A Dynamically Adaptive Hybrid Algorithm for Scheduling Lightpaths in Lambda-Grids

1
A Dynamically Adaptive Hybrid Algorithm for
Scheduling Lightpaths in Lambda-Grids

• Neena R. Kaushik and Silvia M. Figueira
• Santa Clara University
• Presented by Yang-suk Kee

2
Outline

• Background
• Lightpath Scheduling
• Experiments
• Conclusion

3
Background

• Advance reservation
• Guarantees that resources will be available at a
  pre-determined time to participate in the
  execution of a Grid application
• Lambda Grid
• Lightpath
• A wavelength data channel liking multiple optical
  segments
• A single wavelength through the path
• Different wavelength with wavelength conversion
• Data-intensive grid application
• Multiple paths

4
Problem Definition

• Advance reservation of multiple lightpaths
• How to schedule multiple lightpaths requested by
  advance reservation over optical network with no
  converter?

A
Source
Destination
B
D
C
5
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 Dijkstras shortest path algorithm by
  removing the edges that were part of the shortest
  paths.

6
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

A-gtC (4)
Spreading
Packing
7
Wavelength-Balancing Algorithm

• Begin
• For i 1 to number of wavelengths
• For j 1 to number of edge-disjoint paths
• If wavelengthi is available for all segments in
  edge-disjoint pathj
• Allocate wavelengthi for all segments in
  edge-disjoint pathj
• If all requests of user are satisfied
• Print success
• Else
• Print the number of requests satisfied and number
  denied
• End

8
Wavelength-Concentrating Algorithm

• Begin
• For i 1 to number of edge-disjoint paths
• For j 1 to number of wavelengths
• If wavelengthj is available for all segments in
  edge-disjoint pathi
• Allocate wavelengthj for all segments in
  edge-disjoint pathi
• If all requests of user are satisfied
• Print success
• Else
• Print the number of requests satisfied and number
  denied
• End

9
Scheduling Comparison
A-gtC (4), B-gtD (4), A-gtB (1), B-gtD (2) Four
wavelengths per link
A
A
(x)
B
D
B
D
(x)
C
C
Balancing
Concentrating
10
Blocking Probability
Requests for 8-hop lightpaths in a 32-node ring
with chords constant requests.
Requests for 1-hop lightpaths in a 32-node ring
uniform requests
11
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
• gt Hybrid algorithm of balancing and concentrating

12
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

13
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 requests for ligthpaths (from FONTS)

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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-taile
  d
• Number of lightpaths requested
• Constant/uniform/heavy-tailed
• Advance reservation start time
• Poisson distribution
• Number of time slots
• Constant/variable

15
Simple Topology
16
17
18
20
24
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
National Lambda Rail
National Lambda Rail Constant Requests
17
Conclusion Discussion

• Conclusion
• Provides simulation tools for lightpath
  scheduling
• Quality of scheduling algorithms depends on
  traffic characteristics
• Hybrid scheduling achieved lower blocking
  probability
• Discussion
• Blocking probability represents network
  utilization properly?
• This hybrid algorithm is close to balancing
  algorithm except the case of ring topology.
• Need more study about the degree of nodes, length
  of hops, and network utilization