Network Simulator 2

ns-2 seminar Network Simulator 2 - Introduction for Beginners - 2008. 03. 18 CNLAB

Scope  Basic Requirements for Using ns-2 1) C++ 2) Tcl & OTcl 3) Object Orientation concepts 4) ns-2 Mechanisms (ns-2 Core & Utilities) 5) Application-specific Implementation Architectures . Wired ~ to Wireless world . Lower Layer ~ to Higher Layer . Variety of architectural specifics

Scope  Introduction  Some Basic Concepts - Architectural Views - Plumbing & Duality - Tcl basics  OTcl Linkage Architecture  Object Orientation in OTcl  Elemental Procedures in ns-2 programming - Network creation - Agents & others

Introduction  Ns has began as a variant of the REAL network simulator in 1989, and has evolved substantially in the past few years.  In 1995 ns development was supported by DARPA through the VINT project at LBL, Xerox PARC, UCB, and USC/ISI. - VINT : Virtual InterNet Testbed http://www.isi.edu/nsnam/ns/  The latest version :ns-2.32 [2007] : hundreds * 1000 LOC

Introduction  Related Research area - functionality & application - Network Layer . Routing : unicast, multicast, MPLS . QoS : IntServ / DiffServ . Queuing Disciplines - Transport . TCP . Reliable multicast . Congestion control - Application . Web Caching . Multimedia . Traffic Sources - Wireless world . Mobile IP . Ad hoc routing . Sensor MAC

Introduction  NS-2 Directory ns-allinone Tcl8.x TK8.x OTcl tclcl ns-2 nam-1 . . . tcl C++ code ... ex test mcast lib examples validation tests OTcl code

Introduction  What is NS-2 ? - Discrete Event Simulator -Packet-level - Link layer and up - Wired and Wireless worlds  Languages - Tcl (Tool Command Language) - OTcl (MIT Object-oriented Tcl) - C++ - Some others

Introduction  Tcl Interpreter with Extents - OTcl : Object-oriented support, extending Tcl/Tk - TclCL : C++ and OTcl Linkage (interface) - Discrete Event Scheduler (ordered list of events) - Data Network (the Internet) Components Event Scheduler ns-2 tclcl Network Component Users Otcl tcl8.x

Basic Concepts – Architectural View  Object-oriented (C++, OTcl) • - Reusability • - Maintenance  Scalability + Extensibility - Control / “Data” separation . OTcl for control (scenarios) . C++ for “data” - Split OTcl / C++ objects  Duality Needs Linkage  Modular approach - Fine-grained Object composition

Basic Concepts – Architectural View  Simplified User’s View of NS - NS-2 is basically the Tcl & OTcl Interpreter with network simulation object libraries.

Basic Concepts – Architectural View  Layered View of the NS [an example] - OTcl : Application, Scenario, or Upper Layer - C++ : Lower Layer or Protocol/Packet Layer

Basic Concepts – Architectural View  Components domain Relationship View of the NS - NS-2 is written in C++ with OTcl Interpreter as the Front-End. - Simulator objects are implemented in the Compiled hierarchy (C++ domain), but instantiated through the Interpreter.

Basic Concepts - Architecture  Nodes

n0 n1 Port Classifier Multicast Node dmux_ Addr Classifier classifier_ Node entry Node entry dmux_ entry_ entry_ Multicast Classifier classifier_ multiclassifier_ Basic Concepts - Architecture  Nodes Unicast Node Classifier : Address, Multicast, Multipath

n0 n1 duplex link n1 entry_ head_ enqT_ queue_ deqT_ link_ ttl_ drophead_ drpT_ tracing simplex link Basic Concepts - Architecture  Links

n0 n1 Port Classifier Addr Classifier n1 entry_ 0 Node entry head_ dmux_ enqT_ queue_ deqT_ link_ ttl_ 1 entry_ classifier_ drophead_ drpT_ Basic Concepts - Architecture  Nodes & Links

n0 n1 Port Classifier Port Classifier Addr Classifier Addr Classifier 0 1 dmux_ dmux_ 1 0 entry_ entry_ classifier_ classifier_ Link n1-n0 Basic Concepts - Architecture  Routing Link n0-n1

dst_=0.0 dst_=1.0 Agent/TCP Agent/TCPSink agents_ agents_ 0 1 1 0 Basic Concepts - Architecture  Transport n0 n1 Port Classifier Port Classifier Addr Classifier Addr Classifier 0 0 dmux_ dmux_ Link n0-n1 entry_ entry_ classifier_ classifier_ Link n1-n0

Application/FTP dst_=0.0 dst_=1.0 0 1 1 0 Basic Concepts - Architecture  Application : Traffic Generator n0 n1 Port Classifier Port Classifier Agent/TCPSink Addr Classifier Addr Classifier Agent/TCP 0 0 agents_ agents_ dmux_ dmux_ Link n0-n1 entry_ entry_ classifier_ classifier_ Link n1-n0

Basic Concepts - Architecture  Object Hierarchy TclObject NsObject other objects Classifier Connector Queue Delay Agent Trace AddrClassifier McastClasifier DropTail RED TCP Enq Deq Drop ... Reno SACK

Basic Concepts - Architecture  Some differences between NS-2 & Real network - Node : no queue, above network layer, no lower layer on the basic Node (not in mobile node) - Link : Compound object with Queues - No physical media, but simulated environment - No real data or payload transmissions, except in special applications (web), which uses special transport. - Normally, the ultimate Packet Transmissions are done by calling the next object’s method (recv( )).

Basic Concepts - Plumbing  Network Topology Setupusing - Network Objects : Nodes & Links *cf) NsObject - Plumbing Library functions  Plumbing : for Network Setup • - Plumbing Data Paths among the Network Objects • by setting the “Neighbor” pointers of an Object to • the Address of an appropriate object. • - Plumbing modules are implemented as member • functions of the base Simulator object. • - neighbor_,target_ variables are key to plumbing • transmission : target_recv( )

Basic Concepts - Duality TclCL linkage Pure C++ objects Pure OTcl objects C++ / OTcl split objects C++ OTcl ns OTcl & C++ Share Class Hierarchy

Basic Concepts - Duality  C++ / OTcl Separation - C++ for “Data” . Per Packet action : Packet Headers accessed - OTcl for Control . Periodic or Triggered action (~ Scenario scheduling) . Network(Topology) Creation : Application procedure - Tradeoff between Composability and Speed (+) - Learning/debugging are more difficult (-)  Separation on Dual planes need Linkage to compose

Basic Concepts - Duality  OTcl : Interpreted hierarchy - Create Network - Create Connection (wired) - Create Traffic  C++ : Compiled hierarchy - Packet processing methods - OTcl command Interpreter . object::command( ) method : one of the linkage

Basic Concepts - Duality  Otcl domain set tcp [new Agent/TCP] $tcpadvance 10  C++ domain int TcpAgent::command(int argc, const char*const* argv) { if (argc == 3) { if (strcmp(argv[1], “advance”) == 0) { int newseq = atoi(argv[2]); …… return(TCL_OK); } } return (Agent::command(argc, argv); }

Basic Concepts – Tcl/OTcl  Tcl / OTcl Basics - proc command : define a global procedure . proc create_topology { - set command : assign a value to a variable . set count 10 . $self set count 10 - Substitutions . Command substitution : brackets as command - set cnt [ $self set count ] cnt = 10 - set cnt [ expr $cnt + $cnt ] set cnt to 20 . Variable substitution : ex) $count  10 $ns at [ $ns now ] “$selfsend $class $rate"

C++ / OTcl Linkage - snapshot view  Export C++ class to Otcl [Create C++ object from OTcl] •Creating a new network object class in C++, & also an instance of this object in Otcl, needs a Linkage object derived from the TclClass (C++ domain).  Export C++ class variables to OTcl •Thenew network object class in C++ may have some parameter variables, also to be configured from Otcl. Export C++ Object Control Commands to OTcl •Giving the control of new C++ object to Otcl, via the Otcl command interpreter: command() function.  Execute an OTcl command from C++ •Execute an OTcl command from the new C++ object.

C++ / OTcl Linkage

C++ / OTcl Linkage - TclObject  TclObject : base class - Basic hierarchy in ns-2 for split objects - Mirrored in both C++ & OTcl - NsObject : the superclass of all network component objects that handle packets   Connector, Classifier subclasses - Connector : having only one output data path - Classifier : having multiple output data path (Router) - Node : Compoundobject ~ Node Entry, Classifier objects - Link : ’’ ~ Queue, Delay, TTL objects..

C++ / OTcl Linkage - TclObject  TclObject : Hierarchy and Shadowing C++ class hierarchy OTcl class hierarchy TclObject TclObject Agent static TcpClass : public TclClass { public: TcpClass():TclClass(“Agent/Tcp"){} TclObject* create(int,const char*const*) { return (new TcpAgent());} }; Agent TcpAgent Agent/TCP _o123 *tcp Agent/TCP OTcl shadow object Agent/TCP C++ object

C++/OTcl Linkage - TclObject  TclObject Creation & Deletion - Global Procedures : new{ }, delete{ } - Example : set tcp [ new Agent/TCP ] … delete $tcp

Agent/TCP constructor parent constructor TclObject constructor invoke parent constructor create C++ object which C++ obj to create? – TclClass complete initialization complete initialization create OTcl shadow object parent (Agent) constructor AgentTCP constructor TclObject (C++) constructor invoke parent constructor invoke parent constructor do nothing, return bind variables and return bind variables and return C++ / OTcl Linkage – TclObject set tcp [newAgent/TCP] invoke parent constructor OTcl C++

C++/OTcl Linkage - TclObject::bind()  Linking C++ member variable to OTcl object variable • Bound variables can be configured from Both C++/OTcl.  C++ domain TcpAgent::TcpAgent( ) { // Constructor bind(“window_”, &wnd); … … } // other type : bind_time(), bind_bool(), bind_bw()  OTcl domain set tcp [new Agent/TCP] $tcp set window_ 200

C++ / OTcl Linkage - TclObject::command()  Export C++ Object Control Commands to OTcl int MyAgent::command(int argc, const char*const* argv ) { if (argc == 2) { if (strcmp(argv[1], “call-my-func”) == 0) { MyPrivFunc( )); return (TCL_OK); } } return (Agent::command(argc, argv)); } - Effect : Implement OTcl methods in C++ - Trap point : OTcl method cmd{ }

C++ / OTcl Linkage - TclObject::command() OTcl space no such procedure $tcp send TclObject::unknown{} $tcp cmd send C++ space TcpAgent::command() match “send”? Yes No Invoke parent: return Agent::command() process and return

mirroring OTcl C++ TclObject TclObject NsObject ?? Agent Agent TcpAgent Agent/TCP C++ / OTcl Linkage – TclClass • Static class TcpClass : public TclClass { • public: • TcpClass() : TclClass(“Agent/TCP”) { } • TclObject* create(int, const char*const*) { • return (new TcpAgent( ) ); • } • } class_tcp;

C++ / OTcl Linkage – TclClass  Class TclClass ( inC++ ) - This compiled class is pure virtual class : only 2 functions •Construct the interpreted class hierarchy to mirror the compiled class hierarchy. •Method toCreate instances of the associated TclObject. - For the static variableclass_tcp, ns-2 will execute the constructor of TcpClass. The constructor specifies the interpreted class explicitly as “Agent/TCP”. - This sets up the related methods and the interpreted class hierarchy in the Otcl space. Next slide - This class isassociated with the class TcpAgent, and when the user issues “new …”, TcpClass::create( ) is invoked.  TcpAgent is created.

C++ / OTcl Linkage – TclClass  Interpreted Class Hierarchy construction (more) - When the object constructor is executed, the TclClass constructor stores the name of the class, and inserts this object into Linked List of TclClass objects. - During initialization, TclClass::bind() is invoked. - For each object in the List, bind() invokes register{… } with the class name as its argument. - register{ } establishes the class hierarchy, creating the class required. class TcpAgent : public Agent { public: TcpAgent( ); // Constructor protected: int command(int argc, const char* const* argv); int xxx_; };

C++ / OTcl Linkage – Tcl  Singleton class with a handle to Tcl interpreter  Usage - Invoke OTcl procedure from C++ : 4 methods - Obtain OTcl evaluation results : tcl.result( ) - Pass a result string to OTcl : tcl.result(*s), tcl.resultf(*s)

C++ / OTcl Linkage – Tcl  Execute an OTcl command from C++ Tcl& tcl = Tcl::instance(); tcl.eval (“puts \ “Message from MyPrivFunc\””); or char wrk[128]; sprintf(wrk, “$s recv %d”, name(), result); tcl.eval (wrk); tcl.evalc (“puts \ “Message from MyPrivFunc\””); tcl.evalf (“puts \ “ my_var1 = %d\””, my_var1); tcl.evalf (“puts \ “ my_var2 = %d\””, my_var2);

C++ / OTcl Linkage - summary  TclObject - Unifies Interpreted (OTcl) and Compiled (C++) class hierarchies - Seamless access (Method call and Variable access) between OTcl and C++  TclClass - The mechanism that makes TclObject work - Interpreted hierarchy & shadowing methods  Tcl - Primitives ( in C++ ) to access Tcl interpreter

Object Orientation in OTcl  Some Differences between C++ & OTcl - OTcl Class vs. C++ Class architecture . OTcl attaches methods to Object or Class (evolving) . C++ has single Class Declaration - C++/OTcl Split Objects . Implement methods in either language . Define instance variables in either C++ or Otcl  Through in different Syntax & Forms

Object Orientation in OTcl  Class structures comparison Class Link Link instproc init { src dst } { $self next $self instvar fromNode_ toNode_ … set fromNode_ $src set toNode_ $dst ………… } Link instproc head { } { $self instvar head_ return $head_ } class PingAgent : public Agent { public: PingAgent( ); int command(int argc, const char* const* argv); void recv (Packet*, Handler*); protected: int off_ping_; };

Object Orientation in OTcl  Some Differences between C++ / OTcl - instvar : to define/access member variable - instproc : to define member function (procedure) - OTcl init{ } vs. C++ Constructor( ) - $self this - Syntax checking in Tcl/OTcl . No new line from “{”+ body, but only after “{” . if {, } elseif {, …

OTcl Basics Class Mom Mom instproc greet {} { $selfinstvar age_ puts “$age_ years old mom: How are you doing?” } Class Kid -superclass Mom Kid instproc greet {} { $selfinstvar age_ puts “$age_ years old kid: What’s up, dude?” } set mom [new Mom] $mom set age_ 45 set kid [new Kid] $kid set age_ 15 $mom greet $kid greet 45 years old mom: How are you doing? 15 years old kid: What's up, dude?

Elemental Tcl Procedures in ns-2 programming - Creating the Event Scheduler - [Turn on tracing] - Creating network - Setup routing - Insert errors - Creating connection(Agents) - Creating traffic - Configuring Algorithmic Scenario specific to this App …. - Start ns simulation

Example Procedures # Application code Tcl/OTcl Script. set end 200.0 set warmup 20.0 # For Stable data timing set linkrate 5Mb # May be Adjusted. set ns [new Simulator] # ns Created : First line of App create_topology # Creating topology... create_agents # Creating agents... create_sources # Creating traffic sources... create_conditioners # Creating conditioners... configure_scheduler # Configuring Queue Scheduler... $ns at $end "end" $ns run # Starting simulation...

Creating Event Scheduler  Create event scheduler set ns [new Simulator]  Scheduling Events $ns at <time> “<event>” <event> : any legitimate ns/tcl commands  Start scheduler $ns run

Register Event Deque Object B Object A Dispatch Dispatch Event Scheduling Event Queue Target object Event (Packet) Time Scheduler

Network Simulator 2 - Introduction for Beginners - 2008. 03. 18 CNLAB