Fast Restoration Signaling in Optical Networks

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1 Fas Resoraion Signaling in Opical Neworks Radim Baroš and Swapnil Bhaia Deparmen of Compuer Science Universiy of New Hampshire Durham, NH 84, USA rbaros, ABSTRACT As WANs coninue o form he framework for deploying mission-criical applicaions, he need for faul resilience and fas resoraion assumes greaer imporance. This paper examines exising schemes for fas resoraion signaling in a wavelengh-roued opical core and inroduces an improved signaling scheme based on Opical Burs Swiching and Jus-Enough-Time pah esablishmen. Scaling experimens show ha he proposed scheme ouperforms exising schemes. KEYWORDS Opical Burs Swiching, Resoraion, Signaling. 1 Inroducion Over he years, large scale daa neworks have undergone significan change no only wih respec o he volume and naure of he raffic hey carry bu also in regard o he criicaliy of heir role, and he level of service demanded of hem. WANs have evolved from simple, bes-effor and specialized daa neworks used by a few, ino complex, heerogenous, muli-layered, all-pervasive backbones guaraneeing an array of criical services o a global user populaion. Opical neworks, wih heir erabi-wide links and cu-hrough, wavelengh-roued archiecure, seem wellsuied o implemen unified and homogenous, ye mulipurpose neworks o address he diverse daa ranspor needs of he fuure. In such a scenario, since opical neworks would provide all he services currenly provided by separae neworks, he issue of reliabiliy and availabiliy becomes all he more criical. Moreover, in mos applicaions, he unified ranspor nework may be he only resource driving a user s business. Therefore, nework downime, no maer how small, may enail significan losses for he user. This paper proposes a new scheme for fas signaling for resoraion, based on Opical Burs Swiching (OBS, a unique, emerging paradigm for opical nework design [1]. The paper discusses various issues involved in implemening fas resoraion signaling in backbone ranspor neworks. Exising schemes are described and a new scheme for resoraion signaling is hen proposed. Experimens o evaluae This research was suppored in par by NSF-ARI gran No Corresponding auhor. he proposed scheme are described followed by a discussion of he resuls. Background Efficien resource allocaion has been a he cener of much of he recen work in he area of resoraion. As challenging as his problem may be, i is no he focus of our work. This paper addresses he problem of measuring and comparing he delay inheren o he signaling schemes currenly used for lighpah seup. We assume ha a pah wih sufficien resources has been found and he only ask remaining is o reserve i. We proceed by making he following assumpions abou he nework. A cu-hrough, all-opical (i.e., no inermediae o-e-o conversion wavelengh-rouednework (WRN is primarily 1 composed of fiber-links connecing nodes which conain opical swiching elemens such as Opical Add/Drop Muliplexers (OADMs and Opical Cross Connecs (OXCs []. The all-opical naure of he signal pah allows he nework o be ransparen and makes i ideal for use as a raw, high-bandwidh Opical Transpor Nework (OTN. A lower bandwidh IP nework, known as he Daa Communicaion Nework (DCN serves as a conrol plane o he OTN and is primarily used for exchange of signaling messages [, 4]. A DCN node conrols an OXC in he OTN and can insruc he OXC o execue a paricular cross-connec operaion. When a lighpah reques arrives a he, i compues a primary pah o he node and using a signaling scheme, ses up he lighpah by exchanging messages wih oher conrolling DCN nodes. Once he pah has been se up compleely, he node forwards incoming raffic ono i. When a faul occurs, he flow of raffic o he sops and he raffic sream is subjeced o heavy packe-loss. In his siuaion, raffic delivery o he node needs o be resumed as quickly as possible [5] in order o minimize packe-loss. We shall focus on single or muliple link or node failures in he OTN. We assume he OTN o be - node conneced and he DCN o be faul-free and reliable. 1 An all-opical WRN consiss of a plehora of oher devices as well, bu none of hese are perinen from he perspecive of he curren discussion. A node failure can be modeled as a muliple link failure. The DCN can be proeced using 1+1 proecion swiching as discussed in [4].

2 .1 Curren Schemes We shall look a wo differen schemes ha are currenly used for acivaion of he alernae pah. The firs one is implemened by exensions o he RSVP proocol [6] while he second one can be implemened using plain IP or oher sandard signaling schemes such as GMPLS [4]. The following subsecions discuss each scheme and derive average ime esimaes o complee each phase of he resoraion process from deecion o raffic-swiching. Term! "# " $" %&' $!" ( $ *+",.- // " Descripion hop disance from o node upsream o failed link, (nodes in OTN lengh of working pah, (nodes in OTN lengh of alernae pah, (nodes in OTN diameer of DCN, (nodes lengh of fiber link beween adjacen OTN nodes, (miles speed of opical signal propagaion hrough he OTN fiber links, (miles/second ime by which he daa burs mus lag conrol header, (seconds ime o decide Loss Of Ligh, (5 ms propagaion delay per link in DCN, (8 s/mile processing delay per node in DCN, ( ms ime o decide link failure, (seconds ime o resore raffic, (seconds faul indicaion signaling delay, (seconds ime o seup alernae pah, (seconds ime o swich raffic from working pah o alernae pah, (1 ms ime o perform a cross-connec operaion (1 ms Table 1. Terms and values used in analysis and experimens as suggesed in [4].. Preliminary Definiions Please refer o Table 1 for a descripion of he erminology. Before we delve ino esimaing he delay for each scheme, we shall define he delay for a pah. If and ;: 4<5#98 is he delay incurred due o a message ravelling hops hrough he DCN and he OTN respecively, hen: =;4 5#98>?A@B5 CD;EFC 8 EFDD (1 : 4 ( We shall follow he discussion in [] and calculae he resoraion delay as conribued by each phase of resora- raffic Figure 1. scheme. FIS ion. Hence: HIHIH JIJIJ HIHIH JIJIJ FIS KIKIK KIKIK LIL LIL faul UIUIU VIV UIUIU VIV dropped primary pah secondary pah The RSVP/Backup Tunnel serial resoraion $" > "# " EW %X& ' EF $" ( EW $ *+",. RSVP/Backup Tunnels Figure 1 illusraes he RSVP/Backup Tunnel resoraion scheme. This resoraion scheme is based on he MPLS proecion scheme inroduced in [6]. In his approach, he failed headend 4 informs he node (which is hops away from i abou he failure hrough a FIS message. The node ses up he alernae pah by sending a reques o he firs node on i. Each node forwards he reques downsream wihou acually waiing o complee he cross connec. The node reurns an acknowledgemen which ravels he same roue upsream. Each node forwards i (upsream as is, wih a posiive acknowledgemen in i if he cross connec a is sie was successfully compleed. If no, i pus a negaive acknowledgemen. When he acknowledgemen reaches he, i knows if he pah is seup by examining he ype (posiive or negaive of he acknowledgemen. The ime required o complee each phase of he resoraion process is as follows:! "# "=> (4 %X& ' =;4 5 Y8 (5 $" ( =;4 5 Y8 (6 $" > Y8 E Z^@ X@B465_ 98 È $ *+",.4 Acivaion Archiecure Figure illusraes he Acivaion archiecure discussed in [4]. In his approach, as soon as a failure occurs, nodes downsream o he failed headend sense a loss of ligh. The node among hese nodes, on sensing LOL, mulicass an alernae pah seup message o each node on he alernae pah. The message also conains he address of he node upsream o he node o which he message is sen. On receiving such a message a node on he alernae pah exracs he address of is upsream neighbor from i and exchanges wavelengh and por informaion 4 The node immediaely upsream o he failed link. ( (

3 raffic primary pah faul dropped secondary pah raffic Cnrl 1 Cnrl faul Burs Cnrl Cnrl primary pah secondary pah 8 Figure. OBS acivaion archiecure. Figure. The parallel acivaion archiecure. wih i. Afer his, each node ses up is cross connecs and a complee alernae ligh-pah is esablished. The ime required o complee each phase of he resoraion process is as follows: "# " > (8 %X& ' >? : 4 5# 8 (9 $" ( >[Z\@. =465_ 98 (1 $" > E : 4 5_ 8 E =;4 5_ 98 E $ *+", Proposed OBS-based Scheme (11 Opical Burs Swiching is a recen paradigm for opical nework design. In OBS, a conrol packe is firs sen o reserve bandwidh and configure swiches along he pah, followed by a burs of daa wihou waiing for an acknowledgemen of he connecion esablishmen [1]. OBS hus belongs o he family of ell-and-go, one-way reservaion proocols. OBS allows he daa burs o be fairly large (order of megabyes hus reducing overhead and can allow use of ou-of-band signaling for ransmission of conrol packe. OBS relies on he he Jus-Enough-Time proocol for is operaion. When a burs needs o be sen, he ransmiing end calculaes he ime required by he conrol packe o reach he farhes node on he pah. I hen ransmis he conrol packe and afer waiing for ime, sends he daa burs. This allows jus enough ime for he swiches along he pah o configure hemselves so ha he following daa burs is roued correcly o he desinaion. We now propose wo alernae pah acivaion schemes based on OBS..1 Fas reroue wih serial OBS acivaion Figure illusraes our proposed scheme. The scheme is based on he Fas Re-roue scheme discussed in []. In his approach, he failed headend, upon sensing he failure, ries o seup an alernae pah iself. In he pah seup phase, he DCN headend consrucs an OBS conrol packe conaining informaion abou iming and wavelengh of he daa burs o follow. When is upsream neighbor receives he conrol packe, i exracs informaion abou he source of OTN!"! #"#!"! #"#!"! #"# $"$ %"% $"$ %"% DCN $"$ %"% O.... O for serial OBS-based aciva- Figure 4. Calculaing $" ( ion. 4 O O he following daa burs and iniiaes a cross-connec operaion in he OXC ha i conrols. I hen updaes he conrol packe wih burs informaion for he nex node and forwards i on. The forwards he conrol packe furher on downsream oward he hrough every node on he alernae pah. Thus, he whole pah is seup using he Jus Enough Time (JET burs swiching echnique. [8, 9, 1] sugges ha such a signaling scheme which couples daa burss in a high speed OTN and conrol packes in a slower DCN is indeed pracicable. Since he ransmiing node (i.e., he node immediaely upsream o he failed link does no wai for an acknowledgemen of pah seup before forwarding raffic on he alernae pah, he ime o seup he pah is significanly reduced. Moreover, he raffic sream can be resumed even before all he nodes on he pah have received he conrol packe, as long as i can be guaraneed ha he daa burs always lags behind he conrol packe. The ime required o complee each phase of he resoraion process is as follows:! "# "=> (1 %&' >'& (1 As shown in Figure, he alernae pah for his scheme begins a he failed-headend, goes hrough he and ends a he. Thus, as per he figure, if he se of nodes in he alernae pah is: ( >.-/1-41.@@.@51.-6 *,+,+,+ hen, order o guaranee ha he daa burs always follows he conrol packe, he following consrain (illusraed by Figure 4 needs o be saisfied: d

4 / / raffic 1 faul Cnrl Burs primary pah secondary pah 8 OTN O... O... O 1 O 1 1 d Figure 5. OBS acivaion archiecure. DCN 8 ( E where is he ime by which he daa burs is required o lag behind he conrol packe, is he ime aken by he burs o ravel o node hrough he OTN, and is he ime aken by he conrol packe o ravel o node hrough he DCN. Hence: $" > $" ( >X5 E X5 ( 8 (! 8 E $ *+", (14 (15. Fas Reroue wih OBS Acivaion In he serial OBS acivaion archiecure, roue seup signaling messages flow serially saring a he node upsream o he failure and along he re-roued alernae pah. However, his signaling scheme can be furher improved by combining i wih he parallel acivaion archiecure inroduced in [4]. Figure 5 illusraes our proposed scheme. In his hybrid signaling scheme, he node, mulicass separae OBS conrol packes o all he nodes on he alernae pah over he DCN in parallel. Real inerneworks are organized as ransi-sub hierarchical srucures [11]. As a resul, he hop disance beween a pair of nodes in an inernework such as he DCN does no grow linearly wih he geographical disance beween hem. Hence, he larges hop disance ha an OBS conrol packe is required o ravel before he daa burs can be ransmied will always be smaller in case of he parallel OBS scheme han in he serial OBS acivaion archiecure. This is refleced in he way $" ( is esimaed for he serial and parallel archiecures. For his scheme! "# " and!%x& ' remain same as in Eqn. (1 and Eqn. (1. From Figure 5, following an argumen similar o he one in he previous secion, we arrive a he same 5 expression for $" as Eqn. (15: $" > E X5 (! 8 E $ *+", (16 We now describe he experimens carried ou in order o compare he performance of he four schemes discussed above. 5 Here "$# sill represens DCN delay, bu unlike serial OBS acivaion, %'&(+*-, " #/.1 "$# does no necessarily hold for inerneworks in his case. Figure 6. Calculaing $" ( for parallel OBS-based acivaion. 4 Experimenal Evaluaion Experimenal measuremens were performed in order o sudy he effec of each of he acivaion schemes on he resoraion ime. An experimenal run consised of measuring he average resoraion ime using he esimaes calculaed above for each of he four acivaion schemes for a given OTN and DCN nework pair. Table 1 shows he ypical values of various parameers used in he calculaion of resoraion ime as suggesed in [4]. The Georgia Tech Inerne Topology Modeler (g-im was used in order o generae pure-random [11], undireced OTN and DCN graphs. The OTN graphs were generaed using he Fla Random Graph model provided by he gim whereas he Transi-Sub Graph model was used o represen DCN srucure [11, 1]. The g-im package offers ways o conrol he nework opology model, he number of nodes, he edge probabiliy, he node-link disribuion and he geographical nework size for he graphs generaed. In order o be represenaive of real neworks, he geographical sizes of he OTN and he DCN were always mainained equal. A mapping was developed from each node in he OTN o a unique node in he DCN o model is conroller. Using he geographical posiion informaion provided by g-im for each node in a graph, he mapping funcion ensured ha an OTN node was always mapped o he approximaely 6 neares DCN node. Furhermore, he lenghs of edges beween a pair of OTN nodes were hen se o he disance beween heir conrolling DCN nodes o ensure a sound model. The OTN generaed was always much smaller han he DCN in node-coun (excep in Experimen. Each daa poin was obained by running measuremens on ses of a leas en differen randomly generaed OTN/DCN pairs. Only -node conneced 6 18:9<; graphs were used as OTNs for any experimen. All possible shores pahs in an = 6 >?8@9A; -node OTN were considered o be primary pahs. All possible nodeand link-disjoin second-shores pahs in an = -node OTN were considered o be secondary or alernae pahs. Each 6 For each OTN node, he DCN node wih he smalles Euclidian disance from i was chosen. However, his sill does no guaranee he bes geographical superimposiion of he DCN on he OTN wih all disances minimized.

5 Resoraion ime (ms OBS -OBS DCN Size DCN Size (nodes Resoraion ime (ms OBS -OBS Number of pahs Number of pahs OTN Size (nodes Figure. Resoraion ime v/s OTN and DCN size (Edge probabiliy: DCN =.1, OTN = Alernae Pah Lengh (nodes Figure 8. Resoraion ime v/s alernae pah lengh (OTN size = 1 nodes, DCN size = 48 nodes; OTN edge probabiliy =.1 and ha of DCN =.19. daa poin represens he mean of he ime o resore raffic from a primary pah (shores pah o is node- and link-disjoin secondary (second-shores pah. The Sanford GraphBase [1] library was used for wriing rouines o perform measuremens. The Walrus Graph Visualizaion ool from CAIDA was used for visualizing graphs. 4.1 OTN and DCN Size In Experimen 1, DCN and OTN were expanded wo-fold 8 a every run. The pure-random model was used for generaing edges wih edge probabiliies. 9 and.1 for he OTN and DCN respecively. The average resoraion ime from all primary pahs o all secondary pahs in each randomly generaed OTN was measured for each of he four acivaion schemes. Figure shows he performance of each of he four acivaion schemes for differen sizes of he OTN and he size of he DCN (scaled down en-fold a which he measuremen was performed. As seen in he figure, he proposed serial and parallel OBS-based schemes ouperform heir non-obs counerpars. 4. Alernae Pah Lengh In Experimen, he OTN and DCN sizes were held consan. The resoraion ime for all alernae pah-lenghs was measured over a se of en random DCN/OTN pairs. The pure-random model was used for generaing edges wih edge probabiliies.1 and.19 and sizes fixed a 1 and 48 nodes for he OTN and he DCN respecively. Figure 8 shows he performance of each of he four schemes on varying pah lenghs, and he disribuion of pah lenghs hp:// 8 Since he DCN is a ransi-sub graph, he nodes in he DCN increased by a facor of. where is he number of nodes in a sub. 9 A relaively higher edge-probabiliy is required in order o guaranee -node connecedness using he g-im package. Resoraion ime (ms OBS OBS DCN-Links OTN-Links OTN & DCN size (nodes Figure 9. Resoraion ime v/s nework size (edge probabiliy of OTN =.4 and ha of DCN =.18. (scaled down en-fold in he OTN graphs on which he measuremens were performed. As seen from he resuls, OBS acivaion scheme scales beer han all he oher schemes as pah lengh increases. Similarly, parallel acivaion also scales well wih pah lengh bu performs worse han is OBS cousin. schemes hus benefi from he srucure of he DCN whereas serial schemes do no. 4. Nework Size In Experimen, he random DCN/OTN pairs were generaed wih boh conaining he same number of nodes. The nework size (i.e., sizes of boh he OTN and he DCN were doubled for every run and he resoraion ime for all possible pahs was measured for each of he four schemes. The pure-random model was used for generaing edges wih edge probabiliies se o.4 and.18 for he OTN Links

6 Resoraion ime (ms OBS -OBS DCN Links (conneciviy Figure 1. Resoraion ime v/s DCN conneciviy (OTN size = 1 nodes, DCN size = 56 nodes; edge probabiliy of OTN =.1. and DCN respecively. Figure 9 shows he resuls of Experimen. I shows he performance of each of he four schemes for varying nework size wih informaion abou he number of links in he OTN and DCN (scaled down en-fold in he OTN/DCN graphs on which measuremens were performed. As seen in Figure 9, parallel OBS acivaion scheme exhibis he bes performance as nework size increases, followed by plain parallel acivaion. 4.4 DCN Conneciviy In Experimen 4, he conneciviy of he DCN was gradually increased. The sizes of he OTN/DCN pairs generaed were held consan. The pure-random model was used for generaing edges wih edge probabiliies se o.1 for he OTN and varied for he DCN. A every run, he edge probabiliies for he DCN were doubled. As seen from Figure 1, parallel acivaion schemes exhibi sable scaling performance as compared o serial schemes. Again, OBSbased schemes ouperform heir non-obs counerpars. 5 Conclusion This paper focused on he delay inheren o various lighpah acivaion schemes using he novel [4] OTN-DCN model wih dissimilar daa and conrol laencies. Two exising schemes were discussed and wo varians of a new scheme were proposed. The four schemes were compared hrough experimens based on he ime-o-resore meric. Iniial resuls from he experimens confirm ha he proposed schemes offer lower seup delays hus minimizing packe loss during resoraion. The proposed schemes also exhibi resilien scaling behavior benefiing from he naural srucure of DCN inerneworks. Acknowledgemens The auhors would like o hank he reviewers for heir helpful commens and suggesions. References [1] C. Qiao, Opical Burs Swiching (OBS - A New Paradigm for an Opical Inerne, Journal of High Speed Neworks, vol. 8(1, pp , [] T. E. Sern and K. Bala, Muliwavelengh Opical Neworks: A Layered Approach. Addison Wesley Longman, [] G. P. Ausin, B. T. Doshi, C. J. Hun, R. Nagarajan, and M. A. Qureshi, Fas, Scalable, and Disribued Resoraion in General Mesh Opical Neworks, Bell Labs Technical Journal, vol. January-June, pp. 6 81, 1. [4] B. T. Doshi, S. Dravida, P. Harshavardhana, O. Hauser, and Y. Wang, Opical Nework Design and Resoraion, Bell Labs Technical Journal, vol. January-March, pp , [5] A. Gandhi and R. Baroš, Dynamic issues in MPLS service resoraion. Deparmen of Compuer Science, Universiy of New Hampshire Technical Repor TR 1-5, November 1. [6] K. Owens, V. Sharma, S. Makam, and C. Huang, A pah proecion/resoraion mechanism for MPLS neworks. Work in progress [draf-chang-mpls-pahproecion-.x], July 1. [] D. Haskin and R. Krishnan, A mehod for seing an alernaive label swiched pahs o handle fas reroue. Work in progress [draf-haskin-mpls-fasreroue-5.x], November. [8] G. Li, J. Yaes, D. Wang, and C. Kalmanek, Conrol Plane Design for Reliable Opical Neworks, IEEE Communicaions Magazine, vol. 4 No., pp. 9 96, February. [9] I. Baldine, G. N. Rouskas, H. G. Perros, and D. Sevenson, JumpSar: A Jus-In-Time Signaling Archiecure for WDM Burs-Swiched Neworks, IEEE Communicaions Magazine, vol. 4 No., pp. 8 89, February. [1] C. Qiao, Labeled Opical Burs Swiching for IP-Over-WDM Inegraion, IEEE Communicaions Magazine, vol. 1, pp. 4 4,. [11] K. Calver, M. Doar, and E. W. Zegura, Modeling Inerne Topology, IEEE Communicaions Magazine, June 199. [1] E. W. Zegura, K. Calver, and M. J. Donahoo, A Quaniaive Comparison of Graph-based Models for Inerne Topology, IEEE/ACM Transacions on Neworking, vol. 5, No. 6, December 199. [1] D. E. Knuh, The Sanford GraphBase: A Plaform for Combinaorial Compuing. ACM Press, 199.