ns2 Tutorial, part 2

1
ns-2 Tutorial, part 2

• Dave Anderson, Xiaowei Yang
• (Modified from Polly Huangs slides)

2
Outline

• Ns-2 internals
• script -gt internal structure
• How to Extend ns

3
Script Code

• Create a topology
• Set ns new Simulator
• set n0 ns node
• set n1 ns node
• ns duplex-link n0 n1 1Mb 10ms DropTail
• Add Transport agents
• set tcp new Agent/TCP
• ns attach-agent n0 tcp
• set tcpsink new Agent/TCPSink
• ns attach-agent n1 tcpsink
• tcp connect tcpsink
• Add application
• set ftp new Application/FTP
• ftp attach-agent tcp

Create a schedule ns at 0.5 "ftp start" ns
at 4.5 "ftp stop" Run the simulation ns run
FTP
TCP
1Mb
n0
n1
10ms
4
Discrete Event-Driven Simulator
time_, uid_, next_, handler_
head_ -gt
handler_ -gt handle()
insert
time_, uid_, next_, handler_
ns at 0.5 ftp start ns at 4.5 ftp
stop ns run
5
Ns Node
set n0 ns node set n1 ns node
6
Network Topology - Link
ns duplex-link n0 n1 1Mb 10ms DropTail
7
Routing
Link n0-n1
8
Transport
n0
n1
Port Classifier
Port Classifier
Addr Classifier
Addr Classifier
0
0
agents_
dmux_
dmux_
Link n0-n1
entry_
entry_
classifier_
classifier_
Link n1-n0
set tcp new Agent/TCP ns attach-agent n0 tcp
9
Application
n0
n1
Port Classifier
Port Classifier
Addr Classifier
Agent/TCP
Addr Classifier
Agent/TCPSink
0
0
agents_
agents_
dmux_
dmux_
Link n0-n1
entry_
entry_
classifier_
classifier_
Link n1-n0
set ftp new Application/FTP tcp attach-agent
ftp
10
Packet Flow
n0
n1
Port Classifier
Port Classifier
Application/FTP
Addr Classifier
Agent/TCP
Addr Classifier
Agent/TCPSink
0
0
Link n0-n1
entry_
entry_
Link n1-n0
11
Packet Format
header
data
12
Extending ns-2 Simulator
13
otcl and C The Duality
C
otcl

• C for data
• per packet action
• otcl for control
• periodic or triggered action

14
Adding New Classes
procedures
variables
otcl
C
15
TclClass
Static class TcpClass public TclClass
public TcpClass() TclClass(Agent/Echo)
TclObject create(int, const charconst)
return (new EchoAgent()) class_echo
16
TclObject bind()

• C
• EchoAgentTcpAgent()
• bind(msglen_, len_)
• otcl
• Agent/Echo set msglen_ 50

17
TclObject command()

• C
• Int EchoAgentcommand(int argc, const
  charconst argv)
• if (argc 2)
• if (strcmp(argv1, send) 0)
• send()
• return(TCL_OK)
• else if (strcmp(argv1, recv) 0)
• send()
• return(TCL_OK)
• return (Agentcommand(argc, argv)
• otcl
• set echo new Agent/Echo
• echo send