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Advances in Optical Network Design with p -Cycles: Joint optimization and pre-selection of candidate p -cycles (work in progress) Wayne D. Grover, John Doucette grover@trlabs.ca, doucette@trlabs.ca TR Labs and University of Alberta Edmonton, AB, Canada

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Advances in Optical Network Design with p-Cycles:

Joint optimization and pre-selection of candidate p-cycles

(work in progress)

Wayne D. Grover, John Doucette

grover@trlabs.ca, doucette@trlabs.ca

TRLabs and University of Alberta

Edmonton, AB, Canada

Related papers available at: www.ee.ualberta.ca/~grover

IEEE LEOS Summer Topicals 2002

Mont Tremblant, Quebec, Canada

July 2002

outline
Outline
  • What are p- Cycles ?
    • Why do we say they offer “mesh-efficiency with ring-speed ?”
  • Optimal design with p-Cycles
    • non-joint or “spare capacity only design”
    • jointly optimized design
  • What makes a “good” p-Cycle ?
    • The idea of Preselection
    • Preselection by Topological Score, by A Priori Efficiency (AE)
  • Application of Preselection to Joint and non-joint p_cycle Design Problems
important features of p cycles
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 on ADM-like nodal devices
  • a unit-capacityp-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
  • Only two nodes do any real-time switching for restoration
    • protection capacity is fully preconnected
    • switching actions are known prior to failure
the unique position p cycles occupy
The Unique Position p-Cycles Occupy
  • p -cycles:
    • BLSR speed
    • mesh efficiency

Path rest, SBPP

Speed

Span (link)rest.

200 ms

BLSR

“50 ms”

50 %

100 %

200 %

Redundancy

backgrounder p cycles
Backgrounder: p-Cycles

Ring network:

p-Cycle:

Spare Capacity

x2 protection coverage on each“straddling” span

Protection Coverage

Able to restore 9 working wavelength channels

Able to restore 29 working wavelength channels

(on 19 spans)

motivation for joint optimization

1 spare

2 spares

2 spares

2 spares

1 spare

1 spare

route length = 2

route length = 2+ε

2 spares

1 spare

2 spares

1 spare

2 spares

1 spare

2 λ

2 λ

Motivation for Joint Optimization
  • In “joint” optimization the working route assignments are chosen in conjunction with survivability considerations:
    • example of the effect this can have:

2 working channel-hops

12 spares in total

TOTAL Capacity = 14

2+ε working

6 spares in total

TOTAL Capacity = 8+ ε

approaches to p cycle network design
Approaches to p-Cycle Network Design

(non-joint)

(joint)

Route all lightpath requirementsvia shortest-paths

enumerateeligible working routes

enumerategraph cycles

enumerategraph cycles

I.L.P. solution forp-cycle formation

Heuristic algorithm(s) forp-cycle formation

“all in one” I.L.P. solution

working routes &working capacity

working routes &working capacity

p-cycles& spare capacity

p-cycles& spare capacity

integer linear programming i l p formulation for the joint problem
Integer Linear Programming (I.L.P) Formulation (for the joint problem)
  • Objective Function:
    • Minimize { total cost of working and spare capacity }
  • Subject To:
    • A. All lightpath requirements are routed.
    • B. Enough WDM channels are provisioned to accommodate the routing of lighpaths in A.
    • C.The selected set of p-cycles give 100% span protection.
    • D. Enough spare channels are provisioned to create the p-cycles needed in C.
    • E. Integer p-cycles decision variables, integer capacity
comments approaches to p cycle network design
Comments : Approaches to p-Cycle Network Design
  • Non-joint problem:
    • several heuristic algorithms under development
    • however, optimal solution is quite fast too
    • no real difficulties here
  • Joint design problem:
    • I.L.P more complex to solve (coupled integer decision variables and constraint systems)
  • Idea: use I.L.P. but with reduced number of “preselected” candidate cycles
    • need some a priori view as to what makes a candidate cycle a promising as p-cycle
preselection criteria 1 topological score ts
Preselection Criteria: (1) Topological Score (TS)

TS

Credit rules:

+1 for an “on-cycle”protection relationship

+2 for a “straddling span”protection relationship

Examples

6 spans, all on-cycle(equiv. To a ring)

TS= 6

7 spans on-cycle

2 straddlers

TS = 7 + 2*2 = 11

“on-cycle”

“straddlers”

By itself TS tends to like large cycles (Hamiltonian maximizes TS):no regard to corresponding cost of the cycle

preselection criteria 2 a priori efficiency ae
Preselection Criteria: (2) a Priori Efficiency (AE)

Examples

AE

AE is defined as:

TS j--------------

Cost of cyclej

TS= 6

Cost = 6 hops

--> AE = 1

Note: all rings have AE = 1

TS= 11

Cost = 7 hops

--> AE = 1.57

  • Preselection hypothesis:
  • choose a “small” number of elite cycle candidates based on AE
  • Let I.L.P. formulation assemble final design
cost239 european study network
COST239 European Study Network
  • Pan European optical core network
  • planning model defined by COST 239 study group for optical networks
  • 11 nodes, 26 spans
  • Average nodal degree = 4.7
  • Demand matrix
    • Distributed pattern
    • 1 to 11 lightpaths per node (average = 3.2)

Copenhagen

London

Berlin

Amsterdam

Brussels

Luxembourg

Prague

Zurich

Paris

Vienna

Milan

results 1 benefits of preselection by ae metric non joint design
Results(1): Benefits of Preselection by AE Metric (non-joint design)

COST239 non-joint designs:

Solution quality vs. No. candidate p-cycles in designc

500 cycles

2000 cycles

results 2 benefits of ae metric pre selection joint design
Results(2): Benefits of AE Metric Pre-Selection (Joint Design)

COST239 joint designs:

Solution quality vs. No. candidate p-cycles in designc

200 cycles

2000 cycles

benefits of ae metric pre selection joint design
Benefits of AE Metric Pre-Selection (Joint Design)

Additional Test Network:20 nodes, 40 spans, 190 demand pairs

2000 cycles

18,000 cycles

mipgap

where the preselection heuristic can really help exponential nature of cycle enumeration
Where the Preselection Heuristic Can Really Help... Exponential Nature of Cycle Enumeration

Illustrated for 40 nodes and a varying # of spans (hence connectivity)

The preselection strategy will help us keep the problem sizes manageable, i.e., in thisrange, avoiding the “combinatorial explosion” that happens over here.

how much does joint design improve efficiency
How Much Does Joint Design Improve Efficiency?

COST-239Joint design uses 5% more working capacity, and 43% less spare capacity for total network capacity reduction of 13%.

Network redundancy = 39%

working

spare

(4 p-cycles)

(7 p-cycles)

joint

non-joint

summary main findings
Summary : Main Findings
  • “Jointly optimized” p-cycle protected OTNs can be extremely efficient:
    • as little as 39% redundancy observed (for 100% span protection)
  • Joint design is a more complex problem, however:
    • Solution time reduced by preselection of a small number of elite cycle candidates based on AE

Further Work and Applications:

Other test networks

Incremental application to dynamic demands

Strategies for wavelength conversion

Design heuristics