Outline

1. Outline • Introduction to WDM network design and optimization • Integer Linear Programming approach • Physical Topology Design • Unprotected case • Dedicated path protection case • Shared path & link protection cases • References

2. Dedicated Path Protection (DPP) • 1+1 or 1:1 dedicated protection (>50% capacity for protection) • Both solutions are possible • Each connection-request is satisfied by setting-up a lightpath pair of a working + a protection lightpaths • RFWA must be performed in such a way that working and protection lightpaths are link disjoint • Additional constraints must be considered in network planning and optimization • Transit OXCs must not be reconfigured in case of failure • The source model can not be applied to this scenario

3. Dedicated Path Protection (DPP) Flow formulation, VWP • New symbols • xl,k,c,t= number of WDM channels carried by link l in the direction k assigned to the t-th connection between source-destination couple c • Rationale: for each connection request, route a link-disjoint connection  route two connection and enforce link-disjoint constraint

4. Dedicated Path Protection (DPP)Route formulation (RF), VWP • New symbols • rc,n,t= 1 if the t-th connection between source destination node couple c is routed on the n-th admissible path • R(l,k),c= set of all admissible paths connecting source destination node couple c passing through link (l,k)

5. ILP application to WDM network design Route formulation (RF) II, VWP • Substitute the single path variable rc,nby a protected route variable r’c,n(~ a cycle) • No need for representation in terms of interference (crossing) between paths • Identical formulation to unprotected case

6. Scalability of RF and FF in DPP case • Flow and Route formulation can be applied only in small networks, due to their limited scalability • Route formulation: the number of possible w/s paths in a network becomes too large, when the number of nodes and links grows • Constrained routing (sub-optimal) • Flow formulation: slightly more scalable than RF with network dimension, FF suffers more severely the increase of traffic amount • For a deeper analysis of these approaches [RaMu99], [MiSa99], [BiGu95], [CaPaTuDe98]

7. Outline • Introduction to WDM network design and optimization • Integer Linear Programming approach • Physical Topology Design • Unprotected case • Dedicated path protection case • Shared path & link protection cases • References

8. Shared Path Protection (SPP) • Protection-resources sharing • Protection lightpaths of different channels share some wavelength channels • Based on the assumption of single point of failure • Working lightpaths must be link (node) disjoint • Very complex control issues • Also transit OXCs must be reconfigured in case of failure • Signaling involves also transit OXCs • Lightpath identification and tracing becomes fundamental • Sharing is a way to decrease the capacity redundancy and the number of lightpaths that must be managed

9. Link Protection N o r m a l C o n n e c t i o n • Link protection (≥50% capacity for protection) • Each link is protected by providing an alternative routing for all the WDM channels in all the fibers • Protection switching can be performed by fiber switches (fiber cross-connects) or wavelength switches • Signaling is local; transit OXCs of the protection route can be pre-configured • Fast reaction to faults • Some network fibers are reserved for protection • Link-shared protection (LSP) • Protection fibers may be used for protection of more than one link (assuming single-point of failure) • The capacity reserved for protection is greatly reduced O M S p r o t e c t i o n ( l i n k p r o t e c t i o n )

10. Link Protection • Different protected objects • Fiber level • Wavelength channel level FAULT EVENT (1) (2)

11. Link ProtectionSummary results • Comparison between different protection technique on fiber needed to support the same amount of traffic • Switching protection objects at fiber or wavelength level does ot sensibly affects the amount of fibers. • This difference increase with the number of wavelength per fiber

12. Outline • Introduction to WDM network design and optimization • Integer Linear Programming approach to the problem • Physical Topology Design • Unprotected case • Dedicated path protection case • Shared path protection case • Link protection • Logical Topology Design • References

13. References • Books • [Mu97] B. Mukherjee, Optical Communication Networks, McGraw-Hill, 1997, New York • [StBa99] T. E. Stern and K. Bala, Multiwavelength Optical Networks: A Layered Approach, Addison Wesley, 1999 • [RaSi02] R. Ramaswami and K. N. Sivarajan, Optical Networks: A Practical Perspective, Morgan& Kauffman Academic Press, 2002 • [RaGu01] C. S. Ram Murthy, M. Gurusamy, WDM Optical Networks: Concepts, Design, and Algorithms, Prentice Hall, 2001 • [Wi99] H. Paul Williams, Model building in mathematical programming, John Wiley & Sons,1999

14. References • Articles • [WaDe96] N. Wauters and P. M. Deemester, Design of the optical path layer in multiwavelength cross-connected networks, Journal on selected areas on communications,1996, Vol. 14, pages 881-891, June • [CaPaTuDe98] B. V. Caenegem, W. V. Parys, F. D. Turck, and P. M. Deemester, Dimensioning of survivable WDM networks, IEEE Journal on Selected Areas in Communications, pp. 1146–1157, sept 1998. • [ToMaPa02] M. Tornatore, G. Maier, and A. Pattavina, WDM Network Optimization by ILP Based on Source Formulation, Proceedings, IEEE INFOCOM ’02, June 2002. • [CoMaPaTo03] A.Concaro, G. Maier, M.Martinelli, A. Pattavina, and M.Tornatore, “QoS Provision in Optical Networks by Shared Protection: An Exact Approach,” in Quality of service in multiservice IP Networks, ser. Lectures Notes on Computer Sciences, 2601, 2003, pp. 419–432. • [ZhOuMu03] H. Zang, C. Ou, and B. Mukherjee, “Path-protection routing and wavelength assignment (RWA) in WDM mesh networks under duct-layer constraints,” IEEE/ACM Transactions on Networking, vol. 11, no. 2, pp.248–258, april 2003. • [BaBaGiKo99] S. Baroni, P. Bayvel, R. J. Gibbens, and S. K. Korotky, “Analysis and design of resilient multifiber wavelength-routed optical transport networks,” Journal of Lightwave Technology, vol. 17, pp. 743–758, may 1999.

15. References • Articles • [ChGaKa92] I. Chamtlac, A. Ganz, and G. Karmi, “Lightpath communications: an approach to high-bandwidth optical WAN’s,” IEEE/ACM Transactionson Networking, vol. 40, no. 7, pp. 1172–1182, july 1992. • [RaMu99] S. Ramamurthy and B. Mukherjee, “Survivable WDM mesh networks, part i - protection,” Proceedings, IEEE INFOCOM ’99, vol. 2, pp. 744–751, March 1999. • [MiSa99] Y. Miyao and H. Saito, “Optimal design and evaluation of survivable WDM transport networks,” IEEE Journal on Selected Areas in Communications, vol. 16, pp. 1190–1198, sept 1999. • [BaMu00] D. Banerjee and B. Mukherjee, “Wavelength-routed optical networks: linear formulation, resource budgeting tradeoffs and a reconfiguration study,” IEEE/ACM Transactions on Networking, pp. 598–607, oct 2000. • [BiGu95] D. Bienstock and O. Gunluk, “Computational experience with a difficult mixed integer multicommodity flow problem,” Mathematical Programming, vol. 68, pp. 213–237, 1995. • [RaSi96] R. Ramaswami and K. N. Sivarajan, Design of logical topologies for wavelength-routed optical networks, IEEE Journal on Selected Areas in Communications, vol. 14, pp. 840{851, June 1996.

16. References • Articles • [BaMu96] D. Banerjee and B. Mukherjee, A practical approach for routing and wavelength assignment in large wavelength-routed optical networks, IEEE Journal on Selected Areas in Communications, pp. 903-908,June 1996. • [OzBe03] A. E. Ozdaglar and D. P. Bertsekas, Routing and wavelength assignment in optical networks, IEEE/ACM Transactions on Networking, vol. 11, no. 2, pp. 259-272, Apr 2003. • [KrSi01] Rajesh M. Krishnaswamy and Kumar N. Sivarajan, Design of logical topologies: A linear formulation for wavelength-routed optical networks with no wavelength changers, IEEE/ACM Transactions on Networking, vol. 9, no. 2, pp. 186-198, Apr 2001. • [FuCeTaMaJa99] A. Fumagalli, I. Cerutti, M. Tacca, F. Masetti, R. Jagannathan, and S. Alagar, Survivable networks based on optimal routing and WDM self-heling rings, Proceedings, IEEE INFOCOM '99, vol. 2, pp. 726-733,1999. • [ToMaPa04] M. Tornatore and G. Maier and A. Pattavina, Variable Aggregation in the ILP Design of WDM Networks with dedicated Protection , TANGO project, Workshop di met\ag progetto , Jan, 2004, Madonna di Campiglio, Italy

17. Path-protected WDM mesh networksA an optimization tool for dedicated path-protection • Optimal design of WDM networks under static traffic with dedicated path-protection (1+1 or 1:1) • The heuristicoptimizationmethod can be applied to multifiber mesh networks, with or without wavelength converters • It allows to setup protected lightpaths so to minimize the amount of fiber deployed in the network • Each connection request is satisfied by setting up a working-protection (W-P) lightpath pair under the link-disjoint constraint

18. Heuristic static design by dynamic RFWA Heuristic design and optimization scheme Sort connection requests Setup the lightpaths sequentially Idle network, unlimited fiber Prune unused fibers Identify fibers with only k used ls for k = 1 to W Prune unused fibers Attempt an alternative RFWA for the identified lightpaths • Connection request sorting rules • Longest first • Most requested couples first • Balanced • Random • Processing of an individual lightpath • Routing, Fiber and Wavelength Assignment (RFWA) criteria • Dijkstra’s algorithm performed on the multifiber layered graph

19. Path-protected WDM mesh networksCase-study • National Science Foundation Network (NSFNET): USA backbone • Physical Topology • 14 nodes • 44 unidirectional links • Design options • W: 2, 4, 8, 16, 32 • 8 RFWA criteria

20. Heuristic static design by dynamic RFWA RFWA-criteria labels

21. Heuristic static design by dynamic RFWA Total number of fibers m H m L VWP V W P W P V W P W P WP S P L L R S P L L R S P L L R S P L L R 500 500 5 0 0 5 0 0 410 404 2 400 400 4 0 0 4 0 0 4 8 1 6 300 300 3 0 0 3 0 0 3 2 213 207 200 200 2 0 0 2 0 0 114 109 64.5 59.7 100 100 1 0 0 1 0 0 39.4 36.2 0 0 0 0 2 4 8 16 32 C 3 C 1 C 7 C 5 C 4 C 2 C 8 C 6 • The initial sorting rule resulted almost irrelevant for the final optimized result (differences between the sorting rules below 3%) • Hop-metric minimization performs better • Variations of M due to RFWAs and conversion in the mH case below 5% . Total fiber number, M Total fiber number, M Number of wavelengths, W

22. Heuristic static design by dynamic RFWA Fiber distribution in the network (6,5) (0,1) (4,4) (0,0) (2,2) (0,0) (4,4) (2,2) (2,2) (5,6) (6,6) (6,6) (6,5) (4,4) (3,4) (2,2) (2,2) (2,3) (2,2) (2,2) (2,2) (2,2) • NSFNet with W = 16 wavelengths per fiber, mL SP RFWA criteria • The two numbers indicate the number of fibers in the VWP and WP network scenarios • Some links are idle

23. Heuristic static design by dynamic RFWA Wavelength conversion gain • Wavelength converters are more effective in reducing the optimized network cost when W is high

24. Heuristic static design by dynamic RFWA Saturation factor V W P W P VWP m L m H m L m H WP L L R S P L L R S P L L R S P L L R S P 1 1 1.2 1.2 0.985 0.972 0.97 0.936 0.929 0 . 9 5 0 . 9 5 0.884 1 1 0.862 0.787 2 0 . 9 0 . 9 0.758 4 0.668 0.8 0.8 0 . 8 5 0 . 8 5 8 1 6 0 . 8 0 . 8 0.6 0.6 3 2 0 . 7 5 0 . 7 5 0.4 0.4 0 . 7 0 . 7 0.2 0.2 0 . 6 5 0 . 6 5 0 . 6 0 . 6 0 0 C 1 C 3 C 2 C 4 C 6 C 8 C 5 C 7 2 4 8 16 32 • A coarser fiber granularity allows us to save fibers but implies a smaller saturation factor • VWP performs better than WP • Variations of r due to RFWAs and metrics in the VWP case below 5% . . C = number of used wavelength channels r r Saturation factor, Saturation factor, Number of wavelengths, W

25. Heuristic static design by dynamic RFWA Optimization: longer lightpaths... , D • Compared to the initial routing (shortest path, which is also the capacity bound) the fiber optimization algorithm increases the total wavelength-channel occupation (total lightpath length in number of hops) • C is increased of max 10% of CSP in the worst case CSP = number of used wavelength channels withSP routing and unconstrained resources(capacity bound)

26. Heuristic static design by dynamic RFWA …traded for fewer unused capacity • Compared to the initial routing (shortest path) the fiber optimization algorithm decreases the total number of unused wavelength-channels • U is halved in the best case • Notes • Initial SP routing curve:data obtained in the VWP scenario (best case) • Optimized solution curve:averaged data comprising the WP and VWP scenarios

27. Heuristic static design by dynamic RFWA Convergence of the heuristic optimization • The algorithm appears to converge well before the last iteration • Improvements of the computation time are possible • Note: convergence is rather insensitive to the initial sorting rule and to the RFWA criteria

28. Case-study networksComparison of SF with heuristic optimization (VWP) N S F N E T V W P E O N V W P 4 0 0 1 6 0 0 s o u r c e f o r m . 3 5 0 1 4 0 0 s o u r c e f o r m . h e u r i s t i c 3 0 0 h e u r i s t i c 1 2 0 0 2 5 0 1 0 0 0 2 0 0 Total fiber number, M 8 0 0 Total fiber number, M 1 5 0 6 0 0 1 0 0 4 0 0 5 0 2 0 0 0 0 0 5 1 0 1 5 2 0 2 5 3 0 3 5 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 Number of wavelengths, W Number of wavelengths, W • ILP by SF is a useful benchmark to verify heuristic dimensioning results • Approximate methods do not share this property .

29. Case-study networksComparison of SF with heuristic optimization (VWP) • The absolute error diminishes with W (as the number of fibers) • The percent error increases with W

30. Case-study networksComparison of SF with heuristic optimization (WP) N S F N E T W P N S F N E T V W P 4 0 0 4 0 0 h e u r i s t i c s o u r c e f o r m . 3 5 0 3 5 0 s o u r c e f o r m h e u r i s t i c 3 0 0 3 0 0 2 5 0 2 5 0 2 0 0 Total fiber number, M 2 0 0 Total fiber number, M 1 5 0 1 5 0 1 0 0 1 0 0 5 0 5 0 0 0 0 5 1 0 1 5 2 0 2 5 3 0 3 5 0 5 1 0 1 5 2 0 2 5 3 0 3 5 Number of wavelengths, W Number of wavelengths, W • The optimized values of the cost function in the WP and WVP case are very close • Improvements due to the adoption of wavelength conversion are modest in static network design

31. Heuristic static design by dynamic RFWA Concluding remarks • A heuristic method for multifiber WDM network optimization under static traffic has been proposed and applied to various physical network scenarios • Good sub-optimal solutions in terms of total network fiber resources can be achieved with a reasonable computational effort • The method allows to inspect various aspects such as RFWA performance comparison and wavelength converter effectiveness • Future possible developments • Upgrade to include also lightpath protection in the WDM layer • Improvement of the computation time / memory occupancy