a dynamically adaptive hybrid algorithm for scheduling lightpaths in lambda-grids neena r. kaushik...
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A Dynamically Adaptive Hybrid Algorithm for Scheduling Lightpaths in Lambda-Grids
Neena R. Kaushik and Silvia M. FigueiraSanta Clara University
Presented by Yang-suk Kee
Background
Advance reservation• Guarantees that resources will be available at a pre-determin
ed time to participate in the execution of a Grid application Lambda Grid
• Lightpath A wavelength data channel liking multiple optical segment
s A single wavelength through the path Different wavelength with wavelength conversion
Data-intensive grid application Multiple paths
Problem Definition
Advance reservation of multiple lightpaths • How to schedule multiple lightpaths requested by advance re
servation over optical network with no converter?
B D
C
A
),,( 2es tt
),,( 1es tt
Source Destination
Lightpath Scheduling
Skeleton• Step1: determines edge-disjoint paths • Step2: determines wavelengths for paths
Edge-disjoint path• nth edge-disjoint path
A path that does not share any of its edges with the previous n-1 edge-disjoint paths
1st edge-disjoint path is the shortest path• Algorithm
Repeat Dijkstra’s shortest path algorithm by removing the edges that were part of the shortest paths.
Lightpath Scheduling Schemes Spreading
• Balances the wavelength assignment throughout the available edge-disjoint paths
Packing• Concentrates the wavelength assignment in the shortest
path first followed by the alternate edge-disjoint paths
Spreading Packing
B D
C
A
B D
C
A),( 21 ),( 21
),,,( 4321
A->C (4)
Wavelength-Balancing Algorithm
BeginFor i = 1 to number of wavelengths
For j = 1 to number of edge-disjoint pathsIf wavelength[i] is available for all segments in edge-
disjoint path[j]Allocate wavelength[i] for all segments in edge-
disjoint path[j]If all requests of user are satisfied
Print successElse
Print the number of requests satisfied and number denied
End
Wavelength-Concentrating Algorithm
BeginFor i = 1 to number of edge-disjoint paths
For j = 1 to number of wavelengthsIf wavelength[j] is available for all segments in edge-
disjoint path[i]Allocate wavelength[j] for all segments in edge-
disjoint path[i]If all requests of user are satisfied
Print successElse
Print the number of requests satisfied and number denied
End
Scheduling Comparison
Balancing Concentrating
B D
C
A
A->C (4), B->D (4), A->B (1), B->D (2)Four wavelengths per link
B D
C
A
(x)
(x)),( 21 ),( 21
),( 21
),( 21
)( 3
)( 3
)( 3
),,,( 4321
),,,( 4321
Blocking Probability
Requests for 1-hop lightpaths in a 32-node ring: uniform requests
Requests for 8-hop lightpaths in a 32-node ring with chords: constant requests.
Lessons
From the experiments using simple topologies• Partial mesh/ring/ring with spike/ring with chord
Balancing algorithm has similar or better blocking probability than concentrating one in most cases
Concentrating algorithm is better• With short hop (1-hop)
Shorter time slots provide lower blocking probability
=> Hybrid algorithm of balancing and concentrating
Hybrid Algorithm of Balancing and Concentrating begin firstpass = 1; while (firstpass is not equal to 3)
• for i = 1 to number of wavelengths for j = 1 to number of edge-disjoint paths
if first pass is equal to 1 and edge-disjoint path has more than x-hops
Continue … check if it satisfies balance algorithm
end (for edge-disjoint paths loop)• end (for number of wavelengths loop)• Increment firstpass by 1
end (while loop) return the number of requests satisfied end
Experimental Setup
Metric of quality• Blocking probability (denial rate)
Simulation-based• FONTS (Flexible Optical Network Traffic Simulator)
Generates on-demand and advance reservation requests Uses Stochastic models
• LRSS (Lightpath Request Scheduling Simulator) Simulates scheduling algorithms Takes as input the network topology and a trace of reque
sts for ligthpaths (from FONTS)
request
rejectB N
NP =
FONTS (Flexible Optical Network Traffic Simulator) Request arrival time
• Poisson distribution Source node/Destination node
• Constant/uniform/arbitrary probability Size of data to transfer (Tera bytes)
• Constant/uniform/arbitrary probability/heavy-tailed Number of lightpaths requested
• Constant/uniform/heavy-tailed Advance reservation start time
• Poisson distribution Number of time slots
• Constant/variable
Simple Topology
Requests for 1-hop lightpaths in a 32-node ring: uniform requests
All schemes except balancing are identical
Requests for 8-hop lightpaths in a 32-node ring with chords: constant requests.
16 17 18
20 24
Conclusion & Discussion
Conclusion• Provides simulation tools for lightpath scheduling• Quality of scheduling algorithms depends on traffic characteri
stics• Hybrid scheduling achieved lower blocking probability
Discussion• Blocking probability represents network utilization properly?• This hybrid algorithm is close to balancing algorithm except t
he case of ring topology.• Need more study about the degree of nodes, length of hops,
and network utilization