1. p-Cycles, Ring-Mesh Hybrids and “Ring-Mining:” Options for New and Evolving Optical Networks Wayne D. Grover grover@trlabs.ca TRLabs and University of Alberta TRLabs and University of Alberta Edmonton, AB, Canada web site for related papers etc: web site for related papers etc: http://www.ee.ualberta.ca/~grover/ http://www.ee.ualberta.ca/~grover/ Please see also www.drcn.org ( “DRCN 2003” )www.drcn.org OFC 2003, Tuesday March 25 2003, Atlanta, Georgia

2. A note to recipients following OFC 2003 Dear colleague It is my pleasure to provide you with the following softy-copy of the presentation slides I used at OFC 2003. If you wish to rely on this work, you may cite the related OFC paper as follows: W. D. Grover, “p-Cycles, Ring-Mesh Hybrids and Ring-Mining: Options for New and Evolving Optical Networks,” Optical Fiber Communication Conference (OFC 2003), Atlanta, March 2003, Paper TuI1, Vol. 1, pp. 201- 203. The paper (just cited) in the OFC Proceedings also gives further individual references on p-cycles, ring-mesh hybrids, and “ring-mining” that may be of use to you. Thank you very much for your interest in this work. Any feedback, comments or questions are most welcome. Best regards, Wayne Grover grover@trlabs.ca, March 31, 2003

3. Wayne D. Grover OFC 2003 3 Purpose and Outline Three recent developments involving both ring and mesh-like attributes (1) p- Cycles –“mesh-efficiency with ring-speed ” (2) Forcer-clipping ring-mesh hybrids –selective use of BLSR rings within a mesh network (3) “Ring Mining” –re-use existing ring infrastructure to support mesh-based growth Unifying theme: getting the best of both ring and mesh new ideas and options for network planners to consider

4. Wayne D. Grover OFC 2003 4 p-Cycles

5. Wayne D. Grover OFC 2003 5 p-Cycles - an “on-cycle” failure Reaction to an “on-cycle” failure is logically identical to a unit-capacity BLSR loopback reaction loopback “on-cycle” spans have both working and spare capacity like a BLSR

6. Wayne D. Grover OFC 2003 6 p-Cycles - a “straddling span” failure Reaction to a straddling span failure is to switch failed signals onto two protection paths formed from the related p-cycle Break-in Straddling spans have two protected working signal units and have no spare capacity

7. Wayne D. Grover OFC 2003 7 A lot ! Re-consider the example: It consumes 13 unit-hops of spare capacity It protects one working signal on 13 spans and two working on 9 spans i.e., spare / working ratio = (13*1 + 9*2 ) / 13 = 42% How much difference can this make ? A fully-loaded Hamiltonian p-cycle reaches the redundancy limit, 1/(d-1) x2

8. Wayne D. Grover OFC 2003 8 Example of a whole p-cycle network design Working span capacities arising from one unit of demand on each node-pair: Total working capacity: 158 units 8 1 5 6 9 4 9 4 4 10 7 3 2 13 11 10 7 6 14 5 7 6 7

9. Wayne D. Grover OFC 2003 9 Design Solution: 53.8 % overall redundancy A1A1 B1B1 C1C1 D2D2 E2E2 Total protection capacity:85 units Redundancy:53.8% Optimal configuration dynamically computable or self-organized p-Cycle Copies Total:7

10. Wayne D. Grover OFC 2003 10 Understanding why p-cycles are so efficient... 9 Spares cover 9 Workers 9 Spares cover 29 working on 19 spans Spare Working Coverage UPSR or BLSR p-Cycle …with same spare capacity “the clam-shell diagram”

11. Wayne D. Grover OFC 2003 11 ADM-like nodal device for p-cycle networking

12. Wayne D. Grover OFC 2003 12 Summary: Important Features of p-Cycles Working paths go via shortest routes over the graph p-Cycles are formed only in the spare capacity Can be either OXC-based or based on ADM-like nodal devices a unit-capacity p-cycle protects: –one unit of working capacity for “on cycle” failures –two units of working capacity for “straddling” span failures Straddling spans: –there may be up to N(N-1)/2 -N straddling span relationships –straddling spans each bear two working channels and zero spare –-> mesh capacity efficiency Only two nodes do any real-time switching for restoration –protection capacity is fully pre-connected –switching actions are known prior to failure –-> BLSR speed

13. Wayne D. Grover OFC 2003 13 Ring-Mesh Hybrid Networks based on the “forcer-clipping” principle

14. Wayne D. Grover OFC 2003 14 The architecture of integrated ring-mesh transport Physical Topology Logical Demand Ring-2 Ring-1 Selected “Forcer clipping” Rings “ Residual Mesh” ADM Glassthrough X-connect hybrid transport network

15. Wayne D. Grover OFC 2003 15 The Forcer Concept Working, spare, forcer strength

16. Wayne D. Grover OFC 2003 16 The Concept of “Forcer Clipping” Rings Hypothesis: Certain rings can efficiency “clip the tops off ” strong forcers in the mesh, resulting in savings exceeding the cost of the rings. Self-contained BLSR “clips” off strong forcers Reduces & levels underlying mesh Residual mesh forcer landscape and “forcer-clipping” rings Forcer span spare capacity Forcer span ‘hidden’ forcer “forcer” landscape of a pure- mesh network economies arise from: 1) enhancement of the residual mesh capacity efficiency, due to forcer clipping 2) creation of a well-loaded ring, displacing working quantities from the mesh, lowering relative termination costs.

17. Wayne D. Grover OFC 2003 17 A F G Z E C B (9,10) (7,14) (16,14) (10,10) (16,0) (9,10) (14,20) (29,16) (30,15) Pure mesh: Redundancy = 129 / 154 = 84 % (9,9) (7,8) (16,8) (10,9) (16,3) (9,10) (2,9) (17,10) (18,9) Test ring 1: Revised mesh: Redundancy = 84 / 106 = 0.79 Capacity return ratio = (129-84) + (154-106) 4 x 12 x 2 = 97 % (9,10) (0,13) (4,3) (10,10) (16,0) (9,10) (14,20) (17,17) (30,14) Test ring 2: Revised mesh: Redundancy = 117 / 123 = 0.95 Capacity return ratio = (129-117) + (154-123) 4 x 12 x 2 = 45 % Example of Forcer-clipping effects CRR: Capacity return ratio = total mesh capacity reduction total capacity of ring placed High CRR --> good economics Example uses a 12 unit-capacity ring

18. Wayne D. Grover OFC 2003 18 Heuristic Algorithm based on “Forcer Clipping” Forcer analysis of initial mesh Find all cycles of network graph Use forcer assessments to build ranked “short-list” of ring placements Place a “short-list” ring Residual mesh re-design Assess total economic impact Callable CPLEX Place max-payback ring and permanently alter the residual mesh design Repeat until no further rings prove-in no further gain from any ring at least one ring proves in

19. Wayne D. Grover OFC 2003 19 Evidence of a true Cross-Architectural Optimum design point

20. Wayne D. Grover OFC 2003 20 Understanding why the hybrid works A good forcer clipping ring pays for itself by: –(1) attaining good utilization for itself, while displacing mesh capacity –(2) enhancing the mesh efficiency through forcer-levelling. But even when ring transport is up to 40% cheaper than mesh, a hybrid is optimum; not a pure ring outcome. why? (1) “rings must be rings” …closing the circle limits ring efficiency. (2) mesh residual approaches limiting efficiency

21. Wayne D. Grover OFC 2003 21 “Mining the Rings”: serving demand growth through ring to mesh conversion

22. Wayne D. Grover OFC 2003 22 The “Ring-mining” Perspective 1) “Cap and grow:” Keep all current demands in the ring network and serve new demands in a new mesh network built on top of it 2) “Ring Mining:” Convert ring capacity to mesh capacity by conversion and/or re-use of transmission equipment cap the rings grow new mesh convert operation to mesh break open the rings i.e. What rings? - I only see capacity on the ground.

23. Wayne D. Grover OFC 2003 23 Approaches to studying the ring-mining idea Q1 “pure ring mining”: If rings were simply “broken up” and reconfigured in a mesh architecture, how much total growth over existing demand could be served without having to add any new capacity? Such that: all d i,j demand quantities are multiplied by all (scaled up) demands are routed all (scaled up) demands are 100% span-restorable the total of routing and restoration flows over any span uses only the capacity of the prior rings (W+P) Maximize  a total uniform growth multiplier

24. Wayne D. Grover OFC 2003 24 Sample Results 35 % of the test cases could sustain a doubling of the demand or more. Three test networks could sustain ~ 3 x growth in demand... 17 ring-based test networks Ring mining tests on 17 efficient multi-ring network designs Each design is at exhaust under its initial demand matrix

25. Wayne D. Grover OFC 2003 25 Why / How Ring Mining works … (1) Ring protection capacity is reclaimed –for general use as mesh working and spare capacity –100% redundancy is reduced to mesh redundancy (2) Ring “stranded capacity” is freed. (3) New (growth) demands follow shortest-path routes over the facilities graph.

26. Wayne D. Grover OFC 2003 26 Ring Mining with Selective Capacity Addition Pure mesh growth requires a high immediate investment in capacity Ring Mining with selective additions defers expenditure until 50% to 290 % growth. Test case for 32 node, 45 span network initially with 7 rings covering 42 spans (3 “span eliminations”) optimized to serve the baseline demand before ring-to-mesh conversion. Range where other test case ring networks transition from pure ring mining to selected capacity additions

27. Wayne D. Grover OFC 2003 27 Ring-Mining to p-cycles as the target architecture Ring 4 Ring 5 Two (of seven) rings in the initial ring-based design: protect 24 spans use 29 units spare capacity Spare/working ratio = 121 % plus ring-constrained working routes

28. Wayne D. Grover OFC 2003 28 Convert those two rings to one p-cycle p-cycle No new capacity added 8 ADMs have p-cycle straddling span interface units added All other ADMs re-used as-is. 7units of protection capacity reclaimed as working 15 spans obtain on-cycle protection 5 spans obtain (x2) straddler protection fully loaded spare / working ratio 17/(17+5*2) = 63% pus working paths take shortest routes over topology

29. Wayne D. Grover OFC 2003 29 Straddling Span Interface Unit (SSIU) Converts an ADM to function as a p-cycle node Long haul Local Add Drop Channels W S W WW W S W Existing Ring ADM /OADM Additional Local Add Drop Channels p-cycle straddling span interface unit “Extra Traffic” line-rate access to protection

30. Wayne D. Grover OFC 2003 30 Summary Three new options and architectural principles described – p-Cycles Mesh efficiency with ring-speed – Ring-mesh hybrids based on forcer-clipping principle Selective continued use of rings Possible target architecture of ring mining –“Ring- mining” A strategy for evolving legacy ring networks to a mesh future … provide additional options and strategies for vendors and operators considering new and evolving optical networks. All involve aspects of harnessing both ring and mesh efficiencies

31. Wayne D. Grover OFC 2003 31 Selected References and Further Reading [1] W. Grover, D Stamatelakis, "Bridging the ring-mesh dichotomy with p-cycles", Proc. DRCN 2000, Munich. [2] -------, "Cycle-oriented distributed preconfiguration: Ring-like speed with mesh-like capacity…," Proc. ICC'98, 1998, pp. 537-543. [3] ------, "OPNET Simulation of Self-organizing Restorable SONET Mesh Transport Networks", Proc. OPNETWORKS '98 (CD-ROM), Wash. D.C., April 1998, paper 04. [4]-----, "IP layer restoration … based on virtual protection cycles," IEEE JSAC, Oct. 2000, pp. 1938 - 1949. [5] D. A. Schupke, et.al., "Optimal configuration of p-cycles in WDM networks," Proc. ICC'02, NYC, 2002. [6] L.Lipes, "Understanding the trade-offs associated with sharing protection," OFC 2002, ThGG121. [7] W. D. Grover, J. E. Doucette, "Advances in optical network design with p-cycles: Joint optimization and pre-selection …," in Proc. IEEE-LEOS Topical Meetings, Quebec, July 15-17, 2002. [8] W.D. Grover, D.Y. Li, "The forcer concept and its applications to express route planning in mesh survivable networks," JNSM (Plenum Press), vol. 7, no.2, June 1999, pp. 199-223. [9] W. D. Grover, R. G. Martens, "Optimized Design of Ring-Mesh Hybrid Networks," DRCN 2000, Munich, April 2000. [10] M. Clouqueur, et. al. "Mining the Rings: Strategies for Ring-to-Mesh Evolution," DRCN 2001, Budapest, October 2001.

32. Supplementary slides

33. Wayne D. Grover OFC 2003 33 The Unique Position p-Cycles Occupy Redundancy Speed “50 ms” 100 %50 %200 % Path rest, SBPP Span (link) rest. UPSR 200 ms p -cycles: BLSR speed mesh efficiency BLSR

34. Wayne D. Grover OFC 2003 34 Test Case Example of a whole network design Pattern of non-identical working span capacities: Demands:1 unit (between every node pair) Working capacities:1 - 13 units Total working capacity:168 units 1 4 7 4 12 10 4 4 8 3 11 10 9 13 3 3 5 9 7 7 11

35. Wayne D. Grover OFC 2003 35 Test Case #4 Solution Optimal solution: A3A3 B1B1 C1C1 D4D4 E1E1 F1F1 G2G2 Spans with overlapping cycles:16 Total protection capacity:120 units Distance-weighted redundancy:65.9% p-Cycle Copies Total:13

36. Wayne D. Grover OFC 2003 36 Efficiency of p-Cycles (Logical) Redundancy = 2 * no. of straddling spans + 1* no. on-cycle spans ------------------------------------------------------------------ no. spans on cycle 7 spans on-cycle, 2 straddlers : 7 / ( 7 + 2*2) = 0.636 Example: Limiting case: p-cycle redundancy = N / ( N 2 - 2N)

37. Wayne D. Grover OFC 2003 37 Protection 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

38. Wayne D. Grover OFC 2003 38 Optimal Spare capacity design with p-cycles

39. Wayne D. Grover OFC 2003 39 Optimal Spare capacity design - Typical Results “Excess Sparing” = Spare Capacity compared to Optimal Span- Restorable Mesh i.e., “mesh-like” capacity

40. Wayne D. Grover OFC 2003 40 Results in COST239 European Study Network Ref [5] to the paper… Pan European optical core network 11 nodes, 26 spans Average nodal degree = 4.7 Demand matrix –Distributed pattern –1 to 11 lightpaths per node pair (average = 3.2) 8 wavelengths per fiber wavelength channels can either be used for demand routing or connected into p-cycles for protection Copenhagen London Amsterdam Berlin Paris Brussels Luxembourg Prague Vienna Zurich Milan WDM designs could have as little as 34% redundancy for 100% span restorability

41. Wayne D. Grover OFC 2003 41 Summary p-Cycles offer a promising new option for efficient realization of network protection –are preconfigured structures –use simple BLSR-like realtime switching –but are mesh-like in capacity efficiency Other recent advances can be superficially confused with p-cycles: –enhanced rings reduce ring network redundancy by sharing protection capacity between adjacent rings –oriented cycle (double) covers adopt a undirectional graph cycle- covering approach to avoid span overlaps Neither involves straddling spans; spans with working but no spare capacity –Both aim to approach their lower limits of 100% redundancy from well above 100% –p-cycles are well below 100% redundancy

42. Wayne D. Grover OFC 2003 42 Corroborating Results... See: Schupke et al… ICC 2002 Schupke found p-cycle WDM designs could have as little as 34% redundancy for 100% span restorability

43. Wayne D. Grover OFC 2003 43 Some Results ( ….. where optimal and heuristic can be compared ) Ring cost factor = 0.8 Objective function values, (% savings), execution time, number of rings “Cost savings” are relative to objective function value for “pure-mesh” * * result obtained with MIPGAP = 200

44. Wayne D. Grover OFC 2003 44 Results ( ….. where optimal and heuristic can be compared ) Ring cost factor = 0.6 Objection function values (total cost), execution times, and number of rings placed * result from optimal formulation after 24 hours

45. Wayne D. Grover OFC 2003 45 Other Results (“ where only the heuristic can go”): Heuristic #2 % savings over optimal pure mesh Number of rings placed CPU time Net #4 19 nodes 39 spans Net #5 16 nodes 29 spans Net #6 27 nodes 48 spans 23.8% 8 rings 11.9 hrs 38.6% 12 rings 1.0 hr 39.5% 11 rings 2.3 hrs

46. Wayne D. Grover OFC 2003 46 Summary of Main Findings The “forcer-clipping” hypothesis is suggested as an effective principle in ring-mesh hybrid network design. Advent of DCS with integrated ADM shelf functionality motivates / enables this type of true hybrid. Heuristics observed to be within ~ 5% of optimal for test cases –This is taken as confirming the basic validation of the forcer-clipping insight. Heuristic #2 seems superior, and executes in reasonable time for large problems –Heuristic 2 thought to be “selecting in” more co-forcer and latent-forcer combinations which the economic trial placements then discover and exploit This work suggests that in general even mesh networks should be examined for “express ring” opportunities.

47. Wayne D. Grover OFC 2003 47 Other possibilities in ring-mining strategies ADM removal (and salvage?) is another option. Re-terminate line system on OCX directly. Not all ADMs need to be converted to facilitate the ring-to-mesh evolution –Some ADMs can remain in “re-use mode” in degree-2 sites of the overall mesh network Cost of ADM “conversion” and the line capacity accessed are the main parameters.

48. Wayne D. Grover OFC 2003 48 Ring-mining” access to ring capacity … can be many alternatives “nail up” ADM in max add/drop configuration and access protection capacity via “extra traffic” ports. OC-n ring ADM working protection working protection “extra traffic” (Or…) just salvage ADMs and re-terminate optical lines on OXCs maximal working add / drop up to 2 x OC-n total capacity to mesh cross-connect

49. Wayne D. Grover OFC 2003 49 Growth Multiples supported by ring to p-cycle evolution

50. p-Cycle straddling span interface Long haul Local Add Drop Channels W S W WW W S W Ring ADM /OADM Additional Local Add Drop Channels p-cycle straddling span interface unit Cross-office Electrical/optical ring line rate interface “Extra Traffic” line-rate access to protection fiber(IF – 1 ) “Extra Traffic” line-rate access to protection fiber(IF – 2 ) All Working fiber pairs ( ring line-rate ) that can be used to interface with straddler spans. Patent Pending Assuming that the protection fiber ( S) is independently accessible through the “extra traffic” feature interface Source : “Ring-like speed with mesh-like capacity” presentation to Nortel by Dr Wayne Grover on 29 th Aug 2002 : http://www.ee.ualberta.ca/~gro ver Device used to interface straddling spans.

51. Wayne D. Grover OFC 2003 51 Staddling Span Interface Unit (SSIU) Converts an existing ADM to function as a p-cycle node W W P W P ADM LS tributary add/ drop additional LS tributary add/ drop W WW p-cycle straddling span interface unit