Enhancing MPLS QoS routing algorithms by using the Network Protection Degree paradigm. *

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1 Enhancng MPLS QoS routng algorthms by usng the Networ Protecton Degree paradgm. * Euseb Calle, Jose L Marzo, Anna Urra, Pere Vla Broadband Comm. and Dstrbuted Systems Insttut d Informàtca aplcacons (IA) Unverstat de Grona, 77 Grona, SPAIN e-mal: {euseb, marzo, aurra, perev}@ea.udg.es Abstract- IP based networs stll do not have the requred degree of relablty requred by new multmeda servces, achevng such relablty wll be crucal n the success or falure of the new Internet generaton. Most of exstng schemes for QoS routng do not tae nto consderaton parameters concernng the qualty of the protecton, such as pacet loss or restoraton tme. In ths paper, we defne a new paradgm to develop new protecton strateges for buldng relable MPLS networs, based on what we have called the Networ Protecton Degree (NPD). Ths NPD conssts of an a pror evaluaton, the Falure Sensblty Degree (FSD), whch provdes the falure probablty and an a posteror evaluaton, the Falure Impact Degree (FID), to determne the mpact on the networ n case of falure. Havng mathematcal formulated these components, we pont out the most relevant components. Expermental results demonstrate the benefts of the utlzaton of the NPD, when used to enhance some current QoS routng algorthms to offer a certan degree of protecton. I. INTRODUCTION New networ technology enables ncreasngly hgher volumes of nformaton to be carred. Varous dfferent types of msson-crtcal, hgher-prorty traffc are now transported over these networs. In ths scenaro, when offerng better qualty of servce, the consequences of a fault n a ln or node become more pronounced. A new concept of qualty of protecton s requred. Networ relablty can be provded through dfferent fault management mechansms appled at dfferent networ levels and tme scales. Although most concepts and methods dscussed n ths paper are applcable to dfferent networ technologes, whch mplement the logcal path paradgm, our wor focuses manly on MultProtocol Label Swtchng (MPLS) networs. MPLS fault restoraton mechansms usually establsh bacup Label Swtch Paths (LSPs). Wth these bacups, traffc can always be re-routed when a falure occurs. MPLS also provdes sutable fault detecton and fault recovery actuaton, whch allow effectve utlzaton of bacup paths. ([], [2] and [7]). A crucal aspect n the development of a fault management system s the creaton and routng of bacup paths. Several schemes have been proposed ([3], [4], and [5]) for routng new LSPs whch guarantee certan QoS parameters (such as resource utlzaton or mnmzng the request rejecton rato). However, most of these schemes do not tae nto consderaton other aspects, such as networ falure probablty, or parameters concernng the qualty of the protecton, such as pacet loss or restoraton tme. We wll dscuss networ protecton, nvolvng the creaton of fast and sutable recovery mechansms, n the context of these parameters and whch of them have most nfluence. Wth ths am we propose new concepts for calculatng a Networ Protecton Degree (NPD), such as the Falure Sensblty Degree (FSD) or the Falure Impact Degree (FID). A mathematcal formalzaton s developed for each concept and several experments are presented to support these formulatons. Ths paper s organzed as follows: n Secton II, the new Networ Protecton Degree concept s presented and formalzed. In Secton III and IV, the formulatons, supported by experments are dscussed. Fnal Secton summarzes and concludes the paper. II. NETWORK PROTECTION DEGREE In ths secton, we analyze the man components whch defne the Networ Protecton Degree (NPD). There are two man components of NPD: the Falure Senstvty Degree (FSD) and the Falure Impact Degree (FID). The FSD concerns the statstcal analyss of networ falure (ths s an a pror analyss). On the other hand, the FID evaluates the mpact on the networ when the falure occurs (ths s an a posteror analyss). In ths wor, FID s expressed n terms of well-nown parameters such as pacet loss and recovery tme. * Ths wor has been partally supported by Specal Acton (Spansh Mnstry Scence and Technology)TIC22-5-E. GLOBECOM /3/$7. 23 IEEE Authorzed lcensed use lmted to: UNIVERSITAT DE GIRONA. Downloaded on September 7, 29 at 4:39 from IEEE Xplore. Restrctons apply.

2 In a real networ, several technologes coexst: dfferent wrng (or dfferent physcal layers) and dfferent types of nodes (dfferent provders, old and new equpment, etc.) all worng together. Ths means that the actual probablty of falure of any one of these elements s sgnfcantly dfferent from any of the others. Although t s mpossble n practce to determne whch partcular segment n a networ wll fal and when, the probablty of falure can be calculated. A networ operator can apply predcton technques based on fault statstcs. Eventually, a probablty of falure can be explctly assgned, manually, n order to decde upon a specfc degree of protecton. We wll refer to ths probablty as Ln Falure Probablty (LFP). In case of a new segment beng set up, where there s no nowledge concernng falures, a hgh value LFP would ntally be assgned. After a certan amount of normal functonng (no faults) a set of statstcal nformaton s obtaned and the ntal LFP can be updated (hopefully decreased) to a more realstc value. The mechansms and methods for computng all the falure probabltes (LFPs) n a networ are beyond the scope of ths wor. In the wor we present here, we assume that nowledge of these probabltes s already nown or readly avalable. Moreover, although ther values may vary n tme, ths nformaton s assumed to be stable. A way to evaluate the FSD would be a useful tool for networ provders, helpng them to set the desred degree of protecton for ther customers and allowng them to guarantee QoS n terms of relablty and avalablty (dependng on the SLA - Servce Level Agreement). In secton 2. we dscuss usng ths nformaton for calculatng the sensblty to falure of an LSP. On the other hand, the mpact to the networ n the event of ths path falng can be evaluated n terms of recovery delay and pacet loss. The term Recovery Delay (T REC ) s defned as the perod of tme between the fault and the traffc restoraton to the correspondng bacup path. Pacet Loss (P LS ) s defned as the total lost pacets durng the T REC. Therefore, the Falure Impact Degree (FID) s calculated based on T REC and P LS. In the followng sectons, a method for calculatng FID and a study of the crucal factors when usng bacup protecton mechansms are presented. Ths provdes us wth a good nowledge about the segments of the networ whch are the most crtcal n case of falure. 2. Falure Sensblty Degree The Falure Sensblty Degree (FSD) expresses the total probablty of falure of the networ. LSPs can cross through dfferent lns each wth ts own Ln Falure Probablty (LFP). Therefore, we assume n ths wor that all LFP s are nown (by calculaton or heurstcally) and they are also ndependent of each other. These values are normally very small; we assume that LFP<<. A LSP fals f any segment (.e., an ndvdual ln or a combnaton of nodes and lns) along the path fals. However, t s easer to evaluate the nverse probablty,.e., the probablty that all the lns nvolved wor fne. Let consder the nverse probablty of ln falure as LFP -., (.e. the probablty that the ln wors fne). Therefore, the overall (LSP) probablty of no-falure (the nverse of a LSP falure probablty LSP_FP) s: LSP _ FP LFP ( LFP Number of lns of the LSP () By smplfyng all products and powers of LFP (as they are very small values by hypothess) the product of ths term s transformed nto the followng: LSP _ FP Number of lns of the LSP (2) But agan, the LSP Falure Probablty can be calculated as the nverse of LSP_FP -, therefore: LSP_ FP LSP_ FP Number of lns of the LSP (3) As expected, the total probablty of falure of a LSP can be approxmated by the sum of ln falure probabltes. It s also useful to assgn a bnary value to each segment to now whenever a ln should be protected. Ths s defned as the Ln Protecton Requrements (LPR). Ths can be easly obtaned by assgn LPR to those lns wth LFP and LPR wth LFP >. Ths allows us an easy calculaton of the total LSP Number of Lns to Protect (LSP_NLP). Hence, LSP_NLP s calculated as: Number of lns of the LSP (4) In consequence, FSD can be defned as an array of the Falure Probablty of all current LSPs (LSP_FP) n the networ (formula (5)), or as an array Number of Lns to be Protected per LSP (LSP_NLP) (formula (6)). FSD_FP (LSP_FP, LSP_FP 2, LSP_FP N ) (5) FSD_NLP (LSP_NLP, LSP_NLP 2, LSP_NLP N ) (6) Where: N Number of LSPs n the networ ( LFP ) LFP LSP _ NLP ( LPR LFP) LFP ) GLOBECOM /3/$7. 23 IEEE Authorzed lcensed use lmted to: UNIVERSITAT DE GIRONA. Downloaded on September 7, 29 at 4:39 from IEEE Xplore. Restrctons apply.

3 These arrays allow defnng dfferent strateges to evaluate the FSD. Wth (5) the number of LSPs out of an specfc LSP_FP can be computed. Wth (6) we can determne, not only a falure probablty expressed on the average of the number of lns to be protected per LSP, but the protecton requrements (number of lns wth bacup requrements). In secton IV several experments to evaluate ths second opton are carred out. 2.2 Falure Impact Degree (FID) In ths Secton, we show how we calculate the Falure Impact Degree (FID). As mentoned above, ths metrc concerns delays and pacet loss n case of falure. Let us start wth delays. It s well nown that any protecton mechansm based on the establshment of bacup paths follows a set of steps for recoverng faults. Each step needs a certan amount of tme,.e., the Recovery Delay (Tme of Recovery T REC ), to carry on wth the correspondng functons. Ths tme conssts of the followng: Tme for detectng the fault T DET (for nstance a sgnal from lower levels). Notfcaton tme T NOT to nform (.e, send a message to) the node responsble for swtchover. Tme for bacup setup, routng and sgnalng T BE. Tme for traffc swtchover T SW, from actve path to bacup path. Therefore, the T REC can be evaluated by smple addton, as the followng expresson shows: T REC T DET + T NOT + T BE + T SW (7) The Pacet Loss (P LS ) s proportonal to ths T REC and to the transmsson Rate R TR [8]. The pacet loss n the faulty ln (P FL ), that s to say, the pacets lost when the ln that was carryng them faled, should also be added to the equaton. The resultng expresson s: P LS R TR * T REC + P FL (8) Therefore, t can be sad that the Falure Impact Degree s a functon, g, whch depends on the pacet loss and recovery tme: FID g (T REC, P LS ) (9) Fg shows the most common used MPLS protecton methods (global and local bacups). The advantages and dsadvantages of these, and other, mechansms are wdely dscussed n the lterature [], [2],and [3]. In our prevous wor [6], and [7], Pacet Loss and Recovery Delay are consdered as well as pacet reorderng and resource consumpton. Bascally, Local Bacups offers a soluton respect to Pacet Loss and Recovery Tme problems of the Global Bacup. Nevertheless, when the number of lns to protect n the path s elevated Local Bacups are not sutable, due to elevated resource consumpton. In order to formulate FID for each protecton method we have assumed the followng smplfcatons: Ingress node Node Global Bacup path Worng path D (,a) Node a Local Bacup Node b Fg.. Global and Local LSP Bacup Paths. Egress Node Node e ) The fault detecton tme, T DET, depends on several factors (such as the level of the networ where the fault s detected, or the performance of the swtch components). However, these aspects affect all protecton mechansms equally. Moreover, the swtchover tme, T SW, s neglgble wth respect to the notfcaton tme, T NOT, and to the bacup establshment tme, T BE. For the purpose of smplfcaton, they have not been consdered n FID formulaton. 2) Most of currently proposals consder nevtable the pacet loss at the faled ln P FL. However, there are some recent approaches that propose the utlzatons of bufferng and taggng technques to avod such loss [9]. Whether or not these technques are used, n both cases pacet loss s stll neglgble n relaton to the total amount of pacet loss, hence they are not consdered n ths wor 3) The most sgnfcant elements, n terms of delay, of Pacet Loss and the Recovery Delay (dervng from (4) and (5)) are the notfcaton tme, T NOT, and the bacup establshment tme, T BE. However, further analyss of T BE mples a better analyss of the dverse routng algorthms because T BE s proportonal to the tme needed to get a new route. The frst element to loo at s T NOT.. T NOT s proportonal to the propagaton tme for the message, T PR, and the dstance from the node where the fault s detected (a-node) to the responsble of the swtchover (-node) (see fg. ). Although ths dstance, D(,a), should be expressed n a real metrc (meters, Km, etc.), D(,a) s n fact expressed n terms of the number of hops for the purposes of smplfcaton. Therefore, the calculaton for fault notfcaton s: T NOT D(,a) * T PR () Then, the FID s obtaned usng (7),(8) and (9): FID f ( D(,a) * T PR, D(,a) * T PR * R TR ) (2) As expected, pacet loss s proportonal to the restoraton tme whch depends on dstance (D(,a) as defned) and on the propagaton tme T PR.. In concluson, the greater the dstance, (or, the greater the propagaton tme), the worse the mpact of a falure s. Reducng the propagaton tme of the fault notfcaton would reduce the mpact. Unfortunately ths depends on the physcal topology whch s, for a gven networ, a statc GLOBECOM /3/$7. 23 IEEE Authorzed lcensed use lmted to: UNIVERSITAT DE GIRONA. Downloaded on September 7, 29 at 4:39 from IEEE Xplore. Restrctons apply.

4 parameter, and therefore dffcult to modfy. Thus, any effort to mnmze the mpact of falure should be amed at tryng to reduce the dstance from the node where the fault occurs and the node, whch carres out the swtchover. III. NETWORK PROTECTION DEGREE APPLICATION. In the prevous secton, we showed how we calculated the two components to evaluate the Networ Protecton Degree, NPD: the Falure Sensblty Degree, FSD (an a pror component) and the Falure Impact Degree, FID (an a posteror component). The protecton Degree can be expressed as a functon, f, of these two components: NPD f (FSD, FID) (3) We beleve NPD wll allow developers to create new or mprove current QoS routng strateges. In [4] some QoS routng algorthms are defned and analyzed, such as Wdest Shortest Path (WSP) or Shortest Wdest Path (SWP). Both are based on resource optmzaton and load balancng. Recently, more complex approaches have appeared. [5], and [6], focused on resource optmzaton and the mnmzaton of rejected requests. However, most of these algorthms do not consder networ protecton, at least not as a prorty. By usng the calculaton of NPD, some of these methods can easly be enhanced. For nstance, n order to enhance WSP we propose three new routng algorthms to add certan protecton parameters n the route selecton. Twce of them taes n consderaton FSD formulaton explaned n secton 2., n order to acheve LSPs wth less falure probablty and protecton requrements. Wth the am of consderng the FID another routng algorthm ntegratng falure probabltes and dstances (D(,a)) has been developed. In all these algorthms a pre-computaton of a -WSP algorthm s developed. Over the set of possble LSPs dfferent protecton strateges are appled: ) PWSP_FP, Protected WSP consderng the Falure Probabltes; the LSP wth the lowest falure probablty LSP_FP s selected. S S D S2 S D D4 Fg 2. Networ Topology 2 D ) PWSP_NLP, Protected WSP consderng the Number of Lns to Protect;. the LSP wth the lowest Number of LSPs (LSP_NLP) s selected. 3) PWSP_FPD, Protected WSP consderng the Falure Probabltes and Dstances (D(,a). In ths case, the objectve s to reduce not only the falure probablty, but the falure mpact (mnmzng the dstance D(,a), as explaned n secton 2.2). Each ln of a LSP s weghted by the product of the dstance D(,a) by the LFP. Wth the total sum of these values, the LSP wth the lowest value s selected. For all these algorthms, f there are several such paths wth the same characterstcs, one of them s randomly selected. IV. EXPERIMENTAL CALCULATION OF NPD. In ths secton, the NPD s evaluated n two networ scenaros. For these experments we used the same topology, (see Fg. 2), as n several other studes such as [5], or [6]. The capacty of the lns s 2 and 48 (bolded lnes) unts. But these capactes are scaled by, n order to experment wth thousand of LSPs. Each ln s bdrectonal (.e., t acts le two undrectonal lns of half of that capacty). There are 5 nodes and 28 lns. There are four Ingress-Egress node pars (see fg.2). Ln Falure Probabltes (LFPs) are assgned accordng to fgure 2. There are lns to be protected, whch represents a 4.7 percent of the networ. In all smulaton experments descrbed n ths paper, LSP requests arrved randomly, at the same average rate for all node pars. We assume that all lns are long lve (.e., statc case ). For each experment, 2 trals wth 3 LSP demands were conducted. The bandwdth allocaton for the LSPs s unformly dstrbuted between, 2 and 3 unts. Results have been obtaned by mplementng the QoS routng algorthm proposed n prevous secton. Case a: Number of lns to be protected: fgure 3.a) shows an analyss of the average of the number of lns to be protected (NLP) per LSP. Charts show that all routng schemes wth protecton (PWSP algorthms) have smlar NLP results. In the case of applyng a WSP, the NLP per LSP sharply ncreases (about 35 % more). Ths leads us to state that: a) WSP routng ncreases the probablty of falure (due to a major number of lns wth a certan falure probablty), and b) t ncreases the resource consumpton f these lns are protected wth bacups. Case b: Falure mpact degree: In ths case we have analyzed the reducton n the FID, based on dstance (D(,a)). Fg 3.b) shows the dstrbuton of LSPs wth lns to be protected at dfferent dstances. Results, as expected, GLOBECOM /3/$7. 23 IEEE Authorzed lcensed use lmted to: UNIVERSITAT DE GIRONA. Downloaded on September 7, 29 at 4:39 from IEEE Xplore. Restrctons apply.

5 NLP per LSP Number of LSP (N) a) Tral Number b) Dstance 8,8 Number of LSP (N) c) Tral Number Request Rejecton Rato,6,4,2,,8, d) Tral Number WSP PWSP_NLP PWSP_FP PWSP_FPD Fg. 3. a) Number of lns to be protected. b) Falure mpact Degree Analyss. c) Falure mpact Degree Analyss. d) Request Rejecton Raton shows that PWSP_FPD has the best performance, allocatng the major number of lns to be protected at dstance. Agan, WSP shows the worst behavor dstrbutng a bg number of lns to be protected at dstances D(,a)>. Case c: Optmzng the Networ Falure Degree: Fg. 3 shows the number of LSPs out of a pre-set NPD threshold. The NPD (formula [3]) s evaluated n terms of notfcaton dstances (formula [2]) gvng the FID value and falure probabltes (formula [5]) to evaluate the FSD. We have computed those LSPs wth dstances D(,a)> (large FID) and LSP_FP>2-4 (large FSD). In ths case the best opton, once agan, s the PWSP_FPD. However PWSP_NLP and PWSP_FP shows a smlar protecton degree better than the WSP. Case d: Request Rejecton Rato: Cases A, B and C have demonstrated that PWSP mproves the NPD, expressed by the FSD and the FID. However t s mportant to remar that these algorthms do not deterorate the number of requests accepted. Fgure 3.d) shows that all these algorthms eep a Request Rejecton Degree over -5%. Although, n ths case, the best performance s offered by the WSP. CONCLUSIONS In ths paper, we have proposed a new mechansm for evaluatng the Networ Protecton Degree (NPD), whch has two components: the Falure Sensblty Degree (FSD) and the Falure Impact Degree (FID). Experments have demonstrated the benefts of NPD applcaton when used to mprove the well-nown routng algorthm WSP, whch has been enhanced becomng a Protected WSP, PWSP n our study. Ths leads to a reducton n the FSD and FID, n terms of a reducton n the number of protected lns (NPL) and ts probablty of falure. Besdes reducng the NPL, the resource consumpton when usng local bacups s reduced. PWSP algorthms also reduce the mpact n case of falure by decreasng the number of LSPs wth crtcal (large) dstances D(, a) and falure probabltes. In short, the presented formalzaton of the NPD paradgm should allow networ and servce provders to apply better QoS routng strateges that wll mprove the relablty of ther networs. REFERENCES [] Changcheng Huang, Vshal Sharma, Ken Owens, Srnvas Maam, "Buldng relable MPLS Networs usng a path protecton mechansm", IEEE Communcatons Magazne, Mar 22 [2] D. Hasn, R. Krshnan "A Method for Settng an Alternatve Label Swtched Paths to Handle Fast Reroute". (Wor n progress) Internet Draft. Nov 2. [3] R. Guern, D. Wllams, A. Orda. QoS Routng Mechansms and OSPF Extensons. Proceedngs of IEEE Globecom 997. [4] M. Kodalam, T.Lashman. "Mnmum Interference Routng wth Applcatons to MPLS Traffc Engneerng". IEEE Infocom 2. [5] S. Subhash, M. Waldvogel, P. Warhede. "Profle-Based Routng: A New Framewor for MPLS Traffc Engneerng". QofIS'. [6] J. L. Marzo, E.Calle, C. Scoglo, T. Anjal "Addng QoS Protecton n Order to Enhance MPLS QoS Routng". To appear n ICC 23. [7] J. L Marzo, E. Calle, C. Scoglo, T. Anjal "QoS On-Lne Routng and MPLS Multlevel Protecton: a Survey" to appear n IEEE Communcatons Magazne, October 23. [8] L. Hundessa, J. Domngo-Pascual Relable and Fast Reroutng Mechansms for a Protected Label Swtched Path Proceedngs of Globecom 22. GLOBECOM /3/$7. 23 IEEE Authorzed lcensed use lmted to: UNIVERSITAT DE GIRONA. Downloaded on September 7, 29 at 4:39 from IEEE Xplore. Restrctons apply.