1 part ii: ns internals. usc information sciences institute 2 outline fundamental concept split...

11

Part II: ns Internals

22USC INFORMATION SCIENCES INSTITUTEUSC INFORMATION SCIENCES INSTITUTE

Outline

Fundamental concept Split object: C++/OTcl linkage

Plumbing Wired Wireless

Scaling


OTcl and C++: The Duality

C++ OTcl

Pure C++objects

Pure OTclobjects

C++/OTcl split objects

ns


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

bind(): link variable values between C++ and OTcl TclObject

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

TclClass Create and initialize TclObject’s

Tcl C++ methods to access Tcl interpreter

TclCommand Standalone global commands

EmbeddedTcl ns script initialization


TclObject

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

$tcp set packetSize_ 1024$tcp set packetSize_ 1024

$tcp advanceby 5000$tcp advanceby 5000


TclObject: Hierarchy and Shadowing

TclObject

Agent

Agent/TCP

Agent/TCP OTcl shadow object

_o123Agent/TCP C++

object

*tcp

TclObject

Agent

TcpAgent

OTcl classhierarchy

C++ classhierarchy


TclObject::bind()

Link C++ member variables to OTcl object variablesC++TcpAgent::TcpAgent() {

bind(“window_”, &wnd_);… …

} bind_time(), bind_bool(), bind_bw()

OTclset tcp [new Agent/TCP]set tcp [new Agent/TCP]$tcp set window_ 200$tcp set window_ 200


Initialization of Bound Variables

Initialization through OTcl class variablesAgent/TCP set Agent/TCP set window_window_ 50 50

Do all initialization of bound variables in ~ns/lib/ns-default.tcl Otherwise a warning will be issued

when the shadow object is created


Implementation of Bound Variables

Class InstVar One object per bound variable –

expensive! InstVarInt, InstVarReal, …

Created by TclObject::bind() Create instance variable in OTcl stack Enable trap read/write to OTcl variable

using Tcl_TraceVar()Tcl_TraceVar() Connect to C++ variable in the trap


TclObject::command()

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


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);}


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


TclObject: Creation and Deletion

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

……

delete $tcpdelete $tcp


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 object

complete initialization

complete initialization

which C++ object to create? – TclClass


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;

Static class TcpClass : public TclClass {public:

TcpClass() : TclClass(“Agent/TCP”) {}TclObject* create(int, const char*const*) {

return (new TcpAgent());}

} class_tcp;


TclClass: Mechanism

Initialization at runtime startup

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

TclClass::init()

for each staticallydefined TclClass

TcpClass::bind()

e.g.

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


Class Tcl

Singleton class with a handle to Tcl interpreterUsage Invoke OTcl procedure Obtain OTcl evaluation results Pass a result string to OTcl Return success/failure code to OTcl


Class Tcl

Tcl& 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;

}


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()); }


EmbeddedTcl

Pre-load OTcl scripts at ns runtime startup Recursively load ~ns/tcl/lib/ns-lib.tcl:~ns/tcl/lib/ns-lib.tcl:

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

Load everything into a single C++ string Execute this string at runtime startup

Tcl::init(): load ~tclcl/tcl-object.tcl~tclcl/tcl-object.tcl

Tcl_AppInit(): load ~ns/tcl/lib/ns-lib.tcl~ns/tcl/lib/ns-lib.tcl


EmbeddedTcl

How it works tcl2c++tcl2c++: provided by TclCL, converts

tcl scripts into a C++ static character array

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


Summary

TclObject Unified interpreted (OTcl) and compiled

(C++) class hierarchies Seamless access (procedure call and

variable access) between OTcl and C++

TclClass The mechanism that makes TclObject

work

Tcl: primitives to access Tcl interpreter


Outline

Fundamental concept Split object

Plumbing Wired world Wireless world

Scaling


ns Internals

Discrete event schedulerNetwork topologyRoutingTransportPacket flowPacket formatApplication


Discrete Event Scheduler

time_, uid_, next_, handler_

head_ ->head_ ->

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

handler_ -> handle()

time_, uid_, next_, handler_

reschedule

insert


Network Topology: Node

n0 n1

Addr Classifier

Port Classifier

classifier_

dmux_

entry_

Node entry

Unicast Node

Multicast Classifier

classifier_

dmux_

entry_

Node entry

Multicast Node

multiclassifier_


Network Topology: Link

n0 n1

enqT_ queue_ deqT_

drophead_ drpT_

link_ ttl_

n1 entry_

head_

tracing simplex link

duplex link


Routing

n0 n1

Addr Classifier

Port Classifier

classifier_

dmux_

entry_

Node entry 0

1 enqT_ queue_ deqT_

drophead_ drpT_

link_ ttl_

n1 entry_

head_


Routing (con’t)

n0 n1

Addr Classifier

Port Classifier

classifier_

dmux_

entry_

0

1

Addr Classifier

Port Classifier

classifier_

dmux_

entry_

1

0Link n0-n1

Link n1-n0


Transport

0

1

n0 n1

Addr Classifier

Port Classifier

classifier_

dmux_

entry_

0 Agent/TCP

agents_

Addr Classifier

Port Classifier

classifier_

dmux_

entry_

1

0Link n0-n1

Link n1-n0

0 Agent/TCPSinkagents_

dst_=1.0 dst_=0.0


Application: Traffic Generator

0

1

n0 n1

Addr Classifier

Port Classifier

classifier_

dmux_

entry_

0 Agent/TCP

agents_

Addr Classifier

Port Classifier

classifier_

dmux_

entry_

1

0Link n0-n1

Link n1-n0

0 Agent/TCPSink

agents_

dst_=1.0 dst_=0.0Application/FTP


Plumbing: Packet Flow

0

1

n0 n1

Addr Classifier

Port Classifier

entry_

0 Agent/TCP Addr Classifier

Port Classifier

entry_

1

0Link n0-n1

Link n1-n0

0 Agent/TCPSink

dst_=1.0 dst_=0.0Application/FTP


Packet Format

header

dataip header

tcp header

rtp header

trace header

cmn header

...

ts_

ptype_

uid_

size_

iface_


Outline



ns scaling


Abstract the Real World

Packet headersMobile nodeWireless channelForwarding and routingVisualization


Wireless Packet Format

header

data

ts_

ptype_

uid_

size_

iface_

IP header

......

cmn header

LL

MAC 802_11

......

ARP

wireless headers


Mobile Node Abstraction

Location Coordinates (x,y,z)

Movement Speed, direction, starting/ending

location, time ...


Portrait of A Mobile NodeNode

ARP

Propagation and antenna models MobileNode

LL

MAC

PHY

LL

CHANNEL

LL

MAC

PHY

Classifier: Forwarding

Agent: Protocol EntityNode Entry

LL: Link layer object

IFQ: Interface queue

MAC: Mac object

PHY: Net interface

protocolagent

routingagent

addrclassifier

portclassifier

255

IFQIFQ

defaulttarget_


Mobile Node: Components

Link Layer Same as LAN, but with a separate ARP

module

Interface queue Give priority to routing protocol packets

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


Mobile Node: Components

Network interface (PHY) Parameters based on Direct Sequence Spread

Spectrum (WaveLan) Interface with: antenna and propagation

models Update energy: transmission and reception

Radio Propagation Model Friss-space attenuation(1/r2) at near distance Two-ray Ground (1/r4) at far distance

Antenna Omni-directional, unity-gain


Wireless Channel

Duplicate packets to all mobile nodes attached to the channel except the senderIt is the receiver’s responsibility to decide if it will accept the packet Collision is handled at individual

receiver O(N2) messages grid keeper


Grid-keeper: An Optimization


Outline



ns scaling


ns Scaling

Limitations to simulation size Memory Run time

Solutions Abstraction Fine-tuning (next session)


020406080

100120140160180

0 100 200 300 400 500 600

Number of Nodes (degree ~ 1.77)

Mem

ory

in M

BMemory Footprint of ns

Dense Mode

128MB

430


1

10

100

1000

10000

0 200 400 600


Use

r Tim

e in

Sec

Run Time of ns

Dense Mode


Culprit: Details, Details

Dense mode tries to capture packet-level behavior Prunes, Joins, …

Let’s abstract it out Centralized multicast SessionSim


Centralized Multicast

s

n1 n2

n3 n4 n5


Dense Mode Multicast

s

n1 n2n2

n3 n4n4 n5

RouteComputatio

nUnit

receiver

data

prune

source



Usage

$ns mrtproto CtrMcast$ns mrtproto CtrMcast

Limitation No exact dynamic behavior, e.g.,

routing convergence time Does not mean to replace DM


Further Abstraction

Remove all intermediate nodes and linksDo not model: Detailed queueing Detailed packet delivery

ns Object Sizes

Multicast Node 6KB

Duplex link 14KB


SessionSim

ReplicationDelayTTL

Session Helper:

Session Multicast

Detailed Packet Distribution

s

n1 n2n2

n3 n4n4 n5

receiver

data

sourcen4n4 n2n2

s


SessionSim

Usageset ns [new SessionSim]set ns [new SessionSim]

instead of

set ns [new Simulator]set ns [new Simulator]

Limitation Distorted end-to-end delay Packet loss due to congestion


Memory Footprint of ns

020406080

100120140160180

0 100 200 300 400 500 600


Mem

ory

in M

B

Dense Mode


SessionSim


Run Time of ns

1

10

100

1000

10000

0 100 200 300 400 500 600


Use

r Tim

e in

Sec

Dense ModeCentralized Multicast

SessionSim


Distortion of Centralized Multicast

# Packets in transit

0

2

4

6

8

10

12

0 0.5 1 1.5 2

Time (in sec)

# o

f pa

cket

s in

tra

nsit

DM

CtrMcast


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

Seco

nds


Footnotes

My sim still uses too much memory? OrI want large detailed simulation, e.g., Web traffic pattern?

Fine-tune your simulator We’ll cover it this afternoon

1 part ii: ns internals. usc information sciences institute 2 outline fundamental concept split...

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