RPI Graph and Statistics Package for ns User Manual and Tutorial
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1. the display instance procedure on the graph object The display method plot using the default PlotDevice We have not defined a default plot device in this script Instead we pass the graph directly to two different plot devices Note that often times there is little need for more than one plot device since plot devices create intermediate files of the desired type e g xdvi creates encapsulated postscript files for each graph Multiple plot devices is more useful when the desired file type is not generated as an intermediate file when displaying the graph in a window as in ex4 tcl T gt proc finish set xgraph_plotter new xgraph set eps_plotter new postscript xgraph_plotter plot util_graph eps_plotter plot util_graph xgraph_plotter close eps_plotter close Cea Es set util_graph new Graph UtilizationVersusTime n0 n1 0 1 util_graph set title_ Bottleneck Utilization vs Time util_graph set output_filename_ bneck_util_vs_time Vad a Figure 6 Example 4 Output to a file and to an X window using xgraph 3 5 Example 5 Bottleneck link statistics We now move on to demonstrating how to collect statistics using the statistics functions included with the graph package The objective of these statistics gathering tools is to simplify statistics gathering over the standard methods provided by ns To include the link statistics gathering functions do the following source2. Figure 4 Example 2 Display multiple graphs using xdvi files All temporary files are by default written to a temporary directory located in tmp expx where x is replaced with smallest integer that has not already been used in the naming of another exp directory in tmp The user can change the default directory by setting tmp_directory_ global variable before instantiating any Graph objects However this is only advisable if the user is sure that the directory used to store temporary files resides on the same machine that is executing the script since writing across a network will not only slow down the simulation but may adversely affect other users sharing the network If the user does not set the output_filename_ data member then the output file is placed in tmp_directory_ with a default name specific to the Graph class 3 4 Example 4 Multiple Plot Devices Note that the caller can output the same graph object to both a file and a window by using two plot devices In ex4 tcl we use xfig and postscript to generate encapsulated postscript while displaying the graph using xfig We show the relevant code snippet in Figure 6 Notice that we do not call an E Graph set plot_device_ new fig lsa set util_graph new Graph UtilizationVersusTime n0 n1 0 1 util_graph set title_ Bottleneck Utilization vs Time util_graph set output_filename_ bneck_util_vs_time ee E Figure 5 Example 3 Outputting Graphs to Files
3. env NS tcl rpi link stats tcl To begin gathering statistics on a link spanning from nodes nO to n1 do the following set stats new LinkStats n0O n1 We show code snippets from examples ex5 tcl in figure 7 The calls to get utilization get mean queue delay and get packet arrivals returns the link statistics gathered from the moment the link stats object was instantiated In this case that means reporting statistics gathered from the beginning of the simulation There are many more statistics we could report by simply calling any of the instance procedures in table 4 ame N proc finish global nO ni tcpO tcpl stats output link statistics puts Bottleneck statistics puts Utilization stats get utilization puts Number of drops stats get packet drops puts Mean queue delay stats get mean queue delay puts Number of arrivals stats get packet arrivals Deed create topology w bottleneck between nO and nl set stats new LinkStats n0 n1 za E Figure 7 Example 5 Gathering link statistics If you wish to gather statistics starting from some time into the simulation then simply in stantiate the LinkStats object at that time If you want to gather statistics over consecutive time intervals then you can reset the link statistics at the end of each time interval by calling the LinkStats reset instance procedure If you want to collect a link s statistics for overlapping intervals
4. Type run test suite sh This will test the RPI Graphing and Statistics package You should see the following output ByteCounter Test PASSED DelayMonitor Test PASSED file tools tcl test PASSED link stats Tests PASSED all 59 tests on the link stats tcl file After the text above the test suite calls graph _test graph test tcl which generates a set of graphs and displays them using a variety of plot devices The suite first employs the xdvi PlotDevice that uses the postscript and latex PlotDevices to create graphs and descriptive text respectively The xdvi PlotDevice then displays the generated DVI file using the xdvi appli cation Carefully inspect the generated plots for correctness against the plots bearing the label Com parison Graph Because of the visual nature of the graphing tools and slight differences between versions of the various graphing applications we found that the only reliable way to test the Plot Device classes was through visual inspection NOTE That your output may not look exactly the same as the provided comparison graphs Look for differences in content rather than small differences in presentation e g ignore font differences 3 Tutorial All of these examples assume a working knowledge of ns If you have not created ns scripts before then consult the ns documentation and write a few test scripts before proceeding from here Currently the graph package provides the graphs shown in
5. ak kgs Pa mL 0 8 H 4 S 0 6 b i J w N 5 0 4 H 3 X i i 4 0 2 L sample interval 0 1s 0 1 1 1 1 1 1 1 1 1 0 0 5 1 1 5 2 2 5 3 3 5 4 4 5 5 time seconds Figure 3 Graph generated by ex1 tcl 3 2 Example 2 Outputting to Various Plot Devices The graph package can output graphs to windows or files using various applications or formats for displaying saving graphs We show the current set of supported plot devices in table 2 In graph v6 1 1 examples ex2 tcl we provide an example script that uses an xdvi plot device to display multiple graphs in the same window in the designated order One of the first things we do in this script is to create a plot device Graph set plot_device_ new xdvi Here we create an instance of the xdvi class and assign it to the Graph plot_device_ class member Whenever a graph object is instantiated it by default uses the plot device defined in the When closed display all graphs plotted with this device us acroread ing acroread Uses postscript PlotDevice and the pdflatex application fig Output to fig file via gnuplot ghostview Output eps via gnuplot then display using ghostview gnuplot Show plot in X window using gnuplot gnuplot35 Show plot in X window using gnuplot 3 5 no comments Output to eps file using the postscript PlotDevice and run latex to create a latex file that includes the graphs pdf Output to pdf file from eps using epstopdf postscript Output
6. get goodput Returns goodput in bps over the bottleneck capacity Table 5 TCP statistics gathering instance procs 4 1 When to Use NAM Graph and Stats nam tracing is best used to generate animations For any simulation containing more than a handful of nodes containing bottlenecks with large bandwidths gt 10 Mbps and or running more than a couple of seconds nam tracing will probably be too slow nam is slow because in order to generate network animations ns outputs to a trace file every time a packet enters departs or is dropped from any queue in the simulated network Simply turning nam tracing off often reduces simulation run times by an order of magnitude In particular if you are parsing nam traces to generate statistics then perhaps you should consider using some other tool Graph objects sit on a single link or deal with a single TCP agent Unless the user wants to generate graphs for every link in the simulated network installing Graph objects will probably yield significantly less overhead in terms of simulation run time and disk space consumption than generating graphs by post processing nam traces Of course the Graph objects are best used for generating graphs any other use of the Graph classes or their respective intermediate files is suspect The Graph objects generate trace files though substantially smaller than nam traces and useful statistics might be derived from these traces However if you only want to
7. goodput cov tcplist C O V across the passed TCP agents C O V is standard deviation over the mean Calculates the sum of the packets sent across t total data ket ist A Bote Oba Canna cmon enue the passed TCP agents i e connections Calculates the sum of the packet retransmis get total retransmitted packets tcplist sions across the passed TCP agents i e con nections Calculates the sum of the retransmission time get total retransmission timeouts tcplist outs across the passed TCP agents i e con nections Table 6 TCP statistics functions operating on lists bytes that arrived at the head of the queue Usually the few extra objects represents negligible overhead However if the script writer has particularly tight performance constraints then the script writer will have to write his or her own objects designed specifically to gather the desired statistics 5 Other Performance Issues with Graphs There are two other important performance issues with regard to the graph classes 1 where to output files and 2 using averaging intervals The cost of outputting to one file is not necessarily the same as the cost of outputting to another file The disparity is particularly large between local and remotely mounted files A trace file should probably never be placed on a volume mounted across a network because each write may generate a packet Consider for nam that this would mean generating a packe
8. operate on a list of tcp agents In this case returning the standard deviation in goodput and the sum of the data packets sent respectively across the passed list of agents The above examples can be found in examples ex6 tcl 4 Performance Issues When one is running large or long simulations there are various considerations to take into account with respect to the tools used for gathering statistics or generating statistics Our tools have been defined to introduce reasonable overhead though in some cases simulation performance constraints may drive one to design task specific tools We outline some of the performance considerations in this section 13 Returns the number of packets transmitted containing new data Returns the number of bytes transmitted containing new data The number of useful bytes in each useful packet is the packet size minus the TCP and IP headers The header size is determined by tcpip_base_hdr_size_ defined in NS tcl lib ns default tcl In ns 2 1b95 tcpip_base_hdr_size_ is set to 40 get useful packets get useful bytes Returns the rate of useful bits transmitted by the network Uses get useful bytes to determine the total number of useful bits Packets that have been lost but not yet detected by the source are counted as useful because our measure is based on state maintained by the TCP source In a long simulation this should have negligible impact on the goodput measure get goodput bps
9. table 1 Except for the XY class an instance of any of these classes gathers statistics directly from an ns simulation and renders a plot when the instance s plot member function i e TCL instproc is called The XY class simply allows script writers to generate a plot from an arbitrary set of x y coordinates The XY class represents a way for a script writer to use the PlotDevice classes as a generic interface to a variety of output devices CWndVersusTime TCP congestion window size versus time FlowQLenVersusTime sampled per flow queue contribution versus time Point ToPointDelay VersusTime delay between two points on the network QDelay VersusTime sampled queuing delay versus time QLenVersusTime sampled queue length versus time RateVersusTime arrival rate versus time over constant interval length REDQueueVersusTime avg queue instant queue versus time RTTVarianceVersusTime TCP variance in round trip time versus time RTTVersusTime TCP round trip time versus time Sequence TCP sequence number versus time SRTTVersusTime TCP smoothed round trip time versus time Utilization VersusTime utilization versus time over constant interval length XY plot x y coordinates from an input file Table 1 Provided Graph classes 3 1 Example 1 Graphing link statistics To include the graph package we preface every experiment script with the following source env NS tcl rpi graph tcl The graph package contains several graphs for gatheri
10. to encapsulated postscript via gnuplot postscript35 Output to eps via gnuplot 3 5 no comments When closed display all graphs plotted with this device using xdvi xgraph Show plot in X window using xgraph latex xdvi Table 2 Supported plot devices Graph plot_device_ class member All of the classes can be instantiated by passing a plot device object to their respective init instprocs This allows you to use a different plot device for each graph object if you so wish We show the relevant snippets from the ex2 tcl script in figure 4 Not shown in figure 4 we create a topology containing a bottleneck between nodes n0 and n1 We then define two TCP connections that pass through the bottleneck The first of these two connections has the TCP agent object tcp0 Shown in figure 4 we create three graph objects of which the first two install statistics gathering objects into the bottleneck link from nO to n1 The last graph object traces the congestion window of tcp0 When the simulation completes we output each of the graphs to encapsulated postscript by calling each object s display instproc Next we close the plot device causing the plot device to compile a latex file that references the eps files generated by each graph object The latex compiler outputs an dvi file which the plot device then opens using xdvi 3 3 Example 3 Outputting Graphs as Files Often we want to generate graphs as files for in
11. RPI Graph and Statistics Package for ns User Manual and Tutorial David Harrison RPI CS Department June 18 2003 Abstract This user manual contains an installation guide and a short tutorial for the RPI graphing tools for ns 1 Introduction The RPI graph and statistics package provides a set of classes for generating commonly used plots and gathering commonly important statistics The graph package abstracts data collection from rendering Each graph object instantiates a set of data collection objects which are attached to components in a network topology as the simulation runs the data collection objects collect data often outputting the data to an intermediate file After simulation the graph object conforms the data to a canonical format and then sends it to a PlotDevice for rendering By substituting plot devices the user can cause the same graph to be output to a window or a file using gnuplot fig xgraph xdvi ghostview or acroread In Figure 1 we show a utilization graph that collects data from a link in an ns simulation and then outputs to a gnuplot plot device The gnuplot plot device translates the data and commands from the utilization graph into gnuplot commands The gnuplot application then generates an encapsulated postscript file Other scenarios include rendering a graph with multiple plot devices for example to generate a postscript file while simultaneously displaying the data in an X window using xgraph Or multipl
12. asured over some small interval get min byte queue length Same as get min byte queue length except the re sult is returned in units of bytes Table 4 LinkStats statistics instance procedures 12 3 6 Example 5 TCP statistics The most direct way to obtain TCP statistics is to simply query the bound variables defined for the Agent TCP class For example if we define a TCP agent tcpO then we can do the following without extending ns 2 puts Number of data packets transmitted by flow 0 tcpO set ndatapack_ puts Number of data packets transmitted by flow 1 tcp1 set ndatapack_ puts Retransmission timeouts for flow 0 tcpO set nrexmit_ puts Retransmission timeout for flow 1 tcp1 set nrexmit_ When using our TCP statistics gathering functions it is necessary to include the tcp stats tcl package This loads the definitions shown in tables 5 and 6 source env NS tcl rpi tcp stats tcl Then initialize various counters by calling init stats init stats can also be called to simply reset the the statistics for both our extensions and the statistics gathered by ns 2 1b5 er tcp init stats eed At some later time such as when finish is called you can output tcp statistics as follows puts Goodput Variance get goodput stddev tcpO tcpi puts Total TCP packets get total data packets tcpO tcp1 In the example above get goodput stddev and get total data packets
13. clusion in a report or paper In the previous example we showed how to output into xdvi In this example we consider outputting to a fig file for later annotation using xfig With this example we also take into consideration where generated files are placed in the file system We show code snippets for Example 3 in Figure 5 Example 3 differs from Example 2 only in that we use a different plot device in this case fig and we explicitly tell util_graph to output to the file named bneck_util_vs_time in the current working directory Note that this is not the exact filename of the output file The plot device appends an id unique to the plot device and then appends a file type extension The actual output file s name is bneck_util_vs_time_O fig Note that setting output_filename_ does not affect the location of any trace or other temporary an b Graph set plot_device_ new xdvi Praa proc finish global util_graph qlen_graph cwndO_graph util_graph display qlen_graph display cwndO_graph display Graph set plot_device_ close run nam exit 0 define a bottleneck between nO and n1 set util_graph new Graph UtilizationVersusTime n0 n1 0 1 util_graph set title_ Bottleneck Utilization vs Time set glen_graph new Graph QLenVersusTime n0 n1 qlen_graph set title_ Bottleneck Queue Length Versus Time set cwndO_graph new Graph CWndVersusTime tcp0 cwndO_graph set title_ cwnd of flow O versus Time z
14. determine a single statistic across the length of a simulation then the functions found in link stats tcl or tcp stats tcl are probably better for the job The link stats tcl and tcp stats tcl functions generate far less overhead than either nam or the Graph classes simply because none of the link stats tcl or tcp stats tcl generate trace or other intermediate files Instead the LinkStats object installs counters in the link being monitored Incrementing a counter introduces far less overhead than outputting to a file When the user later requests the statistic the corresponding components are then queried However the LinkStats object installs objects for measuring a large array of link statistics Sometimes this means installing unnecessary counters or similar objects into the links being monitored For example the LinkStats object installs objects at the tail and head of the link s queue Placing an object at the queue s head is unnecessary if the script writer only wants to know the number of 14 Calculates mean goodput in bps across the t dput P Sare meon ecco TPR passed TCP agents i e connections Calculates variance in goodput bps across t dput i teplist pour gccapunnversance Upis the passed TCP agents i e connections Calculates the standard deviation in goodput get goodput stddev tcplist in bps across the passed TCP agents i e con nections Calculates the Coefficient of Variation get
15. e graphs may be output to the same acroread plot device so that the graphs appear in a single acroread window in the given order 2 Installation Presumably you already have the distribution and have installed ns 2 The graph package has been tested with ns 2 1 b5 ns 2 1b9a and ns 2 26 There may be incompatibilities with other ns versions If you have not downloaded the graph package then get it from http www ecse rpi edu harrisod graph v6 1 1 tar gz In order for the statistics and graphing packages to function you must define two environment variables the NS environment variable must point to the root of the ns source code tree and the NSVER environment variable must contain the ns version number e g ns 2 1b5 has version I am now in the EECS department at UC Berkeley and can be reached at harrisod eecs berkeley edu 2 Simulation _ ByteCounter byte arrivals in last interval et postscript gnuplot UtilizationVersusTime F po inati x y values PlotDevice x y values et eect plot title gnuplot f axes labels commands encapsulated postscript Figure 1 UtilizationVersusTime Graph outputting via gnuplot PlotDevice 2 1b5 The following directions apply to ns version 2 1b5 and ns 2 1b7 Make a backup of your ns source code tree before attempting this installation Before continuing make sure the following are in yo
16. ng statistics about traffic passing through a link including queue length versus time utilization versus time rate versus time and queue delay versus time In this example we will show how to graph utilization over given fixed intervals versus time Assume we have created a topology with a known bottleneck spanning ns nodes n0 and n1 Next we add the lines shown in figure 2 to our script To collect statistics for our graph we instantiate a Graph UtilizationVersusTime object The arguments nO and n1 tell the graph object to collect statistics for the link spanning between nodes nO and n1 The 0 1 argument tells the graph object that it should measure utilization over 0 1 second intervals When the simulation finishes we call util_graph display to tell the graph object to show a window containing our utilization versus time plot generated using gnuplot We show the complete source code for this script in graph v6 1 1 examples ex1 tcl and the generated graph in figure 3 Kea E proc finish global util_graph util_graph display exit 0 create graph of utilization vs time for link n0 n1 et util_graph new Graph UtilizationVersusTime n0 n1 0 1 J Me define nodes nO and ni and link spanning them s Figure 2 Utilization versus time script ex1 tcl Bottleneck Utilization vs Time T T T T T T T T 1 M Viet DYI ace i Pr Pk a ay
17. output i e less transient behavior is revealed 6 LinkStats and TCP Stats and Long Run Times When simulations are run for long times or when bottleneck bandwidths are high it is quite possible that certain signed long integers 32 bit will overrun causing erroneous results from LinkStats objects To fix this problem the user should perform some worst case analysis of the number of bytes or packets that will pass through a link before running a simulation We specifically mention bytes because byte counters tend to increment much faster than any other counters in a simulation To avoid overruns the simulation script must periodically reset the corresponding counters by calling LinkStats reset member function i e TCL instproc or TCP s init stats member function depending on the statistic that is in danger of an overrun The simulation script can then either store the intermediate values of the statistic for later post processing or only rely on the final value 16
18. rns the number of byte arrivals at the tail of the queue 8 over time get packet arrivals Returns the number of packet arrivals at the tail of the queue get byte arrivals Returns the number of byte arrivals at the tail of the queue get packet drops Returns the number of packets dropped get byte drops Returns the number of bytes dropped get packet departures Returns the number of packets that departed the queue get byte departures Returns the number of bytes that departed the queue get mean queue delay Returns the mean delay experienced by packets tran siting the queue get queue delay variance Returns the variance in delay experienced by packets transiting the queue get queue delay stddev Returns the standard deviation in delay experienced by packets transiting the queue get mean packet queue length Returns the mean packet queue length This is not the same as the mean queue length seen by an arriving packet which would not take into account idle times in the mean get mean byte queue length Same as get mean packet queue length except the result is returned in units of bytes get max packet queue length Returns the maximum queue length in packets get max byte queue length Returns the maximum queue length in bytes get min packet queue length Returns the minimum queue length in bytes Typi cally this would be zero except when me
19. t on the real network for every packet arrival departure or drop in the simulated network A single NAM simulation can easily swamp a file server while simultaneously drastically slowing down simulation run times Instead trace and other intermediate files are usually output to a temporary directory In UNIX tmp resides on a workstation s local hard drive therefore that is why the Graph package by default places all intermediate as well as output files in tmp see Example 3 Now this brings us to the second important performance issue averaging Several of the Graph classes allow the user to specify whether to output instantaneous or time averaged val ues For example QLenVersusTime s third argument to its init instproc i e its constructor is sample_interval By default the sample interval is set to 1 denoting that QLenVersusTime 15 should record the queue length at every arrival and departure of a packet This results in partic ularly large generated files and slow run times but it also allows the user to easily see transient queuing behavior If the user wishes to improve simulation run times or reduce the size of trace files the user can set sample_interval to a positive value denoting the time interval over which the queue length is averaged At the end of each interval the average is output to the graph s trace file Larger averaging intervals result in shorter run times at the expense of generating graphs with smoother
20. then create two LinkStats objects each at a time when you want to begin collecting statis tics then retrieve the statistics at the end of their respective intervals Installing more than one LinkStats object on a link is particularly useful when you want to record statistics for the whole simulation as well as for the steady state i e skipping some time to eliminate initial transients We provide the code for this complete example in graph v6 1 1 examples ex4 tcl 10 init n0 nl gmon Instantiates a LinkStats object spanning between n0 and nl You must have previously created these two nodes and a link spanning these nodes More than one LinkStats object can span between n0 and n1 By default the LinkStats object uses an instance of the RPIQueueMonitor class to collect statistics You can install your own queue monitor using the optional third argument reset resets all statistics to the initial state Table 3 Special instance procedures for LinkStats 11 get utilization Returns the link utilization as the number of bytes departing the queue as the number of bytes that could have departed the queue get packet utilization avgpktsz Returns the link utilization as the number of packets that departed the bottleneck link times the average packet size over the number of average sized pack ets that could have departed the link The argument specifies the average packet size get throughput Retu
21. ur search path e nam e acroread e ghostview e gnuplot e latex e pdflatex e xdvi e and xgraph nam is necessary to run network animations The remaining applications are used in the process of creating graphs Not all of the applications are necessary to use the graph package though some PlotDevice classes will not function See Table 2 for the list of PlotDevice classes and the dependencies between these classes and the applications 1 If you have an earlier version of the graph package then remove it as follows but only after backing up your ns source code tree gt cd NS gt rm r rpi gt rm r tcl rpi 2 Change to a temporary directory and then untar graph as follows gt gunzip graph v6 1 1 tar gz gt tar xf graph v6 1 1 tar gt cd graph v6 1 1 3 Move directories from the distribution into your NS distribution gt cp r rpi NS gt cp r tcl rpi NS tcl rpi gt cd NS 4 Insert the following lines in your ns Makefile eee INCLUDES I Irpi 0BJ_CC haz rpi byte counter o rpi delay monitor o rpi file tools o rpi rate monitor o rpi rpi flowmon o rpi rpi queue monitor o Ea Here INCLUDES and OBJ_CC should already appear in your Makefile refers to an omission of lines already appearing in your Makefile 5 Rebuild ns gt cd NS gt rm gen gt make depend gt make 6 Test ns Change to the directory NS tcl rpi tests
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