NS-2 Internal Structure and Extension 

ICU 공학부

김승운

(swkim@icu.ac.kr)

 

2  

Contents 

• Internal structure of NS-2 objects
• NS-2 Extension using OTcl object inheritance
• NS-2 Extension using C++ object inheritance
• Debugging

 
 

• Original Materials from
  • http://www.isi.edu/nsnam/dist/ns-workshop00/
  • http://www.isi.edu/nsnam/ns/ns-tutorial/tutorial-02/index.html
  • Network Laboratory ns-2 tutorial by Changhee Joo (http://netlab.snu.ac.kr/~cjoo/)

 

3  

Contents 

• Internal structure of NS-2 objects
• NS-2 Extension using OTcl object inheritance
• NS-2 Extension using C++ object inheritance
• Debugging

 

4  

Ns Internals 

• Tcl commands translates into
  • series of object creation
  • plumbing of these objects
• Step-by-step review of how each network component gets set up in ns
  • Network Topology: Node, Link
  • Routing
  • Transport: Agent
  • Packet flow
  • Packet format

 

5  

Hierarchy of Network Components 

TclObject 

NsObject 

Connector 

Classifier 

Delay 

AddrClassifier 

Agent 

McastClasifier 

Queue 

Trace 

DropTail 

RED 

TCP 

Enq 

Deq 

Drop 

Reno 

SACK 

Handler

 

6  

TclOject & NsObjevt 

• TclObject
  • Defined in $ns/../tclcl-1.15/{tclcl.h, Tcl.cc}
  • Functions of command, trace, bind
• NsObject
  • Defined in $ns/common/object.{h, cc}
  • Inherit class TclObject
  • Functions of recv, handle, reset
    • handle(Event *e) { recv(Packet *e); }

 

7  

Connector 

• Single input, single output
  • Used for normal packet processing
  • Examples: Queue, Agent, Delay, Trace
• Defined in $ns/common/connector.{h, cc}
• Variables:
  • NsObject* target_
• Functions
  • send(Packet* p, Handler* h) {target_->recv(p,h);}
  • recv(Packet* p, Handler* h) {send(p,h);}
  • drop(Packet* p) {Packet::free(p);}

 

Connector 

recv(p,h) 

send(p,h)

 

8  

Classifier 

• Single input, multiple output
  • Used for routing
  • Examples: AddrClassifier, PortClassifier
• Defined in $ns/classifier/classifier.{h, cc}
• Variables:
  • NsObject** slot_
  • NsObject* default_target_
• Functions
  • install(int slot, NsObject* p) {slot_[slot] = p;}
  • find(Packet* p) {return slot_[classify(p)];}
  • recv(Packet* p, Handler* h) { 
        NsObject* node = find(p); 
        node->recv(p, h); }

 

Classifier

 

9  

Network Topology: Node 

• Defined in $ns/common/node.{h, cc}, $ns/tcl/lib/ns-node.tcl
• Standalone class in Otcl
• Most components are TclObjects

 

n0 

n1 

Addr Classifier 

Port Classifier 

classifier_ 

dmux_ 

entry_ 

Node entry 

Unicast Node 

Multicast Classifier 

classifier_ 

dmux_ 

entry_ 

Node entry 

Multicast Node 

multiclassifier_ 

set n0 [$ns_ node] 

set ns_ [new Simulator –multicast on]

set n1 [$ns_ node] 

0 

0 

1

 

10  

Node Addressing 

• Two basic address styles available:
  • flat and hierarchical
• Default flat address:
  • 32 bits each for node and port id
• Default hier address:
  • 3 levels of hierarchy
  • 10 11 11   or   1 9 11 11 if mcast specified
• Different bit allocation possible for specific hier addresses

 

11  

Hierarchical Node 

n2 

Node

entry 

Level 1 

Level 2 

Level 3 

Address

classifier 

To Port

demux 

$ns_ node-config –addressing hier

 

12  

Network Topology: Link 

n0 

n1 

enqT_ 

queue_ 

deqT_ 

drophead_ 

drpT_ 

link_ 

ttl_ 

n1 entry_ 

head_ 

tracing 

simplex link 

duplex link 

[$ns_ duplex-link $n0 $n1 5Mb 2ms drop-tail] 

• Defined in $ns/tcl/lib/ns-link.tcl
• Standalone class in Otcl

 

13  

Queue 

• Location where packets may be held or dropped
• Implement
  • Packet scheduling – CBQ, FQ, SFQ, DRR
  • Buffer Management – drop-tail(FIFO), RED
• Defined in $ns/queue/queue.{h, cc}
  • Inherit class Connector
  • Include an instance of PacketQueue
  • Virtual functions of enque and deque
    • recv calls enque
    • resume calls deque and target_->recv

 

Queue 

PacketQueue 

recv 

resume 

enque 

deque

 

14  

Queue blocking 

• Queue is blocked (stop transmitting)
  • When a packet is in transit
• Transmit a packet with queue handler
  • target_->recv(p, &ph_);
  • target_ (LinkDelay) is responsible for scheduling the handler after transmission
  • Hander calls resume

 

15  

Transport 

n0 

n1 

Addr Classifier 

Port Classifier 

classifier_ 

dmux_ 

entry_ 

Agent/TCP 

agents_ 

Addr Classifier 

Port Classifier 

classifier_ 

dmux_ 

entry_ 

Agent/TCPSink 

agents_ 

dst_=1.0 

dst_=0.0 

set tcp [new Agent/TCP]

$ns_ attach-agent $n0 $tcp 

set tcpsink [new Agent/TCPSink]

$ns_ attach-agent $n1 $tcpsink 

$ns_ connect $tcp $tcpsink 

0 

0 

1 

0

 

16  

Agent 

• Defined in $ns/common/agent.{h,cc} & $ns/tcl/lib/ns-agent.tcl
• Internal states
  • Node address
  • Destination address
  • Fixed packet size
  • Type in packet header (protocol type)
  • IP flow ID, priority, Flags

 

17  

Agent Functions 

• Packet allocation
  • allocpkt()
• Main entry point
  • recv(Packet*, Handler*)
  • For incoming and/or outgoing packets
    • TcpAgent for incoming ACK, PingAgent for both
  • Packet forwarding
    • send(Packet* p, Handler* h) { 
          target_->recv(p, h); 
      }

 

18  

Application: Traffic Generator 

n0 

n1 

Addr Classifier 

Port Classifier 

classifier_ 

dmux_ 

entry_ 

Agent/TCP 

agents_ 

Addr Classifier 

Port Classifier 

classifier_ 

dmux_ 

entry_ 

Agent/TCPSink 

agents_ 

dst_=1.0 

dst_=0.0 

Application/FTP 

set ftp [new Application/FTP]

$ftp attach-agent $tcp

$ns at 1.2 “$ftp start” 

0 

0 

1 

0

 

19  

Routing  

n0 

n1 

Addr Classifier 

Port Classifier 

classifier_ 

dmux_ 

entry_ 

Node entry 

0 

1 

enqT_ 

queue_ 

deqT_ 

drophead_ 

drpT_ 

link_ 

ttl_ 

n1 entry_ 

head_ 

0 

Agent/TCP 

agents_ 

Application/FTP

 

20  

n0 

n1 

Addr Classifier 

Port Classifier 

classifier_ 

dmux_ 

entry_ 

0 

1 

Addr Classifier 

Port Classifier 

classifier_ 

dmux_ 

entry_ 

1 

0 

Link n0-n1 

Link n1-n0 

Agent/TCP 

agents_ 

Application/FTP 

Agent/TCP 

Routing (con’t)

 

21  

Routing 

• Three function blocks
  • Routing agent
    • Exchange routing packets
  • Route logic
    • Perform actual route computation
  • Classifier
    • Forward packet

 

22  

Routing module (RtModule) 

• Routing Module
  • Manage function blocks
  • Interface with node to organize its own classifier
• Functionalities
  • Management – register/unregister at node
  • Routing – add/delete-route
  • Transport – attach/detach agent
• Node configures its classifiers through RtModule

 

23  

When add-route? 

• $ns run
  • $ns/tcl/lib/ns-{lib, rtmodule, route}.tcl
  • Simulator get-routelogic
    • New RouteLogic
  • RouteLogic configure
    • Agent/rtProto/Static init-all (or other rtProto)
    • Simulator compute-routes
    • Simulator compute-flat-routes (or hier-routes)
  • RouteLogic compute
  • Simulator populate-flat-classifier
    • Node add-route (for each node)

 

24  

Plumbing: Packet Flow 

0 

1 

n0 

n1 

Addr Classifier 

Port Classifier 

entry_ 

0 

Agent/TCP 

Addr Classifier 

Port Classifier 

entry_ 

1 

0 

Link n0-n1 

Link n1-n0 

0 

Agent/TCPSink 

dst_=1.0 

dst_=0.0 

Application/FTP

 

25  

Packet 

• Fundamental unit of exchange between objects
  • Information to link a packet on to a list or queue
  • Contain packet headers
• Packet Header
  • Per-protocol information
  • New protocols may define their own header or may extend existing headers

 

26  

Packet Format 

header 

data 

ip header 

tcp header 

rtp header 

trace header 

cmn header 

... 

ts_ 

ptype_ 

uid_ 

size_ 

iface_

 

27  

Wireless Network Components 

• Packet headers
• Mobile node
• Wireless channel
• Forwarding and routing

 

28  

Wireless Packet Format 

header 

data 

ts_ 

ptype_ 

uid_ 

size_ 

iface_ 

IP header 

...... 

cmn header 

LL 

MAC 802_11 

...... 

ARP 

wireless

headers

 

29  

Mobile Node Abstraction 

• Location
  • Coordinates (x,y,z)
• Movement
  • Speed, direction, starting/ending location, time ...

 

30  

Portrait of A Mobile Node 

Node 

ARP 

Propagation and antenna models  

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 

protocol

agent 

routing

agent 

addr

classifier 

port

classifier 

255 

IFQ 

IFQ 

defaulttarget_

 

31  

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

 

32  

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

 

33  

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

 

34  

Contents 

• Internal structure of NS-2 objects
• NS-2 Extension using OTcl object inheritance
• NS-2 Extension using C++ object inheritance
• Debugging

 

35  

ns Directory Structure 

TK8.4 

OTcl 

tclcl 

Tcl8.4 

ns-2 

nam-1 

tcl 

ex 

test 

lib 

... 

... 

examples 

validation tests 

C++ code 

OTcl code 

ns-allinone 

mcast

 

36  

Extending ns in OTcl 

• If you don’t want to compile
  • source your changes in your sim scripts
• Otherwise
  • Modifying code; recompile
  • Adding new files
    • Change Makefile (NS_TCL_LIB), tcl/lib/ns-lib.tcl
    • Recompile

 

37  

Example: Agent/Message 

n0 

n1 

n4 

n5 

n2 

n3 

128Kb, 50ms 

10Mb, 1ms 

10Mb, 1ms 

C 

C 

cross

traffic 

S 

R 

msg agent

 

38  

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

 

S 

R 

pkt: 64 bytes

of arbitrary string  

Receiver-side

processing

 

39  

Agent/Message: Step 1 

• Define sender

    Class Sender –superclass Agent/Message 

    # Message format: “Addr Op SeqNo”

    Sender instproc send-next {} {

          $self instvar seq_ agent_addr_

          $self send “$agent_addr_ send $seq_”

          incr seq_

          global ns

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

    }

 

40  

Agent/Message: Step 2 

• Define sender packet processing

 

    Sender instproc recv msg {

          $self instvar agent_addr_

          set sdr [lindex $msg 0]

          set seq [lindex $msg 2]

          puts "Sender gets ack $seq from $sdr"

    }

 

41  

Agent/Message: Step 3 

• Define receiver packet processing

 

    Class Receiver –superclass Agent/Message

    Receiver instproc recv msg {

          $self instvar agent_addr_

          set sdr [lindex $msg 0]

          set seq [lindex $msg 2]

          puts “Receiver gets seq $seq from $sdr”

          $self send “$agent_addr_ ack $seq”

    }

 

42  

Agent/Message: Step 4 

• Scheduler and tracing

 

    # Create scheduler

    set ns [new Simulator] 

    # Turn on Tracing

    set fd [open message.tr w]

    $ns trace-all $fd

 

43  

Agent/Message: Step 5 

• Topology

    for {set i 0} {$i < 6} {incr i} {

          set n($i) [$ns node]

    }

    $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(5) 10Mb 1ms DropTail

    $ns duplex-link $n(0) $n(2) 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(1) $n(0) 5

 

44  

Agent/Message: Step 6 

• Routing

 

    # Packet loss produced by queueing 

    # Routing protocol: let’s run distance vector

    $ns rtproto DV 

 

45  

Agent/Message: Step 7 

• Cross traffic

    set udp0 [new Agent/UDP]

    $ns attach-agent $n(2) $udp0

    set null0 [new Agent/Null]

    $ns attach-agent $n(4) $null0

    $ns connect $udp0 $null0 

    set exp0 [new Application/Traffic/Exponential]

    $exp0 set rate_ 128k

    $exp0 attach-agent $udp0

    $ns at 1.0 “$exp0 start”

 

46  

Agent/Message: Step 8 

• Message agents

    set sdr [new Sender]

    $sdr set seq_ 0

    $sdr set packetSize_ 1000 

    set rcvr [new Receiver]

    $rcvr set packetSize_ 40 

    $ns attach-agent $n(3) $sdr

    $ns attach-agent $n(5) $rcvr

    $ns connect $sdr $rcvr

    $ns at 1.1 “$sdr send-next” 

 

47  

Agent/Message: Step 9 

• End-of-simulation wrapper (as usual)

 

    $ns at 2.0 finish

    proc finish {} {

          global ns fd

          $ns flush-trace

          close $fd

          exit 0

    }

    $ns run

 

48  

Agent/Message: Result 

• Example output

    % ./ns msg.tcl

Receiver gets seq 0 from 3

Sender gets ack 0 from 5

Receiver gets seq 1 from 3

Sender gets ack 1 from 5

Receiver gets seq 2 from 3

Sender gets ack 2 from 5

Receiver gets seq 4 from 3

Sender gets ack 4 from 5

Receiver gets seq 7 from 3

 

49  

Add Your Changes into ns 

TK8.3 

OTcl 

tclcl 

Tcl8.3 

ns-2 

nam-1 

tcl 

ex 

test 

lib 

... 

... 

examples 

validation tests 

C++ code 

OTcl code 

ns-allinone 

mcast 

mysrc 

msg.tcl

 

50  

Add Your Change into ns 

• tcl/lib/ns-lib.tcl

    Class Simulator

    …

    source ../mysrc/msg.tcl

• Makefile

NS_TCL_LIB = \

    tcl/mysrc/msg.tcl \

    …

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

  make depend and make

 

51  

Contents 

• Internal structure of NS-2 objects
• NS-2 Extension using OTcl object inheritance
• NS-2 Extension using C++ object inheritance
• Debugging

 

52  

Extending ns in C++ 

• Modifying code
  • make depend
  • Recompile
• Adding code in new files
  • Change Makefile
  • make depend
  • recompile

 

53  

Creating New Components 

• Guidelines
• Two styles
  • New agent based on existing packet headers
  • Add new packet header

 

54  

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)

 

55  

New Agent,  Existing Header 

• TCP jump start
  • Wide-open transmission window at the beginning
  • From cwnd_ += 1 To cwnd_ = MAXWIN_

 

56  

TCP Jump Start – Step 1 

TclObject 

NsObject 

Connector 

Classifier 

Delay 

AddrClassifier 

Agent 

McastClasifier 

Queue 

Trace 

DropTail 

RED 

TCP 

Enq 

Deq 

Drop 

Reno 

SACK 

JS 

Handler

 

57  

Reminder: C++/OTcl Linkage 

$ns/tcp/tcp.{h,cc}

class TcpAgent : public Agent {

public:

    TcpAgent();

    …

}

static class TcpClass: public TclClass {

public:

    TcpClass() : TclClass(“Agent/Tcp”){}

    TclObject* create(int , const char*const*) {

          return (new TcpAgent()); }

} class_tcp; 

Class Definition 

TclClass

 

58  

Reminder: C++/OTcl Linkage 

$ns/tcp/tcp.{h,cc}

TcpAgent::TcpAgent(): Agent(PT_TCP), … {

    bind_(“t_seqno_”, &t_seqno_);

    …

}

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

    if (argc == 3) {

          if (strcmp(argv[1], “advance”) == 0) {

                …  

          }… } … 

}

$ns/tcl/lib/ns-agent.tcl: 

    Agent/TCP instproc init {} {… }

$ns/tcl/lib/ns-default.tcl: 

    Agent/TCP set t_seqno_ 0  … 

Class Body 

Otcl setting

 

59  

TCP Jump Start – Step 2 

• New file: tcp-js.h

#include “tcp.h”

class JSTCPAgent : public TcpAgent {

public:

    virtual void set_initial_window() {

          cwnd_ = MAXWIN_;

    }

private:

    int MAXWIN_;

};

 

60  

TCP Jump Start – Step 3 

• New file: tcp-js.cc

#include <tclcl.h>

#include “tcp.h”

#include “tcp-js.h”

static class JSTcpClass : public TclClass {

public:

    JSTcpClass() : TclClass("Agent/TCP/JS") {}

    TclObject* create(int, const char*const*){

          return (new JSTcpAgent());

    }

} tcpjs_agent;

JSTcpAgent::JSTcpAgent() {

    bind(“MAXWIN_”, &MAXWIN_);

}

 

61  

TCP Jump Start – Step 4 

• Set default value of MAXWIN_ in tcl
  • $ns/tcl/lib/ns-default.tcl
    • Agent/TCP/JS set MAXWIN_ 1
• Add tcp-js.o in Makefile.in
  • $ns/Makefile.in
    • OBJ_CC = ... 
                     tcp/tcp-js.o \ 
           @V_STOLOBJ@
• Re-configure, make depend and recompile

% configure --enable-debug –with-tcldebug=../tcl-debug-2.0

% make depend

% make

 

62  

TCP Jump Start – Step 5 

• Create an instance of jump-start TCP in your tcl script tcp-js.tcl
  • set tcp [new Agent/TCP/JS]
• Set value of MAXWIN_ for the simulation
  • e.g., $tcp set MAXWIN_ 10;# set MAXWIN_ value to 10
• Run:

% ns tcp-js.tcl

 

63  

TCP vs TCP-JS 

TCP: initial cwnd = 1 

TCP-JS: initial cwnd = 10 

time 

time 

Packet sequence number

 

64  

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!

 

65  

Packet Format 

header 

data 

ip header 

tcp header 

rtp header 

trace header 

cmn header 

... 

ts_ 

ptype_ 

uid_ 

size_ 

iface_

 

66  

How Packet Header Works 

Packet 

next_ 

hdrlen_ 

bits_ 

size determined

at compile time 

size determined

at compile time 

size determined

at compile time 

…… 

hdr_cmn 

hdr_ip 

hdr_tcp 

size determined

at simulator

startup time

(PacketHeaderManager) 

PacketHeader/Common 

PacketHeader/IP 

PacketHeader/TCP

 

67  

Example: Agent/Message 

• New packet header for 64-byte message
• New transport agent to process this new header

 

68  

New Packet Header – Step 1 

• Create header structure
  • Construct your own fields
  • Define offset_ and access function

struct hdr_msg {

    char msg_[64];

    static int offset_;

    inline static int& offset() { return offset_; }

    inline static hdr_msg* access(Packet* p) {

          return (hdr_msg*) p->access(offset_);

    }

    /* per-field member functions */

    char* msg() { return (msg_); }

    int maxmsg() { return (sizeof(msg_)); }

};

 

69  

New Packet Header – Step 2 

• Create a static class performing Otcl linkage
  • Bind offset_ using bind_offset in its constructor
• PacketHeader/Message

static class MessageHeaderClass :

                            public PacketHeaderClass {

public:

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

                                   sizeof(hdr_msg)) {

          bind_offset(&hdr_msg::offset_);

    }

} class_msghdr;

 

70  

New Packet Header – Step 3 

• Enable tracing (packet.h):

enum packet_t {

    PT_TCP,

    …,

    PT_MESSAGE, // Packet Type

    PT_NTYPE // This MUST be the LAST one

};

class p_info {

    ……

          name_[PT_MESSAGE] = “message”;

          name_[PT_NTYPE]= "undefined";

    ……

};

 

71  

New Packet Header – Step 4 

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

 

foreach prot {

    Common

    …

    Message # Protocol name

    …  }{

  add-packet-header $prot

}

 

72  

Accessing the Header – Step 5 

• hdr_msg* mh = hdr_msg::access(p);
  • Calls p->access with offset_ of Message
  • Returns starting location of Message header
• Accesssing Message structure
  • mh->msg()

 

73  

Agent/Message – Step 1 

TclObject 

NsObject 

Connector 

Classifier 

Delay 

AddrClassifier 

Agent 

McastClasifier 

Queue 

Trace 

DropTail 

RED 

TCP 

Enq 

Deq 

Drop 

Reno 

SACK 

Message

 

74  

Agent/Message – Step 2 

• C++ class definition

// Standard split object declaration

static … 

class MessageAgent : public Agent {

public:

    MessageAgent() : Agent(PT_MESSAGE) {}

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

    virtual void recv(Packet*, Handler*);

};

static class MessageClass : public TclClass {

public:

        MessageClass() : TclClass("Agent/Message") {}

        TclObject* create(int, const char*const*) {

                return (new MessageAgent());

        }

} class_message;

 

75  

Agent/Message – Step 3 

• Packet processing: send

int MessageAgent::command(int, const char*const* argv)

{

    Tcl& tcl = Tcl::instance();

    if (strcmp(argv[1], "send") == 0) {

           Packet* pkt = allocpkt();

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

           // We ignore message size check...

           strcpy(mh->msg(), argv[2]);

           send(pkt, 0);

          return (TCL_OK);

    }

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

}

 

76  

Agent/Message – Step 4 

• Packet processing: receive

void MessageAgent::recv(Packet* pkt, Handler*)

{

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

    // OTcl callback

    char wrk[128];

    sprintf(wrk, "%s recv {%s}", name(), mh->msg());

    Tcl& tcl = Tcl::instance();

    tcl.eval(wrk); 

    Packet::free(pkt);

}

 

77  

Contents 

• Internal structure of NS-2 objects
• NS-2 Extension using OTcl object inheritance
• NS-2 Extension using C++ object inheritance
• Debugging
  • OTcl/C++, memory

 

78  

Debugging C++ in ns 

• C++/OTcl debugging

 

• Memory debugging
  • purify
  • dmalloc

 

79  

C++/OTcl Debugging 

• Usual technique
  • Break inside command()
  • Cannot examine states inside OTcl!
• Solution
  • Execute tcl-debug inside gdb

 

80  

C++/OTcl Debugging 

(gdb) call Tcl::instance().eval(“debug 1”)

15: lappend auto_path $dbg_library

dbg15.3> w

*0: application

15: lappend auto_path $dbg_library

dbg15.4> Simulator info instances

_o1

dbg15.5> _o1 now

0

dbg15.6> # and other fun stuff

dbg15.7> c

(gdb) where

#0 0x102218 in write()

......

 

81  

Installing tcl-debug in ns-2 

1. tcl-debug-2.0 설치

   http://www.isi.edu/nsnam/ns/ns-debugging.html의 Tcl-level Debugging 부분을 참조하여 tcl-debug.tar.gz 파일을 다운로드 받음

   ns-2.xx와 parallel하도록 ~/ns-allinone-2.xx/tcl-debug-2.0 디렉토리에 압축 품

   tcl-debug-2.0/INSTALL 화일을 참조하여 다음과 같이 설치

1$ ./configure --enable-gcc

2$ make

3$ make install

2. ns-2.xx에 tcp-debug 추가

   ns-2.xx/ns_tclsh.cc 화일에 다음 두 문장을 추가

// 시작부에 tcldbg.h를 include

29^th line : #include "tcldbg.h” // 이 라인을 추가할 것

// TclAppInit(Tcl ...) 함수 내에 Tcldbg_Init(interp); 추가

42^nd line : Tcl::init(interp, "ns");

43^rd line : Tcldbg_Init(interp);  // 이 라인을 추가할 것

    ns-2.xx를 다시 컴파일

1$ ./configure --enable-debug --with-tcldebug=../tcl-debug-2.0

2$ make depend

3$ make

 

82  

Memory Debugging in ns 

• Purify
  • Set PURIFY macro in ns Makefile
  • Usually, put -colloctor=<ld_path>
• Gray Watson’s dmalloc library
  • http://www.dmalloc.com
  • make distclean
  • ./configure --with-dmalloc=<dmalloc_path>
  • Analyze results: dmalloc_summarize

 

83  

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

 

84  

Pitfalls 

• Scalability vs flexibility
  • Or, how to write scalable simulation?
• Memory conservation tips
• Memory leaks

 

85  

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++

 

86  

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

 

87  

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

 

88  

Memory Conservation Tips 

• Remove unused packet headers
• Avoid trace-all
• Use arrays for a sequence of variables
  • Instead of n$i, say n($i)
• Avoid OTcl temporary variables
• Use dynamic binding
  • delay_bind() instead of bind()
  • See object.{h,cc}

 

89  

Memory Leaks 

• Purify or dmalloc, but be careful about split objects:

for {set i 0} {$i < 500} {incr i} {

          set a [new RandomVariable/Constant]

}

• It leaks memory, but can’t be detected!
• Solution
  • Explicitly delete EVERY split object that was new-ed

 

90  

Final Word 

• When extended ns dumps OTcl scripts!
  • Find the last 10-20 lines of the dump
  • Is the error related to “_o*** cmd …” ?
    • Check your command()
  • Otherwise, check the OTcl script pointed by the error message

 

Thank you

 

Multiple inhertitance

 

Domain/cluster/nodes

 

Domain, cluster. nodes

• droped: LL (1 packet only, drop due to arp), IFQ
• MAC: collision detection
• PHY: Carier Sense threshold, Receive Threshold. Packets above CSThresh are able to cause a collision.
• IFQ: can be any queue, droptail or priority, etc.

 

- or change Makefile.in, make distclean, then

 

Multiple inhertitance

 

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