Presenter:

1
On Adaptive Routing in Wavelength-Routed Networks
Authors Ching-Fang Hsu Te-Lung Liu Nen-Fu Huang

• Presenter
• Jonathan Murphy

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Overview

• Background Information
• Adaptive Routing Algorithms
• Analytical Model
• Numerical Results
• Conclusion

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Background Information

• Alternate Routing
• Predefined set of paths assigned for each s-d
  pair
• If ever s-d pair has only one path, its fixed
  routing
• Adaptive Routing
• Routing path dynamically determined based on
  present state of network

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Background Information

• Assumption All wavelength routers have full
  wavelength conversion capabilities
• Therefore, wavelength assignment is not
  discussed, only routing
• Adaptive routing is focus for this paper

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Adaptive Routing Algorithms

• Shortest Path Strategy (SP)
• Objective is to minimize
• Link cost
• Wavelength conversion cost

Wavelength conversion cost
Link Cost

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Adaptive Routing Algorithms

• Shortest Path Strategy (SP)
• Advantage
• Minimizes use of resources
• Disadvantage
• Does not balance link utilization
• One link may be overburdened while another is not
  used at all

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Adaptive Routing Algorithms

• Least-Loaded Path Strategy (LLP)
• Objective is to balance link utilization
• F(ei) Number of free wavelengths
• For each possible path, find the link with the
  fewest number of free wavelengths
• Select the Path with the largest value

Maximize

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Adaptive Routing Algorithms

• Least-Loaded Path Strategy (LLP)
• Advantages
• Balances link utilization across the network
• Disadvantages
• May lengthen connection paths
• Wasted bandwidth
• Higher blocking rate

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Adaptive Routing Algorithms

• Weighted-Shortest Path Strategy (WSP)
• Focus of this paper
• Tries to balance utilization without cost of
  increased resource usage or blockage
• Hybrid method of above to strategies
• Minimize value of BPsd X CPsd
• BPsd Busy Factor
• CPsd Cost of links on path from s to d

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Adaptive Routing Algorithms

• Goal Minimize value of BPsd X CPsd
• BPsd Busy Factor
• CPsd Cost of links on path from s to d

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Analytical Model

• Exploits single-link model
• Analysis of blocking probability
• Extended to develop blocking performance of
  Weighted-Shortest Path Model
• Also uses overflow model
• Used to obtain set of non-linear mathematical
  equations
• Final stage
• Use successive substitution in iterative fashion
  for final solution

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Analytical Model

• Assumptions
• Every node is a full wavelength router
• All connection calls request circuit connections
• Arrival of connection requests is Poisson process
  with individual arrival rates.
• Assume wavelength conversion cost zero

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Analytical Model

• Begin with the distribution of the number of free
  wavelengths on a single link
• Can be done because of Poisson process of
  connection requests
• From here can find the blocking probability of a
  link
• Now, Find the distribution of the number of free
  wavelength channels on a single path
• Use and create a recursion function based on
  single link information above

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Analytical Model

• Find the traffic load of a specific route
• Use a cost function
• Use this to determine probability that cost of
  current link is less than all other links
• Find network-wide blocking probability
• Calculate blocking probability of specific route
• Use this to find network-wide block probability
  equation, P
• Finally, use successive substitution of all above
  formulas to evaluate P

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Numerical Results
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Numerical Results

• Compares the three strategies (as well as the
  analytical model performance for blocking)
• Compares across the 3 network topologies as well

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Numerical Results
Available of wavelengths

• Blocking probability (W4)

Logarithmic Scale
Number of connection requests per unit connection
holding time
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Numerical Results

• Blocking probability (W4)

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Numerical Results

• Blocking probability (W4)

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Numerical Results

• Blocking probability (W8)

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Numerical Results

• Blocking probability (W8)

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Numerical Results

• Blocking probability (W8)

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Numerical Results

• Blocking probability results
• Blocking probability is higher with increasing
  traffic load for all strategies
• Both SP and WSP better than LLP
• LLP takes more hops thus uses more bandwidth
• SP and WSP have similar performance
• WSP 12 less than SP when W8 and connections
  150 in NSFNET
• WSP 16 less for interconnected rings when W8
  and connections 50

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Numerical Results

• Overall WSP is best at higher loads
• Also, results of analytical model within an
  acceptable range
• Best with mesh network though

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Numerical Results

• Average Number of Hops (W4)

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Numerical Results

• Average Number of Hops (W4)

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Numerical Results

• Average Number of Hops (W4)

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Numerical Results

• Average Number of Hops (W8)

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Numerical Results

• Average Number of Hops (W8)

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Numerical Results

• Average Number of Hops (W8)

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Numerical Results

• Average of hops results
• LLP taking more hopes very obvious here
• SP and WSP very close
• Notice that average of hops decreases as
  connection requests
• Blocking probability increases here
• Therefore, networks ability to grant longer
  connections (and thus more hops) decreases
• Especially true when W4

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Numerical Results

• Standard Deviation of Link Utilization (W4)

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Numerical Results

• Standard Deviation of Link Utilization (W4)

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Numerical Results

• Standard Deviation of Link Utilization (W4)

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Numerical Results

• Standard Deviation of Link Utilization (W8)

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Numerical Results

• Standard Deviation of Link Utilization (W8)

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Numerical Results

• Standard Deviation of Link Utilization (W8)

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Numerical Results

• Standard Deviation of Link Utilization results
• LLP performs best here!!!
• But at cost previously mentioned
• WSP performs significantly better than SP

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Conclusion

• Weighted-Shortest Path (WSP) adaptive routing
  strategy proposed
• Seeks to combine best features of SP and LLP
• Analytical model proposed as well
• Results
• WSP works well
• Analytical model is accurate
• Best with mesh network