Introduction to ns2

1
Introduction to ns-2
2
Outline

• Part 1 model and simulate Internet traffic
• Part 2 an introduction to ns-2
• What is ns-2
• Fundamentals
• Writing ns-2 codes
• Wireless support
• Traces support and visualization
• Emulation
• Related work
• Part 3 trace-driven network simulation

3
What is ns-2

• History
• What does it support

4
Ns Goals

• Support networking research and education
• Protocol design, traffic studies, etc
• Protocol comparison
• Provide a collaborative environment
• Freely distributed, open source
• Share code, protocols, models, etc
• Allow easy comparison of similar protocols
• Increase confidence in results
• More people look at models in more situations
• Experts develop models
• Multiple levels of detail in one simulator

5
Alternatives

• Experimentation
• Private lab
• Public testbed (e.g. Planetlab)
• Shared labs (e.g. Utah Emulab)
• Analysis
• Other simulator
• Custom simulators
• Other general simulators

• Operational details, but
• Limited scale
• Expensive, limited flexibility
• Higher overhead
• Can provide understanding, but
• Limited details
• Important niches
• Limited re-use

6
History of ns-2

• History
• Cornell REAL simulator -1989
• VINT project (UCB, Xerox ,USC/ISI) 1995
• USC/ISI SAMAN/CONSER project 1999
• Size
• 220K lines of codes
• 45 C
• 31 OTcl
• 23 test suite/example/documents
• 400 pages of mannual
• Very steep learning curve for a new user!
• The most popular non-commercial discrete event
  packet-level simulator
• Used by 10000 users from 1000 institutes from
  50 countries
• 300 posts to ns-users_at_isi.edu every month

7
ns-2 support

• Platform
• FreeBSD, Linux, Solaris, Windows and Mac
• Release
• Periodical release 6 months
• current release ns-2.27, Jan 18, 2004
• Daily snapshot
• Validation
• 100 test suites and 100 examples

8
What ns-2 can simulate

• Wired network
• Traffic model and applications
• Transport protocol
• Routing and Queuing
• QoS
• LANs
• Wireless network
• Ad hoc routing and mobile IP
• Sensor network
• Propagation model/Energy model
• WLAN (802.11)
• Satellite
• Error modules
• Tracing, visualization, emulation, various
  utilities

9
Wired network

• Application
• HTTP, web caching
• telnet, FTP, RealAudio
• CBR, on-off source
• Transport
• UDP, TCP (almost all variants of TCP), RTP
• SRM, PLM, LMS, PGM
• Routing
• Unicast (DV, LM, etc) and multicast routing (PIM
  etc)
• Hierarchical routing
• Manual routing
• Broadcasting
• MPLS
• Queuing
• RED, FIFO, FQ, SFQ, DRR, CBQ
• Diffserv and IntServ
• ECN

10
Wireless network

• Ad-hoc network routing
• AODV, DSR, TORA, DSDV
• Mobile IP
• ARP
• Radio propagation model
• Friss-space attenuation
• Two-ray ground reflection model
• Shadowing model
• Sensor network
• Direct diffusion
• SMAC
• WLAN
• Ad-hoc mode
• Infrastructure mode
• Satellite
• Geostationary
• LEO
• Energy model
• Omni-directional antenna with unity gain

11
Ns Components

• Ns, the simulator itself
• Nam, the network animator
• Visualize ns (or other) output
• Nam editor GUI interface to generate ns scripts
• Pre-processing
• Traffic and topology generators
• Post-processing
• Simple trace analysis, often in Awk, Perl, or Tcl

12
Installation

• Getting the pieces
• Tcl/TK 8.x
• http//dev.scriptics.com
• OTcl, TclCL, ns-2, nam-1 http//www.isi.edu/nsnam
  /dist
• Other utilities
• http//www.isi.edu/nsnam/ns/ns-build.html
• Tcl-debug, GT-ITM, xgraph,

13
Getting Help

• ns-2 build questions
• http//www.isi.edu/nsnam/ns/ns-build.html
• ns-users_at_isi.edu
• ns-users-request_at_isi.edu
• subscribe ns-users in body
• Archive http//www.isi.edu/nsnam/ns

14
Resources

• Tcl (Tool Command Language)
• http//dev.scriptics.com/scripting
• OTcl (MIT Object Tcl)
• otcl/doc/tutorial.html (in distribution)
• ns manual
• Latex sources are included in distribution
  ns/doc
• http//www.isi.edu/nsnam/ns/ns-documentation.html

15
Cautions

• Abstraction of the real world is necessary for a
  simulator
• You must justify the usage of the simulator based
  on your research goals

16
Question?
17
Outline

• Part 1 model and simulate Internet traffic
• Part 2 an introduction to ns-2
• What is ns-2
• Fundamentals
• Writing ns-2 codes
• Wireless support
• Traces support and visualization
• Emulation
• Related work
• Part 3 trace-driven network simulation

18
Prerequisite

• Some programming experience of object-oriented
  language (such as C, Java)

19
Discrete Event Simulation

• Model world as events
• Simulator has list of events
• Scheduler take next one, run it, until done
• Each event happens in an instant of virtual
  (simulated) time, but takes an arbitrary amount
  of real time
• Ns uses simple model single thread of control gt
  no locking or race conditions to worry about

20
Discrete Event Examples
simple queuing model
Consider two nodes on an Ethernet
t1, A enqueues pkt on LAN t1.01, LAN dequeues
pkt and triggers B
t1.0 A sends pkt to NIC As NIC starts carrier
sense t1.005 As NIC concludes cs, starts
tx t1.006 Bs NIC begins reciving pkt t1.01
Bs NIC concludes pkt Bs NIC passes pkt to app
detailed CSMA/CD model
21
Ns Architecture

• Object-oriented (C, OTcl)
• Lots of code reuses (e.g. TCP TCP variants)
• Use TclCl to bind C and OTcl together
• Modular approach
• Fine-grained object composition
• From the simulator to a single event
• Reusability
• Maintenance
• Performance (speed and memory)
• Careful planning of modularity

Network Components
TclCL
Event Scheduler
OTcl
Tcl
C
ns-2
22
C and OTcl Separation

• data / control separation
• C for data
• per packet processing, core of ns
• fast to run, detailed, complete control
• OTcl for control
• Simulation scenario configurations
• Periodic or triggered action
• Manipulating existing C objects
• fast to write and change
• running vs. writing speed
• ? Learning and debugging (two languages)

23
Control vs. Data

• Create topology
• Setup routing
• Create transport connection
• Create traffic

• Details of links and nodes
• Details of a routing protocol
• Details of TCP implementation
• Details of a packet

C
OTcl
24
Otcl and C The Duality
C
user simulation scripts
C/OTcl split objects
otcl
ns

• OTcl (object variant of Tcl) and C share class
  hierarchy
• TclCL is glue library that makes it easy to share
  functions, variables, etc

25
Basic Tcl

• variables
• set x 10
• puts x is x
• functions and expressions
• set y pow x 2
• set y expr xx
• control flow
• if x gt 0 return x else
• return expr -x
• while x gt 0
• puts x
• incr x 1

• procedures
• proc pow x n
• if n 1 return x
• set part pow x expr n-1
• return expr xpart
• Also lists, associative arrays, etc.
• gt can use a real programming language to build
  network topologies, traffic models, etc.

26
Compare Otcl to C

• Object oriented extension of Tcl
• C constructor/destructor gt OTcl init/destroy
  method
• C this gt OTcl self
• OTcl methods always virtual
• C static variable gt OTcl class variable
• Multiple inheritance is supported

27
Basic otcl

• Class Person
• constructor
• Person instproc init age
• self instvar age_
• set age_ age
• method
• Person instproc greet
• self instvar age_
• puts age_ years old How are you doing?

• subclass
• Class Kid -superclass Person
• Kid instproc greet
• self instvar age_
• puts age_ years old kid Whats up, dude?
• set a new Person 45
• set b new Kid 15
• a greet
• b greet

gt can easily make variations of existing things
(TCP, TCP/Reno)
28
Using ns
Problem
Result analysis
Simulation model
Modify ns
Setup/run simulation with ns
29
C/OTcl Linkage
30
TclObject

• Basic hierarchy in ns for split objects
• Mirrored in both C and OTcl
• Example
• set tcp new Agent/TCP
• tcp set packetSize_ 1024
• tcp advanceby 5000

31
TclObject Hierarchy and Shadowing
C class hierarchy
OTcl class hierarchy
TclObject
TclObject
Agent
Agent
TcpAgent
Agent/TCP
tcp
_o123
Agent/TCP OTcl shadow object
Agent/TCP C object
32
TclObjectbind()

• Link C member variables to OTcl object
  variables
• C
• TcpAgentTcpAgent()
• bind(window_, wnd_)
• OTcl
• set tcp new Agent/TCP
• tcp set window_ 200

33
TclObjectcommand()

• Implement OTcl methods in C
• Trap point OTcl method cmd
• Access the shadow object
• Send all arguments after cmd call to
  TclObjectcommand()

34
TclObjectcommand()
OTcl space
no such procedure
tcp send
TclObjectunknown
tcp cmd send
C space
TcpAgentcommand()
match send?
Yes
No
Invoke parent return Agentcommand()
process and return
35
TclObjectcommand()

• OTcl
• set tcp new Agent/TCP
• tcp send 10
• C
• int TcpAgentcommand(int argc,
• const charconst argv)
• if (argc 3)
• if (strcmp(argv1, send) 0)
• int newseq atoi(argv2)
• return(TCL_OK)
• return (Agentcommand(argc, argv)

36
TclObject Creation and Deletion

• Global procedures new, delete
• Example
• set tcp new Agent/TCP
• delete tcp

37
TclObject Creation and Deletion
invoke parent constructor
OTcl
C
38
TclClass
Static class TcpClass public TclClass
public TcpClass() TclClass(Agent/TCP)
TclObject create(int, const charconst)
return (new TcpAgent()) class_tcp
39
NsObject

• Other important objects
• NsObject has recv() method
• Connector has target() and drop()
• BiConnector uptarget() downtarget()
• Class hierarchy
• NsObject
• Connector
• PingAgent
• BiConnector
• Mac802_11

40
Class Tcl

• Singleton class with a handle to Tcl interpreter
• Tcl tcl Tclinstance()
• Usage
• Invoke OTcl procedure
• tcl.evalc(callbackX)
• Obtain OTcl evaluation results
• clock_ atof(tcl.result())
• Pass a result string to OTcl
• tcl.resultf(g, clock())
• Return success/failure code to OTcl
• tcl.error(command not found)

41
Class Tcl

• Tcl tcl Tclinstance()
• if (argc 2)
• if (strcmp(argv1, now) 0)
• tcl.resultf(g, clock())
• return TCL_OK
• tcl.error(command not found)
• return TCL_ERROR
• else if (argc 3)
• tcl.eval(argv2)
• clock_ atof(tcl.result())
• return TCL_OK

42
Class TclCommand

• How to implement an OTcl command ns-random in
  C
• class RandomCommand public TclCommand
• public
• RandomCommand() TclCommand("ns-random")
  
• virtual int command(int argc, const
  charconst argv)
• int RandomCommandcommand(int argc, const
  charconst argv)
• Tcl tcl Tclinstance()
• if (argc 1)
• sprintf(tcl.buffer(), "u",
  Randomrandom())
• tcl.result(tcl.buffer())

43
Brief summary

• TclObject
• Unified interpreted (OTcl) and compiled (C)
  class hierarchies
• Seamless access (procedure call and variable
  access) between OTcl and C
• TclClass
• Establish interpreted hierarchy
• Shadowing objects
• Tcl primitives to access Tcl interpreter

44
Question?
45
Ns programming

• Create the event scheduler
• Turn on tracing
• Create network
• Setup routing
• Insert errors
• Create transport connection
• Create traffic
• Transmit application-level data

46
Creating Event Scheduler

• Create event scheduler
• set ns new Simulator
• Schedule events
• ns at lttimegt lteventgt
• lteventgt any legitimate ns/tcl commands
• ns at 5.0 finish
• Start scheduler
• ns run

47
Event Scheduler

• Event at-event and packet
• List scheduler default (FIFO)
• Heap good for many events (O(log n)
• Calendar queue
• A priority queue having N buckets each with width
  w. An item with priority p goes in bucket
  (p/w)N
• Real-time scheduler
• Synchronize with real-time
• Network emulation
• set ns_ new Simulator
• ns_ use-scheduler Heap
• ns_ at 300.5 self halt

48
Some scheduler-related commands

• Set now ns now
• ns cancel lteventgt
• ns after ltdelaygt lteventgt
• Execute lteventgt after ltdelaygt
• ns dumpq
• Dump all events in the scheduler queue

49
Discrete Event Scheduler
time_, uid_, next_, handler_
head_ -gt
head_ -gt
handler_ -gt handle()
insert
time_, uid_, next_, handler_
50
Hello World - Interactive Mode

• Batch mode
• simple.tcl
• set ns new Simulator
• ns at 1 puts \Hello World!\
• ns at 1.5 exit
• ns run
• swallow 74 ns simple.tcl
• Hello World!
• swallow 75

• Interactive mode
• swallow 71 ns
• set ns new Simulator
• _o3
• ns at 1 puts \Hello World!\
• 1
• ns at 1.5 exit
• 2
• ns run
• Hello World!
• swallow 72

51
Tracing and Monitoring I

• Packet tracing
• On all links ns trace-all open out.tr w
• On one specific link ns trace-queue n0 n1tr
• ltEventgt lttimegt ltfromgt lttogt ltpktgt ltsizegt -- ltfidgt
  ltsrcgt ltdstgt ltseqgt ltattrgt
• 1 0 2 cbr 210 ------- 0 0.0 3.1 0 0
• - 1 0 2 cbr 210 ------- 0 0.0 3.1 0 0
• r 1.00234 0 2 cbr 210 ------- 0 0.0 3.1 0 0
• Event tracing (support TCP currently)
• Record event in trace file ns eventtrace-all
• E 2.267203 0 4 TCP slow_start 0 210 1

52
Tracing and Monitoring II

• Queue monitor
• set qmon ns monitor-queue n0 n1 q_f
  sample_interval
• Get statistics for a queue
• qmon set pdrops_
• Record to trace file as an optional
• Flow monitor
• set fmon ns_ makeflowmon Fid
• ns_ attach-fmon slink fmon
• fmon set pdrops_

53
Tracing and Monitoring III

• Visualize trace in nam
• ns namtrace-all open test.nam w
• ns namtrace-queue n0 n1
• Variable tracing in nam
• Agent/TCP set nam_tracevar_ true
• tcp tracevar srtt_
• tcp tracevar cwnd_
• Monitor agent variables in nam
• ns add-agent-trace tcp tcp
• ns monitor-agent-trace tcp
• srm0 tracevar cwnd_
• ns delete-agent-trace tcp

54
Ns Internals

• Tcl commands translates into
• series of object creation
• plumbing of these objects

55
Creating Network

• Nodes
• set n0 ns node
• set n1 ns node
• Links and queuing
• ns ltlink_typegt n0 n1 ltbandwidthgt ltdelaygt
  ltqueue_typegt
• ltlink_typegt duplex-link, simplex-link
• ltqueue_typegt DropTail, RED, CBQ, FQ, SFQ, DRR,
  diffserv RED queues

56
Network Topology Node
Unicast Node
0
0
1
Set ns_ new Simulator multicast on Set n1 ns_
node
set n0 ns_ node
57
Node Addressing

• Two basic address styles available flat and
  hierarchical
• Default flat address 32 bits each for node and
  port id
• Default hier address
• 3 levels of hierarchy
• 10 11 11 or 1 9 11 11 if mcast specified
• Different bit allocation possible for specific
  hier addresses

58
Hierarchical Node
n2
Address classifier
To Port demux
Node entry
Level 3
Level 2
Level 1
ns_ node-config addressing hier
59
Classifiers

• Table of n slots
• When a packet is received
• classify() identifies the slot to forward the
  packets
• Address Classifiers
• Parse address in packet
• Methods
• Install
• Elements
• Clear

60
Network Topology Link
ns_ duplex-link n0 n1 5Mb 2ms drop-tail
61
Connectors

• Connectors
• Receive incoming packets, and transmit them to
  their target_
• Different types of connectors
• Queue
• Holds a certain number of packets. Packets
  exceeding their queue-size are sent to the
  queues drop-target_
• LinkDelay
• Model delay/bandwidth of the link
• TTLChecker
• Decrements TTL on each packet, drops the packet
  if the TTL becomes 0
• DynaLink
• Transmit packets if the link is up, drop packet
  otherwise
• Trace

62
Creating Network LAN

• ns make-lan ltnode_listgt ltbandwidthgt ltdelaygt
  ltll_typegt ltifq_typegt ltmac_typegt ltchannel_typegt
• ltll_typegt LL
• ltifq_typegt Queue/DropTail,
• ltmac_typegt MAC/802_3
• ltchannel_typegt Channel

63
Setup Routing

• Unicast
• ns rtproto lttypegt
• lttypegt Static, Session, DV, cost, multi-path
• Multicast
• ns multicast (right after new Simulator)
• ns mrtproto lttypegt
• lttypegt CtrMcast, DM, ST, BST
• Other types of routing supported source routing,
  hierarchical routing

64
Routing..
65
..Routing
Link n0-n1
66
Class RouteLogic

• Route configuration
• rtproto -gt configure -gt compute-routes
• Query nexthop
• ns get-routelogic lookup n1 2
• Recompute route on topology change
• ns get-routelogic notify

67
Inserting Errors

• Creating Error Module
• set loss_module new ErrorModel
• loss_module set rate_ 0.01
• 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

68
Network Dynamics

• Link failures
• Hooks in routing module to reflect routing
  changes
• Four models
• ns rtmodel Trace ltconfig_filegt n0 n1
• ns rtmodel Exponential ltparamsgt n0 n1
• ns rtmodel Deterministic ltparamsgt n0 n1
• ns rtmodel-at lttimegt updown n0 n1
• Parameter list
• ltstartgt ltup_intervalgt ltdown_intervalgt
  ltfinishgt

69
Creating Connection and Traffic I

• 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

• CBR
• set src new Application/Traffic/CBR
• Exponential or Pareto on-off
• set src new Application/Traffic/Exponential
• set src new Application/Traffic/Pareto
• src attach-agent udp

70
Creating Connection and Traffic II

• 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

• FTP
• set ftp new Application/FTP
• ftp attach-agent tcp
• Telnet
• set telnet new Application/Telnet
• telnet attach-agent tcp

71
Creating Traffic Trace Driven

• Trace driven
• set tfile new Tracefile
• tfile filename ltfilegt
• set src new Application/Traffic/Trace
• src attach-tracefile tfile
• ltfilegt
• Binary format (native!)
• inter-packet time (msec) and packet size (byte)

72
Transport
n0
n1
Port Classifier
Port Classifier
Addr Classifier
Addr Classifier
0
0
0
1
dmux_
dmux_
entry_
entry_
classifier_
classifier_
set tcp new Agent/TCP ns_ attach-agent n0 tcp
set tcpsink new Agent/TCPSink ns_ attach-agent
n1 tcpsink
ns_ connect tcp tcpsink
73
Application
n0
n1
Port Classifier
Port Classifier
Agent/TCPSink
Addr Classifier
Agent/TCP
Addr Classifier
0
0
agents_
agents_
0
1
dmux_
dmux_
entry_
entry_
classifier_
classifier_
set ftp new Application/FTP ftp attach-agent
tcp ns at 1.2 ftp start
74
Packet Flow
n0
n1
Application/FTP
Port Classifier
Port Classifier
Agent/TCPSink
Addr Classifier
Agent/TCP
Addr Classifier
0
0
Link n0-n1
entry_
entry_
Link n1-n0
75
Application objects I

• Exponential
• packetSize_
• burst_time_
• idle_time_
• rate_
• CBR
• packetSize_
• rate_
• interval_
• random_
• maxpkts_

76
Application objects II

• Pareto
• packetSize_
• burst_time_
• idle_time_
• rate_
• shape_
• Telnet
• interval_
• FTP
• maxpkts_
• All above are virtual applications
• focus only on size and time when data are
  transferred

77
Application-Level Simulation

• Simulate applications that actually transfer
  their own data
• e.g. simulate various webcaching algorithms
• Features
• Build on top of existing transport protocol
• Transmit user data, e.g., HTTP header
• Two different solutions
• TCP Application/TcpApp
• UDP Agent/Message

78
Compare to Real World

• More abstract (much simpler)
• No addresses, just global variables
• Connect them rather than name lookup/bind/listen/a
  ccept
• Easy to change implementation
• Set tsrc2 new agent/TCP/Newreno
• Set tsrc3 new agent/TCP/Vegas

79
Summary Generic Script Structure

• set ns new Simulator
• Turn on tracing
• Create topology
• Setup packet loss, link dynamics
• Create routing agents
• Create
• - multicast groups
• - protocol agents
• - application and/or setup traffic sources
• Post-processing procs
• Start simulation

80
Question?
81
Two examples

• Multicast
• Web traffic

82
Example Multicast Routing

• Dynamic group membership

time 1.25s
n2
1.5Mb, 10ms
1.5Mb, 10ms
n0
n1
G1
1.5Mb, 10ms
n3
G2
83
Multicast Step 1

• Scheduler, tracing, and topology
• Create scheduler
• set ns new Simulator
• Turn on multicast
• ns multicast
• Turn on Tracing
• set fd new mcast.nam w
• ns namtrace-all fd

84
Multicast Step 2

• Topology
• Create nodes
• set n0 ns node
• set n1 ns node
• set n2 ns node
• set n3 ns node
• Create links
• ns duplex-link n0 n1 1.5Mb 10ms DropTail
• ns duplex-link n0 n2 1.5Mb 10ms DropTail
• ns duplex-link n0 n3 1.5Mb 10ms DropTail

85
Multicast Step 3

• Routing and group setup
• Routing protocol lets run distance vector
• ns mrtproto DM
• Allocate group addresses
• set group1 Node allocaddr
• set group2 Node allocaddr

86
Multicast Step 4

• Sender 0
• Transport agent for the traffic source
• set udp0 new Agent/UDP
• ns attach-agent n1 udp0
• udp0 set dst_addr_ group1
• udp0 set dst_port_ 0
• Constant Bit Rate source 0
• set cbr0 new Application/Traffic/CBR
• cbr0 attach-agent udp0
• Start at time 1.0 second
• ns at 1.0 "cbr0 start"

87
Multicast Step 5

• Sender 1
• Transport agent for the traffic source
• set udp1 new Agent/UDP
• ns attach-agent n3 udp1
• udp1 set dst_addr_ group2
• udp1 set dst_port_ 0
• Constant Bit Rate source 0
• set cbr1 new Application/Traffic/CBR
• cbr1 attach-agent udp1
• Start at time 1.1 second
• ns at 1.1 "cbr1 start"

88
Multicast Step 6

• Receiver with dynamic membership
• Can also be Agent/Null
• set rcvr new Agent/LossMonitor
• Assign it to node n2
• ns at 1.2 "n2 join-group rcvr group2"
• ns at 1.25 "n2 leave-group rcvr group2"
• ns at 1.3 "n2 join-group rcvr group2"
• ns at 1.35 "n2 join-group rcvr group1"

89
Multicast Step 7

• End-of-simulation wrapper (as usual)
• ns at 2.0 "finish"
• proc finish
• global ns fd
• close fd
• ns flush-trace
• puts "running nam..."
• exec nam mcast.nam
• exit 0
• ns run

90
Example Web traffic
3
7
2
8
10Mb, 20ms
1.5Mb, 40ms
0
4
1
9
5
6
10
11
91
Web traffic Step 1

• Scheduler and tracing
• Create scheduler
• set ns new Simulator
• instantiate web traffic class
• set pool new PagePool/WebTraf
• Turn on Tracing
• set fd new web.nam w
• ns namtrace-all fd

92
Web traffic Step 2

• Topology
• Create nodes
• for set i 0 i lt 12 incr i
• set n(i) ns node
• ns set src_ list 2 3 4 5 6
• ns set dst_ list 7 8 9 10 11
• Create links
• ns duplex-link n(0) n(1) 1.5Mb 40ms DropTail
• ns duplex-link n(0) n(2) 10Mb 20ms DropTail
• ns duplex-link n(0) n(3) 10Mb 20ms DropTail

93
Web traffic Step 3

• Set up client and server nodes
• pool set-num-client llength ns set src_
• pool set-num-server llength ns set dst_
• set i 0
• foreach s ns set src_
• pool set-client i n(s)
• incr i
• set i 0
• foreach s ns set dst_
• pool set-server i n(s)
• incr i

94
Web traffic Step 4

• Specify the distributions for page arrival, page
  size, object arrival, object size
• set interPage new RandomVariable/Exponential
• interPage set avg_ 1
• set pageSize new RandomVariable/Constant
• pageSize set val_ 1
• set interObj new RandomVariable/Exponential
• interObj set avg_ 0.01
• set objSize new RandomVariable/ParetoII
• objSize set avg_ 10
• objSize set shape_ 1.2

95
Web traffic Step 5

• Schedule web sessions
• Lets schedule two sessions
• pool set-num-session 2
• Lets have 10 pages per session
• set numPage 10
• session 1 starts at time 0.1s
• pool create-session 0 numPage 0.1 interPage
  pageSize interObj objSize
• session 2 starts at time 1.2s
• pool create-session 1 numPage 1.2 interPage
  pageSize interObj objSize

96
Web traffic Step 6

• End-of-simulation wrapper (as usual)
• ns at 10.0 "finish"
• proc finish
• global ns fd
• close fd
• ns flush-trace
• puts "running nam..."
• exec nam web.nam
• exit 0
• ns run

97
Question?
98
Outline

• Part 1 model and simulate Internet traffic
• Part 2 an introduction to ns-2
• What is ns-2
• Fundamentals
• writing ns-2 codes
• Wireless support
• Traces support and visualization
• Emulation
• Related work
• Part 3 trace-driven network simulation

99
Writing ns-2 codes

• Extending ns
• In OTcl
• In C
• Debugging

100
ns Directory Structure
ns-allinone
TK8.3
OTcl
tclcl
Tcl8.3
ns-2
nam-1
C code
...
tcl
ex
test
mcast
lib
...
examples
validation tests
OTcl code
ensure new changes do not break the old codes
101
Extending ns in OTcl

• If you dont want to compile
• source your changes in your simulation scripts
• Otherwise
• Modifying code recompile
• Adding new files
• Change Makefile (NS_TCL_LIB), tcl/lib/ns-lib.tcl
• Recompile

102
Example Agent/Message
n4
n2
128Kb, 50ms
n0
n1
10Mb, 1ms
10Mb, 1ms
n3
n5
message agent
103
Agent/Message
pkt 64 bytes of arbitrary string
Receiver-side processing
S
R

• An UDP agent (without UDP header)
• Up to 64 bytes user message
• Good for fast prototyping a simple idea
• Usage requires extending ns functionality

104
Agent

• A protocol endpoint/enity
• Provide
• a local and destination address (like an IP-layer
  sender)
• Functions to generate or fill in packet fields
• To create a new agent
• Decide its inheritance structure
• Create recv function (and timeout if necessary)
  to process the packets
• Define OTcl linkage if necessary
• Create new header if necessary

105
Exercise

• Define a new class Sender and a new class
  Receiver which are based on class Agent/Message
• Sender
• Send a message to the Receiver every 0.1 sec
• Message contains its address and a sequence
  number
• Receiver
• Receive message from the Sender
• Acknowledge the receive message to the sender
• The acknowledgement contains its address and the
  sequence number of received message

106
Agent/Message Step 1

• Define sender
• class Sender superclass Agent/Message
• Message format Addr Op SeqNo
• Sender instproc send-next
• self instvar seq_ agent_addr_
• self send agent_addr_ send seq_
• incr seq_
• global ns
• ns at expr ns now0.1 "self send-next"

107
Agent/Message Step 2

• Define sender packet processing
• Sender instproc recv msg
• self instvar agent_addr_
• set sdr lindex msg 0
• set seq lindex msg 2
• puts "Sender gets ack seq from sdr"

108
Agent/Message Step 3

• Define receiver packet processing
• Class Receiver superclass Agent/Message
• Receiver instproc recv msg
• self instvar agent_addr_
• set sdr lindex msg 0
• set seq lindex msg 2
• puts Receiver gets seq seq from sdr
• self send addr_ ack seq

109
Agent/Message Step 4

• Scheduler and tracing
• Create scheduler
• set ns new Simulator
• Turn on Tracing
• set fd new message.tr w
• ns trace-all fd

110
Agent/Message Step 5

• Topology
• for set i 0 i lt 6 incr i
• set n(i) ns node
• ns duplex-link n(0) n(1) 128kb 50ms DropTail
• ns duplex-link n(1) n(4) 10Mb 1ms DropTail
• ns duplex-link n(1) n(5) 10Mb 1ms DropTail
• ns duplex-link n(0) n(2) 10Mb 1ms DropTail
• ns duplex-link n(0) n(3) 10Mb 1ms DropTail
• ns queue-limit n(0) n(1) 5
• ns queue-limit n(1) n(0) 5

111
Agent/Message Step 6

• Routing
• Packet loss produced by queueing
• Routing protocol lets run distance vector
• ns rtproto DV

112
Agent/Message Step 7

• Cross traffic
• set udp0 new Agent/UDP
• ns attach-agent n(2) udp0
• set null0 new Agent/NULL
• ns attach-agent n(4) null0
• ns connect udp0 null0
• set exp0 new Application/Traffic/Exponential
• exp0 set rate_ 128k
• exp0 attach-agent udp0
• ns at 1.0 exp0 start

113
Agent/Message Step 8

• Message agents
• set sdr new Sender
• sdr set seq_ 0
• sdr set packetSize_ 1000
• set rcvr new Receiver
• rcvr set packetSize_ 40
• ns attach-agent n(3) sdr
• ns attach-agent n(5) rcvr
• ns connect sdr rcvr
• ns at 1.1 sdr send-next

114
Agent/Message Step 9

• End-of-simulation wrapper (as usual)
• ns at 2.0 finish
• proc finish
• global ns fd
• ns flush-trace
• close fd
• exit 0
• ns run

115
Agent/Message Result

• Example output
• gt ./ns msg.tcl
• Receiver gets seq 0 from 3
• Sender gets ack 0 from 5
• Receiver gets seq 1 from 3
• Sender gets ack 1 from 5
• Receiver gets seq 2 from 3
• Sender gets ack 2 from 5
• Receiver gets seq 3 from 3
• Sender gets ack 3 from 5
• Receiver gets seq 4 from 3
• Sender gets ack 4 from 5
• Receiver gets seq 5 from 3

116
Add Your Changes into ns
ns-allinone
TK8.3
OTcl
tclcl
Tcl8.3
ns-2
nam-1
C code
...
tcl
mcast
lib
ex
test
...
mysrc
examples
validation tests
msg.tcl
OTcl code
117
Add Your Change into ns

• tcl/lib/ns-lib.tcl
• Class Simulator
• source ../mysrc/msg.tcl
• Makefile
• NS_TCL_LIB \
• tcl/mysrc/msg.tcl \
• Or change Makefile.in, make distclean, then
  ./configure --enable-debug ,
• make depend and make

118
Writing ns-2 codes

• Extending ns
• In OTcl
• In C
• New components

119
Extending ns in C

• Modifying code
• make depend
• Recompile
• Adding code in new files
• Change Makefile
• make depend
• recompile

120
Creating New Components

• Guidelines
• Two styles
• New agent based on existing packet headers
• Add new packet header

121
Guidelines

• Decide position in class hierarchy
• I.e., which class to derive from?
• Create new packet header (if necessary)
• Create C class, fill in methods
• Define OTcl linkage (if any)
• Write OTcl code (if any)
• Build (and debug)

122
New Agent, Old Header

• Exercise TCP jump start
• Wide-open transmission window at the beginning
• From cwnd_ 1 To cwnd_ MAXWIN_

123
TCP Jump Start Step 1
TclObject
Handler
NsObject
Connector
Classifier
Delay
AddrClassifier
Agent
McastClasifier
Queue
Trace
DropTail
RED
TCP
Enq
Deq
Drop
JS
Reno
SACK
124
TCP Jump Start Step 2

• New file tcp-js.h
• class JSTCPAgent public TcpAgent
• public
• virtual void set_initial_window()
• cwnd_ MAXWIN_
• private
• int MAXWIN_

125
TCP Jump Start Step 3

• New file tcp-js.cc
• static JSTcpClass public TclClass
• public
• JSTcpClass() TclClass("Agent/TCP/JS")
• TclObject create(int, const charconst)
• return (new JSTcpAgent())
• JSTcpAgentJSTcpAgent()
• bind(MAXWIN_, MAXWIN_)

126
TCP Jump Start Step 4

• Create an instance of jump-start TCP in your tcl
  script tcp-js.tcl
• Set MAXWIN_ value in tcl
• Add tcp-js.o in Makefile.in
• Re-configure, make depend and recompile
• Run yr tcl script tcp-js.tcl

127
Packet Format
header
data
128
New Packet Header

• Create new header structure
• Create static class for OTcl linkage (packet.h)
• Enable tracing support of new header(trace.cc)
• Enable new header in OTcl (tcl/lib/ns-packet.tcl)
• This does not apply when you add a new field into
  an existing header!

129
How Packet Header Works
Packet
size determined at compile time
hdr_cmn
size determined at compile time
size determined at simulator startup
time (PacketHeaderManager)
hdr_ip
size determined at compile time
hdr_tcp

130
Example Agent/Message

• New packet header for 64-byte message
• New transport agent to process this new header

131
New Packet Header Step 1

• Create header structure
• struct hdr_msg
• char msg_64
• static int offset_
• inline static int offset() return offset_
• inline static hdr_msg access(Packet p)
• return (hdr_msg) p-gtaccess(offset_)
• / per-field member functions /
• char msg() return (msg_)
• int maxmsg() return (sizeof(msg_))

132
New Packet Header Step 2

• Otcl linkage PacketHeader/Message
• static class MessageHeaderClass
• public PacketHeaderClass
• public
• MessageHeaderClass() PacketHeaderClass("PacketH
  eader/Message",
• sizeof(hdr_msg))
• bind_offset(hdr_msgoffset_)
• class_msghdr

133
New Packet Header Step 3

• Enable tracing (packet.h)
• enum packet_t
• PT_TCP,
• ,
• PT_MESSAGE,
• PT_NTYPE // This MUST be the LAST one
• class p_info
• name_PT_MESSAGE message
• name_PT_NTYPE "undefined"

134
New Packet Header Step 4

• Register new header (tcl/lib/ns-packet.tcl)
• foreach prot
• Common off_cmn_
• Message off_msg_
• add-packet-header prot

135
Packet Header Caution

• Some old code, e.g.
• RtpAgentRtpAgent()
• bind(off_rtp_, off_rtp)
• hdr_rtp rh (hdr_rtp)p-gtaccess(off_rtp_)
• Dont follow this example!

136
Agent/Message Step 1
TclObject
NsObject
Connector
Classifier
Delay
AddrClassifier
Agent
McastClasifier
Queue
Trace
Enq
Deq
Drop
DropTail
RED
TCP
Message
Reno
SACK
137
Agent/Message Step 2

• C class definition
• // Standard split object declaration
• static
• class MessageAgent public Agent
• public
• MessageAgent() Agent(PT_MESSAGE)
• virtual int command(int argc, const charconst
  argv)
• virtual void recv(Packet, Handler)

138
Agent/Message Step 3

• Packet processing msgAgent send data1
• int MessageAgentcommand(int, const charconst
  argv)
• Tcl tcl Tclinstance()
• if (strcmp(argv1, "send") 0)
• Packet pkt allocpkt()
• hdr_msg mh hdr_msgaccess(pkt)
• // We ignore message size check...
• strcpy(mh-gtmsg(), argv2)
• send(pkt, 0)
• return (TCL_OK)
• return (Agentcommand(argc, argv))

139
Agent/Message Step 4

• Packet processing receive
• void MessageAgentrecv(Packet pkt, Handler)
• hdr_msg mh hdr_msgaccess(pkt)
• // OTcl callback
• char wrk128
• sprintf(wrk, "s recv s", name(), mh-gtmsg())
• Tcl tcl Tclinstance()
• tcl.eval(wrk)
• Packetfree(pkt)

140
Writing ns-2 codes

• Extending ns
• In OTcl
• In C
• Debugging OTcl/C, memory
• Pitfalls

141
Debugging C in ns

• C/OTcl debugging
• Memory debugging
• purify
• dmalloc

142
C/OTcl Debugging

• Usual technique
• Break inside command()
• Cannot examine states inside OTcl!
• Solution
• Execute tcl-debug inside gdb

143
C/OTcl Debugging

• (gdb) call Tclinstance().eval(debug 1)
• 15 lappend auto_path dbg_library
• dbg15.3gt w
• 0 application
• 15 lappend auto_path dbg_library
• dbg15.4gt Simulator info instances
• _o1
• dbg15.5gt _o1 now
• 0
• dbg15.6gt and other fun stuff
• dbg15.7gt c
• (gdb) where
• 0 0x102218 in write()
• ......

144
Memory Debugging in ns

• Purify
• Set PURIFY macro in ns Makefile
• Usually, put -colloctorltld_pathgt
• Gray Watsons dmalloc library
• http//www.dmalloc.com
• make distclean
• ./configure --with-dmallocltdmalloc_pathgt
• Analyze results dmalloc_summarize

145
dmalloc Usage

• Turn on dmalloc
• alias dmalloc eval \dmalloc C \!
• dmalloc -l log low
• dmalloc_summarize ns lt logfile
• ns must be in current directory
• Itemize how much memory is allocated in each
  function

146
Pitfalls

• Scalability vs flexibility
• Or, how to write scalable simulation?
• Memory conservation tips
• Memory leaks

147
Scalability vs Flexibility

• Its 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

148
THE Merit of OTcl
Program size, complexity
low
high
OTcl
C/C
split objects

• Smoothly adjust the granularity of scripting to
  balance extensibility and performance
• With complete compatibility with existing
  simulation scripts

149
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

150
Memory usage

• Simulator 268KB
• Unicast node 2KB
• Multicast node 6KB
• Duplex link 9KB
• Packet 2KB

151
Memory Conservation Tips

• Remove unused packet headers
• Avoid trace-all
• Use arrays for a sequence of variables
• Instead of ni, say n(i)
• Avoid OTcl temporary variables
• tempA Btemp
• Use dynamic binding
• delay_bind() instead of bind()
• See object.h,cc
• Use different routing strategies
• Computing routing tables dominate the simulation
  setup time
• Run on FreeBSD
• use less memory for malloc()

152
Memory Leaks

• Purify or dmalloc, but be careful about split
  objects
• for set i 0 i lt 500 incr i
• set a new RandomVariable/Constant
• It leaks memory, but cant be detected!
• Solution
• Explicitly delete EVERY split object that was
  new-ed

153
Final Word

• My extended ns dumps OTcl scripts!
• Find the last 10-20 lines of the dump
• Is the error related to _o cmd ?
• Check your command()
• Otherwise, check the otcl script pointed by the
  error message

154
Questions?
155
Outline

• Part 1 model and simulate Internet traffic
• Part 2 an introduction to ns-2
• What is ns-2
• Fundamentals
• Writing ns-2 codes
• Traces support and visualization
• Wireless support
• Emulation
• Related work
• Part 3 trace-driven network simulation

156
ns?nam Interface

• Color
• Node manipulation
• Link manipulation
• Topology layout
• Protocol state
• Misc

157
nam Interface Color

• Color mapping
• ns color 40 red
• ns color 41 blue
• ns color 42 chocolate
• Color ? flow id association
• tcp0 set fid_ 40 red packets
• tcp1 set fid_ 41 blue packets

158
nam Interface Nodes

• Color
• node color red
• Shape (cant be changed after sim starts)
• node shape box circle, box, hexagon
• Marks (concentric shapes)
• ns at 1.0 n0 add-mark m0 blue box
• ns at 2.0 n0 delete-mark m0
• Label (single string)
• ns at 1.1 n0 label \web cache 0\
• node label-at up
• node label-color blue

159
nam Interfaces Links

• Color
• ns duplex-link-op n0 n1 color "green"
• Label
• ns duplex-link-op n0 n1 label "abced
• ns duplex-link-op n1 n2 label-color blue
• ns duplex-link-op n1 n2 label-at down
• Queue position
• ns duplex-link-op queuePos right
• Dynamics (automatically handled)
• ns rtmodel Deterministic 2.0 0.9 0.1 n0 n1
• Asymmetric links not allowed

160
nam Interface Topology Layout

• Manual layout specify everything
• ns duplex-link-op n(0) n(1) orient right
• ns duplex-link-op n(1) n(2) orient right
• ns duplex-link-op n(2) n(3) orient right
• ns duplex-link-op n(3) n(4) orient 60deg
• If anything missing ? automatic layout

161
nam Interface Misc

• Packet color
• ns color n blue
• agent set fid_ n
• Annotation
• Add textual explanation to your simulation
• ns at 3.5 "ns trace-annotate \packet drop\"
• Control playback
• ns at 0.0 "ns set-animation-rate 0.1ms"

162
The nam user interface
163
Summary of nam

• Turn on nam tracing in your Tcl script
• As easy as turning on normal tracing
• ns namtrace file
• Specify color/shape/label of node/link
• ns duplex-link-op node1 node2 orient left
• Execute nam
• exec nam filename

164
A live demo
165
namgraph

• Display a graph showing when packets are
  received/dropped.
• Enabling namgraph
• Run the namfilter script on your nam trace file
• exec tclsh /path/to/namfilter.tcl out.nam

166
namgraph
167
The nam editor

• Create simple scenarios graphically
• Good for those who dont want to learn Tcl, but
  only a limited subset of ns is currently available

168
The nam editor
169
Topology generator

• Inet
• GT-ITM
• TIERS
• BRITE

170
Inet topology generator

• from University of Michigan
• AS level Internet topology
• Create topologies with accurate degree
  distributions
• Conversion of Inet output to ns-2 format
• inet2ns lt inet.topology gt ns.topology

171
GT-ITM

• Installation
• Comes with ns-allinone
• Require Knuths cweb and SGB
• Usage
• itm ltconfig_filegt
• Three graph models
• Flat random Waxman
• n-level hierarchy
• Transit-stub

172
GT-ITM Transit-Stub Model
transit domains
transit-transit link
stub-stub link
stub domains
173
Converters for GT-ITM

• sgb2ns
• Convert SGB format to ns config file
• sgb2ns ltSGB_filegt ltOTcl_filegt
• ts2ns output lists of transit and stub nodes
• sgb2hier
• Convert transit-stub information into
  hierarchical addresses
• sgb2hierns ltSGB_filegt ltOTcl_filegt

174
Tiers topology generator

• 3-level hierarchy
• Conversion of Tiers output to ns-2 format
• an awk script tiers2ns.awk is included in
  ns-2/bin to convert the output of tiers into
  ns-2 scripts.

175
BRITE

• From Boston University
• Supports multiple generation models
• flat AS
• flat Router
• hierarchical topologies
• Object-oriented design to allow the flexibility
  to add new topology models
• Can import from Inet, GT-ITM, Skitter,..
• Can export to ns-2, JavaSim, SSFNET format
• Written in Java and C
• GUI support

176
Summary

• http//www.isi.edu/nsnam/ns/ns-topogen.html

177
A quick review of what happened yesterday
178
ns-2 document

• ns-2 website
• ns-2 manual
• ns-2 user mailing list archive

179
Using ns
Problem
Result analysis
Simulation model
Modify ns
Setup/run simulation with ns
180
C/OTcl Linkage
181
TclObject Hierarchy and Shadowing
C class hierarchy
OTcl class hierarchy
TclObject
TclObject
Agent
Agent
TcpAgent
Agent/TCP
tcp
_o123
Agent/TCP OTcl shadow object
Agent/TCP C object
182
TclObject Creation and Deletion
invoke parent constructor
OTcl
C
183
TclClass
Static class TcpClass public TclClass
public TcpClass() TclClass(Agent/TCP)
TclObject create(int, const charconst)
return (new TcpAgent()) class_tcp
184
TclObjectcommand()
OTcl space
no such procedure
tcp send
TclObjectunknown
tcp cmd send
C space
TcpAgentcommand()
match send?
Yes
No
Invoke parent return Agentcommand()
process and return
185
Ns programming

• Create the event scheduler
• Turn on tracing
• Create network
• Setup routing
• Insert errors
• Create transport connection
• Create traffic
• Transmit application-level data

186
Commonly-used objects

• Node
• Link
• Packet
• Error module
• Timer
• Agent
• Application

187
Network Topology Node
Unicast Node
0
0
1
Set ns_ new Simulator multicast on Set n1 ns_
node
set n0 ns_ node
188
Network Topology Link
ns_ duplex-link n0 n1 5Mb 2ms drop-tail
189
Packet Format
header
data
190
How Packet Header Works
Packet
size determined at compile time
hdr_cmn
size determined at compile time
size determined at simulator startup
time (PacketHeaderManager)
hdr_ip
size determined at compile time
hdr_tcp

191
Packet Flow
n0
n1
Application/FTP
Port Classifier
Port Classifier
Agent/TCPSink
Addr Classifier
Agent/TCP
Addr Classifier
0
0
Link n0-n1
entry_
entry_
Link n1-n0
192
ns Directory Structure
ns-allinone
TK8.3
OTcl
tclcl
Tcl8.3
ns-2
nam-1
C code
...
tcl
ex
test
mcast
lib
...
examples
validation tests
OTcl code
ensure new changes do not break the old codes
193
Guidelines

• Decide position in class hierarchy
• I.e., which class to derive from?
• Create new packet header (if necessary)
• Create C class, fill in methods
• Define OTcl linkage (if any)
• Write OTcl code (if any)
• Build (and debug)

194
C/OTcl Debugging

• (gdb) call Tclinstance().eval(debug 1)
• 15 lappend auto_path dbg_library
• dbg15.3gt w
• 0 application
• 15 lappend auto_path dbg_library
• dbg15.4gt Simulator info instances
• _o1
• dbg15.5gt _o1 now
• 0
• dbg15.6gt and other fun stuff
• dbg15.7gt c
• (gdb) where
• 0 0x102218 in write()
• ......

195
Memory Debugging in ns

• Purify
• Set PURIFY macro in ns Makefile
• Usually, put -collocto