1 2nd european ns-2 workshop day 2 polly huang eth zurich huang 18 & 19 april

1

2nd European ns-2 WorkshopDay 2

Polly Huang

ETH Zurich

http://www.tik.ee.ethz.ch/~huang

18 & 19 April

2

Schedule: Yesterday

9-9.50 overview/intro/essential/getting started

10-10.50 tcl/otcl/ns-2 fundamentals

11-11.50 examples - TCP, RED, multicast, web, wireless

Lunch break

1.30-2.20 lab 1 setup/running examples

2.30-3.20 lab 2 tcl/otcl exercises

3.30-4.20 lab 3 simple ns-2 exercise

4.30-5.00 discussion/feedback

3

Schedule: Today

9-9.50 recap/wired internal

10-10.50 wireless internal/making changes

11-11.50 extending ns-2/case studies

Lunch break

1.30-2.20 lab 4 intermediate ns-2 exercise

2.30-3.20 lab 5 getting data you want

3.30-4.20 lab 6 advanced topic (TBD)

4.30-5.00 discussion/feedback

4

tcl Interpreter With Extensions

tcl8.0

otcl

tclcl

ns-2EventScheduler

Netw

orkC

omponent

5

Example Script

set ns [new Simulator]

set n0 [$ns node]

set n1 [$ns node]

n0 n1

set ftp [new Application/FTP]

$ftp attach-agent $tcp

$ns at 0.2 "$ftp start"

$ns at 1.2 ”exit"

$ns run$ns duplex-link $n0 $n1 1.5Mb

10ms DropTailset tcp [$ns create-connection

TCP $n0 TCPSink $n1 0]

6

Basic ns-2: Covered

• wired & wireless

• unicast & multicast

• TCP & UDP

• errors & network dynamics

• ns & nam tracing

• application-level support

7

Basic ns-2: Also But...

• mobile IP

• satellite

• DiffServ

• emulation

8

Outline for This Morning

• ns-2 Internal

• Making changes

• New components– in otcl– otcl and C++ Linkage– in C++

• Debugging

9

ns-2 Internals

• Discrete Event Scheduler

• Network Topology

• Routing

• Transport

• Application

• Packet Flow

• Packet Format

10

Discrete Event Scheduler

time_, uid_, next_, handler_

head_ ->

handler_ -> handle()

time_, uid_, next_, handler_insert

head_ ->

11

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_

12

Network Topology - Link

n0 n1

enqT_ queue_ deqT_

drophead_ drpT_

link_ ttl_

n1 entry_head_

13

Routing

n0 n1

Addr Classifier

Port Classifier

classifier_

dmux_

entry_

Node entry 0

1enqT_ queue_ deqT_

drophead_ drpT_

link_ ttl_

n1 entry_head_

14

Routing (cont.)

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

15

0

1

Transport

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_addr_=1dst_port_=0


16

Application

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_

Application/FTP



17

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

Application/FTP



18

Packet Format

header

data

ip header

tcp header

rtp header

trace header

cmn header

...

ts_

ptype_

uid_

size_

iface_

19

ns-2 Wireless Internal

• Packet headers

• Mobile node

• Wireless channel

20

Wireless Packet Format

header

data

ts_

ptype_

uid_

size_

iface_

IP header

......

cmn header

LL

MAC 802_11

......

ARP

wireless headers

21

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_

22

Mobile Node: Layer 2

• 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

23

Mobile Node: Layer 1

• 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

24

Wireless Channel

• Duplicate packets to all mobile nodes attached to the channel except the sender

• It is the receiver’s responsibility to decide if it will accept the packet– Collision is handled at individual receiver– O(N2) messages grid keeper

25

Grid-keeper: An Optimization

26


• ns-2 Internal

• Making changes


• debugging

27

Making Changes

• In otcl space– source– recompile

• in C++ space– recompile

28

Adding New Components

• in otcl

• otcl and C++ linkage

• in C++

29

New Component Purely in otcl

• Additional <new_stuff>.tcl file

• source <new_stuff>.tcl

• Adding new files– change Makefile (NS_TCL_LIB), tcl/lib/ns-

lib.tcl– recompile

30

Example: Agent/Message

n0 n1

n4

n5

n2

n3

128Kb, 50ms

10Mb, 1ms 10Mb, 1ms

C Ccrosstraffic

S R

msg agent

31

Agent/Message

• A UDP agent (without UDP header)• Up to 64 bytes user message• Good for fast prototyping a simple idea• Usage requires extending ns functionality

SS RR

pkt: 64 bytesof arbitrary string

Receiver-sideprocessing

32

Agent/Message: Step 1

• Define senderclass Sender –superclass Agent/Messageclass Sender –superclass Agent/Message

# Message format: “Addr Op SeqNo”# Message format: “Addr Op SeqNo”

Sender instproc send-next {} {Sender instproc send-next {} {

$self instvar seq_ agent_addr_$self instvar seq_ agent_addr_

$self send “$agent_addr_ send $seq_”$self send “$agent_addr_ send $seq_”

incr seq_incr seq_

global nsglobal ns

$ns at [expr [$ns now]+0.1] "$self send-next"$ns at [expr [$ns now]+0.1] "$self send-next"

}}

33


• Define sender packet processing

Sender instproc Sender instproc recvrecv msg { msg {

$self instvar agent_addr_$self instvar agent_addr_

set sdr [lindex $msg 0]set sdr [lindex $msg 0]

set seq [lindex $msg 2]set seq [lindex $msg 2]

puts "Sender gets ack $seq from $sdr"puts "Sender gets ack $seq from $sdr"

}}

34


• Define receiver packet processing

Class Receiver –superclass Agent/MessageClass Receiver –superclass Agent/Message

Receiver instproc Receiver instproc recvrecv msg { msg {

$self instvar agent_addr_$self instvar agent_addr_

set sdr [lindex $msg 0]set sdr [lindex $msg 0]

set seq [lindex $msg 2]set seq [lindex $msg 2]

puts “Receiver gets seq $seq from $sdr”puts “Receiver gets seq $seq from $sdr”

$self send “$addr_ ack $seq”$self send “$addr_ ack $seq”

}}

35


• Scheduler and tracing

# Create scheduler# Create scheduler

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

# Turn on Tracing# Turn on Tracing

set fd [new “message.nam” w]set fd [new “message.nam” w]

$ns namtrace-all $fd$ns namtrace-all $fd

36


• Topologyfor {set i 0} {$i < 6} {incr i} {for {set i 0} {$i < 6} {incr i} {

set n($i) [$ns node]set n($i) [$ns node]}}$ns duplex-link $n(0) $n(1) 128kb 50ms DropTail$ns duplex-link $n(0) $n(1) 128kb 50ms DropTail$ns duplex-link $n(1) $n(4) 10Mb 1ms DropTail$ns duplex-link $n(1) $n(4) 10Mb 1ms DropTail$ns duplex-link $n(1) $n(5) 10Mb 1ms DropTail$ns duplex-link $n(1) $n(5) 10Mb 1ms DropTail$ns duplex-link $n(0) $n(2) 10Mb 1ms DropTail$ns duplex-link $n(0) $n(2) 10Mb 1ms DropTail$ns duplex-link $n(0) $n(3) 10Mb 1ms DropTail$ns duplex-link $n(0) $n(3) 10Mb 1ms DropTail

$ns queue-limit $n(0) $n(1) 5$ns queue-limit $n(0) $n(1) 5$ns queue-limit $n(1) $n(0) 5$ns queue-limit $n(1) $n(0) 5

37


• Routing

# Packet loss produced by queueing# Packet loss produced by queueing

# Routing protocol: let’s run distance vector# Routing protocol: let’s run distance vector

$ns rtproto DV$ns rtproto DV

38


• Cross trafficset udp0 [new Agent/UDP]set udp0 [new Agent/UDP]$ns attach-agent $n(2) $udp0$ns attach-agent $n(2) $udp0set null0 [new Agent/NULL]set null0 [new Agent/NULL]$ns attach-agent $n(4) $null0$ns attach-agent $n(4) $null0$ns connect $udp0 $null0$ns connect $udp0 $null0

set exp0 [new Application/Traffic/Exponential]set exp0 [new Application/Traffic/Exponential]$exp0 set rate_ 128k$exp0 set rate_ 128k$exp0 attach-agent $udp0$exp0 attach-agent $udp0$ns at 1.0 “$exp0 start”$ns at 1.0 “$exp0 start”

39


• Message agentsset sdr [new Sender]set sdr [new Sender]$sdr set packetSize_ 1000$sdr set packetSize_ 1000

set rcvr [new Receiver]set rcvr [new Receiver]$rcvr set packetSize_ 40$rcvr set packetSize_ 40

$ns attach $n(3) $sdr$ns attach $n(3) $sdr$ns attach $n(5) $rcvr$ns attach $n(5) $rcvr$ns connect $sdr $rcvr$ns connect $sdr $rcvr$ns connect $rcvr $sdr$ns connect $rcvr $sdr$ns at 1.1 “$sdr send-next”$ns at 1.1 “$sdr send-next”

40


• End-of-simulation wrapper (as usual)

$ns at 2.0 finish$ns at 2.0 finish

proc finish {} {proc finish {} {

global ns fdglobal ns fd

$ns flush-trace$ns flush-trace

close $fdclose $fd

exit 0exit 0

}}

41

Agent/Message: Result

• Example output> ./ns msg.tcl> ./ns msg.tclReceiver gets seq 0 from 0Receiver gets seq 0 from 0Sender gets ack 0 from 1Sender gets ack 0 from 1Receiver gets seq 1 from 0Receiver gets seq 1 from 0Sender gets ack 1 from 1Sender gets ack 1 from 1Receiver gets seq 2 from 0Receiver gets seq 2 from 0Sender gets ack 2 from 1Sender gets ack 2 from 1Receiver gets seq 3 from 0Receiver gets seq 3 from 0Sender gets ack 3 from 1Sender gets ack 3 from 1Receiver gets seq 4 from 0Receiver gets seq 4 from 0Sender gets ack 4 from 1Sender gets ack 4 from 1Receiver gets seq 5 from 0Receiver gets seq 5 from 0

42

Add Your Changes into ns

TK8.0 OTcl tclclTcl8.0 ns-2 nam-1

tcl

ex test lib

...

...

examples validation tests

C++ code

OTcl code

ns-allinone

mcastmysrc

msg.tcl

43

Add Your Change into ns

• tcl/lib/ns-lib.tclClass SimulatorClass Simulator……source ../mysrc/msg.tclsource ../mysrc/msg.tcl

• MakefileNS_TCL_LIB = \NS_TCL_LIB = \tcl/mysrc/msg.tcl \tcl/mysrc/msg.tcl \……

– Or: change Makefile.in, make distcleanmake distclean, then ./configure --enable-debug./configure --enable-debug

44

Extending ns in C++

• Adding code in <new_stuff>.{cc,h} files– Change Makefile– make depend– recompile

45

Guidelines

• Decide position in class hierarchy– I.e., which class to derive from?

• Create new packet header (if necessary)

• Create C++ class, fill in methods

• Define otcl linkage (if any)

• Write otcl code (if any)

• Build (and debug)

46

Important Basics

• class hierarchy

• otcl and C++ linkage

47

Class HierarchyTclObject

NsObject

Connector Classifier

Delay AddrClassifierAgent McastClasifierQueue Trace

DropTail RED TCP Enq Deq Drop

Reno SACK

48

otcl and C++: The Duality

C++ OTcl

Pure C++objects

Pure OTclobjects

C++/OTcl split objects

ns

49

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

50

TclObject

• Basic hierarchy in ns for split objects

• Mirrored in both C++ and otcl

• Exampleset tcp [new Agent/TCP]set tcp [new Agent/TCP]

$tcp set packetSize_ 1024$tcp set packetSize_ 1024

$tcp advanceby 5000$tcp advanceby 5000

51

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

52

TclObject::bind()

• Link C++ member variables to otcl object variables

• C++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

53

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

54

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

55

TclObject::command()

• Implement otcl methods in C++

• Trap point: otcl method cmd{}

• Send all arguments after cmd{} call to TclObject::command()

56

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);}

57

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

58

TclObject: Creation and Deletion

• Global procedures: new{}, delete{}

• Exampleset tcp [new Agent/TCP]set tcp [new Agent/TCP]

……

delete $tcpdelete $tcp

59

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

60

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;

61

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()

62

Class Tcl

• Singleton class with a handle to Tcl interpreter

• Usage– Invoke otcl procedure– Obtain otcl evaluation results– Pass a result string to otcl– Return success/failure code to otcl

63

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;

}

64

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()); }

65

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

66

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

67

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

68

Creating New Components

• new agent, old packet headers

• new agent, new packet header

69

New Agent, Old Header

• TCP jump start– Wide-open transmission window at the

beginning– From cwnd_ += 1cwnd_ += 1 To cwnd_ = MAXWIN_cwnd_ = MAXWIN_

70

TCP Jump Start – Step 1TclObject

NsObject




Reno SACK JS

71

TCP Jump Start – Step 2

• New file: tcp-js.h

class JSTCPAgent : public TcpAgent {class JSTCPAgent : public TcpAgent {

public:public:

virtual void set_initial_window() {virtual void set_initial_window() {

cwnd_ = MAXWIN_;cwnd_ = MAXWIN_;

}}

private:private:

int MAXWIN_;int MAXWIN_;

};};

72

TCP Jump Start – Step 3

• New file: tcp-js.ccstatic JSTcpClass : public TclClass {public:

JSTcpClass() : TclClass("Agent/TCP/JS") {}TclObject* create(int, const char*const*) {

return (new JSTcpAgent());}

};JSTcpAgent::JSTcpAgent() {

bind(“MAXWIN_”, MAXWIN_);}

73

New Agent, New Header

• Example: Agent/Message– New packet header for 64-byte message– New transport agent to process this new header

74

New Packet Header

• Create new header structure• Enable tracing support of new header• Create static class for otcl linkage

(packet.h)• Enable new header in otcl (tcl/lib/ns-

packet.tcl)• This does not apply when you add a new

field into an existing header!

75

How Packet Header WorksPacket

next_

hdrlen_

bits_ size determinedat compile time

size determinedat compile time

size determinedat compile time

……

hdr_cmn

hdr_ip

hdr_tcp

size determinedat simulatorstartup time

(PacketHeaderManager)

PacketHeader/Common

PacketHeader/IP

PacketHeader/TCP

76

New Packet Header – Step 1

• Create header structurestruct hdr_msg {struct hdr_msg {

char msg_[64];char msg_[64];static int offset_;static int offset_;inline static int& offset() { return offset_; }inline static int& offset() { return offset_; }inline static hdr_msg* access(Packet* p) {inline static hdr_msg* access(Packet* p) {

return (hdr_msg*) p->access(offset_);return (hdr_msg*) p->access(offset_);}}/* per-field member functions *//* per-field member functions */char* msg() { return (msg_); }char* msg() { return (msg_); }int maxmsg() { return (sizeof(msg_)); }int maxmsg() { return (sizeof(msg_)); }

};};

77


• PacketHeader/Messagestatic class MessageHeaderClass : static class MessageHeaderClass :

public PacketHeaderClass {public PacketHeaderClass {

public:public:

MessageHeaderClass() : MessageHeaderClass() : PacketHeaderClass("PacketHeader/Message",PacketHeaderClass("PacketHeader/Message",

sizeof(hdr_msg)) {sizeof(hdr_msg)) {

bind_offset(&hdr_msg::offset_);bind_offset(&hdr_msg::offset_);

}}

} class_msghdr;} class_msghdr;

78


• Enable tracing (packet.h):enum packet_t {enum packet_t {

PT_TCP,PT_TCP,……,,PT_MESSAGE,PT_MESSAGE,PT_NTYPE // This MUST be the LAST onePT_NTYPE // This MUST be the LAST one

};};class p_info {class p_info {

…………name_[PT_MESSAGE] = “message”;name_[PT_MESSAGE] = “message”;name_[PT_NTYPE]= "undefined";name_[PT_NTYPE]= "undefined";

…………};};

79


• Register new header (tcl/lib/ns-packet.tcl)

foreach pair {foreach pair {

{ Common off_cmn_ }{ Common off_cmn_ }

……

{ Message off_msg_ }{ Message off_msg_ }

}}

80

Packet Header: Caution

• Some old code, e.g.:RtpAgent::RtpAgent() {RtpAgent::RtpAgent() {

…… ……

bind(“off_rtp_”, &off_rtp);bind(“off_rtp_”, &off_rtp);

}}

…………

hdr_rtp* rh = (hdr_rtp*)p->access(off_rtp_);hdr_rtp* rh = (hdr_rtp*)p->access(off_rtp_);

• Don’t follow this example!

81

Agent/Message – Step 1TclObject

NsObject




Reno SACK

Message

82

Agent/Message – Step 2

• C++ class definition// Standard split object declaration// Standard split object declaration

static …static …

class MessageAgent : public Agent {class MessageAgent : public Agent {

public:public:

MessageAgent() : Agent(MessageAgent() : Agent(PT_MESSAGEPT_MESSAGE) {}) {}

virtual int command(int argc, const char*const* virtual int command(int argc, const char*const* argv);argv);

virtual void recv(Packet*, Handler*);virtual void recv(Packet*, Handler*);

};};

83


• Packet processing: sendint MessageAgent::command(int, const char*const* argv)int MessageAgent::command(int, const char*const* argv){{

Tcl& tcl = Tcl::instance();Tcl& tcl = Tcl::instance();if (strcmp(argv[1], "send") == 0) {if (strcmp(argv[1], "send") == 0) {

Packet* pkt = allocpkt();Packet* pkt = allocpkt();hdr_msg* mh = hdr_msg::access(pkt);hdr_msg* mh = hdr_msg::access(pkt);// We ignore message size check...// We ignore message size check...strcpy(mh->msg(), argv[2]);strcpy(mh->msg(), argv[2]);send(pkt, 0);send(pkt, 0);return (TCL_OK);return (TCL_OK);

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

}}

84


• Packet processing: receivevoid MessageAgent::recv(Packet* pkt, Handler*)void MessageAgent::recv(Packet* pkt, Handler*){{

hdr_msg* mh = hdr_msg::access(pkt);hdr_msg* mh = hdr_msg::access(pkt);

// OTcl callback// OTcl callbackchar wrk[128];char wrk[128];sprintf(wrk, "%s recv {%s}", name(), mh->msg());sprintf(wrk, "%s recv {%s}", name(), mh->msg());Tcl& tcl = Tcl::instance();Tcl& tcl = Tcl::instance();tcl.eval(wrk);tcl.eval(wrk);

Packet::free(pkt);Packet::free(pkt);}}

85


• ns-2 Internal

• Making changes


• debugging

86

My ns dumps otcl scripts!

– Find the last 10-20 lines of the dump– Is the error related to “_o4 cmd …” ?

• Check your command()

– Otherwise, check the otcl script pointed by the error message

87

Debugging

• printf() and puts “”

• gdb

• tcl debugger– http://expect.nist.gov/tcl-debug/– place debug 1 at the appropriate location– trap to debugger from the script– single stepping through lines of codes– examine data and code using Tcl-ish commands

88

C++/otcl Debugging

• Usual technique– Break inside command()– Cannot examine states inside otcl!

• Solution– Execute tcl-debug inside gdb

89

C++/otcl Debugging(gdb) (gdb) call Tcl::instance().eval(“debug 1”)call Tcl::instance().eval(“debug 1”)15: lappend auto_path $dbg_library15: lappend auto_path $dbg_librarydbg15.3> wdbg15.3> w*0: application*0: application 15: lappend auto_path $dbg_library15: lappend auto_path $dbg_librarydbg15.4> Simulator info instancesdbg15.4> Simulator info instances_o1_o1dbg15.5> _o1 nowdbg15.5> _o1 now00dbg15.6> # and other fun stuffdbg15.6> # and other fun stuffdbg15.7> dbg15.7> cc(gdb) where(gdb) where#0 0x102218 in write()#0 0x102218 in write()............

90

Memory Debugging in ns

• Purify• Gray Watson’s dmalloc library

– http://www.dmalloc.com – make distclean– ./configure --with-dmalloc=<dmalloc_path>– Analyze results: dmalloc_summarize

http://www.dmalloc.com/

91

dmalloc: Usage

• Turn on dmalloc– alias dmalloc ’eval ‘\dmalloc –C \!*`’– dmalloc -l log low

• dmalloc_summarize ns < logfile– ns must be in current directory– itemize how much memory is allocated in each

function

92

Memory Leaks

• Purify or dmalloc, but be careful about split objects:for {set i 0} {$i < 500} {incr i} {for {set i 0} {$i < 500} {incr i} {

set a [new set a [new RandomVariable/Constant]RandomVariable/Constant]

}}

– It leaks memory, but can’t be detected!

• Solution– Explicitly delete EVERY split object that was

new-ed

93

Memory Conservation Tips

• Avoid trace-alltrace-all

• Use arrays for a sequence of variables– Instead of n$in$i, say n($i)n($i)

• Avoid OTcl temporary variables

• Use dynamic binding– delay_bind()delay_bind() instead of bind()bind()– See object.{h,cc}

94

Scalability vs Flexibility

• It’s tempting to write all-otcl simulation– Benefit: quick prototyping– Cost: memory + runtime

• Solution– Control the granularity of your split object by

migrating methods from otcl to C++

95

The Merit of OTcl

Program size, complexity

C/C++ OTcl

• Smoothly adjust the granularity of scripting to balance extensibility and performance

• With complete compatibility with existing simulation scripts

high low

split objects

96

Object Granularity Tips

• Functionality– Per-packet processing C++– Hooks, frequently changing code otcl

• Data management– Complex/large data structure C++– One-time configuration variables otcl

98

Case Studies

• Network Layer: Network Interface (packet labeler)

• Transport Layer: TCP Jump Start

• Application Layer: Message agent (ping)

99

Case 1: Network Layer

• Network Interface - Packet Labeler

n0 n1 n2

NetworkInterface A NetworkInterface B

100

Class Hierarchy

TclObject

NsObject



DropTail RED TCP Enq Dnq Drop

Reno SACK

Network Interface

101

Network Interface Labeler

• class NetworkInterface– NetworkInterface()– recv(pkt)

• pkt->iface() = label_

– send(pkt)• target->recv(pkt)

– command()• label argv {label_ = argv}

• TclClass(“networkinterface”)

C++ otcl

NetworkInterface networkinterface

set iface [new networkinteface]$iface label A

command(): label

102

Case 2: Transport Layer

• TCP Jump Start– from cwnd += 1– to cwnd = maxwin

103

Class Hierarchy

TclObject

NsObject




Reno SACK JS

104

TCP Jump Start

• class JSTcpAgent– openwin()– slowdown()

• TclClass(“Agent/TCP/JS”)

105

Case 3: Application Layer

• Message sender (ping)

n0 n1 n2

Message Sender Message Sender

106

Class Hierarchy

TclObject

NsObject




Reno SACK MessageAgent

107

Message Sender

• class MessageAgent– MessageAgent()– recv()– send()– command()

• send {send()}

• TclClass(“Agent/Message”)

C++ otcl

MessageAgent Agent/Message

set msg [new Agent/Message]$msg send

command(): send

1 2nd european ns-2 workshop day 2 polly huang eth zurich huang 18 & 19 april

Documents

n1 entry

link n0n1 link n1n0

ns node n0n1

ns node set n1

ns duplexlink

basic ns

discussionfeedback slide

extending ns