L13 - Evaluation Strategies Nick Feamster CS 7260 February...

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Evaluation Strategies Nick Feamster CS 7260 February 26, 2007
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2 Evaluation Strategies Many ways to evaluate new protocols, systems, implementations Mathematical analysis Simulation (ns, SSFNet, etc.) Emulation (emulab) Trace-driven evaluation Wide-area deployment (VINI) Interplay between these areas is not obvious! Various tradeoffs in “realism”, control, etc. A combination may be appropriate
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3 Why Network Simulation? Can capture complexity that analytical models miss Protocol validation Quantitative results Exploration of dynamics Controlled experimental conditions Low cost/barrier to entry Time Collaboration Complexity
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4 Simulation: ns ns :discrete-event network simulator for Internet systems protocol design, large scale systems studies, prototyping, education Why ns? Protocols: TCP, UDP, HTTP, etc. Traffic Models: Web Traffic, CBR, Topology Generation tools Visualization tools
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5 Step 1: Topology # Create simulation object set ns [new Simulator] # Ask ns for nodes set n0 [$ns node] set n1 [$ns node] # Create a duplex link b/w n0 & n1 $ns duplex-link $n0 $n1 1Mb 10ms DropTail # Schedule End $ns at 5.0 "exit 0" # Run Simulation $ns run
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6 Step 2: Attaching Agents Purpose: Transport connections between nodes Various types: TCP, UDP, etc. # Create a UDP agent set udp1 [new Agent/UDP] # Create a Null agent set sink1 [new Agent/Null] # Attach agent udp1 to node n0 $ns attach-agent $n0 $udp1 # Attach agent sink1 to node n1 $ns attach-agent $n1 $sink1 # Connect the agents $ns connect $udp1 $sink1 # Create a TCP agent set tcp1 [new Agent/TCP] # Create a Null agent set sink1 [new Agent/TCPSink] # Attach agent tcp1 to node n0 $ns attach-agent $n0 $tcp1 # Attach agent sink1 to node n1 $ns attach-agent $n1 $sink1 # Connect the agents $ns connect $tcp1 $sink1 UDP TCP
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7 Step 3: Creating Traffic Purpose: Send traffic over links/transport # Create Source set cbr1 [new Application/Traffic/CBR] # Configure Source $cbr1 set packetSize_ 500 $cbr1 set interval_ 0.005 # Attach source to agent $cbr1 attach-agent $udp1 # Schedule cbr on $ns at 0.5 "$cbr1 start" # Schedule cbr off $ns at 4.5 "$cbr1 stop"
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8 Simulation: Advantages and Disadvantages Ease of use Often possible to achieve large scale (federation, etc.) Low cost in time, money, etc. Many “accepted” models
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This note was uploaded on 10/26/2011 for the course CS 7260 taught by Professor Staff during the Spring '08 term at Georgia Institute of Technology.

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L13 - Evaluation Strategies Nick Feamster CS 7260 February...

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