An XML Model for SLA Definition with Key Indicators

Transcription

1 An XML Model for SLA Definiion wih Key Indicaors Emir Tokar, Guy ujolle, Edgard Jamhour, Manoel C. enna, Mauro Fonseca Universiy of aris VI, rue du Capiaine Sco, 755, aris. onifical Caholic Universiy of araná, UCR, GIA, Imaculada Conceição S. 55, 825-9, Curiiba, Brasil. {mauro.fonseca, jamhour, Absrac: This work proposes a XML-based model for defining service level agreemens (SLA). The model has XML elemens o define a semanic o represen key performance indicaors (KI) and key qualiy indicaors (KQI) and he relaionship beween hem. Upper and lower hresholds are associaed o he indicaors in order o indicae warnings or errors condiions. The relaionship beween he indicaors is expressed by reusable funcions which are evoked by he XML-based model. An example of reusable funcion for calculaing he KQI service availabiliy based on KI indicaors is also presened in his paper. Keywords: SLA, KI, KQI, XML.. Inroducion There have been a lo of research effors on Qualiy of Service (QoS) managemen in he las years. These works have been srongly influenced by he Inerne Engineering Task Force (IETF) specificaions, from he early definiion of managemen informaion for TC/I-based neworks o he definiion of a policy based managemen framework (RFC2753), including specificaions of inegraed service (InServ - RFC2475) and differeniaed service (DiffServ - RFC633). The relaed conceps are quie oriened o I infrasrucure managemen, and he underlying objecive is o manage he nework infrasrucure, addressing issues as conrol of admission condiions and packe raffic monioring. The ulimae goal is o assure he qualiy of informaion flow hrough I links. From a differen perspecive he objecive of QoS managemen can be seen as assuring he qualiy of delivered services. The focus is no on defining nework performance parameers bu on finding qualiy indicaors ha reflec a cusomerservice provider common undersanding of wha QoS is. Alhough he involved conceps are he same, hey are considered under a differen poin of view. Service Level Agreemen (SLA) provides he basis for QoS managemen according his second perspecive. I esablishes a wo-way accounabiliy for service ha is negoiaed and muually agreed upon by cusomer and service provider. An SLA defines a se of service level indicaors ha are no derived direcly from he nework

2 2 Emir Tokar, Guy ujolle, Edgard Jamhour, Manoel C. enna, Mauro Fonseca bu from a common view on wha service qualiy means for boh cusomer and service provider. This poin of view inends o align QoS wih business needs by seeking for service level indicaors ha reflecs in improvemen of business ransacions. However, when expressing QoS, service level indicaors mus reflec wha is delivered by a paricular nework making necessary a relaionship beween service level indicaors and nework performance parameers. Moreover, when provisioning I services wih qualiy guaranies, negoiaed service level mus be aken ino accoun, ha is, resources should be configured a nework level accordingly, in order o suppor QoS requiremens. The mapping from SLA needs o nework configuraion is usually done manually and is a difficul and error prone ask. Indeed, auomaic ranslaion of service level indicaors ino nework configuraion parameers is sill an open problem. I requires aking ino accoun proprieary procedures of specific nework elemens and he consrucion of a common semanic for muliple heerogeneous nework elemens across muli domain neworks. Beside of his, anoher issue is how o relae nework performance parameers wih service level indicaors. This mapping is no sraighforward because he firs evaluaes qualiy of flow from he nework perspecive while he second reflecs a negoiaed view of service qualiy. An SLA informaion model ha akes ino accoun his issue is needed ogeher wih he algorihms ha perform he necessary mapping. The main concern of his work is relaed wih mapping SLA indicaors wih nework performance parameers. One objecive is o presen a XML based SLA model ha uses Key Qualiy Indicaor (KQI) and Key erformance Indicaor (KI) conceps for specifying service level indicaors and nework performance parameers, respecively, which includes he necessary elemens o specify he ranslaion from KQI ino KI. The paper is srucured as follows. Secion wo presens some relaed works o he SLA modeling issue. Secion 3 describes he proposed model. Secion 4 presens a funcion for calculaion service availabiliy, illusraing he main conceps presened by he proposed model. Finally, he secion 5 presens he conclusions and poins o fuure developmens 2. Relaed Works Several indusrial and research works have been developed regarding Qualiy of Service (QoS) subjec, using he SLA (Service Level Agreemen) concep. Such a concep has been used for QoS managemen, including communicaion neworks and informaion echnology. This concep has been developed by several IETF conribuions [,2,3]. There are also proposals from several inernaional projecs, as presened below, and has been based on he EGEE publicaion [3], bu we have include some addiional works such as he proposals from he TMForum [4] and 3G [5]. The AQUILA [2] projec defined SLS (Service Level Specificaion) emplaes o sandardize he requess of QoS beween he cusomer and service provider, for he suppor of QoS in I neworks. The idea was o define SLS emplaes o simplify he

3 An XML Model for SLA Definiion wih Key Indicaors 3 process o ranslaing SLS definiions o device configuraions. In he AQUILA archiecure, a reservaion reques is sen by he so called "End-user Applicaion Toolki" (EAT) o he "Admission Conrol Agen" (ACA). The reservaion reques specifies he required resources and QoS level and provides he informaion needed o idenify he flow(s) o which he reservaion applies. Resources are managed by he "Resource Conrol Agen" (RCA). These feaures were defined by semanic conen of SLSs composed of he following aribues: SLS ype, Scope, Flow idenificaion, raffic descripion and conformance esing, erformance guaranees and Service schedule. One goal of he sandardizing SLS, was delivering emplaes of SLS avoiding misakes and complexiy in requess of QoS. The approach proposed was grouping I applicaions by similar QoS behavior and requiremens. This idea is similar o our model ha defines emplaes for key performance indicaors. The requess of QoS in AQUILA are a mixed of SLA and SLS conceps and he focus in he projec was defining SLS emplaes on he negoiaions beween clien and service provides. There is no common furher developmen of he whole sysem. The WSLA [6] is a XML-based web services SLA Language. This model owards web SLAs specificaion and monioring hrough Web Services echnology. The Web Service Level Agreemen language (WSLA) is defined as an XML Schema and covers he definiion of he involved paries, he services guaranees and he service descripion, i comprises he following major pars: paries, service definiion and obligaions. aries describes he paries involved in he managemen of he Web Services, including he signaory paries as well as he supporing paries ha are brough ino SLA o ac on behalf of service provider or cusomer. Service Definiions describe he services he WSLA is applied o, depiced he common undersanding of he conrac paries, in erms of operaions, service s parameers and merics. WSLA provides he abiliy o creae news merics defined as funcions over exising merics and his aggregaion is helpful o formalize requiremens expressed in erms of muliple QoS characerisics, neverheless i gives a SLA model o much generic. Finally, Obligaions defines he service level ha is guaraneed wih respec o SLAarameers defined in he service definiion. This relaion is similar o our relaion approach beween KI and JQI. The WSLA can be applied for iner-domains managemen in business-oriened scenarios for he processes and general applicaions. The CADENUS [7] projec considers a configuraion and provisioning inegraed soluion for end users QoS services. The Service/SLA Model uses specialized services classes and SLS models o compose a SLA. The SLOs (Service Level Objecives) are associaed wih classes: meric, QoS service and policy rules derived from CIM model. This projec is frequenly cied by oher works and projecs, however is no analyzed in [3]. The TEQUILA [8] projec addresses he modeling of DiffServ I neworks wih provisioning and admission conrol. The TEQUILA is focused in inra-domain conex where QoS-based I service offerings are deployed over he whole Inerne. This projec presens he DiffServ specificaion in a layered model and discuss opics like SLA and SLS, moreover, is define SLS emplae. The major aribues of SLS emplae are: Cusomer-userId{Idenifies he cusomer}; Flow descripor{acke sream (DSC, I addresses, ec)}; Service Scope{Geographical region (ingress egress)}; Service Schedule{Specifies when he conrac is applicable}; Traffic descripor{ Traffic envelope (e.g. a oken bucke)}; QoS arameers{qos guaranees

4 4 Emir Tokar, Guy ujolle, Edgard Jamhour, Manoel C. enna, Mauro Fonseca (delay, jier, packe loss)}; Excess Treamen {Traffic condiioning (dropping, remarking)}. Some TEQUILA works aemps o propose IETF sandards for defining a SLS model and requiremens for a negoiaion proocol. This projec is frequenly referenced by oher works and projecs, however is no analyzed in [3]. Differen approaches have been proposed, generaing massive concep diffusion, neverheless wih an elevaed divergence in he definiions and models adoped. In he communicaion neworks domain i is possible o idenify wo major approaches: (i) he firs approach is oriened o he conrol mechanisms, i.e., provisioning neworks elemens in order o assure he QoS levels defined by he SLA. Examples of projecs ha follow his approach are: TEQUILA, QBone [9] and AQUILA. (ii) The second approach is oriened o he service relaionship beween cusomer and he service provider. I includes proposals for defining merics for describing QoS levels and he mechanisms ha could be used o guaranee hese levels [,,2]. This is a general classificaion and does no have he inenion o define a new axonomy, bu only o simplify he presenaion of he works relaed o our proposal. In his work he SLA concep is used in conformiy wih he second approach, being admied he definiion conained in he SLA Managemen Handbook of he TeleManagemen Forum [3]. Oher definiion of SLA can be found in RFC2475 and RFC398. As he qualiy focus is on he service relaionship involving clien/provider, an imporan quesion is raised, in he way o consider adequae merics for his relaion. In his conex he concep of key indicaor appears o idenify he essenial meric for he relaion clien/provider. The concep is exended o faciliae he mapping beween specific parameers of service and specific parameers of echnology by wo new indicaors: key qualiy indicaor (KQI) and key performance indicaor (KI). These new poiners had been inroduced by he TeleManagemen Forum [4], and supply specific measuremens aspecs of applicaion performance or service. The KQI is derived from a number of informaion sources, including merics for calculaing he performance of he service or derived from meric of underlying services as KI. As a service or applicaion is suppored by a service elemens number, a KI differen number can be indispensable o deermine he calculaion of a paricular KQI. According o he TeleManegemen Forum definiion, he mapping beween KQI and KI is applicaion dependen, and can be simple or complex, empirical or formal. Lower Error Threshold Lower Warning Threshold Upper Warning Threshold Upper Error Threshold Fig.. Threshold arameers of KI/KQI. In general way a KQI is defined from a se of KIs and each KI or KQI will have upper hresholds and lower hresholds of warning ("Lower Warning/Upper Warning") and error ("Lower Error/Upper Error"), as shown in figure. The KI hen are combined by empirical or heoreical funcion o calculae he value of he relaed KQI. The relaionship of some parameers (), e.g, packe loss ( ), delay ( 2 ) and oher ( n ), hrough a funcion f (, 2,..., n ) and is relaion wih KQI parameers (S n ) represened for a funcion F (S, S n ). For example, a se of KIs

5 An XML Model for SLA Definiion wih Key Indicaors 5 values signaling warnings can degrade a service unil i provokes he inerrupion, hen, i would have o be considered as an error indicaing a KQI violaion. The funcions definiion of relaionship beween KQI and KIs is an imporan subjec of curren research. Considerable works in his way have been developed for eniies as ITU (R-value) and oher commercial eniies as NeForecas ( In case ha he relaionships of KI and KQI canno be deermined, measuremens in real environmens or laboraories can be developed. In his work we use references o indicaors KI and KQI in scheme XML. A corporaive vision for applicaions, businesses, neworks services, managemen and SLA negoiaion can be goen in he Managemen Handbook [3]. 3. roposed Model wih KI and KQI Indicaors For many years he SLA managemen issue has been inensely researched and has achieved a reasonably maured sae. However, he problem of esablishing a generic iner-organizaional SLA model remains wihou a definiive soluion, even hough one could observe some convergence o he use of XML for mos proposal implemenaions. The model proposed in his work is called KISLA (Key-Indicaor SLA). I adops he concep of describing service levels by using performance indicaors (KI) and defining funcions for evaluaing he KI indicaors wih respec o he qualiy indicaors (KQI). The proposed model combines elemens described by he CADENUS [7] and WSLA [6] projecs, and has proposed some addiional classes as indicaed in he model figures presened in his secion. The KISLA model is implemened in a XML-based language called KISLAML (Key-Indicaor SLA Markup Language). In he KISLAML approach, XML-based elemens are used for describing he eniies and relaionships relaed o a service level agreemen. The KI and KQI definiions and evaluaion are preformed hrough calls o reusable funcions embedded in he markup language. The funcions iself are no described in XML, bu hey are jus evoked by he KISLAML inerpreer. This approach is inspired by he XACML (exensible Access Conrol Markup Language) [5], which is a language for represening policies using a descripive approach. In our opinion, he XACML approach is more human-readable han adoping a purely objec-oriened approach, such as CIM [6]. The idea of defining reusable funcions permis o creae policies where mos semanic definiion is defined by he policy language, insead of being implicily defined by he policy inerpreaion algorihm. Considering his aspec, he WSLA approach has several similariies wih our proposal. I also adops UML for represening a SLA model, which is implemened in a XML-based language. The KI and KQI conceps are no used, bu according o he WSLA, a service has SLA parameers, defining merics which are expressed or evaluaed in erms of cascaded funcions. The possibiliy of creaing merics using cascaded funcions is no explicily suppored by KISLAML, which use in he curren version he approach of XACML. The model proposed by CADENUS [7] for service definiions has inspired he reuse of service classes in our proposal. CADENUS has defined reusable SLA and SLO (Service Level Objecives) emplaes for service model definiions, bu has also

6 6 Emir Tokar, Guy ujolle, Edgard Jamhour, Manoel C. enna, Mauro Fonseca opened he possibiliy of creaing cusomized services. The CADENUS model has impored several CIM class definiions in order o describe merics, QoS services and policy rule definiions. In our proposal, his CIM classes have been replaced he KI and KQI definiions. Nex, i will be presened a shor descripion of he proposed KISLA model and he relaionship beween he KI and KQI indicaors. The <SLAConracType> class is he main elemen of he KISLA model, and i aggregaes hree main classes: <aries>, <Services> and <Responsabiliies>. In order o explain he model, le s consider he following example: a provider agrees wih a cusomer o supply a specific audio service (e.g., CODEC G.9) and classifies his service as being GOLD, wihin a commercial period. I also defines a service availabiliy of 98% wihin he conraced period. The <aries> class describes he eniies involved in he SLA agreemen, i.e., he cusomer and he provider. I aggregaes oher classes used for describing informaion such as name, phone numbers, addresses, and oher daa relaed o he paries in he agreemen. In a ypical SLA model, paries esablish an agreemen, describing he responsibiliies for he engaged services. There are several proposals for modeling paries, services and oher elemens of a SLA agreemen. In paricular, he WSLA version has no elemens for defining he conac informaion for he SLA paries, bu i suggess, for he following versions, he use of inernaional sandards for represening his informaion. In our proposal, SLA paries informaion is expressed using he classes proposed by he CIM version 2.9 [6]. The <Services> class represens he informaion abou he offered service, in his case CODEC G.9, wih service level GOLD. I defines he opology of he service (i.e., end poins of he provider domain) and he validiy period (e.g., commercial period) of he SLA conrac. The service level GOLD is defined in erms of he key performance indicaors (KIs) required for assuring he performance of he offered service. Delay, jier, packe loss and average bi rae are examples of KIs. CIM_OrganizaionalEniy CIM_UserEniy SLAConrac [] +aries CIM_OrgUni CIM_Organizaion CIM_UserConac aries [W] +CIM_OrgUni +CIM_Organizaion +Signaoryrovider +SignaoryConsumer SignaoryaryConac [] +CIM_erson CIM_erson Signaoryary [W] +SignaoryaryConac.. ary [W] {absrac} []roposal [C]Cadenus [W]WSLA Fig. 2. "aries" Definiion The figure 2 presens he classes relaed o he <aries> model. As shown in he figure, mos elemens have been impored from he CADENUS, WLSA and CIM definiions. The <aries> class aggregaes elemens for represening he eniies ha negoiae a service level agreemen: provider and cusomer. Boh paries are

7 An XML Model for SLA Definiion wih Key Indicaors 7 represened by he <Signaoryary> class, which is a specializaion of he absrac class <ary>. As shown in he figure, he pary informaion is represened by he CIM version 2.9 classes [6]. The <Responsabiliies> class represens he condiions ha mus be respeced by he provider wih respec o he offered service. These condiions are expressed in erms of qualiy key indicaors (KQI), which are used for defining he erms under which he offered service will be moniored and evaluaed. The KQI are expressed, preferenially, bu no exclusively, as a funcion of he performance key indicaors (KIs). Availabiliy is an example of KQI, and can be defined in erms of he KIs delay, packe loss and average bi rae. Oher informaion such as penalies for violaing a KQI is also represened by he <Responsabiliies> class. The figure 3 presens he classes relaed o he <Services> model. A SLA can offer several services hrough he <Service> cardinaliy. Examples of services are "CODEC G729", "CODEC H263", generic audio, ec. A service definiion includes he Service Access oin (SA) and he Key erformance Indicaors (KI) definiions. Each service level defined by he provider, e.g., audio GOLD or audio SILVER, is defined in erms of a KI se. The KI se indicaes he performance levels ha mus be saisfied by he provider, and are consrained o a validiy period defined by he <Schedule> class. Noe ha GOLD has no meaning if no associaed o he service "audio". Therefore, a KI se is always relaed o a service. An example of KI se is {delay, packe loss and bi rae}. SLAConrac [] +Services Services +Service..* Service [C] +KeyerformanceIndicaorsSe..*..* +ServiceAccessoin KITemplae []..* KITemplaeSe [] KeyerformanceIndicaorSe [] ServiceAccessoin [C] +kpi_name +Schedule..* +DsAddress +SrcAddress SLOType [] «enumeraion» KIarameerThreshold [] Schedule [W] DesAddress SrcAddress +kpi_hresholds..* KIType [] «enumeraion» UniMericType [W] +BusinessDayService..* +SampleInerval +eriod BusinessDayService SampleInerval [] eriod []roposal [C]Cadenus [W]WSLA Fig. 3. Services class definiions. In order o simplify he process of defining KI ses for services offered by a provider, he KISLA model proposes he use of XML schemas for auomaic validaing he KI definiions. The KITemplaeSe is associaed o a XML schema ha can be seleced from a library, when a service is insaniaed. KITemplaeSe defines a se of reusable KIs ha can be used for describing similar services. For example, he family CODEC G defined by he ITU-T, specifies a se of CODEC specificaions wih similar parameer definiions. Therefore, CODECG is an example of KITemplaeSe and CODEC G729 is an example of KITemplaeSe insaniaion. The idea of creaing KI emplaes has been adaped from he concep proposed by CADENUS.

8 8 Emir Tokar, Guy ujolle, Edgard Jamhour, Manoel C. enna, Mauro Fonseca The srucure of a KITemplaeSe is used for specified parameer of a service, for example, he ITU-T CODEC G series have hree KIs: <acke_loss>, <Jier> and <Delay>, which are used o assure he "audio" qualiy, according o he TMForum definiion for some CODECs ypes [7]. To each elemen is associaed a <SLOType>, which defines he hresholds associaed o he KI, as explained in he secion wo, figure. The accepable meric unis for each hreshold are also defined in he schema, i.e., see "urn:kpi:emplae:se:.:uni:milliseconds" uni ag, fig. 4. As an example, he emplae discussed above could be used for defining he KI se for audio applicaions according o he ITU-T sandard CODEC G.729. The sandard specifies delay limied o 5 ms, jier limied o 5 ms and packe loss limied o.5% of he ransmied packes. These KI values specify he condiions he provider mus assure for he cusomer. In order o saisfy hese condiions, he provider mus ranslae hese parameers ino SLS configuraions, and apply hem o he nework devices ha are affeced by he ServiceAccessoin associaed o he service. For example, he SLS configuraion for he G.729 service correspond o a oken bucke wih he following parameers specified on RFC222 (rae=2, bucke=8, peak=4). The ranslaion process for calculaing he SLSs form he SLA definiions is ou of he scope of his paper. The figure 4 illusraes he insaniaion of he "Delay KI", which corresponds o one of he KIs illusraed in he schema in he figure 2 ("aries" definiion). In he example, here are only upper hreshold, since lower hreshold make no sense for delay. A warning is defined for delay measures beween 3 and 5 milliseconds. All delay measures above 5 milliseconds are considered error evens. <kpi:delay> <kpi:uni>urn:kpi:emplae:se:.:uni:milliseconds</kpi:uni> <kpi:kpi_hresholds> <kpi:hreshold-parameer>uppererrorthreshold</kpi:hreshold-parameer> <kpi:hreshold-value>5</kpi:hreshold-value> </kpi:kpi_hresholds> <kpi:kpi_hresholds> <kpi:hreshold-parameer>upperwarningthreshold</kpi:hreshold-parameer> <kpi:hreshold-value>3</kpi:hreshold-value> </kpi:kpi_hresholds> </kpi:delay> Fig. 4. Example of hresholds for Delay KI The figure 5 presens he classes relaed o he <Responsabiliies> model. This model defines he qualiy indicaors (KQIs) ha mus be saisfied by he provider, wih respec o he accorded service, and he respecive penalies applied when hese KQIs are no respeced. The wo main classes of his model are: <KeyQualiyIndicaor> and <Duies>. The <KeyQualiyIndicaor> class defines how a KQI is calculaed in erms of he KIs indicaed by he <KeyerformanceIndicaorSe> class. The <Schedule> class defines he periodiciy ha he KQI is evaluaed (e.g., daily, weekly, ec.). The KQI evaluaion funcion <KQIFuncion> is defined in a library and evoked by he KISLA markup language inerpreer. As menioned early in his secion, he sraegy of creaing condiions based on reusable expressions was inspired by he XACML approach. The <Duies> class defines he penalies applied o he provider when he <Responsabiliies> are violaed. The penalies are described by he <enaly> class,

9 An XML Model for SLA Definiion wih Key Indicaors 9 and can be calculaed as a funcion of he fees paid by he cusomer for he service, as defined by he <Cos> class. The definiion of KQI funcions is an imporan sep for evaluaing a SLA. In he nex secion i will be presened an example of KQI funcion for calculaing he availabiliy of a service. SLAConrac [] +Responsabiliies Responsabiliies [] +KeyQualiyIndicaors KeyQualiyIndicaor []..* +Duies Duies [] +Schedule +Expression +enaliytype +CosType Schedule [W] KQIFuncion [W] enaliy Cos +KISeNameId +Aribue KeyerformanceIndicaorsSe [] Aribue [] Fig. 5. KQI and KI relaionship in he proposed model +ConracValidiy ConracValidiy []roposal [C]Cadenus [W]WSLA 4. An example: assessmen of service availabiliy As discussed in secion 2, KQI are suiable merics for defining service level under a perspecive ha akes ino accoun an accorded view of service qualiy esablished by cusomer and service provider. Examples of KQI are Service Availabiliy (SA), Mean Time Beween Failures (MTBF) and Response Time (RT) [3]. On he oher hand, KI are echnical indicaors adequae for measuring he performance of underlying nework. Examples of KI are packe loss, delay and jier. In general KI are evaluaed direcly from performance daa colleced from he nework (KI daa), and KQI are compued from specific combinaion of KI daa values. QoS expressed by a KQI mus be clearly undersood by boh paries, bu misundersanding is very common. For example, SA is a well-known indicaor ha has an undersood formula, which indicaes he percenage of ime he service is operaional: OuageInerval SA % = % x% (equaion ) AciviyTime Ouage period can be compued by summing up all inervals when service is disruped. Cusomer ends o consider ha all periods having any kind of problem should be considered as an ouage inerval, wherever service provider ends o do no consider he periods when here is jus some level of service degradaion. If boh cusomer and service provider can agree on wha is service disrupion and wha is service degradaion, degradaion period can be similarly compued by summing up all degradaion inervals. Addiionally service degradaion facor (SDF) complemens SA formula, where SDF varies from o, depending on he weigh given o degradaion period when compuing SA, as follows:

10 Emir Tokar, Guy ujolle, Edgard Jamhour, Manoel C. enna, Mauro Fonseca ( ) OuageInerval + SDF DegradaionInerval = % % (equaion 2) SA% x AciviyTime Ouage and degradaion inervals are defined by he value of a KI daa sample. Le be a KI sample a insan. As menioned in secion 2, a KI has four hresholds, lower and upper error, and lower and upper warning. We have an ouage inerval when is less hen under lower error hreshold and greaer hen upper error hreshold. Similarly, we have a warning inerval when is beween lower error and lower warning, or beween upper warning and upper error. We can hen calculae he ouage period by summing up all error inervals and he degradaion period by summing up all warning inervals (see Figure 7). We have o consider muliple KIs, possibly wih differen sampling raes, when compuing a KQI. Thus, he firs sep is o ge a common sampling period, ha is, heir greaes common divisor. Le α = { KI i i = N } be he se of KIs relaed o SA% KQI. Figure 6 illusraes he procedure for geing a common sampling inerval. T sar and T end are he iniial and final insan of aciviy ime. D is he common sampling inerval, ha is, D = GDC(d i ), I = N, where d i is he duraion of sampling inerval of KI i. nk is he value of a sample for KI n in is k-h sampling inerval. n is he se of all KI n samples. T 2 N 2 N T Sar 2 22 Sar N N 2 2 n Fig. 6. Sample erms of KIs N 4 22 N n n 2 k KIs are measured in differen scales. The second sep is o ge a common scale by normalizing sample values ( nk ) wih respec o KI hresholds. The values beween Lower Warning n and Upper Warning n are se o (zero); hose beween Lower Error and Lower Warning are se o (minus one); hose beween Upper Warning and Upper Error are se o (one); hose under Lower Error are se o 2 (minus wo); and hose above Upper Error are se o 2 (wo). nk is he normalized value of a sample for KI n in is k-h sampling inerval.. for (n o N) do 2. for (k o n ) do 3. nk ( nk > UpperError n )?2 :(( nk > UpperWarning n)?: nk)); 4. nk ( nk< LowerError n)? -2 :(( nk < LowerWarning n)?-: nk)); 5. nk ( nk > LowerWarning n) and ( nk < UpperWarning n)?; 6. end-for; 7. end-for; Figure 7 illusraes he normalizaion procedure. I shows in he lef, samples before normalizaion procedure, and in he righ, afer normalizaion. In his example, n has only values greaer hen Lower Warning. Nk x 2 y Nz k 2 l Nm n n n T T End n n n End

11 An XML Model for SLA Definiion wih Key Indicaors ms samples samples KI hresholds Fig. 7. KIs samples qualified. Les Q k be he value of a KQI sample a inerval I k. Q k should be calculaed from ik. The combinaion of muliple ik ino Q k can be done according o wo principles: (i) Q k will express an excepion condiion (warning or error) when all ik under consideraion are in excepion condiion, prevailing he less severe one. (ii) Q k will express an excepion condiion (warning or error) when a leas one ik is in excepion condiion, prevailing he severes one. In order o combine ik o compue Q k we define wo operaors: and. I is possible o show ha and have he same properies han logical operaors and. Thus, a generic combinaion of ik can be given by an expression evolving and in he Disjuncive Normal Form (DNF). Le s consider he following definiions: α = { KI n n = N } he se of KIs relaed o SA% KQI. α... α W : he subses of α, such ha, {α... α W } is a pariion of α, ha is α = α and α =. U i i=... W I i =... W N i = α i (cardinaliy of α i ). Q k = where KI j α i (equaion 3) i =.. W jk j =... Ni Q k is compued by equaion 3, ouage period can be compued by summing up errors samples (Q k = 2) and degradaion inerval by summing up warning samples (Q k =). SA% is compued by equaion 2. As said before, ouage inerval can be compued by summing up errors samples and degradaion inerval from warning samples. SA is compued by equaion 2. We have developed a monioring video scenario using labeling echnique o mark he sample packes and will be presen in he nex paper, insead of he mahemaic example of KISLA used o presen his paper ha is somehow feasiblely. 5. Conclusion Defining a model for represen SLA informaion is an imporan sep for creaing managemen ools for auomaing he process of provisioning and monioring DiffServ neworks. The work in his paper presens a proposal owards a unified model for represening SLAs called KISLA ha adops he concep of represening SLAs by using he KQI and KI indicaors. This approach shows a grea flexibiliy for describing a large number of services negoiaed in a DiffServ domain. I provides means for defining a common nomenclaure for negoiaions beween cusomers and providers. The KISLA markup language was inspired by he experience acquired by building

12 2 Emir Tokar, Guy ujolle, Edgard Jamhour, Manoel C. enna, Mauro Fonseca policy-based managemen sysems based on boh, purely objec-oriened approaches, such as CIM, and hybrid-approaches, capable of evocaing exernal reusable funcions, such as XACML. We have seen advanages in he hybrid approach, because i permis o creae policies where mos semanic definiion is defined by he policy language, insead of being implicily defined by he policy inerpreaion algorihm. This approach was paricularly useful for adaping he model o he KI and KQI definiions. The work in his paper has developed only he availabiliy KQI funcion, applicable o a limied se of KI indicaors. Fuure works will explore he developmen of oher KQI funcions. The idea is o creae a library of qualiy indicaor funcions ha could be useful for creaing SLA conracs for a large number of applicaions. 6. References [] Rajan, R.; Celeni, E.; Dua, S.; Service Level Specificaion for Iner-domain QoS Negoiaion, draf-somefolks-sls-.x, Inerne Draf, Nov. 2 [2] Salsano, S.; Ricciao, F.; Winer, M.; Eichler, G.; Thomas, A.; Fuenfsueck, F.; Ziegler, T.; Brandauer, C.; Definiion and usage of SLSs in he AQUILA consorium, draf-salsanoaquila-sls-.x, Nov. 2. AQUILA projec websie. URL: hp:// [3] EGEE, Enabling Grids for E-science in Europe. URL hp:// [4] TeleManagemen Forum. URL hp:// [5] 3G. 3rd Generaion arnership rojec (3G). URL: hp:// [6] Ludwig, H.; Keller, A.; Dan, A.; Franck, R.; King, R.. Web Service Level Agreemen (WSLA) Language Specificaion. IBM Corporaion, July 22. [7] CADENUS projec. References a URL: hp://wwwcadenus.fokus.fraunhofer.de [8] Goderis, D.; e al. D.: Funcional Archiecure Definiion and Top Level Design, TEQUILA rojec Traffic Engineering for Qualiy of Service in he Inerne, a Large Scale (IST ), Sep. 2. [9] QBone. "QBone Bandwidh Broker Archiecure. URL: hp://qbone.inerne2.edu/bb/. [] Tosic, V.; agurek, B.; Esfandiari, B.; ael, K. Managemen of Composiions of E- and M-Business Web Services wih muliple Classes of Service. roceedings of he 8h IEEE/IFI NOMS 22, Florence, Ialy, Apr. 22. [] Keller, A.; Kar, G.; Ludwig, H.; Dan, A.; Hellersein. J.L. Managing Dynamic Services: A Conrac based Approach o a Concepual Archiecure. roceedings of he 8h IEEE/IFI NOMS 22, Florence, Ialy, Apr. 22. [2] Sahai, A.; Machiraju, V.; Sayal, M.; Moorsel, A.; Casai, F. Auomaed SLA Monioring for Web Services, 8h IFI/IEEE Nework Operaions and Managemen Symposium, NOEMS 22. Ialy, Apr. 22. [3] TeleManagemen Forum. SLA Managemen Handbook, Volume 4, Enerprise erspecive, G45. The Open Group. Oc 24. [4] TeleManagemen Forum. Wireless Service Measuremens Handbook, GB923. Las release - GB923v3, Mar. 24. [5] XACML - OASIS. exensible Access Conrol Markup Language (XACML) Version.. OASIS, Feb. 23. URL: hp:// [6] DMTF. Common Informaion Model (CIM) Specificaion v 2.9. Disribued Managemen Task Force, Inc. Jun [7] EGEE DJRA4., Specificaion of Inerfaces for Bandwidh Reservaion Service. Apr. 26. URL: hps://edms.cern.ch/file/554//egee-djra v2..doc