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1 st COST270 Workshop on Reliability of Optical Networks, Systems and Components December 13, 2001 - EMPA, Dubendorf, Switzerland Dominic Schupke Claus Gruber Munich University of Technology Institute of Communication Networks Wayne Grover Demetrios Stamatelakis TRLabs, University of Alberta p-Cycles: Network Protection with Ring-speed and Mesh-efficiency

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

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Background and Motivation 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 Shopping list : A, D, H, I, L (and K) please...keep the rest

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Background - ideas of mesh preconfiguration

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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 p-Cycles: Basics

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A single p-cycle in a network: p-Cycles: Basics

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Protected spans: 9 on-cycle (1 protection path)

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Protected spans: 9 on-cycle (1 protection path) 8 straddling (2 protection paths) p-Cycles: Basics

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

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

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Optimal Spare capacity design with p-cycles

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

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

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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 Implementation

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

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

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0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 Protection / Working Capacity Ratio cylce length (km) Results: VWP Network

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

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1.0 * Demand, Times in Seconds Cycle- length (km) Graph Creation RoutingCycle Search AMPL-data Creation AMPLCPLEXSum 30000,530,8410,120,480,240,312,51 35000,530,8641,230,990,630,7645 40000,530,87173,142,430,843,37181,18 45000,530,87617,625,692,493,98631,18 50000,490,851497,7111,083,945,681519,75 55000,520,872944,719,075,549,212979,91 60000,50,874750,3528,167,2316,484803,59 65000,550,918509,0146,439,6622,138588,69 all0,560,888653,0346,049,6222,098732,22 VWP Calculation Times

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

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7044 7051 7072 7124 7231 7427 7704 8003 7468 7534 7552 7613 7880 8210 6400 6600 6800 7000 7200 7400 7600 7800 8000 8200 8400 3500400045005000550060006500all cycle length (km) Used Links for Demands and Protection fixed metric (1.0) 34% 44% 59% 52% Results: Routing Dependence adapting metric

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So far: elementary cycles Non-Simple Cycles: + more cycles contribute to solution space (better or equal results) - many cycles found, cycle degeneration Shape of p-Cycles

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3000 3500 4000 elementary, 10 * Demand non-simple, 10 * Demand elementary, 1.0 * Demand non-simple, 1.0 * Demand 0 0,2 0,4 0,6 0,8 1 1,2 cycle length (km) No. of cycles (max. 4000km, 10 * Demand) elementary: 864 (25) non-simple:13046 (29) Time for cycle search: elementary: 170.1 s non-simple: 18.4 h Results: Non-simple Cycles Protection / Working Capacity Ratio

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

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

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Another p-cycle example This 6-span p-cycle covers 4 x 2 + 6 = 14 working demands for each unit of spare capacity on itself Recent Theoretical results: (1)p-cycles are most efficient possible pre- configured structure. (2)up to S protection relationships per link in p-cycle, where S = # spans in cycle.

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Further comparing p-cycles to rings

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ADM-like capacity-slice nodal device for p-cycle networking

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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.

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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 ground is the database

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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

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Overview of DCPC protocol

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How DCPC discovers best p-cycles (2)

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How DCPC discovers best p-cycles (1)

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DCPC Performance studies

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Illustrating the Real time phase

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Adapting p-cycles to the IP-layer …

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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

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Span versus Node Restoration Restoration Layer-Strategy Choice Unavailability of Spans/Nodes in the Different Layers Feasibility of IP Restoration in the Different Layers

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IP p-Cycle Properties p-Cycles are Virtual Circuits –Consume Zero Capacity until used –Well suited to MPLS-like Emerging Standards p-Cycles are Pre-planned –Centrally or Distributed (~DCPC) –Designed prior to Failure –At Failure, a p-Cycle requires no time to Setup or Use p-Cycles can restore Node and Span Failures

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(1)Network setup: logical p-cycle establishment in routing tables. –p-cycles are established as virtual circuits using MPLS or a small number of reserved IP addresses (2) Real-time phase: nodal p-cycle behavior: –encapsulation, –deflection, –re-introduction IP-layer p-cycles

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Insertion of an IP packet into a p-cycle –If the packets normal routing table entry indicates forwarding into a now-dead port, encapsulate the packet with the p-cycle address for dead neighbour router, route encapsulated packet (I.e, into p-cycle) –The IP packet is encapsulated in a p-cycle packet and routed along the p-cycle Operation of IP-layer p-cycles

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IP Packet p-Cycle Packet Encapsulation Routing Table p-cycle Packet Operation of IP-layer p-cycles

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Insertion of an IP packet into a p-cycle… –The p-cycle packet packet contains the IP packet two new fields: –The ID of the p-cycle on which the packet belongs –The cost of the original pre-failure path for the IP packet Operation of IP-layer p-cycles

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Router Processing of a p-cycle packet arrival –(a) the router checks if it has a routing entry (with a functional port) for the encapsulated IP packets destination; if no, continue the packet along the p-cycle –(b) If yes to (a), test ; is cost of local continuing route option >= cost in p-cycle packet (I.e., from the encapsulation point); If yes, continue along the p-cycle. If no, remove the IP packet from the p-cycle packet and route it normally from this node. Operation of IP-layer p-cycles

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Failed Link Router Data De-Encapsulation Data Encapsulation Router p-cycle (a) On-Cycle Failure (1 restoration Path) (b) Straddling Failure (2 Restoration paths)

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Capacity Planning for Span Restoration with p-cycles Integer Program Formulation –chooses a set of p-cycles to restore all Span failures –Failed working demands may be re-routed over all available p-cycles –User-defined input constraint on number of p-cycles in the design –Objective: Minimize the Max Restoration-induced total flow on any span (i.e., min (max (oversubscription)) –subject to: The maximum over-subscription is over all Span Failures Every span failure is covered Hop count limit is respected Design limiting number of p-cycles

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9/12 3/6 Pre-Failure flow 4.5/6 10.5/12 4.5/6 Straddling Failure Flow lost = 3 Split 1.5 units each way around p-cycle Max subscription = 10.5/12 = 0.875 12/6 On-Span Failure Flow lost = 9 9 units around p-cycle Max (over-) subscription = 12/6 = 2 Installed capacity Illustrating restoration-induced over- subscription of capacity

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Integer Program design results Run in Bellcore network –Minimally provisioned to be fully mesh- span restorable Some sample results

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This set of five p-cycles producing 20% over- subscription for any IP span restoration Allowed 15 design p-cycles, max over-subscription goes to 2% Sample Result

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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 Router Failure Restoration using Node-Encircling p-Cycles Node- Encircling p- cycle Other Nodes Encircled Node

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p-Cycles are Virtual Circuits/Protection Structures which can redirect Packets around Failures –Plain IP is Connectionless but p-Cycles can be realized with MPLS, IP Tunneling/Static Routes Router Restoration using Node-Encircling p-Cycles Node Failure

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An encircling p-cycle for node k includes all nodes that are logically adjacent (directly connected) to node k but not node k itself. Encircling p-cycles may be visually (graphically) apparent as such, may require a Figure 8, and / or may be non-apparent, I.e., logically, but not graphically encircling. –A special case of Figure-8ing is when the Figure 8 loop is logically required to go down and back the same span, to include one or more degree 2 sites. The important property is that the encircling structure intercepts all transiting flows through the subject node. –Examples of each case follow... Key concept / extension of basic p- cycles: node encircling p-cycles

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Router Restoration using p-Cycles p-Cycle Examples Simple, Apparent Simple, Non-Apparent Non-Simple (Segment) Non-Simple (Figure 8) final demo.....

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Packet Routing (Pre-Failure) Path Cost = 3 But … Failure IP Encapsulate P-Packet Operation of node-encircling p-cycles

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(Infinite) > 3 (3) == 3 (2) < 3 ! P-packet continues along p-cycle until the local path cost is less than at entry P-Packet At which point the IP packet is unencapsulated and routed as usual P-Packet IP 1 unit of cost per link Operation of Node-encircling p-cycles

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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 Concluding Comments

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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

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[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 References on p-Cycles

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Backup Slides

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Rings... Fast, but capacity - inefficient

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Two main types of survivable ring....(1) UPSR Unidirectional Path-switched Ring...Principle of operation

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Protection fibre Working fibre 1 2 3 4 5 UPSR Animation... Tail-end Switch

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UPSR (OPPR)...line capacity requirement Consider a bi-directional demand quantity between nodes A, B: d A,B. - A to B may go on the short route - then B to A must go around the longer route Thus, every (bi-directional) demand pair circumnavigates the entire ring. Hence in any cross section of the ring, we would find one unidirectional instance of every demand flow between nodes of the ring. Therefore, the line capacity of the UPSR must be: A D E B C A -> B B -> A The UPSR must have a line rate (capacity) greater (or equal to) the sum of all the (bi-directional) demand quantities between nodes of the ring.

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Protection fibres Working fibres Loop-back 1 2 3 4 5 (4 fiber) BLSR Animation...

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BLSR …(OPSR) line capacity requirement both directions of a bi-directional demand can follow the short (or long) route between nodes Bandwidth reuse The line capacity of the BLSR must be: Planning issues / inefficiencies: - better than UPSR for non-hubbed - capacity dependence on demand pattern - stranded capacity - span exhaust A D E B C A -> B B -> A The BLSR must have a line rate (capacity) greater (or equal to) the largest sum of demands routed over any one span of the ring.

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Mesh... Capacity - efficient, but (traditionally) slower, and hampered by DCS / OCX port costs

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Basics of Mesh-restorable networks (28 nodes, 31 spans) 30% restoration 70% restoration 100% restoration span cut

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Basics of Mesh-restorable networks (28 nodes, 31 spans) span cut 40% restoration 70% restoration 100% restoration

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Basics of Mesh-restorable networks Spans where spare capacity was shared over the two failure scenarios ?..... This sharing efficiency increases with the degree of network connectivity nodal degree

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Mesh networks require less capacity as graph connectivity increases ~ 3x factor in potential network capacity requirement

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p-cycles.. Fast, and capacity efficient....

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