Measurements and Modeling Table of Contents 1 Measurements 2 Modeling and its Shortcomings 3 Example of a Network Simulator NS EECS122 UCB 1 Problem with Measurements Real System measure Result EECS122 UCB Real system does not exist Implementation of real test system is too expensive too dangerous Measurements would interfere with normal operation of the real system 2 Modeling Process Real System generate measure Result Model measure infer Modeling Result There are Analytical models and Simulation models EECS122 UCB 3 Disadvantage of Modeling Models give only an indication of the behavior of the real system Models are an abstraction of the reality Many details are not considered Real systems are complex Therefore Differences between measurements in models and reality exist EECS122 UCB 4 Example TCP Sequence Number Measured in Simulator and Reality Simulator Reality EECS122 UCB 5 EE122 Projects S03 Assignment No 2 and No 3 Analysis of ns simulation runs showing the behavior of flows under different control mechanisms Different TCPs and router implementations Implementation of ns module to analyze the impact of end user decisions in C Adaptive routing and call control EECS122 UCB 6 Modeling Using the Network Simulator ns ns is discrete event simulator targeted at networking research ns started in 1985 ns simulates TCP UDP routing and multicast protocols over wired and wireless local and satellite networks EECS122 UCB 7 Simulation System tcl script input Create a simulator object set ns new Simulator Define different colors for data flows ns color 1 Bluens Simulator Basics ns color 2 Red NAM output ns classes Open the nam trace filens Simulator Basics ns set nf open project b task 1I nam w ns namtrace all nf open the measurement output files set f0 open project b task 1I out0 tr w set f1 open project b task 1I out1 tr w set f2 open project b task 1I out2 tr w Gnuplot output Throughput Measurement of all UDP and TCP Flows 1 throughput all flows throughput udp flows 0 8 0 6 0 4 0 2 EECS122 UCB 8 0 0 1 2 3 4 5 6 ns Architecture Object oriented C and OTcl Control operations in Otcl Class hierarchy extract EECS122 UCB 9 ns Simulator Basics Simulator API is a set of methods belonging to a simulator object Simulator object is created with set netsim new Simulator Tcl script initializes the packet format creates a scheduler handles time timers and events Scheduler access through simulator methods Example ns at 0 0 ftp start Tcl script EECS122 UCB 10 Tcl Script Example create simulator set ns new Simulator create node set n0 ns node set n1 ns node create link between nodes ns duplex link n0 n2 10Mb 10ms DropTail create a TCP agent and attach it to node n0 set tcp0 new Agent TCP ns attach agent n0 tcp0 tcp0 set window 40 tcp0 set packetSize 460 set sink new Agent TCPSink ns attach agent n1 sink create an FTP source application and attach it to tcp set ftp new Application FTP ftp attach agent tcp0 EECS122 UCB 11 Tcl Script Example cont open the nam trace file and measurement output file set nf open project b nam w ns namtrace all nf set f0 open project b tr w schedule events ns at 0 0 ftp start ns at 3 0 puts nf ns now t ns now ns at 6 0 ftp stop ns at 6 01 dump simulation result into files ns flush trace Execute NAM and Gnuplot exec nam project b nam exec pgnuplot project b dem stop the simulation exit 0 start the execution ns run EECS122 UCB 12 NAM Network Animator Reads trace file generated by ns Example of trace file V t A t A t c t c t n t v n h i i a 1 0a5 a 0 1 p 0 o 0xffffffff c 31 a 1 1 m 2147483647 s 0 1 n Blue 2 n Red 0 s 0 S UP v circle c black i black NAM EECS122 UCB 13 Gnuplot Graphic Tool Is distributed under the gnu license Needs a script file e g project b dem and file containing the data which has to be plotted Example plot Throughput Measurement of all UDP and TCP Flows 1 throughput all flows throughput udp flows 0 8 0 6 0 4 0 2 0 EECS122 UCB 0 1 2 3 4 5 6 14 Literature and Help for ns http www isi edu nsnam ns FAQ ns related mailing list Tutorial Manual EECS122 UCB 15
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