1 st COST270 Workshop on Reliability of Optical Networks, Systems and Components

1. p-Cycles: Network Protectionwith Ring-speed and Mesh-efficiency 1st COST270 Workshop on Reliability of Optical Networks, Systems and Components December 13, 2001 - EMPA, Dubendorf, Switzerland Dominic SchupkeClaus Gruber Munich University of Technology Institute of Communication Networks Wayne GroverDemetrios Stamatelakis TRLabs, University of Alberta

2. Outline • Motivation • Basics • p-Cycles in WDM Networks • Self-organization of p-Cycles • p-Cycles in IP Router Restoration (Overview) • Summary

3. “ Ring “ A. 50 msec restoration times B. Complex network planning and growth C. High installed capacity for demand-served D. Simple, low-cost ADMs E. Hard to accommodate multiple service classes F. Ring-constrained routing “Mesh” G. Up to 1.5 sec restoration times H. Simple, exact capacity planning solutions I. well under 100% redundancy J. Relatively expensive DCS/OXC K. Easy / efficient to design for multiple service classes L. Shortest-path routing Background and Motivation “ Shopping list” :A, D, H, I, L (and K) please...keep the rest

4. p-Cycles: Basics • For meshed networks • Pre-reserved protection paths (before failure) • Based on cycles, like rings • Also protects straddling failures, unlike rings • Local protection action, adjacent to failure (in the order of some 10 milliseconds) • Shared capacity • “pre-configured protection cycles” p-cycles

5. p-Cycles: Basics • A single p-cycle in a network:

6. p-Cycles: Basics • Protected spans: • 9 „on-cycle“ (1 protection path)

7. p-Cycles: Basics • Protected spans: • 9 „on-cycle“ (1 protection path) • 8 „straddling“ (2 protection paths)

8. Restoration using p-cycles If span i fails,p-cycle j provides one unit of restoration capacity i j If span i fails,p-cycle j provides two units of restoration capacity j i

9. Combination of p-Cycles • Optimization problem: Find a set of cycles which minimizesthe protection capacity 10 6 6 Demand(capacity: 22) 6 10 4 10 6 4 4 10 6 Two p-cycles (protection capacity: 36) A possible p-cycle (protection capacity: 40) 10 6

10. p-Cycles in WDM-Networks • VWP • „virtual wavelength path“ • Nodes have full wavelength conversion capabilities • Wavelength can change on the path • WP • „wavelength path“ • Nodes have no wavelength conversion capabilities • Wavelength cannot change on the path

11. p-Cycles in WDM-Networks • VWP • No impact on p-Cycles: • WP • p-cycle must use same wavelength as path: p-Cycle protects demand C-G

12. Implementation • Multi-layered: • Demand Topology • Duct Topology • Routing und Cycle Search • Fiber Topology • Graph-based Approach: • Library of Efficient Data Types and Algorithms (LEDA) • Network Planning Library (NPL) • Optimization (Integer Linear Programming) • AMPL • CPLEX, LPSOLVE

13. Implementation Read Demands, Duct-Topologyand Parameters Demands, Ducts Demands, Ducts, Fibers Create Graphs (Demands, Ducts, Fibers) Demands, Ducts, Fibers Routing of the Demands (Dijkstra, First λ Fit) Ducts, Fibers Search for Potential Cycles Create ILP Model (AMPL) Solve Model (CPLEX, LPSOLVE) Demands, Ducts, Fibers p-Cycles-Allocation und Visualization

14. Case Study: COST 239 • 2 fibers per duct • 128 wavelengths per fiber

15. 1.0 * Demand 2.5 * Demand 3000 3500 5.0 * Demand 4000 4500 5000 10.0 * Demand 5500 6000 6500 all Results: VWP Network 1,2 1,1 1 0,9 Protection / Working Capacity Ratio 0,8 0,7 0,6 0,5 0,4 cylce length (km)

16. Results: WP Network 1.6 1.4635 1.4 1.3629 1.2 1.2919 0.8442 1 0.7061 Protection / Working Capacity Ratio 1.2939 0.8 1.1558 1.0907 0.6 0.4 0.6943 (300 MB) 0.2 0.6312 0 WP-Network 1 2 VWP-Network 3 4 cycle length(km) 5 1.0 * Demand

17. VWP Calculation Times Cycle- Graph Routing Cycle AMPL-data AMPL CPLEX Sum length Creation Search Creation (km) 3000 0,53 0,84 10,12 0,48 0,24 0,3 12,51 3500 0,53 0,86 41,23 0,99 0,63 0,76 45 4000 0,53 0,87 173,14 2,43 0,84 3,37 181,18 4500 0,53 0,87 617,62 5,69 2,49 3,98 631,18 5000 0,49 0,85 1497,71 11,08 3,94 5,68 1519,75 5500 0,52 0,87 2944,7 19,07 5,54 9,21 2979,91 6000 0,5 0,87 4750,35 28,16 7,23 16,48 4803,59 6500 0,55 0,91 8509,01 46,43 9,66 22,13 8588,69 all 0,56 0,88 8653,03 46,04 9,62 22,09 8732,22 1.0 * Demand, Times in Seconds

18. Impact of Demands-Routing • Optimal set of p-cycles is depending on routing: Investigation of shortest path routing with adapting metric (inverse of free capacity on span) 6 6 6 12 6 6 12 6 12 6 12 4*12 = 48 7*6 = 42

19. Results: Routing Dependence 59% 8400 8210 8200 8003 fixed metric (1.0) 8000 7880 52% 7800 44% 7704 7613 7552 7534 7600 7468 7468 7427 Used Links for Demands and Protection 7400 7231 7124 7200 7072 7051 7044 adapting metric 7000 34% 6800 6600 6400 3500 4000 4500 5000 5500 6000 6500 all cycle length (km)

20. i.e., “mesh-like” capacity Optimal Spare capacity design - Typical Results • “Excess Sparing” = Spare Capacity compared to Optimal Span-Restorable Mesh

21. Understanding why (optimally planned) p-cycles are so efficient... Spare p-Cycle…same spare capacity UPSR or BLSR Working Coverage 9 Spares cover 19 Workers 9 Spares cover 9 Workers “the clam-shell diagram”

22. Further comparing p-cycles to rings

23. ADM-like “capacity-slice” nodal device for p-cycle networking

24. Self-organization of the p-cycles ... • p-cycles certainly could be centrally computed and configured. • based on the preceding formulation However, an interesting option is to consider if the network can adaptively and continually self-organize - a near-optimal set of p-cycles within itself, - for whatever demand pattern and capacity configuration it currently finds.

25. Self-organization of the p-cycles • Based on an extension / adaptation of SHN™ distributed mesh restoration algorithm • “DCPC” = distributed cycle pre-configuration protocol • Operates continually in background • Non-real time phase self-organizes p-cycles • Real time phase is essentially BLSR switching • p-cycles in continual self-test while in “storage” • Centralized “oversight” but not low-level control • Method is autonomous, adaptive • Networks actual state on the groundis the database

26. Key concepts of DCPC protocol • Node roles: • Cycler node state , Tandem node state • DCPC implemented as event-driven Finite State Machine (FSM) • Nodal interactions are (directly) only between adjacent nodes • Indirectly between all nodes (organic self-organization) • via “statelets” on carrier / optical signal overheads • Three main steps / time-scales / processes • Each nodes act individually, “exploring” network from its standpoint as cycler node. • All nodes indirectly compare results • Globally best p-cycle is created

27. Overview of DCPC protocol

28. How DCPC discovers “best p-cycles” (2)

29. How DCPC discovers “best p-cycles” (1)

30. DCPC Performance studies

31. Illustrating the Real time phase

32. Adapting p-cycles to the IP-layer …

33. IP Network Restoration • IP Networks are already “Restorable” • Restoration occurs when the Routing protocol updates the Routing Tables • This update can take a Minute or more - Packets are lost until this happens • Speed-up of IP Restoration is needed • Not losing packets would be great too • Also some control over capacity / congestion impacts needed • p-cycles proposed as “fast” part of a fast + slow strategy that retains normal OSPF-type routing table re-convergence

34. (b) Straddling Failure (2Restoration paths) (a) On-Cycle Failure (1 restoration Path) Data Encapsulation Router Failed Link Data De-Encapsulation p-cycle Router Operation of IP-layer p-cycles

35. Router Failure Restoration using“Node-Encircling” p-Cycles • Node Encircling p-Cycles. Each Node has a p-Cycle dedicated to its failure • For each Node, a p-Cycle is chosen which includes all logically “Adjacent” Nodes but not the Protected Node Other Nodes Encircled Node Node-Encircling p-cycle

36. Node Failure Router Restoration using“Node-Encircling” p-Cycles p-Cycles are Virtual Circuits/Protection Structures which can redirect Packets around Failures • Plain IP is Connectionless but p-Cycles can be realized withMPLS, IP Tunneling/Static Routes

37. Concluding Comments Investigation on WDM-networks: • p-cycles are suitable and efficient for converting and non-converting WDM-networks • Short off-line calculation times for fully converting networks • Results are depending on demands routing • Only some improvement by non-simple cycles Outlook: • Partial wavelength conversion • Multiple failures

38. Concluding Comments • p-cycles offer new approaches to both WDM and IP-layer transport • “ mesh-like efficiency with ring-like speed ” • Capacity-planning theory • for 100% span restoration in WDM / Sonet with mesh sparing • for controlled worst-case over-subscription in IP-layer • “Node-encircling” p-cycles • fast integrated restoration against either router or link-failures • Nortel has implemented span-restoration via IP p-cycles • ~ 10 msec restoration time, no packet loss in their experiments • Ongoing studies: • Integrated planning of composite node / link restoration p-cycles • Availability analysis of p-cycles

39. References on p-Cycles • [1]W.D. Grover, D. Stamatelakis, "Cycle-Oriented Distributed Preconfiguration: Ring-like Speed with Mesh-like Capacity for Self-planning Network Restoration," Proc. IEEE International Conf. Commun. (ICC'98), Atlanta, June 8-11, 1998. pp. 537-543.  • [2]D. Stamatelakis, W.D. Grover, "Theoretical Underpinnings for the Efficiency of Restorable Networks Using Pre-configured Cycles ("p-cycles")", to appear in IEEE Transactions on Communications, accepted December 1999 (contact TRLabs for an advance copy) • [3]W.D. Grover, D Stamatelakis, "Bridging the ring-mesh dichotomy with p-cycles", Proc. Design of Reliable Communication Networks (DRCN 2000), Technical University of Munich, April 2000, pp. 92-104. • [4]D. Stamatelakis, W.D. Grover, "Rapid Restoration of Internet Protocol Networks using Pre-configured Protection Cycles," Proc. 3rd Can. Conf. On Broadband Research (CCBR'99), Nov. 7, 9, Ottawa, 1999 • [5] D.A. Schupke, C.G. Gruber, A. Autenrieth, “Optimal Configuration of p-Cycles in WDM Networks,” submitted to ICC 2002