1. Survivability in Optical Networks Xuezhou Ma CSC778 Optical Networks Computer Seience NC Sate University

2. Outline What is optical network survivability and why it is a problem. Diagram for existing techniques Research and literatures Comparison of approaches One interesting direction for future work

3. What and Why? The survivability of a network refers to a network’s capability to provide continuous service in the presence of failures. Optical Fibers with extremely large capacity has becomes dominant transport medium. So the interruption, for even short periods of time, may have disastrous consequences.

4. Resources used for recovery are not pre-reserved but chosen from available when the failure occurs. More efficient than predesigned protection on capacity but may require longer recovery time and overhead. relies on resources (fibers, capacity, etc.) dedicated to protection purposes. These dedicated resource keeps idle when no failure happens. The use of capacity is thus not efficient, but recovery speed can be guaranteed. Recovery solution is predesigned but resources are allocated in real time. Require more complicated algorithm on pre-plan stage.

5. Predesigned Protection Lookback recovery against double-link failure [Choi, H. 04] 2 backup paths are pre-reserved for each link. One method with failure-site identification One method without failure-site identification Problems with this approach??

6. Predesigned Protection (cont’d) Another technique used predesigned protection: [Ou, C. 04] partition a large optical network into smaller domains apply shared-path protection to the optical network such that an intra-domain lightpath does not use resources of other domains and the primary/backup paths of an inter-domain lightpath exit a domain (and enter another domain) through a common domain-border node.

7. Traffic Entry Control Sub-Graph Routing against SRLG failures [Datta, P. 03] Suppose all failures (SRLG or single link) are pre-known. Accept or reject a demand request, based on following test. Problem? How about arbitrary failure combination?

8. Hybrid Approach P-Cycles against multi-fauilures [Wang, H. 05] Offline centralized calculation: for each link e, k cycles pass through e are pre-computed and recorded in a cycle pool table. Online distributed selection: k cycles are ordered by their scores. Cycles with higher scores have higher chance to be selected. Challenge: How to get info and maintain PPT on each node? How many cycles needed to be computed?

9. Dual Homing Problem description [Sasaki, G. 08] Some lightpath is unprotected (can be failed) Some lightpath is protected (will survive failures) Setup a pair of lightpaths to two “hub” nodes which have a protected lightpath between.

11. Survivable Routing of WDM Virtual Topology Notation: Physical Topology: nodes interconnected by optical fibers Virtual Topology: set of lightpaths (end-to-end logical channels) Lightpaths routing: mapping of lightpaths over physical fibers Survivability and lightpath routing: Suppose both physical and virtual topologies are 2-connected. Multiple lightpaths may be routed over the same physical link, and therefore, one link failure will break more than one lightpaths. Problem definition: routing the lightpaths on a physical network in such a way that the logical topology remains connected in the event of any single physical link failures (e.g., fiber cut).  NP-Hard

12. Survivable Routing of WDM Virtual Topology (Cont’d)

13. Survivable Routing of WDM Virtual Topology (Cont’d) Approaches: Integer Linear Programming (ILP) for optical solution [Modiano, E. 02]. Bounded solution space for ring virtual topology [Modiano, E. 02] Disjoint alternate path (DAP) routing the lightapth s.t. there exists an alternate path for each lightpath and share no optical link [Crochat, O. 98] An easy solution for ring physical topology [Lee, H. 03]

14. Survivable Routing of WDM Virtual Topology (Cont’d) Shortest path routing (SPR) Simple but may not work [Modiano, E. 02] a simple relaxation that applies the survivability constraints only to cuts that include a single node, would prevent a single node from getting disconnected in the event of a fiber Cut[8].

15. Comparison Predesigned protection not a efficient use of capacity Dynamic Restoration Complicated algorithm Relies on protection mechanism at upper layer. Hybrid Large overhead Other approaches??

16. Future Work An best-effort fast lightpath routing algorithm: Rout the lightpaths following the shortest path algorithm For each node k, attempt to spread the lightpaths initiating at k over all k’s physical links. (spread at first hop) The assignment of first-hop link for each lightpath is decided by the alternative shortest path.

17. Reference Sub-graph Routing: a Novel Fault-Tolerant Architecture for Shared-Risk Link Group Failures in WDM Optical Networks", P. Datta, M. T. Frederick, A. K. Somani, Proc. Design of Reliable Communication Networks (DRCN), Banff, Alberta, Canada, October, 2003. Subpath protection for scalability and fast recovery in optical WDM mesh networks", by Canhui Ou, Hui Zang, N. K. Singhal, Keyao Zhu, L. H. Sahasrabuddhe, R. A. MacDonald, B. Mukherjee, IEEE Journal on Selected Areas in Communications, Volume 22, Issue 9, Nov. 2004 Pages 1859 - 1875. P-cycles in Multi-failure Network Survivability", Hongxia Wang and H. T. Mouftah, Proc. ICTON, 2005 Loopback recovery from double-link failures in optical mesh networks", Hongsik Choi, Subramaniam, S., Hyeong-Ah Choi, IEEE/ACM Transactions on Networking, Dec. 2004, Volume: 12, Issue: 6 page(s): 1119- 1130 Fumagalli, A.; Valcarenghi, L., "IP restoration vs. WDM protection: is there an optimal choice?," Network, IEEE , vol.14, no.6, pp. 34-41, Nov/Dec 2000 Iannaccone, G.; Chen-Nee Chuah; Bhattacharyya, S.; Diot, C., "Feasibility of IP restoration in a tier 1 backbone," Network, IEEE , vol.18, no.2, pp. 13-19, Mar-Apr 2004 Mohan, G.; Murthy, C.S.R., "Lightpath restoration in WDM optical networks," Network, IEEE , vol.14, no.6, pp. 24-32, Nov/Dec 2000 Modiano, E.; Narula-Tam, A., "Survivable lightpath routing: a new approach to the design of WDM-based networks," Selected Areas in Communications, IEEE Journal on , vol.20, no.4, pp.800-809, May 2002

18. Reference (cont’d) Sasaki, G.; Rozic, C., "Cost Efficient Survivable IP Over WDM With Dual Homing," Optical Fiber communication/National Fiber Optic Engineers Conference, 2008. OFC/NFOEC 2008. Conference on, vol., no., pp.1-3, 24-28 Feb. 2008 Javed, M.S.; Thulasiraman, K.; Guoliang Xue, "Logical Topology Design for IP-over-WDM Networks: A Hybrid Approach for Minimum Protection Capacity," Computer Communications and Networks, 2008. ICCCN '08. Proceedings of 17th International Conference on , vol., no., pp.1-7, 3-7 Aug. 2008 Pin-Han Ho; Mouftah, H.T., "Issues on diverse routing for WDM mesh networks with survivability ," Computer Communications and Networks, 2001. Proceedings. Tenth International Conference on , vol., no., pp.61-66, 2001 Rani, S.; Sharma, A.K.; Singh, P., "Survivability strategy with congestion control in WDM optical networks," High Capacity Optical Networks and Enabling Technologies, 2007. HONET 2007. International Symposium on , vol., no., pp.1-4, 18-20 Nov. 2007 Lee, H., H. Choi, et al. "Survivable embedding of logical topologies in WDM ring networks." Inf. Sci. Inf. Comput. Sci. 149(1-3): 151-160. 2003 Crochat, O.; Le Boudec, J.-Y., "Design protection for WDM optical networks," Selected Areas in Communications, IEEE Journal on , vol.16, no.7, pp.1158-1165, Sep 1998

19. Question?