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Optical network resilience Availability of WDM networks

Place for logos of authors’ institutions. Optical network resilience Availability of WDM networks. Branko Mikac , Faculty of Electrical Engineering and Computing , branko.mikac@fer.hr Robert Inkret , Faculty of Electrical Engineering and Computing , inkret@tel.fer.hr.

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Optical network resilience Availability of WDM networks

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  1. Place for logos of authors’ institutions Optical network resilienceAvailability of WDM networks Branko Mikac, Faculty of Electrical Engineering and Computing, branko.mikac@fer.hr Robert Inkret, Faculty of Electrical Engineering and Computing, inkret@tel.fer.hr

  2. Availability model levels of WDM network

  3. Dependency Logical connection L ij dependent independent dependent independent cable cables cables none common cable cables cables none fibres fibr es fibres fibres parts OAs OAs OAs OAs S (1) P (1) ij ij S (2) P (2) ij ij : : S (n) P (n) ij ij S (1) P (1) ji ji S (2) P (2) ji ji : : S (n) P (n) ji ji Spare paths (S) Primary paths (P)

  4. Availability evaluation • Bottom-up approach  availability modelling and evaluation from network components to the network level. • Availability data • failure rate   1 FIT (failures in time) = 1 failure per 109 hours • mean time to repair (MTTR) (hours) • Data origin • From the ground and life testing • Reliability handbooks: • RDF 93 (France Telecom) • RDF2000/UTEC80810 (France Telecom) (COST 270) • MIL HDBK 217 standards etc.

  5. Failure rate data for optical components • Data existence • Do not exist - for new components • Data exist • but they are not available because of confidentiality • available, but different data from different sources • Data sources • field data (from operators) • life test data (from vendors or operators) • private communication • estimates and guesses (data for new or not available components and devices) based on “old” data • Type of data presentation • statistical distribution or range • mean value

  6. Data and evaluation accuracy • High diversity of data  high diversity of availability figures • MIL 213 standard (pesimistic data) • operators (RDF, BT) • vendors • Recommendations: • ITU-T: G.911 (4/97) Parameters and calculation for reliability and availability of fibre optic systems • ETSI - EN 300 416 v.1.2.1 (1998-08) Network Aspects (NA) – Availability performance of path elements of international digital paths • Two types of availability analyses • to find out absolute availability figure of system or network in order to compare it to availability requirements • to compare different system or network architectures or protection/restoration scenarios

  7. Failure rate data for optical components • Data existence • Do not exist - for new components • Data exist • but they are not available because of confidentiality • available, but different data from different sources • Data sources • field data (from operators) • life test data (from vendors or operators) • private communication • estimates and guesses (data for new or not available components and devices) based on “old” data • Type of data presentation • statistical distribution or range • mean value

  8. Failure rates (1) Type Short Range Typical Unit • Fibre (per km) (extrinsic data) OF 100-300 200 fit/km • Fibre (per km) (intrinsic data) OF - negl. fit/km • Dispersion compensation fibre DCF - negl. fit/km • Erbium doped fibre EDF - negl. fit/km • Laser pump LP 100-400 300 fit • Laser transmitter TX 100-400 300 fit • Tunable transmitter TTX 745 fit • External modulator EM 2000-5000 3000 fit • Integrated laser modulator ILM 1000-2000 1500 fit • Optical receiver RX 100-400 250 fit • Tunable receiver TRX 470 fit x - active components

  9. Failure rates (2) Type Short Range Typical Unit • Multiplexer (4  / 16 ) MUX - 100 fit • Demultiplexer (4  / 16 ) DEMUX - 100 fit • Optical switch OX - 1000 fit • Wavelength selective coupler WSC 100-200 150 fit • Coupler CPL 50 fit • Isolator IS 50 fit • Fusion splice FS 50 fit • Connector CON 50-100 75 fit • Splitter 1:2 SPL 50 fit • EDFA (1 LP) EDFA1 800 fit • IP router IPR ? x - active components

  10. Repair rates Repair rate μ=1/Mean time to repair (MTR) • Distribution of repair times - useful in simulation • Mean time to repair - approximation of distribution data • indoor repairing 2 - 6 hours • outdoor repairing 6 - 21 hours

  11. Generic Availability Modeling

  12. Transport entity specifications • The network provides its services through means of transport entities • Transport entities are defined according to the:ARCHITECTURAL PARADIGMS • Switching • Topological • Protection & Restoration

  13. Architectural Paradigms • Switching • Defines transport entity through which service is provided to higher layers (clients) • Fiber, wavelength, packet, burst, time-slot, … • Protection & Restoration (P&R) • Actions performed during service provisioning, and service life cycle • Topological • Traffic routing patterns • … and protection & restoration to a certain extent

  14. P & R Paradigms - Classification • Backup transport entity provisioning time, relative to the service life cycle. • Protection • Restoration • Backup transport entity provisioning time, relative to the moment of failure • Proactive • Reactive • Dedication of the backup transport entity to the working • Dedicated • Shared

  15. P & R Paradigms - Classification • Level of switching action • Path (end-to-end) • Span • Directionality • Bidirectional • Unidirectional • Action after the failure have been resolved • Revertive • Non-revertive

  16. Protection: A principle

  17. P & R Paradigms - Relations

  18. Topological Paradigms • Ability to exploit given topology of OTN • Used in the context of different routing patterns • Some examples: • Ring • Mesh • Routing and rerouting mechanism will exploit an arbitrary topology in a mesh-like way • P-Cycles • A mix of ring and mesh topological paradigms • Best of two worlds? • Ring-link speed with mesh-like resource utilization

  19. Ring: DP-WSHR (OCh/DPRing)

  20. Ring: SP-WSHR (OCh/SPRing)

  21. Ring: SL-WSHR (OMS/SPRing)

  22. Ring: Comparison

  23. Mesh: 1+1 protection

  24. Mesh: Path restoration

  25. Mesh: Dynamic restoration

  26. Mesh: Span restoration f1 Spare pathA(f1)

  27. Mesh: Span restoration f2 Spare path A(f2)

  28. p-Cycles (1/2) • Basic ideas: • working communications can use shortest (wavelength) paths • spare capacity is used to create pre-configured protection cycles • thus, p-Cycles

  29. p-Cycles (2/2) • span (link) • on a cycle • straddling (it’s end nodes are on a cycle) • they’re like rings: • with protection for on-cycles and straddling spans • ring speed: only two nodes perform real-time actions • mesh efficiency: protection of on-cycle and straddling failures

  30. Availability calculation procedures: Assumptions (1/2): • Entity = network element • Can be in either of the two states • Faulty • Non-faulty • Represented by the boolean variables: • xi denotes non-faulty state of the component i • Faulty state is a complement of xi

  31. Availability calculation procedures: Assumptions (2/2): • Two classes of entities: • Simple • Markov model – distributions of failure and repair times • Examples: photonic devices • Availability: probability of an entity being in non-faulty state • Complex • State is defined by Boolean expression defining non-faulty state of an entity • Boolean expression • Boolean operators (AND and OR) connecting other Boolean expressions and Boolean variables • Availability: probability of a Boolean expression

  32. An example: DWDM link (1/4) Boolean variable

  33. An example: DWDM link (2/4) • Boolean expression (BE): • Two wavelength channels • One per each direction • BE for a logical channel (LCh)

  34. An example: DWDM link (3/4) • System availability graph (SAG): • Boolean AND = series • Boolean OR = parallel

  35. An example: DWDM link (4/4) • Availability: • Assuming that all of the Boolean variables are independent (i.e. failure of one entity does not influence failure of other) • Exceptions: natural disasters, excessive optical power in optical amplifier

  36. SAG vs. Boolean Expression (1/2) • An example: Boolean connection • Composed of logical channels • Virtual endpoints in SAG • A complex entity is available if there is a path between endpoints

  37. SAG vs. Boolean Expression (2/2) • Sub-graphs in SAG • An example: Logical channel within a Logical connection

  38. Another example: 1+1 protection in mesh network Product terms (PT)

  39. Trouble is… • Boolean expressions are evaluated into form of union of product terms: • Union is non-disjoint (in general), and thus, probability is not simply a sum of product term probabilities

  40. Put another way… • The BIG problem is: • How to convert union (or sum) of non-disjoint product terms (SNDPT) into disjoint one? • The major issue in availability calculation procedure! • Classification of procedures: • Analytical • Simulation (Monte-Carlo)

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