Download Network Simulator – NS2

Network Simulator – NS-2
1
JIA-HUI HUANG
INSTITUTE OF COMPUTER SCIENCE AND
INFORMATION ENGINEERING
NATIONAL TAIPEI UNIVERSITY OF
TECHNOLOGY
2007.10.15
Reference
2
 http://140.116.72.80/~smallko/ns2/ns2.htm
 http://www.isi.edu/nsnam/ns/
 Ns document
Outline
3
 Introduction
 Installation
 TCL script
 Related tools
 New protocol for NS
 Examples
 Conclusion
Introduction
4
 Methods for network research
 Analytical
General expression or close form
 Mathematical model


Emulation
Real code
 Duplicates the functions of one system with a different system


Simulation
Abstract model
 Behavior of system

Introduction (cont.)
5
 Self-Developed
 Without strong persuasion
 Simulation frameworks
 Commercial
OPNET
 QualNet
 OMNEST (commercial version of OMNetT++)


Free
NS-2 (network simulator version 2)
 OMNetT++

Introduction (cont.)
6
 Ns-2 is a discrete event simulator
 Scheduler
 Advance of time depends on the timing of events
 Object-oriented simulator
 C++ : fast to run, slower to change – protocol implementation
 Otcl : slower to run, fast to change – simulation configuration
 Components
 Ns – simulator itself
 Nam – network animator

Visualize ns (or other) output
Introduction (cont.)
7

Pre-processing


Traffic and topology model
Post-processing

Trace analysis, often in awk, perl, or tcl
 Simulation procedure
Problems
Simulate the
environment
Modify
Run with ns-2
Analysis the
result
Finish
Yes
Finish the
simulation
No
Installation
8
 Platform
 Unix
 Windows (cygwin)
 Packages
 Tcl/tk
 Otcl tclcl
 Ns-2
 Nam
 Xgraph
 C++ compiler
 Ns AllInOne package
Installation (cont.)
9
 Cygwin, AllInOne installation (windows)
 http://140.116.72.80/~smallko/ns2/setup_en.htm
 Installation problems
 http://www.isi.edu/nsnam/ns/ns-problems.html#general
 Cygwin setup
 gcc
 Ns-2 setup
 Path setting
 Cygwin/home/user-name/.bashrc
 Testing (startxwin.bat) - ~/ns-allinone-x.x/ns-x.x/ns-tutorial/examples
TCL script
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 TCL script for scenario setup
 Scenario script format
 Simulator object
 Trace file
 Finish procedure
 Network setup (node, link, agent, parameter…)
 Other procedure, if any
 Event scheduling (run simulation, stop simulation …)
TCL script (cont.)
11
 Example topology
CBR
0
#Create a simulator object
set ns [new Simulator]
#Open the nam trace file
set nf [open out.nam w]
$ns namtrace-all $nf
#Define a 'finish' procedure
proc finish {} {
global ns nf
$ns flush-trace
#Close the trace file
close $nf
#Execute nam on the trace file
exec nam out.nam &
exit 0
}
1
#Create two nodes
set n0 [$ns node]
set n1 [$ns node]
#Create a duplex link between the nodes
$ns duplex-link $n0 $n1 1Mb 10ms DropTail
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#Create a UDP agent and attach it to node n0
set udp0 [new Agent/UDP]
$ns attach-agent $n0 $udp0
# Create a CBR traffic source and attach it to udp0
set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 500
$cbr0 set interval_ 0.005
$cbr0 attach-agent $udp0
#Create a Null agent (a traffic sink) and attach it to node n1
set null0 [new Agent/Null]
$ns attach-agent $n1 $null0
#Connect the traffic source with the traffic sink
$ns connect $udp0 $null0
#Schedule events for the CBR agent
$ns at 0.5 "$cbr0 start"
$ns at 4.5 "$cbr0 stop"
#Call the finish procedure after 5 seconds of simulation time
$ns at 5.0 "finish"
#Run the simulation
$ns run
Related tools
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 nsBench
 Graphical User Interface For NS
 Language - java
 Features
Nodes, simplex/duplex links and Lans
 Agents: TCP, UDP, TCP/Reno, …
 Application Traffic: FTP, Telnet, ….
 ….
 http://www.mnlab.cs.depaul.edu/projects/nsbench/

Related tools (cont.)
14
 NSG
 Java based ns2 scenario generator
 For wireless ad-hoc scenario
 Features
wireless node
 Connection between nodes
 Node movement


http://wushoupong.googlepages.com/ns2scenariosgeneratorc
hinese
Related tools (cont.)
15
 Topology Generator
 Georgia Tech Internetwork Topology Models (GT-ITM)
 How closely model correlate with real network ?
Transit-Stub model
 Transit domain



Interconnect stub domains
Example topology
New protocol for ns
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 Packet type
 Structure declaration – packet header
 Name binding


Bind packet header to TCL interface
Usage
 Routing agent
 MANET routing protocol
 Agent object
 Tcl hook
 Important functions
Packet type
17
 Packet header
#include <packet.h>
#define HDR_PROTONAME_PKT(p) hdr_protoname_pkt::access(p)
struct hdr_protoname_pkt {
…. (define some fields of packet)
static int offset_;
inline static int& offset() { return offset_ ; }
inline static hdr_protoname_pkt* access(const Packet* p) {
return (hdr_protoname_pkt*)p->access(offset_);
}
Packet type (cont.)
18
 Name binding
int protoname_pkt::offset_;
static class ProtonameHeaderClass : public PacketHeaderClass {
public:
ProtonameHeaderClass()
PacketHeaderClass("PacketHeader/Protoname",
sizeof(hdr_protoname_pkt)) {
bind_offset(&hdr_protoname_pkt::offset_);
}
}
Packet type (cont.)
19
 Usage
Packet* p = allocpkt();
struct hdr_cmn* ch = HDR_CMN(p);
struct hdr_ip* ih = HDR_IP(p);
struct hdr_protoname_pkt* ph = HDR_PROTONAME_PKT(p);
ph->….
ih->….
ch->…
Routing agent
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 Agent object
#include <agent.h>
….
class NewProtocol : public Agent {
protected :
…
public :
NewProtocol(nsaddr_t);
int command (int, const char*const*);
void recv(Packet*, Handler*);
….
}
Routing agent (cont.)
21
 Tcl hook
 Let NewProtocl to be instantiated from Tcl.
static class ProtonameClass : public TclClass {
public:
ProtonameClass() : TclClass("Agent/Protoname") {}
TclObject* create(int argc, const char*const* argv) {
assert(argc == 5);
return (new Protoname((nsaddr_t)Address::instance().str2addr(argv[4])));
}
}
Routing agent (cont.)
22
 Important functions
 Command()


Operations that we went to make accessible from TCL
 maodv-join-group
 maodv-leave-group
 Example - maodv.cc, MAODV_SimScript.tcl, cbr-5-3-2
Recv ()

Invoked whenever the routing agent receives a packet
Needed changes
23
 Needed changes
 Packet type declaration - \ns-x.xx\common\packet.h
 Tracing support - \ns-x.xx\cmu-trace.h
 Tcl library
Tcl\lib\ns-packet.tcl
 Tcl\lib\ns-default.tcl



Priority queue - \queue\priqueue.cc
Make file
Example1 - TCP slow start
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 Transport layer protocol
 UDP – user datagram protocol (connectionless, unreliable
service)
 TCP – transmission control protocol (connect-oriented,
reliable, with flow and congestion control service)
 Connection-oriented – three-way handshaking
 Reliable – acknowledgment, retransmission
 Flow control – sender won’t buffers by transmitting to much
and too fast
 Congestion control – to limit the total amount of data entering
the internet
Example1 - TCP slow start (cont.)
25
 Important variables for congestion control – slow
start


cwnd – congestion window
ssthresh – defines threshold between two slow start phase and
congestion control phase
 Operations – slow start
 When connection begins, increase rate exponentially fast until
first loss event (slow start phase)
 Set ssthresh = cwnd/2
 Set cwnd = 1 and perform slow start process
 For cwnd >= ssthresh, increase cwnd linearly (congestion
avoidance)
Example1 - TCP slow start (cont.)
26
 TCP standards
 TCP Tahoe – slow start & congestion avoidance



TCP Vegas
TCP Reno



RFC 2581
TCP NewReno


RFC 2581
RFC 2582
FACK (forward acknowledgement)
SACK (selective acknowledgement)

RFC 2018
Example1 - TCP slow start (cont.)
27
 TCP experiment – congestion window
 TCP Tahoe
Slow-start
 Congestion avoidance

Simulation topology
Source1 (TCP)
n2
Source2(UDP)
Value
#. Of nodes
4
Link capability
2Mbps
Simulation time
5(s)
Traffic type
CBR (UDP)
FTP(TCP)
Receiver
n0
n1
parameters
n3
Example2 – queuing system
28
 Queuing systems
 M/M/1
 M/D/1
 …
 Notation
 Arrival process/Service time/Servers
 M = exponential, D = Deterministic, ….
Queuing system – M/M/1 (cont.)
29
 Arrival & departure model
 Poisson arrival
 Exponential distribution
 single server
 Parameters
 Arrival rate λ
 Departure rate (service time) μ

 load  
(stability condition : ρ < 1)


 E[Q]  1  
(# of packets in system)
Queuing system – M/M/1 (cont.)
30
 queue.tcl
 Arrival rate : 30
 Departure rate : 33
 E[Q] = 10
Tips
31
 Ns document is not easy to understand
 Error message is not very useful
 Understand and Implementation
 Implementation issues
 Iterative design
Conclusion
32
 Basic concept of NS2
 Two levels of simulation
 Exist modules for NS beginner
Internet domain structure
33
Example of Internet domain structure