1

Introduction to NS-2

Tutorial overview of NS Create basic NS simulation

Walk-through a simple example Model specification Execution and trace analysis

http://www-net.cs.umass.edu/~honggang/ns-cs653/

2

NS-2, the network simulator

Academic project over 10 years old freely distributed, open source

Currently maintained by ISI (Information Sciences Institute) DARPA + NSF projects

~ 200K LoC, 403 page manual Large user base

mostly academics “de facto” standard in networking

research Main website: http://www.isi.edu/nsnam/ns

3

NS Functionality Discrete event simulator Modeling Network Components

Traffic models and applications• Web, FTP, telnet, audio, sensor nets

Transport protocols• TCP (Reno, SACK, etc), UDP, multicast

Routing and queueing• static routing, DV routing, multicast, ad-hoc routing• queueing disciplines: drop-tail, RED, FQ

Link layer• wired, wireless, satellite

Providing Infrastructure tracing, visualization, error models, etc modify or create your own modules

4

NS components

NS, the simulator itself (this is all we’ll have time for)

NAM, the Network AniMator visualize NS (or other) output GUI input simple Ns scenarios

pre-processing: traffic and topology generators

post-processing: simple trace analysis, often in Awk, Perl, or Tcl

Tutorial: http://www.isi.edu/nsnam/ns/tutorial NS by example: http://nile.wpi.edu/NS/

5

NS Software Structure: C++ and OTCL

Uses two languages

C++ for the core of NS simulator per packet processing fast to run, detailed, complete control

OTCL for control [our focus] simulation setup, configuration fast to write and change

6

Steps when using NS

Create OTCL script for your network model nodes, links, traffic sources, sinks, etc.

Parameterize simulation objects Links: queue sizes, link speeds, … Transport Protocols: TCP flavor and parameters

(more than 30), … Collect statistics

dump everything to trace, post process it gather stats during simulation within OTCL

script modify Ns source code

Run NS multiple times confidence intervals

7

Create a Basic NS Simulation

1. Create event scheduler2. Create nodes and links3. Create connections4. Create traffic sources/sinks5. Enable tracing

8

Create a Basic NS Simulation

1. Create the event scheduler2. Create nodes and links3. Create connections4. Create traffic sources/sinks5. Enable tracing

9

Step 1: Creating Event Scheduler

Create scheduler set ns [new Simulator]

Schedule event $ns at <time> <event> <event>: any legitimate Ns/TCL commands

Start scheduler $ns run

10

Create a Basic NS Simulation

1. Create the event scheduler2. Create nodes and links3. Create connections4. Create traffic sources/sinks5. Enable tracing

11

Step 2: Creating Network (Nodes + Links)

Nodes set n0 [$ns node] set n1 [$ns node]

Links: connect together two nodes $ns duplex-link $n0 $n1 <bandwidth> <delay>

<queue_type> <delay> determines propagation delay <queue_type> determines queueing policy

• DropTail, RED, CBQ, FQ, SFQ, DRR

12

Create a Basic NS Simulation

1. Create the event scheduler2. Create nodes and links3. Create connections4. Create traffic sources/sinks5. Enable tracing

13

Step 3: Create Connections

Transports: TCP, UDP, multicast, etc. transport protocol instances attach to nodes

14

Creating Transport Channels: UDP

source and sink set u_src [new Agent/UDP] set u_dst [new Agent/NULL]

attach them to nodes, then connect to each other $ns attach-agent $n0 $u_src $ns attach-agent $n1 $u_dst $ns connect $u_src $u_dst

15

Creating Transport Channels: TCP source and sink

set t_src [new Agent/TCP/Newreno] set t_dst [new Agent/TCPSink] “Newreno” flavor of TCP

attach to nodes and each other $ns attach-agent $n0 $t_src $ns attach-agent $n1 $t_dst $ns connect $t_src $t_dst

16

Create a Basic NS Simulation

1. Create the event scheduler2. Create nodes and links3. Create connections4. Create traffic sources/sinks5. Enable tracing

17

Step 4: Create Traffic Models

Traffic (applications): Web, ftp, telnet, audio, etc. application objects attach to transport

protocol objects generates traffic into transport protocol

18

Creating Traffic over TCP Channels

How to create a FTP session over TCP? create traffic model

set ftp [new Application/FTP] default is “infinite” file size

attach to TCP channel $ftp attach-agent $t_src

schedule start time $ns at <time> “$ftp start”

19

Creating Traffic over UDP Channels

How to create a CBR (Constant Bit Rate) model over UDP? set cbr [new Application/Traffic/CBR] $cbr set packetSize_ 512 $cbr set interval_ 0.250 $cbr attach-agent $u_src $ns at <time> “$cbr start”

20

Create a Basic NS Simulation

1. Create the event scheduler2. Create nodes and links3. Create connections4. Create traffic sources/sinks5. Enable tracing

21

Tracing: dump everything into a file

Trace packets on individual link Tracefile format:<event> <time> <from> <to> <pkt> <size>--<flowid> <src>

<dst> <seqno> <aseqno>

+ 1 0 2 tcp 900 ------- 1 0.0 3.1 7 15

- 1 0 2 tcp 900 ------- 1 0.0 3.1 7 15

r 1.00234 0 2 tcp 900 ------- 1 0.0 3.1 7 15

+ enqueue- dequeuer received drop

time

nodes involvedin this event

Node 0 Node 1enqueue

receivedequeuedrop

22

Trace packets on individual links Tracefile format:<event> <time> <from> <to> <pkt> <size>--<flowid> <src>

<dst> <seqno> <aseqno>

+ 1 0 2 tcp 900 ------- 1 0.0 3.1 7 15

- 1 0 2 tcp 900 ------- 1 0.0 3.1 7 15

r 1.00234 0 2 tcp 900 ------- 1 0.0 3.1 7 15

+ enqueue- dequeuer received drop

time

nodes involvedin this event

packettype

packetlength

packetflags

flowID source

dest addresses

seqnumber

packetID

Tracing: dump everything into a file

23

Tracing via Monitors

Queue monitor: the queue to access a link

Flow monitor: particular flow within queue to specify a link, we need:

set link [$ns link $n0 $n1] to create a flow monitor:

set fmon [$ns makeflowmon Fid]$ns attach-fmon $link $fmon$ns at <time> “puts $fmon set pdrops_”

24

Introduction to NS-2:

Tutorial overview of NS Create basic NS simulation

Walk-through simple example Model specification Execution and trace analysis

25

Walk-through example

acks

full duplex

acks

full duplex

Node 2Node 0 Node 1

26

Walk-through example2 FTP

sources

One On-Off Source (voice)

acks

12 TCPdest

One On-Off destOne CBR dest

2 Mbps full duplex5 msec prop delay100 packet bufferDrop-tail policy

acks

1 Mbps full duplex10 msec prop delay700 packet bufferDrop-tail policy

10 FTPsources

One UDP2 TCP SACKW_max = 32MSS = 1400

10 TCP NewRenoW_max = 32MSS = 1400

Node 0 Node 1 Node 2

One UDP

One CBR source

12 FTPdest

Two UDPdest

fat link thin link

performance

tracing

27

Introduction to NS-2:

Tutorial overview of NS Create basic NS simulation

Walk-through simple example Model specification Execution and trace analysis

See handout for source code

28

NS Trace file (link n1->n2): NS-trace.txt

...+ 11.533441 1 2 tcp 1440 ------- 12 1.2 2.4 96 2092r 11.535694 1 2 tcp 1440 ------- 12 1.2 2.4 65 1527- 11.537214 1 2 exp 180 ------- 100 0.2 2.13 284 1528- 11.538654 1 2 cbr 1440 ------- 101 1.11 2.14 155 1530r 11.547214 1 2 tcp 1440 ------- 12 1.2 2.4 66 1529+ 11.54728 1 2 tcp 1440 ------- 12 1.2 2.4 97 2095r 11.548654 1 2 exp 180 ------- 100 0.2 2.13 284 1528+ 11.55 1 2 cbr 1440 ------- 101 1.11 2.14 211 2096- 11.550174 1 2 tcp 1440 ------- 12 1.2 2.4 67 1534r 11.560174 1 2 cbr 1440 ------- 101 1.11 2.14 155 1530- 11.561694 1 2 exp 180 ------- 100 0.2 2.13 285 1532+ 11.56222 1 2 tcp 1440 ------- 12 1.2 2.4 98 2097- 11.563134 1 2 tcp 1440 ------- 12 1.2 2.4 68 1537r 11.571694 1 2 tcp 1440 ------- 12 1.2 2.4 67 1534r 11.573134 1 2 exp 180 ------- 100 0.2 2.13 285 1532- 11.574654 1 2 exp 180 ------- 100 0.2 2.13 286 1536...

0.0114sec=180*8/(10^6)+0.01

29

Flow Monitor (link n1->n2) Trace :

packet-trace.txt...10 356 1394.6939635123624 1262 906 0 4 7 3 0 10.5 367 1575.3875777393503 1325 958 0 8 15 7 0 1 1 0 0 11 366 1759.8340061666161 1384 1018 0 8 15 7 0 1 1 0 0 11.5 370 1944.0583990191849 1448 1078 0 8 15 7 0 1 1 0 0 12 380 2131.710863713804 1512 1132 0 8 15 7 0 1 1 0 0 12.5 382 2325.178644727122 1558 1176 0 8 15 7 0 1 1 0 0 13 382 2516.7615454470124 1613 1231 0 8 15 7 0 1 1 0 0 13.5 395 2710.8647514290892 1676 1281 0 8 15 7 0 2 3 1 0 14 421 2912.3462186990751 1747 1326 0 16 31 15 0 2 3 1 0 14.5 432 3130.3858423193769 1805 1373 0 16 31 15 0 2 3 1 0 15 436 3344.5896974377333 1862 1426 0 16 31 15 0 2 3 1 0 15.5 462 3571.3811182311597 1937 1475 0 16 31 15 0 2 3 1 0 16 477 3804.653159658757 1995 1518 0 16 31 15 0 2 3 1 0 16.5 495 4049.5929326563519 2057 1562 0 16 31 15 0 2 3 1 0 17 531 4303.9211771379323 2136 1605 0 16 31 15 0 2 3 1 0 ...

30

Results - Queue Statistics

Red - instantaneous Green - running average

Blue - average w/o transient Purple - packet drops

31

Results - Flow Statistics

Red - TCP flow 1 Green - TCP flow 2

Number of packets in queue mimics TCP Window behavior

32

Results - Flow Statistics

Congestion Windows of Flow 1 and Flow 2

Cumulative dropped packets of Flow 1 and Flow 2

33

Performance Queue Statistics

Multiple runs to obtain confidence intervals