Presenter: Jonathan Murphy On Adaptive Routing in Wavelength-Routed Networks Authors: Ching-Fang Hsu...

Presenter:

Jonathan Murphy

On Adaptive Routing in On Adaptive Routing in Wavelength-Routed NetworksWavelength-Routed Networks

Authors:

Ching-Fang Hsu

Te-Lung Liu

Nen-Fu Huang

OverviewOverview

Background Information

Adaptive Routing Algorithms

Analytical Model

Numerical Results

Conclusion

Background InformationBackground Information

Alternate Routing– Predefined set of paths assigned for each s-d

pair– If ever s-d pair has only one path, it’s fixed

routing

Adaptive Routing– Routing path dynamically determined based

on present state of network

Background InformationBackground 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

Adaptive Routing AlgorithmsAdaptive Routing Algorithms

Shortest Path Strategy (SP)– Objective is to minimize

• Link cost• Wavelength conversion cost

*

Link Cost Wavelength conversion cost


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


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:

*


Least-Loaded Path Strategy (LLP)– Advantages

• Balances link utilization across the network

– Disadvantages• May lengthen connection paths

– Wasted bandwidth

– Higher blocking rate

*


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


– Goal: Minimize value of BPsd X CPsd

• BPsd = Busy Factor

• CPsd = Cost of links on path from s to d

*

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

Analytical ModelAnalytical 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



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


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

Numerical ResultsNumerical Results

Compares the three strategies (as well as the analytical model performance for blocking)

Compares across the 3 network topologies as well


Blocking probability (W=4)


Logarithmic Scale

Number of connection requests per unit connection holding time

Available # of wavelengths

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 W=8 and #connections = 150 in

NSFNET• WSP 16% less for interconnected rings when W=8 and

#connections = 50


Overall WSP is best at higher loads Also, results of analytical model within

an acceptable range– Best with mesh network though


Average Number of Hops (W=4)


Average Number of Hops (W=8)


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 W=4


Standard Deviation of Link Utilization (W=4)


Standard Deviation of Link Utilization (W=8)


Standard Deviation of Link Utilization results LLP performs best here!!!– But at cost previously mentioned

WSP performs significantly better than SP


ConclusionConclusion

Weighted-Shortest Path (WSP) adaptive routing strategy proposed– Seeks to combine best features of SP

and LLPAnalytical model proposed as wellResults–WSP works well– Analytical model is accurate• Best with mesh network

Presenter: Jonathan Murphy On Adaptive Routing in Wavelength-Routed Networks Authors: Ching-Fang Hsu...

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