1 Network Simulator (NS-2) Tutorial These slides can be downloaded from:

2 Agenda  What Is NS?  Elements of Simulation  NS Architecture  NS Internals  Summary

3 What is NS  Discrete event simulator  Packet-level  Protocol stack -Link layer and up for wired networks; -Physical layer and up for wireless networks  Wired and wireless(both local and satellite) Detour

4 History and Status  Now part of VINT(Virtual InterNet Testbed) project -Columbia NEST --> UCB REAL --> NS-1 --> NS-2  Users from approximately -600 institutes -50 countries  Releases -Periodic releases (currently 2.1b9, April 2002) -Nightly snapshots (probably compiles and works, but “unstable”) -Available from: USC/ISI, UC Berkeley, UK mirror

5 Platforms  Most UNIX and UNIX-like systems FreeBSD or *BSD Linux Sun Solaris  HP, SGI  Window 95/98/NT -Some work, some does not  (Emulation only for FreeBSD for now)

6 Functionality of NS  Wired world -Point-to-point link, LAN -Unicast/multicast routing -Transport -Application layer  Wireless -Mobile IP -Ad hoc routing  Tracing, visualization, various utilities

7 Visualization Tools  nam-1 (Network AniMator Version 1) -Packet-level animation -Well supported by ns  xgraph -Conversion from ns trace to xgraph format

8 Getting Started  NS official site: -  A painless tutorial by Marc Greis: -  Another good tutorial from WPI -

9 Getting Help & Reference  Building NS -  NS user mailing list -  NS manual -

10 Agenda  What Is NS?  Elements of Simulation  NS Architecture  NS Internals  Summary

11 Elements of Simulation  Create the event scheduler  [Turn on tracing]  Create network  Setup routing  [Insert errors]  Create traffic  Start simulation  Post-process trace Detour

12 Creating Event Scheduler  Create event scheduler -set ns [new Simulator]  Schedule events -$ns at - : any legitimate ns/tcl commands  Start scheduler -$ns run

13 Tracing  Trace packets on all links -$ns trace-all [open test.out w] cbr cbr r cbr  Trace packets on all links in nam-1 format -$ns namtrace-all [open test.nam w]  Turn on tracing on specific links -$ns trace-queue $n0 $n1 -$ns namtrace-queue $n0 $n1  Must appear immediately after creating scheduler

14 Creating Network  Nodes -set n0 [$ns node] -set n1 [$ns node]  Links and queuing -$ns duplex-link $n0 $n1 - : DropTail, RED, CBQ, FQ, SFQ, DRR

15 Creating Network: LAN  LAN -$ns make-lan - : LL - : Queue/DropTail, - : MAC/802_3 - : Channel

16 Inserting Errors  Creating Error Module -set loss_module [new ErrorModel] -$loss_module set rate_ $loss_module unit pkt -$loss_module ranvar [new RandomVariable/Uniform] -$loss_module drop-target [new Agent/Null]  Inserting Error Module -$ns lossmodel $loss_module $n0 $n1

17 Network Dynamics  Link failures -Hooks in routing module to reflect routing changes  Four models $ns rtmodel Trace $n0 $n1 $ns rtmodel Exponential { } $n0 $n1 $ns rtmodel Deterministic { } $n0 $n1 $ns rtmodel-at up|down $n0 $n1  Parameter list [ ] [ ]

18 Setup Routing  Unicast -$ns rtproto - : Static, Session, DV, cost, multi-path  Multicast -$ns multicast (right after [new Simulator]) -$ns mrtproto - : CtrMcast, DM, ST, BST

19 Creating Connection: UDP or TCP  UDP -set udp [new Agent/UDP] -set null [new Agent/Null] -$ns attach-agent $n0 $udp -$ns attach-agent $n1 $null -$ns connect $udp $null  TCP -set tcp [new Agent/TCP] -set tcpsink [new Agent/TCPSink] -$ns attach-agent $n0 $tcp -$ns attach-agent $n1 $tcpsink -$ns connect $tcp $tcpsink

20 Creating Traffic: On Top of UDP  CBR -set src [new Application/Traffic/CBR]  Exponential or Pareto on-off -set src [new Application/Traffic/Exponential] -set src [new Application/Traffic/Pareto]

21 Creating Traffic: On Top of TCP  FTP -set ftp [new Application/FTP] -$ftp attach-agent $tcp  Telnet -set telnet [new Application/Telnet] -$telnet attach-agent $tcp

22 Creating Traffic: Trace Driven  Trace driven -set tfile [new Tracefile] -$tfile filename -set src [new Application/Traffic/Trace] -$src attach-tracefile $tfile  : -Binary format (native!) -inter-packet time (msec) and packet size (byte)

23 Application-Level Simulation  Features -Build on top of existing transport protocol -Transmit user data, e.g., HTTP header  Two different solutions -TCP: Application/TcpApp -UDP: Agent/Message

24 Agenda Detour ends.  What Is NS?  Elements of Simulation  NS Architecture  NS Internals  Summary

25 NS Architecture  Object-oriented (C++, OTcl)  Scalability + Extensibility -Control/”data” separation -Split C++/OTcl object  Modular approach -Fine-grained object composition Detour ends.

26 C++/OTcl Split Objects C++ OTcl Pure C++ objects Pure OTcl objects C++/OTcl split objects NS 100K 70K

27 C++/OTcl Linkage

28 TclObject: Hierarchy and Shadowing TclObject Agent Agent/TCP Agent/TCP OTcl shadow object _o123 Agent/TCP C++ object *tcp TclObject Agent TcpAgent OTcl class hierarchy C++ class hierarchy

29 The Merit of OTcl Program size, complexity C/C++ OTcl  Smoothly adjust the granularity of scripting to balance extensibility and performance  With complete compatibility with existing simulation scripts high low split objects

30 Scalability vs Flexibility  It’s tempting to write all-OTcl simulation -Benefit: quick prototyping -Cost: memory + runtime  Solution -Control the granularity of your split object by migrating methods from OTcl to C++

31 Object Granularity Tips  Functionality -Per-packet processing  C++ -Hooks, frequently changing code  OTcl  Data management -Complex/large data structure  C++ -One-time configuration variables  OTcl

32 Agenda  What Is NS?  Elements of Simulation  NS Architecture  NS Internals  Summary

33 NS Internals  Discrete event scheduler  Network topology  Routing  Transport  Packet flow  Packet format  Application

34 Discrete Event Scheduler time_, uid_, next_, handler_ head_ ->  Three types of schedulers -List: simple linked list, order-preserving, O(N) -Heap: O(logN) -Calendar: hash-based, fastest, O(1) handler_ -> handle() time_, uid_, next_, handler_ reschedule insert

35 Network Topology: Node n0n1 Addr Classifier Port Classifier classifier_ dmux_ entry_ Node entry Unicast Node Multicast Classifier classifier_ dmux_ entry_ Node entry Multicast Node multiclassifier_

36 Network Topology: Link n0n1 enqT_queue_deqT_ drophead_ drpT_ link_ttl_ n1 entry_ head_ tracing simplex link duplex link

37 Routing n0n1 Addr Classifier Port Classifier classifier_ dmux_ entry_ Node entry 0 1 enqT_queue_deqT_ drophead_drpT_ link_ttl_ n1 entry _ head_

38 Routing (con’t) n0n1 Addr Classifier Port Classifier classifier_ dmux_ entry_ 0 1 Addr Classifier Port Classifier classifier_ dmux_ entry_ 1 0 Link n0-n1 Link n1-n0

39 Transport 0 1 n0n1 Addr Classifier Port Classifier classifier_ dmux_ entry_ 0 Agent/TCP agents_ Addr Classifier Port Classifier classifier_ dmux_ entry_ 1 0 Link n0-n1 Link n1-n0 0 Agent/TCPSink agents_ dst_=1.0 dst_=0.0

40 Application: Traffic Generator 0 1 n0n1 Addr Classifier Port Classifier classifier_ dmux_ entry_ 0 Agent/TCP agents_ Addr Classifier Port Classifier classifier_ dmux_ entry_ 1 0 Link n0-n1 Link n1-n0 0 Agent/TCPSink agents_ dst_=1.0 dst_=0.0 Application/FTP

41 Plumbing: Packet Flow 0 1 n0n1 Addr Classifier Port Classifier entry_ 0 Agent/TCP Addr Classifier Port Classifier entry_ 1 0 Link n0-n1 Link n1-n0 0 Agent/TCPSink dst_=1.0 dst_=0.0 Application/FTP

42 Packet Format header data ip header tcp header rtp header trace header cmn header... ts_ ptype_ uid_ size_ iface_

43 Abstract the Real Wireless World  Packet headers  Mobile node  Wireless channel  Forwarding and routing  Visualization

44 Wireless Packet Format header data ts_ ptype_ uid_ size_ iface_ IP header cmn header LL MAC 802_ ARP Wireless headers

45 Mobile Node Abstraction  Location -Coordinates (x,y,z)  Movement -Speed, direction, starting/ending location, time...

46 Portrait of A Mobile Node Node ARP Propagation and antenna models MobileNode LL MAC PHY LL CHANNEL LL MAC PHY Classifier: Forwarding Agent: Protocol Entity Node Entry LL: Link layer object IFQ: Interface queue MAC: Mac object PHY: Net interface protocol agent routing agent addr classifier port classifier 255 IFQ defaulttarget_

47 Wireless Channel  Duplicate packets to all mobile nodes attached to the channel except the sender  It is the receiver’s responsibility to decide if it will accept the packet -Collision is handled at individual receiver -O(N 2 ) messages  grid keeper

48 Agenda  What Is NS?  Elements of Simulation  NS Architecture  NS Internals  Summary

49 Summary  What can we do with NS?  Architectural overview of NS -split C++/OTcl Object  Inside NS -node, link, routing, tcp, app, wireless extension -how it works

50 References  