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  • BPS2000, Baystack 450 & Passport 8600 (edge ethernet distribution & aggregation) OPTera Packet Edge on OPTera Metro 3000 series & OPTera OC-48 (ethernet over metro optical/Sonet) OPTera Metro 5000 series (ethernet over DWDM) Preside (provisioning & management software) Juniper & Shasta (collateral IP services & routing platforms) Contivity (VPN/secure, encrypted tunnel services)
  • Migration to IP on Optics simpler, lower cost network robustness & QOS needed for some services
  • Protection

    1. 1. Protection and Restoration in Optical Network Ling Huang [email_address]
    2. 2. Outline <ul><li>Introduction to Network Survivability </li></ul><ul><li>Optics in Internet </li></ul><ul><li>Protection and Restoration in Internet </li></ul><ul><li>Optical Layer Survivability </li></ul><ul><ul><li>Protection in Ring Network </li></ul></ul><ul><ul><li>Protection in Mesh Network </li></ul></ul><ul><li>Multi-Layer Resilience </li></ul><ul><li>Conclusion. </li></ul>
    3. 3. Network Survivability <ul><li>A very important aspect of modern networks </li></ul><ul><ul><li>The ever-increasing bit rate makes an unrecovered failure a significant loss for network operators. </li></ul></ul><ul><ul><li>Cable cuts (especially terrestrial) are very frequent. </li></ul></ul><ul><ul><li>No network-operator is willing to accept unprotected networks anymore. </li></ul></ul><ul><li>Restoration = function of rerouting failed connections </li></ul><ul><li>Survivability = property of a network to be resilient to failure </li></ul><ul><ul><li>Requires physical redundancy and restoration protocols. </li></ul></ul>
    4. 4. Optics in the Internet SONET Data Center SONET SONET SONET DWDM DWDM Access Long Haul Access Metro Metro
    5. 5. Optical Network: a Layered vision 1999 2002 2001 <ul><li>Multi-physical layers </li></ul><ul><li>multi & legacy services </li></ul><ul><li>robustness, QOS </li></ul>Thin SONET IP Optics MPLS <ul><li>Fewer physical layers </li></ul><ul><li>IP service dominance </li></ul><ul><li>lower cost </li></ul>SONET IP Optics ATM Layer 3 2 1 0 Packet Optical Inter- working Smart Optical Packet IP/MPLS Layer 2/3 0/1
    6. 6. Protection and Restoration in Internet <ul><li>A well defined set of restoration techniques already exists in the upper electronic layers: </li></ul><ul><ul><li>ATM/MPLS </li></ul></ul><ul><ul><li>IP </li></ul></ul><ul><ul><li>TCP </li></ul></ul><ul><li>Restoration speeds in different layers: </li></ul><ul><ul><li>BGP-4: 15 – 30 minutes </li></ul></ul><ul><ul><li>OSPF: 10 seconds to minutes </li></ul></ul><ul><ul><li>SONET: 50 milliseconds </li></ul></ul><ul><ul><li>Optical Mesh: currently hundred milliseconds to minutes </li></ul></ul>
    7. 7. Why Optical Layer Protection <ul><li>Restoration in the upper layers is slow and require intensive signaling </li></ul><ul><ul><li>On contrary 50-ms range when automatic protection schemes are implement in the optical transport layer. </li></ul></ul><ul><li>Purpose of performing restoration in the optical layer: </li></ul><ul><ul><li>To decrease the outage time by exploiting fast rerouting of the failed connection. </li></ul></ul><ul><li>Main problem in adding protection function in a new layer: </li></ul><ul><ul><li>Instability due to duplication of functions. </li></ul></ul><ul><ul><li>Need the merging of DWDM and electronic transport layer control and management. </li></ul></ul>
    8. 8. Why Optical Layer Protection? <ul><li>Advantages. </li></ul><ul><ul><li>Speed. </li></ul></ul><ul><ul><li>Efficiency. </li></ul></ul><ul><li>Limitation </li></ul><ul><ul><li>Detection of all faults not possible.(3R). </li></ul></ul><ul><ul><li>Protects traffic in units of light paths. </li></ul></ul><ul><ul><li>Race conditions when optical and client layer both try to protect against same failure. </li></ul></ul>
    9. 9. Protection Technique Classification <ul><li>Restoration techniques can protect the network against: </li></ul><ul><ul><li>Link failures </li></ul></ul><ul><ul><ul><li>Fiber-cables cuts and line devices failures (amplifers) </li></ul></ul></ul><ul><ul><li>Equipment failures </li></ul></ul><ul><ul><ul><li>OXCs, OADMs, eclectro-optical interface. </li></ul></ul></ul><ul><li>Protection can be implemented </li></ul><ul><ul><li>In the optical channel sublayer (path protection) </li></ul></ul><ul><ul><li>In the optical multiplex sublayer (line protection) </li></ul></ul><ul><li>Different protection techniques are used for </li></ul><ul><ul><li>Ring networks </li></ul></ul><ul><ul><li>Mesh networks </li></ul></ul>
    10. 10. Protection in Ring Network 1+1 Path Protection Used in access rings for traffic aggregation into central office 1:1 Line Protection Used for interoffice rings 1:1 Span and Line Protection Used in metropolitan or long- haul rings
    11. 11. Protection in Mesh Networks <ul><li>Network planning and survivability design </li></ul><ul><ul><li>Disjoint path idea: service working route and its backup route are topologically diverse. </li></ul></ul><ul><ul><li>Lightpaths of a logical topology can withstand physical link failures. </li></ul></ul>Working Path Backup Path
    12. 12. <ul><li>Reactive </li></ul><ul><ul><li>A search is initiated to find a new lightpath which does not use the failed components after the failure happens . </li></ul></ul><ul><ul><li>It can not guarantee successful recovery, </li></ul></ul><ul><ul><li>Longer restoration time </li></ul></ul><ul><li>Proactive </li></ul><ul><ul><li>Backup lightpaths are identified and resources are reserved at the time of establishing the primary lightpath itself . </li></ul></ul><ul><ul><li>100 percent restoration </li></ul></ul><ul><ul><li>Faster recovery </li></ul></ul>Reactive / Proactive Taxonomy
    13. 13. Path Protection / Line Protection Path Switching: restoration is handled by the source and the destination. Normal Operation Line Switching: restoration is handled by the nodes adjacent to the failure. Span Protection: if additional fiber is available. Line Switching: restoration is handled by the nodes adjacent to the failure. Line Protection.
    14. 14. 1+1 Protection <ul><li>Traffic is sent over two parallel paths, and the destination selects a better one. </li></ul><ul><li>In case of failure, the destination switch onto the other path. </li></ul><ul><li>Pros: simple for implementation and fast restoration </li></ul><ul><li>Cons: waste of bandwidth </li></ul>
    15. 15. 1:1 Protection <ul><li>During normal operation, no traffic or low priority traffic is sent across the backup path. </li></ul><ul><li>In case failure both the source and destination switch onto the protection path. </li></ul><ul><li>Pros: better network utilization. </li></ul><ul><li>Cons: required signaling overhead, slower restoration. </li></ul>
    16. 16. Shared Protection <ul><li>Backup fibers are used for protection of multiple links </li></ul><ul><li>Assume independent failure and handle single failure. </li></ul><ul><li>The capacity reserved for protection is greatly reduced. </li></ul>1:N Protection Normal Operation In Case of Failure
    17. 17. <ul><li>Primary Backup Multiplexing </li></ul><ul><ul><li>Used in a dynamic traffic scenario, to further improve resource utilization. </li></ul></ul><ul><ul><li>Allows a wavelength channel to be shared by a primary and one or more backup paths. </li></ul></ul><ul><ul><li>By doing so, the blocking probability of demands decreases at the expense of reduced restoration guarantee. (An increased number of lightpaths can be established) </li></ul></ul>Multiplexing Techniques <ul><li>A lightpath loses its recoverability when a channel on its backup lightpath is used by some other primary lightpath. </li></ul><ul><li>It regains its recoverability when the other primary lightpath terminates. </li></ul>
    18. 18. <ul><li>Problem Description </li></ul><ul><ul><li>Given a network in terms of nodes (WXCs) and links, and a set of point-to-point demands, find both the primary lightpath and the backup lightpath for each demand so that the total required network capacity is minimized. </li></ul></ul><ul><li>Notation </li></ul><ul><ul><li>N: the set of nodes; </li></ul></ul><ul><ul><li>L: the set of links; </li></ul></ul><ul><ul><li>D: the set of demands </li></ul></ul><ul><ul><li>C ij : the capacity weight for link (ij) </li></ul></ul><ul><ul><li>W ij : the capacity requirement on link (ij) in terms of # of wavelength </li></ul></ul><ul><li>Objective </li></ul><ul><ul><li>Minimize </li></ul></ul>Survivability Design: Joint Optimization Problem
    19. 19. <ul><li>1) Objective function </li></ul><ul><li>2) and 3) the flow conservation constraints for demand d ’s primary path and backup path, respectively. </li></ul><ul><li>4) Logical relationship: the backup path consumes link capacity iff the primary path is affected by the fault. </li></ul><ul><li>5): Restoration route independent of the failure. </li></ul><ul><li>6): Link capacity requirement </li></ul>Integer Programming Formulation
    20. 20. Multi-Layer Resilience
    21. 21. Multi-Layer Resilience
    22. 22. Multi-Layer Counter-Productive Behavior <ul><li>Instant response to Level 1 alarms in high layer causes unnecessary routing activity, routing instability, and traffic congestion </li></ul>Link Down Link recovered through optical protection Routing table Revision (no link) Routing table Revision (with link) Link Rediscovered 10s ms 10s seconds 10s seconds ALARM Link in Traffic Source: RHK
    23. 23. Multi-Layer Interaction
    24. 24. Multi-Layer Interaction
    25. 25. Conclusion <ul><li>Different resilience schemes applicable in optical network have been discussed. </li></ul><ul><li>Network planning and topology design for survivability is computationally intractable and faster heuristic solutions are needed. </li></ul><ul><li>Multi-layer restoration is a hot point in current optical survivability research. </li></ul><ul><li>Joint IP/optical restoration mechanism is the trend in next generation optical network. </li></ul>
    26. 26. Unidirectional Path Switched Ring (UPSR) Signal sent on both working and protected path Best quality signal selected Receiving Traffic N1 send data to N2 N1 N2 Outside Ring = Working Inside Ring = Protection Sending Traffic N4 N3
    27. 27. Unidirectional Path Switched Ring (UPSR) Reply Traffic N2 replies back to N1 Receiving Traffic N1 N2 Outside Ring = Working Inside Ring = Protection N4 N3 Signal sent on both working and protected path Best quality signal selected
    28. 28. Bidirectional Line Switched Ring (2-Fiber BLSRs) Sending/Receiving Traffic Sending/Receiving Traffic N1 send data to N2 & N2 replies to N1 Both Rings = Working & Protection N1 N2 N4 N3
    29. 29. Bidirectional Line Switched Ring (4-Fiber BLSRs) Sending/Receiving Traffic Sending/Receiving Traffic OC-48 N1 send data to N2 & N2 replies to N1 2 Outside Rings = Working 2 Inside Rings = Protection N1 N2 N4 N3