performance evaluation of atm shortcuts in overlaid ip/atm networks jim kurose don towsley...
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Performance Evaluation of ATM Shortcuts
in Overlaid IP/ATM Networks
Jim Kurose Don Towsley
Department of Computer Science
Univ. of Massachusetts, Amherst
Victor Firoiu
Bay Architecture Lab
Nortel Networks
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Outline
The problem: benefit of ATM shortcuts in IP/ATM
Two methods for network performance comparison
Where are ATM shortcuts beneficial?
Conclusion
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ATM Shortcuts - What Benefit ?
Facts– Internet ubiquitous– ATM infrastructure widely deployed
Forwarding IP traffic with bw. resv.– Hop-by-hop in IP– ATM shortcuts
Potential benefits of ATM shortcuts1 Cut through IP processing2 Shorter path in ATM => fewer resv.3 Richer ATM netw. => Lower blocking pr.
In this study: evaluate (2) and (3)
ATM linkIP linkATM shortcutIP routerATM switch
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Comparing Network Performance
Consider two instances of an IP/ATM network:
Define Network Load Ratio R(p):– N1: traffic load (i)i => flow blocking pr. p1
– N2: traffic load (Ri)i => flow blocking pr. p2
– R(p) is such that p1=p2=p
“N2 performs R times better than N1”
N1: using IP routing N2: using ATM routing
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1
3
R1
R2R3
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Computing Network Load Ratio
Algorithm:
Pi() given by Fixed Point Method
Complexity: O(L2CV2FS)L = no. links F = no. Fixed Point iterations
(3..100)
C = max. no. flows / link S = no. Inversion iterations (10..50)
V = no. nodes
Problems– high computational complexity– computes R(p) only for a given p– need R for a range of p values
)(
)()(
12
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pP
pPpR
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Simplification: Asymptotic Load Ratio
Observe: for p<0.1, R(Ni,Nj,p) constant (p)
Define: Asymptotic Load Ratio
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Offered Load
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pPpNNRNNA
pp
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Computing Asymptotic Load Ratio
For networks with all links having same capacity C:
– where i = prob(flow traverses link i)
Similar result conjectured for heterogeneous capacities– verified by simulation
Advantages– low complexity O(LV2), L = no. links, V = no. nodes
– gives performance comparison for a range of p values
iLi
iLiC NNANNA
2
1
max
max),(lim),( 21021
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Accuracy of Asymptotic Load Ratio
Simulation: generate random networks (Nk)k
Compute NLR: R(Ni,Nj,p) for several p, using Fixed Point
Compute ALR: A(Ni,Nj) using simple method
Compute relative error :
Computation time– NLR: 104s, for each p
– ALR: 0.008s),,(
),,(),()(, pNNR
pNNRNNApe
ji
jijiNN ji
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Where are ATM Shortcuts Beneficial?
Simulation– Generate random ATM networks
NA = no. nodes, A = prob(link exists between two nodes)
– Generate IP networks:– For each ATM/IP network pair
map IP nodes to ATM nodes
map IP links to shortest path ATM routes
– Compute Asymptotic Load Ratio
Results– ALR highly correlated with:
– IP to ATM average depth ratio
– IP to ATM diameter ratio
– ALR not correlated with: ave. degree ratio, no. nodes ratio
AIAI NN ,
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Simulation Results
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Conclusion
Proposed two methods for evaluating benefit of ATM shortcuts– low computational complexity– accurate for a wide range of network load
Evaluated IP/ATM topologies where ATM shortcuts increase network capacity– when average route length is decreased
Methodology useful for network designers– asses opportunity for IP/ATM protocols
Future work– extend results for networks with alternate routing– flows with heterogeneous bandwidth requirements