Preserving Survivability During Logical Topology Reconfiguration in WDM Ring Networks

1. Preserving Survivability During Logical Topology Reconfiguration in WDM Ring Networks Hwajung Lee, Hongsik Choi, Suresh Subramaniam, and Hyeong-Ah Choi The George Washington University Supported in part by DARPA under grant #N66001-00-18949 (Co-funded by NSA) DISA under NSA-LUCITE Contract NSF under grant ANI-9973098

2. Outline • Introduction – Network Survivability • Motivation • Problem Formulation • Problem Complexity • Simple Reconfiguration Approach & its Limitation • MinCostReconfiguration Algorithm • Concluding Remarks

3. Introduction IP ATM IP IP SONET/ SDH SONET/ SDH ATM IP WDM Optical Network Physical Fiber Plant Network Survivability • To guarantee for users to use the network service without any interruption. • Each layer has its own fault recovery functions. • Fault propagation

4. Introduction Survivable Logical Topology • Logical topology (Upper Layer) is called survivableif it remains connected in the presence of a single optical link failure. • Faulty Model : Single optical link failure.

5. Introduction Survivable Desirable! Not Survivable Electronic layer is connected even when a single optical link fails Survivable Logical Topology 1 0 Optical Layer = Physical Topo. Upper Layer = Logical Topology 2 5 0 1 3 4 3 4 1 0 2 5 Map each connection request to an optical lightpath. 2 5 3 4

6. … … a c d … … b Introduction Survivable Logical Topology • Sometimes, there is no way to have a Survivable Logical Topology Embedding on a Physical Topology. Optical Layer = Physical Topo. Electronic Layer = Logical Topology e1 b a … … e2 c d 2-Edge Connected

7. Introduction Survivable Logical Topology Design Problem (SLTDP) • Given • a physical topology, and • a logical topology = a set of connection requests. • Objectives • Find a route of lightpath for each connection request, such that the logical topology remains connected after a single link failure if possible. • Otherwise, determine and embed the minimum number of additional lightpaths to make the logical topology survivable.

8. 2n 3 n 2 Introduction H. Lee, H. Choi, S. Subramaniam, and H.-A. Choi, “Survivable Logical Topology Design in WDM Optical Ring Networks,” The 39th Annual Allerton Conference, October 2001, Invited Paper • Survivable LT design possible • Completely connected (i.e., (n-1)-edge connected) • NO survivable LT design when logical topology G is • 2-edge connected • 3-edge connected • 4-edged connected • Degree Constraints • Survivable LT design possible when min. degree >= • No survivable LT design for min. degree <= ( -1) • Experimental Results – Near Optimal

9. # of Ports = 3 # of Wavelength = 3 Add G2\G1 to form G1 G2 Delete G1\G2 Motivation Reconfiguration of Survivable Logical Topologies What if # of Wavelength < 3 or # of Ports < 3 Survivable Logical Topology = G1 Survivable Logical Topology = G2 1 1 0 0 2 2 3 3 Physical Topology = Gp 1 0 3 2

10. Problem Formulation Reconfiguration of Survivable Logical Topologies • Given Two Survivable Logical Topology G1 and G2 on a physical topology Gp • Constraints the number of port p, the number of wavelength W • Objectives During the entire period of reconfiguration, • The logical topology remains survivable • The port p and wavelength W constraints are satisfied.

11. Problem Complexity Problem Complexity • If no p or W constraint exists, In General, the problem can be solved by • Add G2\G1 to form G1 G2. • Delete G1\G2. • Except CASE 1 in the next slide. • If the port and/or wavelength constraints exist(s), more Complicated. • CASE 2 and CASE 3.

12. isolated isolated Problem Complexity CASE 1 • Need to change the directions of some lightpaths in G1 G2. Logical topologies Physical topology 6 6 1 5 1 5 1 6 5 2 4 3 2 4 2 4 3 3 Survivable Survivable 1 6 1 6 2 5 2 5 3 4 3 4

13. Problem Complexity CASE 3 • Need to temporarily delete and re-establish some lightpaths in G1 G2 due to Wavelength Constraints. • Need to temporarily add some lightpaths not in G1 G2 to guarantee the survivability and delete later. 6 6 1 5 1 5 1 6 Logical topologies Physical topology 5 2 4 3 4 2 4 2 3 3 ! ? No ! (W = 4) Yes ! (W = 3) CASE 2 1 6 1 6 2 5 2 5 3 4 3 4 W = 3, p = 4 .

14. Reconfiguration Algorithm Simple Reconfiguration Approach • If the current lightpath setup uses W-1 wavelength in each optical link and upto p-2 ports at each node, • add a lightpath btw each pair of adjacent nodes, • delete all lightpaths in G1 except the above, and • establish all lightpaths in G2 based on its survivable embedding. 1 6 2 5 3 4 W = 4, p = 6

15. Reconfiguration Algorithm Limitation of Simple Reconfiguration Approach W = k + 1

16. Reconfiguration Algorithm Algorithm MinCostReconfiguration Cost = # of add * UnitCostadd +# of delete * UnitCostdelete • Given Input : M1, M2, Gp • Output : Wadd, Wadd = Wreconfig – max{WM1, WM2} • Constraints the number of portp, the number of wavelength W • Objectives • To minimize Wreconfig while reconfiguration cost is preserved minimum. • During the entire period of reconfiguration, • The logical topology remains survivable • The port p and wavelength Wconstraints are satisfied.

17. Wreconfig = max{ML1, ML2} = 4 (= Winitial ) From To ML1 = 4 ML2 = 3

18. Wreconfig = 4 0 1 7 6 2 3 5 4

19. Wreconfig = 4 0 1 7 6 2 3 5 4

20. Wreconfig = 4

21. Wreconfig = 4 0 1 7 6 2 3 5 4

22. Wreconfig = 5

23. Wreconfig = 5

24. Wreconfig = 5 Wadd = Wreconfig - Winitial = 5 – 4 = 1

25. Results Numerical Results# of Simulations per each case = 500n = 8

26. Results Numerical Results# of Simulations per each case = 500n = 16

27. Results Numerical Results# of Simulations per each case = 500n = 32

28. Results Numerical ResultsDiffFactor = 2(|E(G1)-E(G2)|+|E(G2)-E(G1)|)/n(n-1)

29. Concluding Remarks Concluding Remarks • Develop Algorithms • to guarantee min # of Wavelength • to find a proper compromising point of reconfiguration cost and the best number of wavelength under the reconfiguration cost constraint and the number of wavelength constraint.