Developing New Modules in NSin NS2in NS2 - UBC ECEteerawat/publications/NS2/14-NewModules.pdf · Developing New Modules in NSin NS2in NS2 Textbook: T. Issariyakul and E. Hossain,

Developing New Modules Developing New Modules Developing New Modules Developing New Modules Developing New Modules Developing New Modules in NSin NS22

Developing New Modules Developing New Modules in NSin NS22

Textbook: T. Issariyakul and E. Hossain, Introduction to Network Simulator NS2, Springer 2008. 1

OutlineR• Recap

• Automatic Repeat reQuest• Packet Scheduling• SummarySummary


RRecap• 3 Simulation Main Steps3 Simulation Main Steps1. Design and Implementation

– Things to simulate– Assumptions– Performance measure– Code Implementationp

2. Simulation– Network Configuration Phase

Si l ti Ph– Simulation Phase3. Result Compilation

– Debugging and Tracing

Textbook: T. Issariyakul and E. Hossain, Introduction to Network Simulator NS2, Springer 2008.

gg g g– Compute performance measures

3

D i d I l iDesign and Implementation• DesignDesign

1. What would you like to simulate? Draw a conceptual view

2 Wh t hi h d ish t b ild m d l ?2. What hierarchy do you wish to build a new module?C++, OTcl, or both Do you need to bind them?

3. What variables/functions do you need?4 D d OT l i f ?4. Do you need OTcl interface?

• Implementation1. Implement C++/OTcl codes1. Implement C /OTcl codes2. Modify makefile make

3. Develop Simulation script


OutlineR• Recap



A i R QAutomatic Repeat reQuest• Error Control MechanismError Control Mechanism• Based on packet retransmission (i.e.,

acknowledgement (ACK))acknowledgement (ACK))• 3 Main types

– Stop and Wait– Go-back-N: TCP– Selective Repeat Request


S A d W iStop-And-Wait• Transmit and wait for ACK before Transmit and wait for ACK before

transmitting the next packetRetransmit after timeout• Retransmit after timeout

• Reset timeout upon receiving an ACK

1sender 22

timeout

receiver 1

l


packetACK

How many times would you retransmit the lost packet?

7

S A d W iStop-And-Wait• 1-persistent1-persistent• Infinite-persistent

i i • p-persistent: retransmit w.p. p• Finite persistent: retransmit upto K p p

times


S A d W iStop-And-Wait• Let e be error probabilityLet e be error probability

Persistent Type Pr of successful TX Persistent Type Pr. of successful TX 1 1-eInfinite 1Infinite 1p (1-e)/(1-pe)Finite 1 eK+1Finite 1-eK+1


C l ViConceptual View

n0 n1SimpleLink



n0 n1Lossy link



n0 n1Lossy link with ARQ


C l ViConceptual View• Two main mechanismsTwo main mechanisms

– ACK passingCallback mechanism– Callback mechanism


C l Vi• ACK passing

Conceptual ViewACK passing– tARQ_:

• ARQ transmitting unit • ARQ transmitting unit • Keep track of the no. of retransmissions• Decide whether to TX or drop the packetDec de whether to X or drop the packet

– acker_: inform tARQ_ of TX success– nacker : inform tARQ of TX failurenacker_ inform tARQ_ of TX failure


C l ViConceptual View• Two main mechanismsTwo main mechanisms

– ACK passingCallback mechanism– Callback mechanism

callback


callback

15

C l Vi• Callback mechanism

Conceptual ViewCallback mechanismQ: What does link_ do when receiving a

packet?packet?A: Schedule two events: Pkt departure

and arrival Th and arrival//~ns/link/delay.ccvoid LinkDelay::recv(Packet* p, Handler* h) {

This is a queue handler

double txt = txtime(p); Scheduler& s = Scheduler::instance(); s.schedule(target_, p, txt + delay_);

Pkt arrival:packet receptionat the next node


s.schedule(h, &intr_, txt); }

at the next nodePkt departure:Tell the associated queue to resume

16

C l Vi• Callback mechanism

Conceptual ViewCallback mechanismQ: What does link_errmodule do when

receiving a packet and the packet is in error?A: Drop the packet and Tell the queue to resume

// /ns/queue/errmodel cc

This is a queue //~/ns/queue/errmodel.cc

void ErrorModel::recv(Packet* p, Handler* h) {

double delay = Random::uniform(8.0*ch->size()/bandwidth_);i i

qhandler

Scheduler::instance().schedule(h, &intr_, delay);drop_->recv(p); return;

} Pkt departure:Tell the associated queue to resumeDrop the packet


Drop the packet

17

C l Vi• link and linkerrmodule callback to

Conceptual Viewlink_ and linkerrmodule_ callback to tARQ_

• tARQ call back to queuet Q_ call back to queue_• To send packet p downstream:

– queue : recv(qh , p)q _ (q _, p)– tARQ_: recv(arqh_,p)


C l ViConceptual View• Two main mechanisms

– ACK passing– Callback mechanismm m

Callback with ARQ

qh_

arqh_

callback

qh_


callbackwith qh_

19

C I l iC++ Implementation• ARQ Transmitter ClassesARQ Transmitter Classes

– ARQTX,ARQHandler

ARQ R i Cl ss s• ARQ Receiver Classes– ARQRX ARQAcker, ARQNacker


C I l iC++ ImplementationARQTX:ARQTX:

class ARQTx : public Connector {

called by ARQNacker

public:ARQTx();void recv(Packet*, Handler*);

id k(P k t*) id k()

called by ARQAcker

void nack(Packet*); void ack();void resume();

protected:ARQHandler arqh ;

Callback from link_ or linkerrmodule

Queue handler

Q q _;Handler* qh_; Packet* pkt_;ARQStatus status_;int blocked_;

_

Finite persistent ARQ


int retry_limit_; int num_rtxs_;};

21

C I l iARQTx,

C++ ImplementationARQTx::ARQTx() : arqh_(*this)ARQTx,

ARQHandler:_

{num_rtxs_ = 0; retry_limit_ = 0;qh_ = 0;pkt_ = 0;status_ = IDLE;blocked_ = 0;bind("retry_limit_", &retry_limit_);

}

enum ARQStatus {IDLE,SENT,ACKED,RTX,DROP};

class ARQHandler : public Handler {public:public:

ARQHandler(ARQTx& arq) : arq_tx_(arq) {};

void handle(Event*);private:


private: ARQTx& arq_tx_;

};

22


void ARQTx::recv(Packet* p, Handler* h){

qh_ = h;status_ = SENT;bl k d 1blocked_ = 1;send(p,&arqh_);

}



void ARQTx::recv(Packet* p, Handler* h){

qh_ = h;status_ = SENT;bl k d 1blocked_ = 1;send(p,&arqh_);

}


C I l iC++ Implementationnack(p)

ack()

nack(p)

num_rtxs_++;pkt_ = p;

num_rtxs_=0;status_ = ACKED;

num_rtxs_>retry_limit_<=retry_limit_

returnstatus_ = RTX; num_rtxs_ = 0;

status_ = DROP;

return


C I l iC++ Implementationresume()resume()

blocked_=0;

status_

ACKED RTX DROP

status_ = SENT;blocked_ = 1;

drop(pkt_);status_ = IDLE;

ACKED

status_ = IDLE;qh >handle(0);

RTX DROP

send(pkt_,&arqh_); qh_->handle(0);qh_->handle(0);


return

26

C I l iC++ Implementation• ARQ Transmitter ClassesARQ Transmitter Classes

– ARQTX,ARQHandler

ARQ R i Cl ss s• ARQ Receiver Classes– ARQRX ARQAcker, ARQNacker


C I l iC++ Implementationclass ARQRx : public Connector { ppublic:

ARQRx();int command(int argc, const char*const* argv); virtual void recv(Packet* Handler*);virtual void recv(Packet*, Handler*);virtual void resume()=0;Packet *pkt_;

protected: class ARQAcker : public ARQRx { bliARQTx* arq_tx_;

};

public:ARQAcker() {};virtual void resume();

};class ARQNacker : public ARQRx { public:

ARQNacker() {};virtual void resume();


();};

28

C I l iC++ Implementationint ARQRx::command(int argc, const char*const* argv) {

Tcl& tcl = Tcl::instance();if (argc == 3) {

if (strcmp(argv[1], "attach-ARQTx") == 0) {arq_tx_ = (ARQTx*)TclObject::lookup(argv[2]);return(TCL OK);return(TCL_OK);

}

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


C I l iC++ Implementationid ( k * dl * h)void ARQRx::recv(Packet* p, Handler* h)

{pkt_ = p; handler_ = h; resume();

}

void ARQAcker::resume(){

arq_tx_->ack(); send(pkt_,handler_);}

void ARQNacker::resume(){

arq tx ->nack(pkt );


arq_tx_ >nack(pkt_);

}

30

OT l I l iOTcl Implementation• 2 Instprocs to put ARQ in the simple 2 Instprocs to put ARQ in the simple

link:1 Simulator:: link arq{limit from to}1. Simulator:: link-arq{limit from to}2. SimpleLink::link-arq{limit}

Simulator instproc link arq { limit from to } {Simulator instproc link-arq { limit from to } { set link [$self link $from $to] $link link-arq $limit

}


}

31

OT l I l iOTcl ImplementationSimpleLink instproc link-arq { limit } {

$self instvar link_ link_errmodule_ queue_ drophead_$self instvar tARQ_ acker_ nacker_ set tARQ_ [new ARQTx] set acker [ne ARQAcker]set acker_ [new ARQAcker] set nacker_ [new ARQNacker] $tARQ_ set retry_limit_ $limit $acker attach-ARQTx $tARQ $ _ Q $ Q_$nacker_ attach-ARQTx $tARQ_ $queue_ target $tARQ_ $tARQ_ target $link_errmodule_ $link_errmodule_ target $acker_ $acker_ target $link_ $tARQ_ drop-target $drophead_ $link errmodule drop target $nacker


$link_errmodule_ drop-target $nacker_ }

32

T l Si l i S iTcl Simulation Script• Insert the following codes:Insert the following codes://tcp.tcl

set em [new ErrorModel]$em set rate_ 0.1$$em unit pkt$em ranvar [new RandomVariable/Uniform]$em drop-target [new Agent/Null]$ns link-lossmodel $em $n1 $n3$ns link-arq 2 $n1 $n3


R l C ll iResult Collection• Insert the following codes:Insert the following codes://tcp.tclproc show_tcp_seqno {} {

global tcp nsputs "At [$ns now] The final tcp sequence number is [$tcp set t seqno ]"[$tcp set t_seqno_]"

}

$ t 0 0 "$ft t t"$ns at 0.0 "$ftp start"$ns at 10.0 "show_tcp_seqno"$ns at 10.1 "$ns halt"$


$ns run

34

Si l i R lSimulation Result>> ns tcp.tcl>> The final tcp sequence number is 37587


OutlineR• Recap



P k S h d liPacket Scheduling• Not related to the Event SchedulingNot related to the Event Scheduling

Packet scheduler: Which packet should o first?Which packet should go first?


P k S h d liPacket Scheduling• Example of scheduler: (Give me few Example of scheduler: (Give me few

example) Round robin– Round robin

– Max rateDelay based– Delay based

– Fairness basedP i it b d– Priority based



n0 n1SimpleLink


C l ViConceptual ViewLinkSchedn0

n1 n1

n2

...


C l ViConceptual View• Key differencesKey differences

– Flow classifier (flow_clsfr_): Send packets from different flow to packets from different flow to different queue

– Scheduler (sch ): Determine which Scheduler (sch_) Determine which packet should go first• Round robin• Priority based

– Callback mechanism



n1 n1

n2



n1 n1

n2

Callback


C I l iC++ Implementation• Flow classifier: Flow classifier:

– Base class: ClassifierDerived class: FlowClassifier– Derived class: FlowClassifier

• Packet schedulerB l – Base class: Connector PktScheduler

– Derived class: RRScheduler


R P Cl ifiRecap: Port Classifier(1)

//~ns/classifier/classifier-port.ccint PortClassifier::classify(Packet *p)

(1)(3)

y( p){

hdr_ip* iph = hdr_ip::access(p);return iph->dport();

}

(2)


Fl Cl ifiFlow Classifier• FlowClassfier (C++) FlowClassfier (C )

Classifier/Flow (OTcl)

• We only need to define function classify(p):y(p)

//classifier-flow.cc int FlowClassifier::classify(Packet *p)y p{

return hdr_ip::access(p)->flowid(); }


C I l iC++ Implementation• Flow classifier: Flow classifier:

– Base class: ClassifierDerived class: FlowClassifier– Derived class: FlowClassifier

• Packet schedulerB l – Base class: Connector PktScheduler

– Derived class: RRScheduler


C I l i• Two main functionality

C++ ImplementationTwo main functionality1. Determine the next flow and

transmitted the packettransmitted the packet2. Callback Mechanism


C I l iC++ ImplementationV i bl M iVariable Meaningblocked_ True if the PktScheduler is blockedactive_flow_id_ Flow ID of the packet being transmittedpkt_[i] HOL packet of queue iqh_[i] Queue handler corresponding to Queue i


C I l i• Declaration

C++ ImplementationDeclaration

#define MAX_FLOWS 10 class PktScheduler : public Connector { public:

P k t ti f tiPktScheduler(); virtual void handle(Event*); virtual void recv(Packet*, Handler*);

protected:

Packet reception function

Use this function to send packetsp

void send(int fid, Handler* h); virtual void resume(); int getFlowID(Packet* p) {return hdr_ip::access(p)->flowid();};virtual int nextID() = 0;

Callback function

virtual int nextID() 0; Handler* qh_[MAX_FLOWS]; Packet* pkt_[MAX_FLOWS]; int blocked_; int active flow id ;

Pure virtual function:Override by the derived class


int active_flow_id_;

};

50

C I l i• Functions recv(p h) and send(id h)

C++ ImplementationFunctions recv(p,h) and send(id,h)

void PktScheduler::recv(Packet* p, Handler* h)void PktScheduler::recv(Packet p, Handler h){

int fid = getFlowID(p); pkt_[fid] = p;qh_[fid] = h; if (!blocked ) {

PktScheduler

if (!blocked_) { send(fid,this); blocked_ = 1; active_flow_id_ = fid;

}

… …

pkt_ qh_

} }void PktScheduler::send(int fid_idx, Handler* h){ If blocked,


Connector::send(pkt_[fid_idx],h); pkt_[fid_idx] = 0;

}

wait for a call back signal from link_.

51

C I l i• Functions handle() and resume()

C++ ImplementationFunctions handle() and resume()

void PktScheduler::handle(Event*) { resume();}void PktScheduler::handle(Event ) { resume();}void PktScheduler::resume() {

qh_[active_flow_id_]->handle(0); int index = nextID();

qh_

PktScheduler

int index = nextID();blocked_ = 0; if (index >= 0) {

send(index,this); bl k d 1

queue_ queue_ …Polymorphism

blocked_ = 1; active_flow_id_ = index;

}

} ue_[0]

ue_[1]

• The packet has left link


que

que• The packet has left link_

• Fetch another packet

52

C I l i• Packet forwarding mechanism

C++ ImplementationPacket forwarding mechanism

classify hCallback

pkt

classify qh_

this


C I l i• One missing piece

C++ ImplementationOne missing piece How would a PktScheduler select a flow? Class RRScheduler (C++) PktScheduler/RR (OTcl) int RRScheduler::nextID() {

int count = 0; c rrent id ++ c rrent id % MAX FLOWScurrent_id_++; current_id_ %= MAX_FLOWS; while((pkt_[current_id_] == 0)&&(count<MAX_FLOWS)){

current_id_++; current_id_ %= MAX_FLOWS; count++;

}} if (count == MAX_FLOWS)

return -1; else{

return current id ;


return current_id_; }

}

54

OT l I l iOTcl Implementation• Class LinkSch derives from Class LinkSch derives from SimpleLink

•


OT l I l iOTcl Implementation• ConstructorConstructor

Class LinkSch -superclass Link LinkSch instproc init {src dst bw delay num_queues} {

set flow clsfr [new Classifier/Flow] _ _ [ / ]set sch_ [new PktScheduler/RR] set num_queues_ $num_queues $head_ target $flow_clsfr_ for {set i 0} {$i < $num queues } {incr i} { { } { _q _} { } {

set queue_($i) [new Queue/DropTail] $queue_($i) target $sch_ $queue_($i) drop-target $drophead_

} }$sch_ target $link_ $link_ target $ttl_ $ttl_ target [$dst entry] ...


}

56

OT l I l iOTcl Implementation• ConstructorConstructor

Class LinkSch -superclass Link LinkSch instproc init {src dst bw delay num_queues} {

set flow clsfr [new Classifier/Flow] _ _ [ / ]set sch_ [new PktScheduler/RR] set num_queues_ $num_queues $head_ target $flow_clsfr_ for {set i 0} {$i < $num queues } {incr i} { { } { _q _} { } {

set queue_($i) [new Queue/DropTail] $queue_($i) target $sch_ $queue_($i) drop-target $drophead_

} }$sch_ target $link_ $link_ target $ttl_ $ttl_ target [$dst entry] ...


}

57

OT l I l iOTcl ImplementationSimulator instproc sch-link { n1 n2 bw delay num_queues} {

$self instvar link_ queueMap_ nullAgent_ useasim_ set sid [$n1 id] set did [$n2 id] set link_($sid:$did) [new LinkSch

$n1 $n2 $bw $delay $num_queues] }

Simulator instproc add-flow { n1 n2 prio } { $self instvar link_ set sid [$n1 id] set did [$n2 id] $link_($sid:$did) add-flow $fid

} LinkSch instproc add-flow { fid } { $self instvar queue_ flow_clsfr_ $flow_clsfr_ install $fid

$queue ($fid)


$queue_($fid)}

58

T l Si l i S iTcl Simulation Script

Agent/TCP TCPSinkFTP

n1 n3LinkSch

TCPSinkAgent/TCPFTP

…… …

SimpleLink SimpleLink

TCPSinkAgent/TCPFTP

n2


Q: Do we need a receiving Application? Why? Why not?

59

OT l I l iOTcl Implementation$ns sch-link $n1 $n3 5Mb 2ms 10 f { t i 0} {$i $ } {i i} {for {set i 0} {$i < $num_queues} {incr i} {

$ns add-flow $n1 $n3 $i set tcp($i) [new Agent/TCP]; set sink($i) [new Agent/TCPSink] set ftp($i) [new Application/FTP] $ tt h t $ 1 $t ($i) $ tt h t $ 3 $ i k($i)$ns attach-agent $n1 $tcp($i);$ns attach-agent $n3 $sink($i) $ftp($i) attach-agent $tcp($i);$ns connect $tcp($i) $sink($i) $tcp($i) set fid_ $i $ns at 0.0 "$ftp($i) start"

}}proc show_tcp_seqno {} {

global tcp num_queues for {set i 0} {$i < $num_queues} {incr i} {

puts "The final tcp($i) sequence number isputs The final tcp($i) sequence number is [$tcp($i) set t_seqno_]"

} } $ns at 100.0 "show tcp seqno"


$ns at 100.0 show_tcp_seqno $ns at 100.1 "$ns halt" $ns run

60

Si l i R lSimulation Results


OutlineR• Recap



SSummary• Design and ImplementationDesign and Implementation

– Determine what to doDraw a conceptual view– Draw a conceptual view

– OTcl Main componentsC I t l M h i– C++ Internal Mechanism

• Example– Automatic Repeat reQuest– Packet Scheduling Round Robin


Documents

Developing New Modules in NSin NS2in NS2 - UBC ECEteerawat/publications/NS2/14-NewModules.pdf · Developing New Modules in NSin NS2in NS2 Textbook: T. Issariyakul and E. Hossain,