Introduction to NS2

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 well 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

• Create event scheduler
• Create nodes and links
• Create connections
• Create traffic sources/sinks
• Enable tracing

8
Create a Basic NS Simulation

• Create the event scheduler
• Create nodes and links
• Create connections
• Create traffic sources/sinks
• Enable tracing

9
Step 1 Creating Event Scheduler

• Create scheduler
• set ns new Simulator
• Schedule event
• ns at lttimegt lteventgt
• lteventgt any legitimate Ns/TCL commands
• Start scheduler
• ns run

10
Create a Basic NS Simulation

• Create the event scheduler
• Create nodes and links
• Create connections
• Create traffic sources/sinks
• 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 ltbandwidthgt ltdelaygt
  ltqueue_typegt
• ltdelaygt determines propagation delay
• ltqueue_typegt determines queueing policy
• DropTail, RED, CBQ, FQ, SFQ, DRR

12
Create a Basic NS Simulation

• Create the event scheduler
• Create nodes and links
• Create connections
• Create traffic sources/sinks
• 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

• Create the event scheduler
• Create nodes and links
• Create connections
• Create traffic sources/sinks
• 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 lttimegt 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 lttimegt cbr start

20
Create a Basic NS Simulation

• Create the event scheduler
• Create nodes and links
• Create connections
• Create traffic sources/sinks
• Enable tracing

21
Tracing dump everything into a file

• Trace packets on individual link
• Tracefile format
• lteventgt lttimegt ltfromgt lttogt ltpktgt ltsizegt--ltflowidgt
  ltsrcgt ltdstgt ltseqnogt ltaseqnogt
• 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

Node 0
Node 1
enqueue
time

• enqueue
• dequeue
• r receive
• d drop

nodes involved in this event
receive
dequeue
drop
22
Tracing dump everything into a file

• Trace packets on individual links
• Tracefile format
• lteventgt lttimegt ltfromgt lttogt ltpktgt ltsizegt--ltflowidgt
  ltsrcgt ltdstgt ltseqnogt ltaseqnogt
• 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

packet type
packet flags
seq number
time
packet ID

• enqueue
• dequeue
• r receive
• d drop

packet length
flow ID
source dest addresses
nodes involved in this event
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 lttimegt 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
Node 2
Node 0
Node 1
acks
acks
full duplex
full duplex
26
Walk-through example
One CBR source
12 FTP dest
10 FTP sources
2 FTP sources
performance
2 TCP SACK W_max 32 MSS 1400
10 TCP NewReno W_max 32 MSS 1400
One UDP
12 TCP dest
tracing
Node 2
Node 0
Node 1
acks
acks
One UDP
Two UDP dest
1 Mbps full duplex 10 msec prop delay 700 packet
buffer Drop-tail policy
2 Mbps full duplex 5 msec prop delay 100 packet
buffer Drop-tail policy
One On-Off dest One CBR dest
One On-Off Source (voice)
thin link
fat link
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-gtn2) NS-trace.txt

• ...
• 11.533441 1 2 tcp 1440 ------- 12 1.2 2.4 96
  2092
• r 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 1530
• r 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
  2095
• r 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
  1534
• r 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
  1537
• r 11.571694 1 2 tcp 1440 ------- 12 1.2 2.4 67
  1534
• r 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
• ...

0.0114sec1808/(106)0.01
29
Flow Monitor (link n1-gtn2) 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