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Optical Networks – Fault Tolerance (Part 2) Dr. Arunita Jaekel

Optical Networks – Fault Tolerance (Part 2) Dr. Arunita Jaekel. Fault-tolerance in Optical Networks. Faults in Optical Networks Link failures the most common type of fault, where the fiber constituting a link between two nodes in the network does not permit data transmission . Node failures

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Optical Networks – Fault Tolerance (Part 2) Dr. Arunita Jaekel

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  1. Optical Networks – Fault Tolerance (Part 2)Dr. ArunitaJaekel

  2. Fault-tolerance in Optical Networks • Faults in Optical Networks • Link failures the most common type of fault, where the fiber constituting a link between two nodes in the network does not permit data transmission. • Node failures • Channel failures • Software failures • Most papers assume single fault scenario.

  3. Fault-tolerance in Optical Networks • Reasons behind faults in optical layer • Fiber cut • Noise introduced by optical signal regenerators and amplifiers • Cable inside a site may get disconnected • Importance of Fault management in optical networks • Large amount of traffic carried by optical channels • Each fiber carries many channels • Failure may lead to huge data loss

  4. Fault-tolerance in Optical Networks • Categorization of fault management schemes Figure 20

  5. Fault-tolerance in Optical Networks • Protection scheme • Recovery scheme determined at design time • Resources are reserved for each possible failure (link or path). • Faster recovery time and guaranteed recovery • Restoration scheme • Recovery scheme determined after the occurrence of fault • Dynamically search for backup path and available wavelength after failure occurrence. • Efficient in utilizing capacity

  6. Fault-tolerance in Optical Networks • Link protection – backup path reserved around each link • Primary path: N8N4N6N1 • The faulty edge N4N6 is replaced by an alternate route N4N7N6. • Backup path: N8N4N7N6N1 N1 N2 N3 C3 C3 N4 N5 C3 C3 X C3 C3 C3 N6 N7 N8 Primary path Backup path Figure 22: Link protection scheme

  7. Fault-tolerance in Optical Networks • Path Protection • In the case of a fault, for each primary lightpath using the faulty component, the corresponding backup lightpath will be set up. • All data carried by each primary lightpath affected by the fault will be switched over to the corresponding backup lightpath. • Primary and backup paths must be edge-disjoint.

  8. Fault-tolerance in Optical Networks • Path Protection – backup path reserved on a end-to-end basis N1 N2 N3 C3 C3 N4 N5 C2 C1 C1 N6 N7 N8 Primary path C2 Backup path Figure 21: Path protection scheme

  9. Primary 2 3 1 4 6 5 Backup Fault-tolerance in Optical Networks • Dedicated path protection • Dedicated Path Protection • The channel used by a backup lightpath is always reserved for a single primary lightpath. Figure 23: 1:1 Protection

  10. Primary 2 3 1 1 4 2 6 5 Backup Fault-tolerance in Optical Networks • Shared Path Protection ( also called backup multiplexing ) Resources may be shared by two or more backup paths if and only if the corresponding primary paths are edge disjoint. Figure 24: 1:N Protection

  11. ILP for Dedicated Path Protection(DPP) • Given: • Physical fiber network G[N, E]. • A set of channels Kon each fiber. • A set Lof existing connections (lightpaths) in the network. • ae,l= 1, if and only if the lthexisting connection uses edge e(ij)on its primary lightpath. • be,l = 1, if the lthexisting connection uses edge e on its backup lightpath. • kl,p(kl,b) = the channel assigned to the lthprimary (backup) path Integer Variables • xe(ye) = 1, if and only if the primary (backup) route of new lightpath uses physical link e. • wk(zk) = 1, if and only if primary (backup) route of new lightpath is assigned channel k. λ1 2 λ1 λ1 1 3 λ2 Existing Lightpaths 4 1  3 2  1 4  2 4  3 31

  12. ILP for Dedicated Path Protection(DPP) Min Subject to: λ1 2 λ1 λ1 1 3 λ2 1 4 1  3 2  1 4  2 4  3 3  1

  13. ILP for Shared Path Protection(SPP) Min 1  3 2  1 4  2 4  3 3  1 λ1 2 λ1 λ1 1 3 1 λ2 4 New variables: de,l = 1, if primary path of new lightpath and lightpathl both used edge e. dl = 1, if primary path of new lightpath has a common edge with lightpathl

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