Uiversità di Bergamo Facoltà di Igegeria dell Iformazioe e etodi atematici La Protezioe elle Reti di Telecomuicazioe A Priority-Aware Protectio Techique for QoS Eabled WD etworks Fabio artigo
Sommario Itroduzioe Strategie di Protezioe classiche Priority-Aware Shared-Protectio odelli atematici e risultati umerici Iterpretazioe dei risultati
Resiliece i WD etworks The maturig of WD techology: A sigle fiber carries huge amout of data Terabit/s The failure of a etwork compoet: Ca lead to huge loss i data ad reveue Solutio: Protectio a proactive procedure to recover traffic whe a failure occurs: Oe path is referred to as primary path used to carry traffic durig ormal operatio. Extra backup resources are pre-reserved ad activated whe the primary path fails.
Challeges The operator is faced by several challeges: Satisfy the QoS requiremets of the cliet defied through a SLA Service Level Agreemet: A SLA Violatio may cause a certai amout of pealty to be paid by the operator. Out of service criterio Recovery time with degraded SLA Full recovery time Service uavailability Premium Degraded BER0-4 ot spec. 50 ms 0-5 old Degraded BER0-3 50 ms 300 ms 0-4 Silver Fault LOS 500 ms 5 sec Broze Fault LOS 5 sec 5 mi At the same time select a cost effective protectio scheme to achieve this goal 0-3 0-2
Why do we protect? Protectio is ormally doe for the purpose of icreasig the availability of the ed-to-ed coectio. Availability: Availability fractio of time the coectio is up durig etire service time uit: mis/year Availability available Time/available Time+ dow time. Protectio does help to icrease availability: Traffic o failed primary path will be switched to the backup path The more backup resources we have the greater will be the availability
Availability Each etwork compoet is characterized by its availability which depeds upo: Failure rate: ea Time To Failure TTF /Lambda Failure recovery rate: ea Time To Repair TTR /u 5042 FIT/000 miles FITFailure I Time how may failures the compoeet experieces i 0 9 hours
Availability 2 Path availability: Product of i betwee compoets availability Where: A t A i i A i TTF/TTR + TTF ai reaso for failure is related to fiber liks
Availability 3
First Coclusio To reach the 5 9 s objective for log distace coectios we eed to protect the sigal Several protectio schemes exist i the literature: Each oe has its ow advatage ad disadvatage. The most commo: Dedicated Protectio Shared Protectio Still we do t kow with each protectio scheme what is the resultig availability: We ted to combie the advatages from both approaches to use resources efficietly while meetig user s requiremet
Dedicated Protectio X Y S D B C Dedicated Protectio: : or +
Dedicated Protectio Y Z W X S D B C Dedicated Protectio: 2:
Dedicated Protectio Aalysis Advatages Availability is icreased by several orders of magitude Excludig the multiple cocurret failure sceario Availability 00% Drawbacks: Resource redudacy 00%
Shared Protectio X Y S D E F B C Shared Protectio
Shared Protectio Aalysis Advatages Less resources are eeded for protectio compared to dedicated protectio case Drawbacks: Less Availability is obtaied i case of multiple failures
Our Propositio Priority-Aware Shared Protectio Scheme
Priority-Aware Shared Protectio A ew scheme exploitig the advatage of dedicated ad shared protectio may be realized Istead of equally treatig the coectios sharig the protectio chael: A otio of service differetiatio may be itroduced So old coectios ad S Silver coectios may share the same backup path. old coectios ca preempt Silver oes i the utilizatio of backup resources.
athematical odels For both Classical ad Priority Aware protectio Schemes We compute the Availability for every coectio
We have workig paths protected by a sigle protectio path The system ca be modeled with a arkov Chai havig + states State i i paths icludig Workig ad Protectio paths are dow Steady State Probability: Aalysis of : protectio without Service Differetiatio 0 + 3 2 + - -2 2 +µ µ µ 2µ 3µ 4µ + + + + + + + + + A A p ρ ρ ρ ρ ρ µ ρ µ ea Repair Rate ea Failure Rate!!! + +
Aalysis of : protectio without Service Differetiatio Performace of the : Protectio Scheme: ea Uavailability: U µ + 2 p ello stato per >2 ci soo ifatti - coessioi o protette sul totale delle coessioi La probabilità che ello stato ua coessioe scelta a caso fra le sia proprio tra le - o protette è data dal rapporto -/
We have old coectios Silver coectios ea Uavailability for the old ad Silver Coectios: Aalysis of : protectio with Service Differetiatio + 2 p U µ S S U U U µ µ µ S Le coessioi old è come se o vedessero eache quelle Silver viste che possoo preemptarle ell occupare il cammio di backup. Quidi l uavailability U di ua coessioe old è pari a quella di ua coessioe i u sistema co protezioe : L uavailability totale U si coserva.
We have Protectio paths protectig Workig paths We model the system with a arkov Chai with + states State i i paths icludig Workig ad Protectio paths are dow Steady State Probability: Aalysis of : protectio without Service Differetiatio A A p + + + + + + + + + ρ ρ ρ ρ ρ 0 + +- 3 2 + +- +-2 +-3 2 +µ +-µ µ 2µ 3µ 4µ
Aalysis of : protectio without Service Differetiatio Performace of the : Protectio Scheme: ea Uavailability: U µ + + p ello stato per >+ ci soo ifatti - coessioi o protette sul totale delle coessioi La probabilità che ello stato ua coessioe scelta a caso fra le sia proprio tra le - o protette è data dal rapporto -/
We have old coectios Silver coectios ea Uavailability for the old ad Silver Coectios: ea Frequecy of Failure for the old ad Silver Coectios: Aalysis of : protectio with Service Differetiatio + + p U µ S S U U U µ µ µ S + p F µ S S F F F µ µ µ
umeric Results Based o the mathematical we defied for each protectio scheme the resultig availability
umeric Results: :3 Protectio The Priority-Aware scheme allows the provisioig of oe Platium coectio 99.999% which was impossible with the classical scheme. Two old coectios ca be provisioed Availabilty > 99.99%
umeric Results: : Protectio 800 km The Priority-Aware scheme allows the deploymet of oe Platium coectio 99.999% for every value of - old coectios ca be provisioed Availability > 99.99%
Coclusios We proposed a improvemet of the classical shared protectio based o relative priorities We developed a detailed mathematical model to gauge the impact of our propositio We showed that service differetiatio is better achieved through the use of our proposed protectio scheme We developed a simulatio study showig that the proposed scheme achieves high Availability Satisfactio Rates while realizig cost-effectiveess i terms of resource usage i the etwork.