cut/restoratio ca cotiue to be carried after the cut, eve whe the worst case cut occurs (if a fiber betwee two odes either of which is the hub occurs, the the maximum umber of demad pairs routed o a sigle fiber will be lower tha with this worst case cut illustrated i Fig. 3). Oly, if the rig has a eve umber of odes ad demad is ot split, the before the cut, the pairwise demad supported is be supported after the cut. (see Table ), which will be less tha the demad that ca To determie which lik will experiece the most load uder the mesh traffic patter, assume it is the lik from ode k to ode k + (see the liear etwork of Fig. ). This lik will carry load from 5
(-), (-3), (-),... (-) if is eve or odd o questio of demad splittig or ot because there is oly oe path. 3 6 5 3 Fig. -fiber bidirectioal rig after a cut: mesh traffic patter odes ( k + ), ( k + ),...,, ( k + ), ( k + ),...,,... k ( k+ ), k ( k+ ),..., k. This is a total of ( ( k + ) + ) ( k) = ( k)k demad pairs. To fid the value of k for which this term is maximum, take the derivative d ---------------------- ( k)k = k = 0 dk EQ(9) Therefore if is eve, k =. If is odd, the lik with the maximum load will have more odes to the left of the lik tha to the right for the lik directio from left to right (i the liear etwork) ad vice versa for the lik i the opposite directio. Therefore, the lik from ode ------------ + to ode ------------ + + will have the maximum umber of demad pairs i the left to right directio ad for the opposite directio, the lik from ode ------------ + to ode ------------ + will have the maximum load. The maximum o-zero demad value is hece d = ------------ is eve -------------------------- ( is odd ) EQ(0) Similar to the cetralized traffic patter case, uder the mesh traffic patter, EQ(0) is almost the same as for the -fiber BLS before the fiber cut (see Table ). Oly whe is eve, if the demad is ot split, the the demad supported before the cut is less tha the demad that ca be supported after the cut. I summary, if we igore the demad o-splittig case, eve with the -fiber BLS, the etwork throughput supported after a fiber cut/restoratio is the same as before the cut. 6
3. eliable Packet igs (P) eliable Packet ig (P) solutios are beig defied for the MAN applicatio. The mai itet of defiig a ew packet-switched protocol for MANs is that packet-switched etworks support data traffic more efficietly tha circuit-switched etworks, such as SONET rigs. This is because packet switches ca accommodate chagig traffic patters better tha circuit-switched etworks that are operated i a provisioed mode. Before we compare P architectures with SONET rigs uder varyig traffic patters, we first describe a example P architecture ad study the etwork throughput it ca support followig a fiber cut. 3. Descriptio of a P architecture We describe the Spatial euse Protocol (SP) based P architecture proposed by Cisco []. I this solutio, each ode o the rig is a packet switch that examies packet headers to determie whether to drop the packet (at that ode) or whether to forward it o the rig. It is a bidirectioal dual couterrotatig rig. AP is used for rig selectio. The sectio about rig selectio i [] appears to be somewhat uclear. First, hashig o the destiatio address (which is all oe s for a broadcast address) is said to be used to decide o which rig to sed a AP request. Hashig o the same key (address of all oes) will always yield the same choice. Therefore it is uclear why hashig is eeded here. Secod, [] suggests that whe the rig is wrapped, if the destiatio is equidistat o the ier or outer rigs, the hashig is used to determie which rig to use. But whe the rig is wrapped, it becomes a liear etwork as i the case of a -fiber BLS as show i Fig., ad hece there is oly oe choice if the shortest path is to be chose. 3. Computatio of etwork throughput i a SP rig Assumig that the AP procedure i combiatio with the topology map results i the shortest path (from a hop cout poit of view) beig chose for data packets, the etwork throughput of a SP rig before a fiber cut is the same as that of a -fiber BLS. The SP rig, beig bidirectioal ad a dual couter-rotatig rig, is similar to a -fiber BLS. But because the whole badwidth is used for data traffic ad o badwidth is set aside for protectio ulike i the -fiber BLS, the etwork throughput is equal to that of a -fiber BLS. For example, for the mesh traffic patter 7
T SP = 8 ( ) ( ----------------- + ) : E; demad: NS 8 ( ---------------- ) : E; demad: S 8 ( ----------------- + ) : O; demad: D/C EQ() After a fiber cut, the rig wraps aroud at the two edges of the cut usig a procedure called IPS (Itelliget Protectio Switchig). The wrapped rig is exactly the same as a wrapped -fiber BLS. Therefore, after a fiber cut ad IPS restoratio, the etwork throughput of a SP rig drops to that of a wrapped -fiber BLS. Uder a mesh traffic patter assumptio, this throughput is f T SP ( ---------------- ) is eve = ( ----------------- + ) is odd EQ() where the per ode pair demad is give by EQ(0). I summary, i SP rigs, the etwork throughput drops to half after a fiber cut/etwork restoratio.. OPN (Optical Packet Node) based rigs. Descriptio of a OPN rig architecture This OPN (Optical Packet Node) solutio leverages recet advaces i optical ad data processig device techology for developig a ew etwork architecture, called optical flow etworkig [3], which utilizes IP as the basic etworkig techology ad re-cofigurable, multi-wavelegth optics as the trasport mechaism i a highly-itegrated, sigle etworkig device. It combies IP router, Multi- Protocol Label Switchig (MPLS) switch ad WDM crosscoect fuctioality i oe ode. OPNs are capable of routig IP packets as well as switchig wavelegths, eablig sigle-hop or multi-hop add/drop optical flow topologies. As IP traffic chages or icreases, existig lightpaths may be recofigured or additioal lightpaths may be created usig the appropriate OPNs. Alteratively, existig Label Switched Paths (LSPs) ca be recofigured or additioal LSPs may be created. I the istace of a fiber cut or ode failure, OPNs detect ad isolate the fault ad redirect optical flows oto alterate lightpaths (pre-determied or dyamically selected) for miimal IP service disruptio. A OPN is comprised of packet processors (e.g. L3 packet classificatio, filterig, forwardig, 8
multi-class-per-flow queuig, label switchig, packet-over-lightpath adaptatio/de-adaptatio), WDM traspoders, photoic switchig devices, WDM filters, variable optical atteuators ad optical amplifiers. These compoets are itegrated i a sigle uit chassis with commo cotrol ad maagemet. The OPNs may the be used to costruct two-fiber rig physical etwork topologies with logical mesh lightpath coectivity. I the OPN etwork, IP QoS is provided through the use of packet classificatio ad policy cotrol, badwidth-guarateed per-flow queuig, ad traffic cogestio cotrol. With these capabilities, optical flows are created from ed-user source packets with defied class of service (CoS) attributes or policies ad delivered across lightpaths to destiatios i the OPN subet. The policies ad CoS attributes are kow throughout the subet, so service performace ad reliability is guarateed. Service protectio may be provided at the packet level ad/or optical level, depedig o the service provider's etwork protectio strategy ad differetiated service requiremets. For example, OPN etwork protectio ca be provided by both MPLS alterate reroutig ad lightpath protectio. Services may be protected by oe method or the other (or u-protected) depedig o the service provider's CoS offerigs ad ed-users eeds. For this aalysis, the throughput of the OPN rig etwork is compared before ad after recovery from a bi-directioal fiber cut. A trasparet two-fiber WDM optical chael shared protectio rig architecture is used for recovery. I this protectio scheme, the rig supports WDM traffic with multiple wavelegths o two ui-directioal fibers. I each fiber, the wavelegths are partitioed ito two groups: oe for workig traffic ad the other for protectio. Although there are several wavelegth allocatio schemes, the oe adopted here is that the same wavelegth is used for the workig ad protectio chaels. This avoids the eed for wavelegth coversio for protectio switchig. Cotrol liks are established o a ode-to-ode basis for eablig real-time lik fault detectio, protectio triggerig, sigalig, coordiatio ad switchig. Protectio switchig may be performed at odes directly adjacet to the failure or at the ed-odes of the optical chael. The latter switchig cofiguratio avoids uecessary loop-backs i adjacet-ode switchig, resultig i shorter protectio paths.. Computatio of etwork throughput i a Optical Packet Node (OPN) rig For a OPN rig, the rig supports WDM traffic with multiple wavelegths (say k wavelegths) o each fiber. I each fiber, half of wavelegths (say if k is divisible by two) are set for workig traffic ad the other half (say λ k +, λ k λ, λ, λ k 9 ) is reserved for protectio. Although there are several
wavelegths allocatio schemes, same wavelegths are used for the workig ad protectio chaels because of avoidig the eed for wavelegth coversio for protectio switchig. It meas that for example, if we set wavelegths of the workig group as wavelegths of the protectio group as λ ad λ 5. elated work Other aalyses of SONET etworks iclude aalyses of rigs with DCS (Digital CrossCoects) [0], itercoected rigs [], combiatios of SONET ad WDM rigs [] [] [3], SONET ad ATM etworks [], traffic groomig computatios [5], desig problems [6], compariso of service restoratio times [7], ad aalysis of the Automatic Protectio Switchig (APS) protocol [8]. efereces [] T-H. Wu ad. C. Lau, A Class of Self-Healig ig Architectures for SONET Network Appli- 0 λ ad λ compariso with previous aalysis, we make a followig assumptio: for oe fiber, the we should set for the other fiber. To make a cosistet throughput k = λ i where k = i = 0 umberofwavelegthssupportieachfiber EQ(3) For ormal flow, the OPN with two fiber DWDM rig will support the same amout of throughput as a -fiber BLS or SP ig case regardless of the traffic patter because all the demads ca be carried o differet umber of workig wavelegths. For example, for the mesh traffic patter T OPN = 8 ( ) ( ----------------- + ) : E; demad: NS 8 ( ---------------- ) : E; demad: S 8 ( ----------------- + ) : O; demad: D/C EQ() After a cable cut, etwork throughput remais same by usig uused protectio wavelegths. From Fig. 5, after a cable cut, the trasmitter from OPN to cotiues sedig traffic o the workig wavelegths λ, λ, λ k. After wrappig occurs, the receiver at OPN seds theses traffic o the protectio wavelegths i a ier rig ( ) from OPN to OPN 5. At OPN 5, OPN ad OPN 3, those wavelegths bypass the electroic layer ad the trasmit to OPN. Similar restoratio method occurs at OPN. Oe more thig to otice is that we ca use path-level protectio to avoid loop-backs i adjacet ode switchig. λ, λ, λ k
Outer ig => Workig wavelegths: λ λ Kλ Ier ig => Workig wavelegths: λ, k, K k λ k + Protectio wavelegths: λ k, Kλ k + Protectio wavelegths: λ, λkλk OPN 5 OPN TX X X X TX OPN λ λ L, WDM MX/DMX λ k T F Q T T F Q T Access Packet Processor: Forwardig, Queueig WDM MX/DMX λ λ L, λ k λ, λ Lλ k Access k * k λ Photoic Switch λ λ L, λ k OPN OPN 3 Optical Packet Node Fig. 5 -Fiber Optical Packet Node ig catios, IEEE Tras. o Commuicatios, vol. 0, o., pp. 76-756, Nov. 99. [] D. Tsiag, G. Suwala, The Cisco SP MAC Layer Protocol, IETF FC89, Aug. 000. [3] J. Aderso Optical Flow Networkig: A New Architecture for IP Over ecofigurable WDM, NFOEC 00 Techical Proceedigs, July 00 [] B. E. Smith, C. Yackle, SONET Bidirectioal ig Capacity Aalysis: A Pragmatic View, Proc. of IEEE ICC 9, vol., pp. 89-93. [5] J. V. Drake, A eview of the Four Major SONET/SDH igs, Proc. of IEEE ICC93, vol., pp. 878-88, Geeva, 3-6, May 993. [6] Y-C Chig ad H. S. Say, SONET Implemetatio, IEEE Commuicatios Magazie, vol. 3, o. 9, pp. 3-0, Sept. 993. [7] I. Haque, W. Kremer, ad K. aychaudhuri, Self-Healig igs i a Sychroous Eviromet, appeared i SONET/SDH A Sourcebook of Sychroous Networkig, Ed. C. A. Siller ad M. Shafi, IEEE Press, 996, pp. 3-39. [8] A. Leo Garcia, I. Widjaja, Commuicatio Networks, McGraw Hill, 999. [9]. Ballart, Y.-C. Chig, SONET: Now s it the Stadard Optical Network, appeared i SONET/ SDH A Sourcebook of Sychroous Networkig, Ed. C. A. Siller ad M. Shafi, IEEE Press, 996, pp. 9-7. [0]. D. Doverspike, J. A. Morga, ad W. Lelad, Network Desig Sesitivity Studies for Use of Digital Cross-Coect Systems i Survivable Network Architectures, IEEE JSAC, vol., o., pp. 69-78, Ja. 99. []. D. Doverspike, S. Philips ad J.. Westbrook, Future Trasport Network Architectures, IEEE Commuicatios Magazie, vol. 37, o. 8, pp. 96-0, Aug. 999. [] X-Y Li ad P-J. Wa, ad W. Liu, Select Lie Speeds for Sigle-Hub SONET/WDM ig Networks, Proc. of IEEE ICC, year?
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