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1. Figure 1 1 The nscript application showing the graphical editor the toolbox pane the object browser pane and the toolbar e bin Directory containing the jar files with the java classes that conform the application as well as the following directories settings Containing the initial settings for the application libraries loaded by default and the envi ronment default settings lib Libraries of object templates to use in the simulation figs Icons for the toolbar and other stuff e src The java source code for the application e examples Examples from the tutorials in this manual e man This manual Once the downloaded file is unzipped change to the bin directory and run the program with java jar nscript jar 1 3 Afirstlook at the nscript GUI Figure 1 1 shows the nscript graphical user interface The nscript application consists of four main compo nents and some auxiliary controls The main components are e Graphical Editor The place where the edition of the script takes place At the beginning of a session it show a single object labeled ns which represents the simulation environment and provides control of the environment settings such as network dynamics tracing nam tracing animation and simulation time More detailed information on how to configure the environment is provided in the reference to the libraries in Part II of this manual but to see the options that are available select the sel
2. Mame Puntaxtinke indexes boy Ma Leeda Arriburt 7 Vous Bandwidth Mb Delay Loans Forsand Cost 12e EAE Cort 19 atue Discipline OnogTail xeu Gaary 5o amem defmuite Apply Ohjecr Braweer Mi IL rie Figure 2 2 Configuration of the link for the simulation Click on the link This will have the effect of selecting it which is shown by changing its color to blue Notice that once the link is selected its properties appear in Object Browser see figure 2 1 Select the Bandwidth field and change the settings from 10Mb to 1Mb In the same way select the Delay field and change it to 10ms from 20ms Click on the Apply button to save the settings Figure 2 2 shows the how the attributes of the link should look like 2 2 Creating and Configuring Transport Agents Once the topology has been created we need to add transport agents to actually send information packets This agents must be attached to nodes and connected to each other in order for the simulation to succeed Let s do that l 2 3 Select the UDP class from the Transport library Add a UDP agent on top north of NodeO Select the Null class from the Transport library This entity class corresponds to a sink that will receive the packets from the UDPO session created above Add a Null agent Null0 north of Nodel Select the AttachToNode class from the same library and attach agent UDPO to Node by clicking in the cen
3. begin set name env name node end Example 2 a duplex link object relation class DuplexLink node node 0 0 4 0 Bandwidth 10Mb Delay 20ms Forward Cost 1 0 Backward Cost 1 0 Queue Discipline DropTail DropTail RED CBQ FQ SFQ DRR Queue Capacity 50 begin env name duplex link from to Bandwidth Delay Queue Discipline set name env name link from to Queue Capacity 50 env name queue limit from to Queue Capacity Forward Cost 1 0 env name cost from to Forward Cost Backward Cost 1 0 env name cost to from Backward Cost end Example 3 A TCP Agent entity class TCP agent 1 Max Window Size 20 Initial Window 1 Packet Size 1000 35 nscript User s Manual Libraries FlowID None None 12 345678 9 10 begin set name new Agent TCP Max Window Size 20 name set window_ Max Window Size Initial Window 1 name set windowInit_ Initial Window Packet Size 1000 name set packetSize_ Packet Size FlowlD None name set fid_ FlowID end 36 Bibliography BBE 99 Sandeep Bajaj Lee Breslau Deborah Estrin Kevin Fall Sally Floyd Padma Haldar Mark Handley Ahmed Helmy John Heidemann Polly Huang Satish Kumar Steven McCanne Reza Rejaie Puneet Sharma Kannan Varadhan Ya Xu Haobo Yu and Daniel Zappala Improving simulation for net work research Technical Report 99 702b University of Southern California March 1999 revised S
4. the other hand a tabbed pane shows the available object templates or classes that can be used to create objects for the simulation This objects are classified into libraries corresponding to their use in a simu lation The default libraries are Topology Transport Applications and Utilities but additional libraries can be created and added to the environment by using the Open Library option in the File menu e Toolbar Where most of the commands can be launched for actions like opening saving a script ex porting the tcl script or opening a library of simulation objects 1 3 1 Working with the Editor The process of creating a simulation involves selecting the desired object in the ToolBox panel and using the mouse in the Graphical Editor to add objects of the selected type into the simulation There are two generic kinds of objects which were model after the way things work in ns where a typical simulation script consists of creating and configurating simulation objects and relating them to do something usefull For example to create a topology in ns one has to add node objects and then relate them by adding a link between them This process is abstracted as creating entities in this case the nodes and then a relation between them This abstraction works well for other tasks common in ns such as creating transport agents entities and attaching them to nodes relation in this case between a trasnport agent and a node The
5. a line between them Here the order agent application is required 3 Use the Object Browser to configure the CBR application to send 500 byte packets each 005 seconds This involves selecting the CBRO object first and editing the attributes in the Object Browser By this point your diagram should look like figure 2 4 Atthis point everything is set up with the exception that nothing interesting will happen because no events have been scheduled For some data to be transmitted we need to tell the CBR application to start transmitting at some point in the simulation time 2 4 Scheduling Simulation Events To add a simulation event 1 Add two Timer objects that can be found in the Utilities library 2 Setthe names ofthe first of them to 5 and the second 4 5 These are the times when we want something to happen To change the name of an object select it using the select tool and the write the new name in the corresponding text field see figure 2 2 and press the Apply button nscript User s Manual Tutorials 11 CBRO 2 I H dd 1 Nodeo l 8 Nullo Node 1 Figure 2 4 Configuration of the link for the simulation i 5 4D 4 5 yc CERO I H Me T Null Node 1 Figure 2 5 Diagram after the events are added 3 Connect each of these objects 5 and 4 5 to the CBR application object using an ApplicationEvent class This can be found in the Utilities library as well This objects relate a ti
6. and the each object is also specified by describing its class snippet and the particular attributes for it 8 2 Thenscript Library file format Libraries are stored in ASCII text following the format LibraryName LibraryToolBarName LibraryVersion Class Description 1 32 nscript User s Manual Libraries 33 Class Description 2 Class Description n Here is a short description of the required fields e LibraryName A string that provides the name for the library This name is for internal use and no two libraries should have the same name This name will also be used in the toolbar to display the a tab that shows a pane containing all objects that can be created within the library e Library ToolBox Name The name for the tab that will be used to access the objects in this class e Library Version The version of the library for the purpose of version control e Class Descriptions This is the definition of the classes conforming a library the details on this conform the following section 8 2 1 Class file format There are two families of classes supported by the nscript a generic entity class which can be used to create objects represented by icons and a relation class which can be used to relate two iconic objects Both share the same format with the exception of the declaration first line string The general format for both classes is class declaration attribute 1 defaultValue Valuei Value2 ValueN
7. and watch the animation at the times where the ping messages are scheduled to be sent nscript Users Manual Tutorials 25 An important NOTE As a final point try saving your files in the nscript format nss If you come back in a later session and try to open this file you will be prompted by a second Open File dialog box In this case nscript is asking you to locate the file containing the libraries required by the file you are trying to open Locate the ping lib file and open it Chapter 6 Tutorial 6 Tracing A Variable of Interest In this example we will trace the value of the attributes of one of the objects in the simulation as the simula tion progresses over time We will use the Tracer object in the Utilities library to collect the information about the congestion window size for a TCP session during the transmission of a 80k file The final diagram is shown in figure 6 1 Thetopology Build a simple topology a couple of nodes and a duplex link connecting them The transportlayer Create a TCP object close to one of the nodes and a TCPSink object close to the other node Attach them to their respective nodes and build a logical connection between them Connect tool Events Add a timer and set its name to 15 And connect the timer to the TCP Agent using an AgentEvent object Configure this object according to figure 6 2 Tracing the Window Size Add a Tracer object from the Utilities library This class allows a objec
8. attribute 2 defaultValue Valuei Value2 ValueN begin tclPattern lt attribute gt lt target_value gt lt truePattern gt lt falsePattern gt tclPattern lt attribute gt lt target_value gt lt truePattern gt lt falsePattern gt end Where the truePattern will be used whenever the user sets the attribute equals to target value As mentioned above the class definition differs from an entity and a relation object So the syntax for a class declaration can be any of the following entity class class name base class name icon relation class class name from base to base base fig lt style gt width end fig The values of these fields are illustrated in the figure 8 1 and correspond to how the object are displayed in the editor nscript User s Manual Libraries 34 Shape Catalog JC IC Figure 8 1 Icons and line styles supported by the scripter Chapter 9 TclPattern and value substitution The Tcl patterns used in the previous definitions are normal Tcl expression that contain replacement patterns enclosed in So a Tcl expression containting the replace pattern attribute_ name will be replaced with the value of the attribute which is provided by the user through the graphical interface The following examples illustrate the use of the format and are taken from the actual libraries used in the nscript Example 1 a Node object element class Node node 0
9. technique is usefull to generate multiplexed traffic sources Chapter 4 Tutorial 3 Network Dynamics In this chapter we develop a simulation with the purpose of understanding the dynamics of network routing under events such as a link going down and coming back up Please refer also to Marc Greiss tutorial to fully understand the Tcl part of this simulation script 4 1 The Base Topology and Model As always we start by creating the topology for our model which in this case will be a cycle of 8 nodes and duplex links with 1Mb of bandwidth and a delay of 10ms This is shown in figure 4 1 Only one CBR flow will be present connecting UDP and Null agents attached to nodes 0 and 3 We will also use two events to start and stop the flow at time 5 and 4 5 respectively 4 2 Simulating a link failure We want to simulate the network dynamics during the failure of a link To make it interesting let this link be the link between nodes 1 and 2 Nodel and Node2 in the diagram which is in the path of the CBR flow In order to do this we must aie E i Ekt Figure 4 1 Layout for the network dynamics simulation 19 nscript User s Manual Tutorials 20 Ensity class Enwiraameer Enwar Hama nz lied axoil by No Index Attribute Eouting Preen Medal Tire End Tima Trara Fila Anirnaticn Animation Fils trmcm nam Age Animmion Ta X a tiniry cleo tiskok wan Lirilwent Hime Link eant in
10. ToolBox lists the available classes but also gives hints on how to use them Every entity class shows in parenthesis a base class to which it belongs Think of it as a family of classes that share a common behavior On the other hand relation classes will list the base class for the objects it can relate For example as shown in figure 1 2 the UDP Null LossMonitor TCP and TCPSink classes belong to the same agent family or base class The relation object Attach ToNode requires an entity of bass class agent and an entinty of class node in that order The editor checks this to prevent syntactic errors nscript Users Manual Introduction 6 Play for alittle while with these tools and when you feel comfortable get ready for the first script in the next chapter 1 3 2 Saving and opening files You can save your script into a nscript file format that can be read back in a future session That is accom plished by the normal Save As option in the File menu The usual Save and Open dialog boxes are used to accomplish this Another possibility is to export your script to to Tcl which can be run in ns directly Itis important to remember that the Tcl files can not be read back into the nscript environment Unfor tunately at this point we were not able to code that functionality into the package 1 4 What s in this manual In this manual we show how to use nscript to build simple simulations To make the process easier we decided to b
11. ackets produced by these agents Nam will map that ID to a color according to the settings of object Colors0 Events The last step is again to tell the simulator when things start and stop happening e Use the Utilities library to add four Timer events and set the names of them to 5 4 5 1 and 4 e Use the ApplicationEvent object to link each of the timers 5 and 4 5 to application CBRO and timers 1 and 4 to application CBRI see diagram 3 1 e Configure the links from 4 5 e CBRO and 4 SCBRI by settings their events to stop This will tell CBRO to start at 5 and stop sending packets at time 4 5 while CBRI will start at time 1 and end at time 4 nscript User s Manual Tutorials 14 3 HE um D RAE ea a BL CE p LB TE X Hin me faaye oaa s FE hanh M I den fed e s 43 B Fon i mL LE ED ir fete pest Ca Cy hes TE Beci se het seni Figure 3 2 Animation of the simulation using the network animator nam Run the simulation in ns and at the end you will see the corresponding nam animation window shown in figure 3 2 The packets for the flow from UDPO to sink Null0 should be colored red while the flow in the other path should show a green color Using the Object Browser try reconfiguring object ColorsO and rerun the simulation 3 2 Generalizing to an n flow model You may have noticed that the task of creating and configuring each of the flows was practically the same In this section we will develop a more gen
12. am by Ma reed ace inks waae Trea Tb Ffr diem MEE apelin Te delsuhe Amph Figure 4 3 Configuration of the down link event Note that the actual name of the link has to be looked up using the object browser e Change the routing protocols used by the simulator to a Distance Vector dynamic routing protocol In this protocol routing tables are updated dynamically To do this in nscript we can configure the environment object called ns and located in the upper left corner of the editing window We must set the Routing Protocol to DV see figure 4 2 e Add a couple of LinkEvent objects to specify the times at which we want a particular link to go down and up again These objects can be found in the Utilities library e Configure the down event to take DuplexLink1 down at time 2 5 Here DuplexLink1 is assumed to be the name ofthe link connecting nodes 1 and 2 but the actual name ofthe link depends on the order in which the links were added To find out the name of the desired link select it using the Select Tool and get the name from the Object Browser Once the event has been configured it should look like figure 4 3 e Configure the up event to bring the link up at time 3 0 by configuring the second link event object Run the simulation and observe the network dynamick in the time between the link failure and recover The DV routing protocol is repairing itself and is able to reroute the packets as you
13. ase the examples in this manual on the very well known Marc Greiss tutorial see this reference and if possible have a printed copy of it Gre This manual contains e Part I Tutorials A set of tutorials designed to get you up and running with using the script generator e Part II Libraries A detailed reference on how to edit enhance and create new libraries for the scripter Additionally the appendices contain a description of the file formats used by nscript and other techni cal information to improve on it nscript is a work in progress and we appreciate your comments on it Contact information Enrique Campos N fiez Stephen D Patek Department of Systems Engineering Olsson Hall SEAS University of Virginia e mail ec3z virginia edu PartI Tutorials Chapter 2 Tutorial 1 the first tcl script To start we will create a very simple simulation connecting only two computers and establishing a constant bit rate flow from one node to the other The libraries in nscript follow a layer approach so we will follow a layered approach to building the script first creating the topology then the transport layer then finally the application layer and finally simulation events If you have a copy of Marc Greiss tutorial it is interesting to compare the generated by nscript to the one in Greiss introduction You can do this by clicking on the Tcl Tk Script tab at the bottom of the Graphical Editor at any time during the
14. ation between each possi ble pair of objects will be created For more details on the use of arrays please read Part II of these manual Using the array index If you look at the Tcl code generated by our diagram the array name is actually used as an index which can be exploited To illustrate how we can use of the arrays index created above suppose that we want to color each of the 10 flows differently One way to do this is to use the value of the index users as the value of the parameter Flow ID of the agent UDPO Select the UDPO object and change the value of the Flow ID field to users is the Tcl syntax equivalent to saying the value of variable users see figure 3 9 Add a Colors object from the Utilities library Then save and run the script After the simulation is over you should see the nam window showing the animation something like figure 3 10 In summary what we have done is to generalize a two flow simulation to a n flow in this case n 10 To see how the simulation works with more users edit the array using the Edit Arrays option and change 10 nscript User s Manual Tutorials 18 Merle Ca GS Cr E Mendes A Mica e i emnt l Figure 3 10 Animation window for our more complex simulation Notice that instead of the three nodes originally added 12 nodes are created This is the result of using an indexed object In this case the index is of size 10 for a different number and rerun the experiment
15. can see in figure 4 4 It is nscript User s Manual Tutorials 21 NAN o 4 i Wd A 9 Ps Figure 4 4 Result of the network dynamics simulation experiment Using the distance vector DV routing protocol the network is able to recover from loosing a link the routing protocol also allows the network to detect when the link is back up Q also able to know that the link has been restablished and reroute flow to take advantage of that Chapter 5 Tutorial 4 The Ping Agent In Marc Greiss tutorial a dummy Ping agent was created to get an insight of the process of adding new behavior to ns This tutorial completes this part of the manual showing how to add a new agent created for nsinto the graphical environment To add the Ping agent to the graphical environment we have to solve to problems e Create the recv procedure required by the ping object see Gre which is called when a ping packet is received e Create the ping class and include it in the ToolBox so the object can be used inside nscript To solve this problems we will create two entity objects One will represents the recv procedure that we want to add to the simulation and the other the ping object that has to be created 5 1 Creating a new procedure Open a new text file using a text editor and type the following definition This will be discussed later Save the file as ping lib under the nscript 1 0 bin lib directory ping Ping 1 0a
16. cript User s Manual Tutorials Figure 5 3 Configuration of the GenericEvent object to schedule multiple messages 3 rmm Augl i Can ricis nml y Hera d Ere bec Figure 5 2 Completed diagram for the ping exercise Eariny class GamericEvenT event Haimre Gener cEv enr indexes hy Mo Index x Artributu Valum At Tima 1 La Eranti iming mnd Ts at Tima Z zu Frania fing 2 wand At Tima 3 EE Erant SPing mnd at Tima 4 FE Ewant4 Bing 2 mand At Tima 5 14 Evanis Nena At Tima E 1n Erant Bion a St Tima 7 1n Erant 24 Once this is done we can create the Ping agents in the same way that UDP and Null classes were created Also since Ping has base class agent it is possible to attach it to nodes and to connect two of them using the connect object e Create two ping objects e Attach the ping agents to nodes 0 and 1 using the AttachToNode object and e Connect them using the Connect tool from the Transport library e Use a GenericEvent object from the Utilities library This object allows the schedule of multiple generic events this events need not to be related to an object Add one of this objects so that your diagram looks like figure 5 2 The only necessary step is to configure the GenericEvent0 object to schedule a sequence of ping messages Select this object with the Select Tool and configure it so that it shows like figure 5 3 Run the simulation
17. different paths in the topology e Use the Transport library to add two UDP agents e Attach them to nodes 0 and 1 see 3 1 using the AttachToNode tool e Add two Null agents e Attach both of them to node 3 again using the AttachToNode tool e Use the Connect tool to make logical connections UDP agent 1 Null agent 1 and UDP agent 2 5 Null agent 2 12 nscript User s Manual Tutorials 13 yj een E 3 ib am ER uen A GER d p Figure 3 1 Topology for our second more interesting example Application Layer We now create two CBR applications that will use the services of agents UDP1 and UDP2 e Use the Application library to add a couple of CBR applications e Use the AttachToApp from the Transport library to attach UDP1 CBRI and to attach agent UDP2 CBR2 together see the finished diagram in figure 3 1 Packet Colors Now we will like to be able to distinguish the packets of the two flows since they will share a common link in their way to their destination e Use the Utilities library to add a Colors entity object This object configures the simulation to use colors to identify the packets according to their flow ID number e Configure the Colors0 object in the Object Browser to set Colorl to red and Color2 to green using the popup list in the Object Browser e Configure UDP flows to have a Flow ID of 1 for agent UDPO and 2 UDPI using the Object Browser This will set the ID for each of the p
18. ect tool E and nscript Users Manual Introduction 5 lI Transpo lagena Hulllisgentt antities LnsiMgeniramagesT TCAagent TCS i eia in Attack Tohad elagend end er relations CO Pi ef Hae eT Attack ToAprag ent application Figure 1 2 The ToolBox showing the Transport library Available entity components belong to the base class agent while relations provide ways to relate transport agents to other objects The AttachToNode relation that attaches a transport agent to a particular node the Connect relation that connects to agent objects and the AttachToApp that attaches a transport agent to a given application click on the ns object a list of its attributes and their current values is shown at the lower right corner of the application s window which we will call the Object Browser e Object Browser This pane contains the controls through which is possible to configure any object in a simulation It shows the name and class of the selected object as well as other attributes that can be tuned for a simulation It also contains a Use Default button can be used to restore the default values for the parameters of any object and an Apply button to apply the current values to the object being edited e Toolbox This pane located at the upper right corner of the main window shows the available tools that can be used to create a simulation The select tool can be used to select and move objects around On
19. editing process This will switch to a window showing the Tcl code that is required to produce produce the same result in ns Try using it after each of the layers of the simulation has been created to see how things are done using Tcl 2 1 Building the Topology First select the Topology library by click at the tab with the same name that can be found on the ToolBox 1 Click on the list of objects to select the Node class In the rest of this tutorial we ll refer to Select the ClassName class from the LibraryName library as 1 selecting the LibraryName tab and 2 Selecting the ClassName list from the options Node 0 2 On the Graphical Editor click on the place where you want a new node added an small icon O E appears 3 Repeat the operation to create a new Node called Nodel 4 Select the Duplex Link object from the Topology library and create a link between the node objects created in the previous steps by clicking in one node and dragging to the other node By the end of these steps the Graphical Editor window should look like Figure 2 1 2 1 4 Configuring the Link Suppose that we want this newly created link to have a banwdith of IMbps a propagation delay of 10ms and a drop tail queue discipline FIFO To configure this 1 Click on the E Select Tool to change to select mode nscript User s Manual Tutorials 9 2 3 4 Node 0 Nodel Figure 2 1 Topology for the first example Relates Mode Mods
20. eptember 1999 to appear in IEEE Computer FV00 K Fall and J Varadhan The ns manual The VINT Project http www isi edu nsnam ns ns documentation December 2000 Gre Marc Greiss ns tutorial http www isi edu nsnam nsl tutoriallnsbasic html inst 37
21. eric simulation where the number of flows can be easily changed with the help of arrays Anoteonarrays In mathematics to simplify the notation one typically creates an index such as in x o In nscript you can do the same thing to create To avoid repeating the code over and over you can define an index that can be shared by several objects in the simulation Index sets called arrays as they are called in the ithink simulation environment from where the idea was borrowed can only be designated for entity objects Relation objects use the definitions of the entities it connects according to the rules shown in figure 3 8 Object arrays are represented in the diagram as a stack of objects instead of a flat one to clue the user about this indexing The effect of arrays on entities and relations is shown in figure 3 2 Also refer to figure 3 8 3 2 1 First a base model First start anew simulation script and based on the previous tutorials build the diagram shown in figure 3 2 2 You can even use the model from the previous example but taking away nodel and objects UDP1 CBRI Nulll and timer objects 1 and 4 In the new diagram a single flow is defined Now the idea is to use index sets to build a model that contains multiple flows without having to repeat the same drawings nscript User s Manual Tutorials 15 Zu LED poem HH Hui ici Z a Bril a a im CUN DL QM P i P ka us DO ERES E Rs up e CU gemf Fig
22. he code we declare this class unique By using 4 as the drawing parameter we select a generic squared shape Available shapes are described in figure 8 1 in the last part of this manual To understand better the rest of the format of this file take a look at Part II of this manual specifically to the chapter about libraries 5 2 The Ping Agent Add the following lines to the previous text file entity class Ping agent 1 begin set name new Agent Pingl end This adds a new entity class to the library with name Ping and with base class agent As we mentioned before the base class is used by nscript to constrain the user from building syntactically incorrect relations in a simulation Save this file and use the Open Library option in the File menu to open this file and check that the syntax is correct If it is not nscript will simply not open the file without further explanation If it is correct a new tab is added to the ToolBox window containing the classes defined above see figure 5 1 5 3 Simulating Ping Messages e Use the libraries to build a simple topology of two nodes connected by a Duplex Link e After that select the Open Library option from the File menu or alternatively click the open library button in the ToolBar Bi to open the file created in the previous steps ping lib e Use the PingRecv to create a single object and place it close to the environment object to remind us of its nature ns
23. he default libraries These are the libraries that are provided with the version 1 0a of the environment They are classified under the following four libraries e Topology Nodes duplex links and simplex links e Transport UDP TCP TCPSink Null LossMonitor Attachment e Applications CBR ExponentialOn Off Pareto FTP and Telnet nscript User s Manual Libraries 31 e Utilities Tracer Timer ApplicationEvent AgentEvent LinkEvent and GenericEvent The Topology Transport and Applications are equivalent to ns objects and for documentation of how they work refer to the ns documentation FV00 7 4 The Utilities Library This library contains objects specifically created for the nscript environment in order to achieve additional functionality The objects and their functionality is explained in some of the tutorials but here is a small explanation of their workings Tracer Collects information from a member variable of a Otcl object in the simulation You can sepecify when to start collecting information the interval of sampling after the recording process has started the object that is being traced and the member variable of interest The parameters for this class can be seen in Tutorial 6 where the TCP congestion window is traced Timer Represents a time constant It is used together with ApplicationEvent and AgentEvent to schedule agent or application events AgentEvent A relation object that relates a time constant T
24. imer and a transport agent with the purpose of scheduling an action It has a Event parameter that represents the action to be taken at the specified time This object was used in almost all tutorials to schedule the start and stop events for CBR applications ApplicationEvent Exactly the same as the AgentEvent but works with application objects LinkEvent A down or up event in a link which is used to simulate link failures and was shown in Tutorial 4 regarding network dynamics In order for these events to have some effect in the simulation the Distance Vector routing protocol must be selected in the simulation environment see tutorial 4 GenericEvent A generic event that can schedule up to 10 events without any requirements on the events or classes being scheduled This event was used to schedule several ping to be sent in the course of a single simulation see tutorial 5 Chapter 8 The nscript file formats 8 1 Thenscript Document file format The file format for a nsscript environment is defined as Number of arrays Array Name 1 Array Size 1 Array Name 2 Array Size 2 Array Name n Array Size n Number of Objects SnippetName 1 bjectName 1 Entity Specific Attributes Relation Specific Attributes 0bject Attributes SnippetName n bjs 0bjectName n0bjs Entity Specific Attributes Relation Specific Attributes 0bject Attributes First the libraries used in the program are specified
25. is done the simulation will be set up in a way that simple objects will be replaced by arrays of them and whenever a relation exists between a pair the following rule is obeyed e If both objects are indexed by the same array then a relation between corresponding objects will be created for each element in the array This corresponds to a one to one relation between the elements of the two arrays of objects see figure 3 8 nscript User s Manual Tutorials 16 Figure 3 6 The array editor window after adding a new array Figure 3 7 The Object Browser window used to make an object indexed by an array Notice the change in the representation of the object from a plane object to a stack nscript User s Manual Tutorials 17 Same Array Different Array EDD oe c m m Figure 3 8 How a relation between two indexed entities is created If the two entities share the same index set left a relation is created for each copy of the entities On the other hand right if the entities use different arrays a relation is created for each possible pair of entities between the two arrays Ensity class UDP agas Hama junpe indexed bye mpersDILOD Attributm walum Farkat Sira loce GEZE Mastr Uskdelaults Apply Object kowser Iri Vie Figure 3 9 Setting one of the attributes to the value of the index e If objects are use different arrays a all to all approach is used and hence a rel
26. ize in Packets 1 1 1 1 0 1 0 2 0 3 0 4 0 5 0 6 Time in Seconds Figure 6 4 Evolution of the congestion window size recorded using the Tracer object This plot was obtained loading the file into Matlab and plotting one column against the other Part II Libraries Chapter 7 About Libraries There are some practical issues related to the libraries First at start up nscript will always proceed as follows 1 Open the environment file under nscript 1 0 bin settings directory This file contains the description of the environment object ns that is always present in the simulations Do not remove this file You can and will want to modify it to customize the environment to your usual settings and preferences 2 Open the deflibs file located in the same directory This directory contains the list of libraries to be opened by default nscript tries to locate the libraries in the bin lib subdirectory If you want a library created by you self or others to be opened automatically add its name to the list in this file 3 Open each of the libraries specified by the deflibs file 7 1 Changing the default values To change the default values for the objects edit the correponding library file that can be found under the directory nscript 1 0 bin lib Each class definition has a list of attributes and their default values changing this values will do For example suppose that we want to modify the default values for a du
27. lentity class PingRecv procedure 4 begin Agent Ping instproc recv from rtt 1 self instvar node puts node node_ id received ping answer from from with round trip time rtt ms u end This is a library file The first two lines indicate the library name and the name under which the library will be listed in the toolbox The third line identifies the version of the library for the purpose of version control After those definitions classes can be added according to the formats provided in Part II of this manual in section 8 2 In this case we are adding a single class called PingRecv which represents the recv procedure required by the ping class In a few words class declarations for entity classes follow the following format 22 nscript User s Manual Tutorials 23 Saber an nbjacr Ping gene Ping Eerwiprared ure Figure 5 1 ToolBox after the ping library has been opened Notice that the two classes defined show in the corresponding list box entity class lt className gt drawing parameters where is optional and has the mathematical meaning of unique meaning that only one object of this class is allowed in a simulation This unique feature is used in the environment object that is present in all simulations labeled ns Since this object defines the simulation environment only one of those is allowed in a simulation In this case since the receive procedure has to be declared only once in t
28. me and an application by calling any of the applications available commands CBR applications support start and stop among others Your diagram should look like 2 5 4 Select the connection between 4 5 and the CBR application and set the Event attribute to stop This has the following meaning at time 4 5 applications CBR will stop sending info Save the script using the Save option under the File menu At this point you can run the script using ns directly from the nscript application by clicking at the run button in the toolbar y You will be asked to give a name to the script and little after that the nam animation window will appear Note this option does not work under Windows Chapter 3 Tutorial 2 Making it more interesting In this tutorial we will create a more interesting example see Making it more interesting in Gre We will simulate two CBR flows sending information over different paths of a simple topology 3 1 ATwo Flow Model 3 1 1 Build the Topology Follow these steps to obtain the diagram in 3 1 The topology We start by creating three nodes and linking them together with duplex links with 1Mbps capacity and a delay of 10ms e Use the Topology library to create the topology in figure 3 1 e Using the Object Browser configure each of the links to have Bandwidth of 1Mb Delay of 10ms DropTail scheduler Transport Layer Here we create a two UDP based flows and set them to following
29. nscript Version 1 0a USER S MANUAL Enrique Campos N fiez Department of Systems Engineering University of Virginia ec3zQvirginia edu March 13 2001 This work is supported by Consejo Nacional de Ciencia y Tecnologia through scholarship 68428 and the National Science Foundation through grant ANI 9903001 Contents 1 Introduction 1 1 Requirements 12 Installation 1 3 Afirstlookatthenscript GUI ees 1 3 1 Working with the Editor ee 1 3 2 Saving and opening files 2s 1 4 What s in this manual I Tutorials 2 Tutorial 1 the first tcl script 2 1 Building the Topology 2 1 1 Configuring the Link 2 2 Creating and Configuring Transport Agents 0 00 eee eee ee ees 2 3 Creating and Attaching Applications 2 0 0 eA 2 4 Scheduling Simulation Events 2 2 es 3 Tutorial 2 Making it more interesting 3 1 ATwoFlow Model 3 1 1 Build the Topology 3 2 Generalizing to an n flow model ees 3 2 1 3 2 2 First a base model Creating an array 4 Tutorial 3 Network Dynamics 4 1 The Base Topology and Model es 4 2 Simulating a link failure 5 Tutorial 4 The Ping Agent 5 1 Creating a new procedure 5 2 ThePingAgent 5 3 Simulating Ping Messages 6 Tutorial 6 Tracing A Variable of Interest 6 0 1 Plotting the trace file 12 12 12 14 15 19 19 19 22 22 23 23 26 nscrip
30. plex link to be 1Mb a delay of 10ms and RED queueing discipline Looking at file topology lib and looking for the DuplexLink object definition we find relation class DuplexLink node node 0 O 4 0 Bandwidth 10Mb Delay 20ms Forward Cost 1 0 Backward Cost 1 0 Queue Discipline DropTail DropTail RED CBQ FQ SFQ DRR Queue Capacity 50 begin env name duplex link from to Bandwidth Delay Queue Discipline set name env name link from to Queue Capacity 50 env name queue limit from to Queue Capacity Forward Cost 1 0 env name cost from to Forward Cost Backward Cost 1 0 env name cost to from Backward Cost end Change this definition to the following 29 nscript User s Manual Libraries 30 relation class DuplexLink node node 0 0 4 0 Bandwidth 1Mb Delay i0ms Forward Cost 1 0 Backward Cost 1 0 Queue Discipline RED DropTail RED CBQ FQ SFQ DRR Queue Capacity 50 begin env name duplex link from to Bandwidth Delay Queue Discipline set name env name link from to Queue Capacity 50 env name queue limit from to Queue Capacity Forward Cost 1 0 env name cost from to Forward Cost Backward Cost 1 0 env name cost to from Backward Cost end Notice the changes in lines 2 3 and 5 of the definition We tried to some extent to include the correct default values but if we failed it is always possible to co
31. rrect this 7 2 Creating New Libraries In order to create new libraries you need to check that either the library names nor the class names have been used before i e contained in another library If this was the case nscript will simply ignore the class or library definitions Think ofthe classes stored in the libraries simply as templates that can be filled by the user The ping tutorial for example shows the workings of a class which can be separated into tree important parts e Declaration What kind of class entity or relation its base class drawing information for the Graphical Editor e Attribute Declaration What information will be provided by the user and what their default values are e Translation to Tcl A Tcl template that will be filled with the information provided by the user The information on how to specify each of this parts is carefully described in the last chapter of the book Look at the library definition files in the bin lib subdirectory These provide a good example of how to achieve results Note that this will require you to understand how ns works Modifying a class definition from the default libraries will make impossible to open previous sim ulation scripts Therefore we suggest the use of separate library files that can be created for your own purposes If you have library definitions that implement new functionality or that implement better what is provided please let us know 7 3 T
32. t Users Manual Introduction II Libraries 7 About Libraries 7 1 Changing the defaultvalues ooro oca oco ie maciri ee ee 7 2 Creating New Libraries eh 153 Thedetault libraries sni ux ace ote p tee ARA wr dee See ara ee GA The Utilities Library siaa oregano aE ea BR A ls RU EN eer cee a 8 The nscript file formats 8 1 Thenscript Documentfileformat es 82 Thenscript Library file format Re 8 2 7 Class file format s 2 205 39 DYGCUPYGTAG WR vxE YE E PR 9 TclPattern and value substitution 28 29 29 30 31 32 32 32 33 35 Chapter 1 Introduction nscript is a simple tool designed to graphically build simulation scripts for the network simulator ns see BBE 99 It allows to edit graphically using a block metaphore the elements involved in a simulation and produces the necessary Tcl script required to run it under ns Specifically it is designed to aid in the following tasks e Build the topology for a given simulation nscript lets you graphically build a topology e Create and configure the transport agents and network applications and connect them to the physical topology e Schedule simulation events Through the use of special graphical objects nscript makes it possible to trigger events at particular moments or a sequence of moments in the simulation e Trace and plot values of interest nscript is also extensible allowing you to add new classes of objec
33. t member values to be written to a text file It allows you to specify when to start recording and the sampling interval Create a Tracer object and configure it according to figure 6 3 6 0 1 Plotting the trace file When the script is run a file with the same name as this object and a trc extension for trace will be created This file is a text file that stores the times at which the observations in one column and the value of cwnd in the other column See figure 6 4 to observe the results Note the trace file will be written in the directory in which you started running the nscript program not in the file where your simulation script is saved ip mm G 13 ER TFT RE t Figure 6 1 Finished simulation script for the tracing example 26 nscript User s Manual Tutorials 27 glares 15 TORS Hama Agerpen lado bys Ha Index Attribute Velua Event mand Bcc Figure 6 2 Configuration of the AgentEvent object to schedule the delivery of a 80k file Enniry class Trager Timer Hama loen im oxcdl byi Wa Index Velua Ceia Hambar cend Use defaulis Apply Figure 6 3 Configuration of the tracer object to record the cwnd field of the TCP session This variable repre sents the congestion window size of the session The tracing will start with the simulation and will be sampled every hundreth of a second Evolution of the Window Size for Tutorial 6 T T T 20r a T o T Window S
34. ter of agent UDPO and dragging to the center of node NodeO and release the mouse then This particular order agent node is required To know what is the order required look in the ToolBox at the nscript Users Manual Tutorials 10 FY bro NodeO m UE Null Nodel Figure 2 3 Configuration of the link for the simulation line for AttachToNode class It displays AttachToNode agent node meaning that to create a relation of this class we must first provide an agent and then a node 6 Attach agent Null0 to Nodel in the same way 7 Thelast step is to connect the two agents which can be achieved using the Connect class from the Trans port library Select this tool and connect agent UDPO to agent Null0 This connection represents the logical connection between two agents that don t have a direct physical connection By the end of this section your diagram should look like figure 2 3 This represents two computers directly connected through a physical link and two transport agents each attached to one of the computers routers and logically connected to each other The next step is to create an application that sends some data In this case a CBR flow 2 3 Creating and Attaching Applications 1 Select the Application library and create a new CBR application place it north to the UDP agent 2 Select the Transport library again and select the AttachToApp class Attach agent UDPO to application CBRO by creating
35. ts to the graphical environment By organizing the classes of simulation objects into libraries new classes can easily be integrated and used in the graphical environment 1 1 Requirements The nscript application was developed using Java 2 and makes use of the JFC library Swing to implement its user interface To use nscript it is necessary to download version 1 3 of the JDK from http www java sun com To run scripts and visualize the corresponding animations it is necessary to install the ns and the nam ap plication which can be found at http www isi edu nsnam ns The nscript application runs in all platforms with a JVM that supports Java 2 classes but in order to run ns scripts directly a Unix platform is recommended If such platform is not available to use you can still create a simulation script and manually run it in ns To plot some of the file traces you might consider installing gnuplot http www gnuplot org xgraph http www atl external Imco com proj csim xgraph xgraph html or something similar 1 2 Installation The package is distributed as a zip file that unzips to a single directory nscript 1 0 The unzipped directory should contain e README Information on the latest changes nscript Users Manual Introduction 4 ELI CPE Hike Edit feist Help Date V m Toolbar almi am abit Fin wimien Fins ind umed By T Graphical Edibar Object Browser Wie dela ake lint oe ee
36. ure 3 3 Equivalent definitions of the model using arrays left and withoutarrays right Q 5 Oo 4 5 2 CERO OE i choc die sese cna eta erro ere nO H Null Mn ee Node 0 Figure 3 4 Base for the more general simulation model Notice there is only one flow there 3 2 2 Creating an array An array is specified by a name which has to be a valid variable name for Tcl anything without spaces or special characters and the number of copies it will contain To create a new array called users 1 Open the array editor by selecting the Edit Arrays option from the Edit menu That will bring up the window shown in sreenshot 3 2 2 2 Click on the Add button to add a new array definition 3 Edit the array name and change it to users The array editor window should look like 3 2 2 4 Close the array editor window by clicking at the Close button Once this is completed the array will be stored as part of the script Indexing the Existing Objects Select the Null0 agent using the Select Tool and click on the popup labeled Indexed by Select the entry showing the users array and then click the Apply button This tells the editor to consider the Null0 agent not as a single object but as an array of objects indexed by the set users Once this is done you should notice that the array is represented as a small stack of agents instead see figure 3 7 Repeate the same indexing process for the following object UDPO CBRO and Node0 Once this

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