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7/31/2019 Iec00 Internal

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Part II: ns Internals


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USC INFORMATION SCIENCES INSTITUTE 2

Outline

Fundamental conceptSplit object: C++/OTcl linkage

PlumbingWiredWireless

Scaling


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OTcl and C++: The Duality

C++ OTcl

Pure C++objects

Pure OTcl

objects

C++/OTcl split objects

ns


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C++/OTcl LinkageRoot of ns-2 object hierarchy

bind(): link variable values betweenC++ and OTclTclObject

command(): link OTcl methods to C++implementations

TclClass Create and initialize TclObjects

Tcl C++ methods to access Tcl interpreter

TclCommand Standalone global commands

EmbeddedTcl ns script initialization


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TclObject

Basic hierarchy in ns for split objectsMirrored in both C++ and OTclExampleset tcp [new Agent/TCP]$tcp set packetSize_ 1024$tcp advanceby 5000


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TclObject: Hierarchy and Shadowing

TclObject

Agent

Agent/TCP

Agent/TCP OTclshadow object

_o123 Agent/TCP C++

object

*tcp

TclObject

Agent

TcpAgent

OTcl classhierarchy

C++ classhierarchy


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TclObject::bind()

Link C++ member variables to OTcl objectvariables

C++TcpAgent::TcpAgent() {bind( window_ , &wnd_);

}

bind_time(), bind_bool(), bind_bw()OTclset tcp [new Agent/TCP]$tcp set window_ 200


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Initialization of Bound Variables

Initialization through OTcl classvariables

Agent/TCP set window_ 50Do all initialization of bound variables in~ns/lib/ns-default.tcl

Otherwise a warning will be issued whenthe shadow object is created


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Implementation of Bound Variables

Class InstVarOne object per bound variable expensive!

InstVarInt, InstVarReal, Created by TclObject::bind()

Create instance variable in OTcl stack

Enable trap read/write to OTcl variable usingTcl_TraceVar()

Connect to C++ variable in the trap


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TclObject::command()

Implement OTcl methods in C++Trap point: OTcl method cmd{}Send all arguments after cmd{} call toTclObject::command()


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TclObject::command()OTcl

set tcp [new Agent/TCP]$tcp advance 10

C++ int TcpAgent::command(int argc,const char*const* argv) {

if (argc == 3) {if (strcmp(argv[1], advance ) == 0) {

int newseq = atoi(argv[2]);

return(TCL_OK);

}}return (Agent::command(argc, argv);

}


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TclObject::command()

$tcp send TclObject::unknown{} $tcp cmd sendno suchprocedure

TcpAgent::command()

match send?

Invoke parent:return Agent::command()

process and return

Yes No

OTcl space

C++ space


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TclObject: Creation and Deletion

Global procedures: new{}, delete{}Exampleset tcp [new Agent/TCP] delete $tcp


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C++

OTcl

TclObject: Creation and Deletion

invoke parentconstructor

Agent/TCPconstructor

parentconstructor


TclObjectconstructor

create C++object

AgentTCPconstructor



parent (Agent)

constructor

do nothing,return

TclObject (C++)

constructor

bind variablesand return

bind variablesand return

create OTclshadow objectcompleteinitializationcompleteinitialization which C++object to create? TclClass


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TclClass

TclObject

Agent

Agent/TCP

TclObject

Agent

TcpAgent

NsObject ??

OTclC++ mirroringStatic class TcpClass : public TclClass {public:

TcpClass() : TclClass( Agent/TCP ) {}

TclObject* create(int, const char*const*) {return (new TcpAgent ());}

} class_tcp;


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TclClass: Mechanism

Initialization at runtime startup

SplitObject::register{}Create and registerOTcl class Agent/TCP

TclClass::init()

for each staticallydefined TclClass

TcpClass::bind()

e.g.

Agent/TCP::create-shadow{}TclClass::create_shadow()


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Class Tcl

Singleton class with a handle to Tclinterpreter

UsageInvoke OTcl procedureObtain OTcl evaluation results

Pass a result string to OTclReturn success/failure code to OTcl


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Class TclTcl& tcl = Tcl::instance ();if (argc == 2) {

if (strcmp(argv[1], now) == 0) { tcl.resultf (%g, clock()); return TCL_OK;

}tcl.error (command not found); return TCL_ERROR;

} else if (argc == 3) {tcl.eval (argv[2]);clock_ = atof( tcl.result ());return TCL_OK;

}


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Class TclCommand

C++ implementation of global OTcl commands

class RandomCommand : public TclCommand { public:

RandomCommand() : TclCommand("ns-random") {}virtual int command(int argc, const char*const* argv);

};

int RandomCommand::command(int argc, const char*const* argv){

Tcl& tcl = Tcl::instance();if (argc == 1) {

sprintf(tcl.buffer(), "%u", Random::random());tcl.result(tcl.buffer());

}


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EmbeddedTcl

Pre-load OTcl scripts at ns runtime startupRecursively load ~ns/tcl/lib/ns-lib.tcl:source ns-autoconf.tcl

source ns-address.tclsource ns-node.tcl.......

Load everything into a single C++ string

Execute this string at runtime startupTcl::init(): load ~tclcl/tcl-object.tclTcl_AppInit(): load ~ns/tcl/lib/ns-lib.tcl


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EmbeddedTcl

How it workstcl2c++ : provided by TclCL, converts tcl

scripts into a C++ static character arrayMakefile.in:

tclsh8.0 bin/tcl-expand.tcl tcl/lib/ns-lib.tcl | tcl2c++ et_ns_lib >gen/ns_tcl.cc


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Summary

TclObjectUnified interpreted (OTcl) and compiled(C++) class hierarchiesSeamless access (procedure call andvariable access) between OTcl and C++

TclClassThe mechanism that makes TclObject work

Tcl: primitives to access Tcl interpreter


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Outline

Fundamental conceptSplit object

PlumbingWired worldWireless world

Scaling


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ns Internals

Discrete event schedulerNetwork topologyRoutingTransportPacket flowPacket format

Application


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Discrete Event Schedulertime_, uid_, next_, handler_

head_ ->head_ ->

Three types of schedulersList: simple linked list, order-preserving, O(N)Heap: O(logN)Calendar: hash-based, fastest, O(1)

handler_ -> handle()

time_, uid_, next_, handler_

reschedule

insert


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Network Topology: Node

n0 n1

AddrClassifier

PortClassifier

classifier_

dmux_

entry_

Node entry

UnicastNode

MulticastClassifier

classifier_

dmux_

entry_

Node entry

MulticastNode

multiclassifier_


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Network Topology: Link

n0 n1

enqT_ queue_ deqT_

drophead_ drpT_

link_ ttl_

n1entry_ head_

tracing simplex link

duplex link


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Routing

n0 n1

AddrClassifier

PortClassifier

classifier_

dmux_

entry_

Node entry 01 enqT_ queue_ deqT_

drophead_ drpT_

link_ ttl_

n1entry

_

head_


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Routing (cont)

n0 n1

AddrClassifier

PortClassifier

classifier_

dmux_

entry_

01

AddrClassifier

PortClassifier

classifier_

dmux_

entry_

10

Link n0-n1

Link n1-n0


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Transport

01

n0 n1

AddrClassifier

PortClassifier

classifier_

dmux_

entry_

0 Agent/TCPagents_

AddrClassifier

PortClassifier

classifier_

dmux_

entry_

10

Link n0-n1

Link n1-n0

0 Agent/TCPSink agents_

dst_=1.0 dst_=0.0


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Application: Traffic Generator

01

n0 n1

AddrClassifier

PortClassifier

classifier_

dmux_

entry_

0 Agent/TCPagents_

AddrClassifier

PortClassifier

classifier_

dmux_

entry_

10

Link n0-n1

Link n1-n0

0 Agent/TCPSink agents_

dst_=1.0 dst_=0.0 Application/FTP


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Plumbing: Packet Flow

01

n0 n1

AddrClassifier

PortClassifier

entry_

0 Agent/TCP AddrClassifier

PortClassifier

entry_

10

Link n0-n1

Link n1-n0

0 Agent/TCPSink dst_=1.0 dst_=0.0

Application/FTP


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Packet Format

header

dataip header

tcp header

rtp header

trace header

cmn header

...

ts_

ptype_

uid_

size_

iface_


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Outline



ns scaling


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Abstract the Real World

Packet headersMobile node

Wireless channelForwarding and routing

Visualization


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Wireless Packet Format

header

data

ts_

ptype_

uid_

size_

iface_

IP header

......

cmn header

LL

MAC 802_11

......

ARP

wirelessheaders


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Mobile Node Abstraction

LocationCoordinates (x,y,z)

MovementSpeed, direction, starting/ending location,time ...


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Portrait of A Mobile NodeNode

ARP

Propagationand antennamodels

MobileNode

LL

MAC

PHY

LL

CHANNEL

LL

MAC

PHY

Classifier : Forwarding

Agent : Protocol Entity

Node Entry

LL: Link layer object

IFQ : Interface queue

MAC: Mac object

PHY : Net interface

protocolagent

routing

agent

addr

classifier

portclassifier

255

IFQIFQ

defaulttarget_


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Mobile Node: Components

Link LayerSame as LAN, but with a separate ARP module

Interface queueGive priority to routing protocol packetsMac Layer

IEEE 802.11RTS/CTS/DATA/ACK for all unicast packetsDATA for all broadcast packets


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Mobile Node: Components

Network interface (PHY)Parameters based on Direct Sequence SpreadSpectrum (WaveLan)

Interface with: antenna and propagation modelsUpdate energy: transmission and reception

Radio Propagation ModelFriss-space attenuation(1/r 2) at near distanceTwo-ray Ground (1/r 4) at far distance

AntennaOmni-directional, unity-gain


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Wireless Channel

Duplicate packets to all mobile nodesattached to the channel except the

senderIt is the receivers responsibility todecide if it will accept the packet

Collision is handled at individual receiverO(N2) messages grid keeper


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Grid-keeper: An Optimization


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Outline



ns scaling


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ns Scaling

Limitations to simulation sizeMemory

Run timeSolutions

Abstraction

Fine-tuning (next session)


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0

20406080

100

120140160180

0 100 200 300 400 500 600

Number of Nodes (degree ~ 1.77)

M e m o r y i n

M B

Memory Footprint of ns

Dense Mode

128MB

430


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1

10

100

1000

10000

0 200 400 600


U s e r

T i m e

i n

S e c

Run Time of ns

Dense Mode


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Culprit: Details, Details

Dense mode tries to capture packet-level behavior

Prunes, Joins, Lets abstract it out

Centralized multicast

SessionSim


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Centralized Multicast

s

n1 n2

n3 n4 n5


Dense Mode Multicast

s

n1 n2

n3 n4 n5

RouteComputation

Unit

receiverdataprune

source


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Usage$ns mrtproto CtrMcast

LimitationNo exact dynamic behavior, e.g., routingconvergence timeDoes not mean to replace DM


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Further Abstraction

Remove all intermediate nodes and links

Do not model:Detailed queueingDetailed packet delivery

ns Object Sizes

Multicast Node 6KB

Duplex link 14KB


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SessionSim

ReplicationDelayTTL

Session Helper:

Session Multicast

Detailed Packet Distribution

s

n1 n2

n3 n4 n5

receiverdata

sourcen4 n2

s


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SessionSim

Usageset ns [new SessionSim]

instead of set ns [new Simulator]

Limitation

Distorted end-to-end delayPacket loss due to congestion


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Memory Footprint of ns

020406080

100120140160180

0 100 200 300 400 500 600


M e m o r y

i n

M B

Dense Mode


SessionSim


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Run Time of ns

1

10

100

1000

10000

0 100 200 300 400 500 600


U s e r

T i m e

i n S e c

Dense ModeCentralized

Multicast

SessionSim


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Distortion of Centralized Multicast

# Packets in transit

0246

81012

0 0.5 1 1.5 2

Time (in sec)

# o

f p a c k e

t s i n t r a n s i

tDMCtrMcast


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Distortion of SessionSimMean (Diff in E-E Delay)

0

0.02

0.04

0.06

0.08

0.1

0 20 40 60 80 100

Number of Sessions

S e c o n

d s


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Footnotes

My sim still uses too much memory?Or

I want large detailed simulation, e.g.,Web traffic pattern?

Fine-tune your simulatorWell cover it this afternoon

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