LAB 5
Adding New Components
• High level scripting in otcl
• Linking otcl and C++
• Low level in C++
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Adding New Component using
otcl
• Additional <new_stuff>.tcl file
• source <new_stuff>.tcl
• Adding new files
– change Makefile (NS_TCL_LIB), tcl/lib/nslib.tcl
– recompile
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Example: Agent/Message
C
n2
cross
traffic
n0
128Kb, 50ms
10Mb, 1ms
S
n4
C
n5
R
n1
10Mb, 1ms
n3
msg agent
http://nslab.ee.ntu.edu.tw/courses/ns-tutorial/ftw-tutorial.html
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Agent/Message
Receiver-side
processing
string message
S
•
•
•
•
R
A UDP agent (without UDP header)
Up to 64 bytes user message
Good for fast prototyping a simple idea
Usage requires extending ns functionality
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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"
}
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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"
}
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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”
$self send “$addr_ ack $seq”
}
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Agent/Message: Step 4
• Scheduler and tracing
# Create scheduler
set ns [new Simulator]
# Turn on Tracing
set fd [new “message.nam” w]
$ns namtrace-all $fd
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Agent/Message: Step 5
• Topology
for {set i 0} {$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
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Agent/Message: Step 6
• Routing
# Packet loss produced by queueing
# Routing protocol: let’s run distance vector
$ns rtproto DV
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Agent/Message: Step 7
• Cross traffic
set
$ns
set
$ns
$ns
udp0 [new Agent/UDP]
attach-agent $n(2) $udp0
null0 [new Agent/NULL]
attach-agent $n(4) $null0
connect $udp0 $null0
set exp0 [new Application/Traffic/Exponential]
$exp0 set rate_ 128k
$exp0 attach-agent $udp0
$ns at 1.0 “$exp0 start”
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Agent/Message: Step 8
• Message agents
set sdr [new Sender]
$sdr set packetSize_ 1000
set rcvr [new Receiver]
$rcvr set packetSize_ 40
$ns
$ns
$ns
$ns
$ns
attach $n(3) $sdr
attach $n(5) $rcvr
connect $sdr $rcvr
connect $rcvr $sdr
at 1.1 “$sdr send-next”
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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
}
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Agent/Message: Result
• Example output
> ./ns msg.tcl
Receiver gets seq
Sender gets ack 0
Receiver gets seq
Sender gets ack 1
Receiver gets seq
Sender gets ack 2
Receiver gets seq
Sender gets ack 3
Receiver gets seq
Sender gets ack 4
Receiver gets seq
0 from
from 1
1 from
from 1
2 from
from 1
3 from
from 1
4 from
from 1
5 from
0
0
0
0
0
0
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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
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Extending ns in C++
• Adding code in <new_stuff>.{cc,h} files
– Change Makefile
– make depend
– recompile
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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
Write otcl code (if required)
Build
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Class Hierarchy
TclObject
NsObject
Connector
Queue
Delay Agent
DropTail RED
TCP
Reno
Classifier
Trace
AddrClassifier McastClasifier
Enq Deq
Drop
SACK
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C++/otcl Linkage
Root of ns-2 object hierarchy
TclObject
bind(): link variable values between
C++ and OTcl
command(): link OTcl methods to C++
implementations
TclClass
Tcl
Create and initialize TclObject’s
C++ methods to access Tcl interpreter
TclCommand Standalone global commands
EmbeddedTcl ns script initialization
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TclObject: Hierarchy and Shadowing
C++ class
hierarchy
TclObject otcl class
hierarchy
TclObject
Agent
Agent
Agent/TCP
TcpAgent
_o123
*tcp
Agent/TCP otcl
shadow object
Agent/TCP C++
object
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TclObject::bind()
• Link C++ member variables to otcl object
variables
• C++
TcpAgent::TcpAgent() {
bind(“window_”, &wnd_);
… …
}
– bind_time(), bind_bool(), bind_bw()
• otcl
set tcp [new Agent/TCP]
$tcp set window_ 200
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Initialization of Bound Variables
• Initialization through otcl class variables
Agent/TCP set window_ 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
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TclObject::command()
• Implement otcl methods in C++
• Trap point: otcl method cmd{}
• Send all arguments after cmd{} call to
TclObject::command()
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TclObject::command()
$tcp send
OTcl space
no such
procedure
TclObject::unknown{}
$tcp cmd send
C++ space
TcpAgent::command()
Yes
match
“send”?
No
Invoke parent:
return Agent::command()
process and return
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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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TclClass
C++
TclObject
NsObject
Agent
TcpAgent
mirroring
OTcl
Static
class TcpClass
: public TclClass {
public:
TclObject
TcpClass()
: TclClass(“Agent/TCP”) {}
TclObject* create(int, const char*const*) {
return (new TcpAgent());
??
}
} class_tcp;
Agent
Agent/TCP
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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
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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;
}
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Creating New Components
• new agent, no headers
• new agent, new packet header
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DtopTail Round Robin (DTRR) –
Step 1
TclObject
NsObject
Connector
Queue
Delay Agent
DropTail RED
DTRR
TCP
Reno
Classifier
Trace
AddrClassifier McastClasifier
Enq Deq
Drop
SACK
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Adding New Queue (DropTail
Round Robin) using C++
//dtrr-queue.h
class DtRrQueue : public Queue {
public:
DtRrQueue() {
q1_ = new PacketQueue;
q2_ = new PacketQueue;
pq_ = q1_;
deq_turn_ = 1;
}
protected:
void enque(Packet*);
Packet* deque();
PacketQueue *q1_;
PacketQueue *q2_;
int deq_turn_;
// First FIFO queue
// Second FIFO queue
// 1 for First queue 2 for Second
};
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Creating Object
//dtrr-queue.cc
#include "dtrr-queue.h"
static class DtRrQueueClass : public TclClass {
public:
DtRrQueueClass() : TclClass("Queue/DTRR") {}
TclObject* create(int, const char*const*) {
return (new DtRrQueue);
}
} class_dropt_tail_round_robin;
void DtRrQueue::enque(Packet* p) {
…
}
Packet* DtRrQueue::deque(){
…
}
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New Agent, New Header for
Example MANET Unicast Routing
(EMUR)
• Example: Agent/Message
– New packet header for 64-byte message
– New transport agent to process this new
header
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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/nspacket.tcl)
• This does not apply when you add a new
field into an existing header!
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How Packet Header Works
Packet
PacketHeader/Common
next_
hdrlen_
bits_
size determined
at simulator
startup time
(PacketHeaderManager)
size determined
hdr_cmn
at compile time PacketHeader/IP
size determined
at compile time
size determined
at compile time
……
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hdr_ip
PacketHeader/TCP
hdr_tcp
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EMUR Header – Step 1
//emur_pkt.h
struct hdr_emur_pkt {
nsaddr_t pkt_src_; // Node which originated this packet
u_int16_t pkt_len_; // Packet length (in bytes)
u_int8_t pkt_seq_num_; // Packet sequence number
inline nsaddr_t& pkt_src() { return pkt_src_; }
inline u_int16_t& pkt_len() { return pkt_len_; }
inline u_int8_t& pkt_seq_num() { return pkt_seq_num_; }
static int offset_;
inline static int& offset() { return offset_; }
inline static hdr_emur_pkt* access(const Packet* p) {
return (hdr_emur_pkt*)p->access(offset_);
}
};
#define HDR_EMUR_PKT(p) hdr_emur_pkt::access(p)
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EMUR Header – Step 2
//emur.cc
#include <emur_pkt.h>
int Emur_pkt::offset_;
static class EmurHeaderClass : public
HeaderClass {
public:
EmurHeaderClass() :
PacketHeaderClass("PacketHeader/EMUR",
sizeof(hdr_emur_pkt)) {
bind_offset(&hdr_emur_pkt::offset_);
}
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} class_rtEMUR_hdr;
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EMUR Header – Step 3
• Enable tracing (packet.h):
enum packet_t {
PT_TCP,
…,
PT_EMUR,
PT_NTYPE // This MUST be the LAST one
};
class p_info {
……
name_[PT_EMUR] = “EMUR”;
name_[PT_NTYPE]= "undefined";
……
};
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EMUR Timer – Step 1
//emur.h
class Emur; // forward declaration
/* Timers */
class Emur_PktTimer : public TimerHandler {
public:
Emur_PktTimer(Emur* agent) : TimerHandler()
{
agent_ = agent;
}
protected:
Emur* agent_;
virtual void expire(Event* e);
};
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EMUR Class – Step 2
//emur.h
class Emur : public Agent {
/* Friends */
friend class Emur_PktTimer;
/* Private members */
…
Emur_PktTimer pkt_timer_; // Timer for
sending packets.
public:
Emur(nsaddr_t);
int command(int, const char*const*);
void recv(Packet*, Handler*);
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};
EMUR Binding – Step 3
//Emur/Emur.cc
static class EmurClass : public TclClass {
public:
EmurClass() : TclClass("Agent/EMUR") {}
TclObject* create(int argc, const
char*const* argv) {
assert(argc == 5);
return (new
Emur((nsaddr_t)Address::instance().str2add
r(argv[4])));
}
} class_rtEmur;
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EMUR Constructor – Step 4
//Emur/Emur.cc
Emur::Emur(nsaddr_t id) :
Agent(PT_EMUR), pkt_timer_(this) {
bind(“tcl_var_", &cc_var_);
ra_addr_ = id;
}
In Simulation script
Agent/Emur set tcl_var_ 100
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EMUR
Command
–
Step
5
Int Emur::command(int argc, const char*const* argv) {
if (argc == 2) {
if (strcasecmp(argv[1], "start") == 0) {
Start();
//pkt_timer_.resched(0.0);
return TCL_OK;
}
else if (strcasecmp(argv[1], “some_other_func") == 0) {
…
}
}
else if (argc == 3) {
// Obtains corresponding dmux to carry packets to upper layers
if (strcmp(argv[1], “some_var") == 0) {
loc_var_ = atoi (strcmp(argv[2])
return TCL_OK;
}
…
// Pass the command to the base class
return Agent::command(argc, argv);
}
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Emur Packet Receive – Step 6
Void Emur::recv(Packet* p, Handler* h) {
struct hdr_cmn* ch = HDR_CMN(p);
struct hdr_ip* ih = HDR_IP(p);
if (ih->saddr() == ra_addr()) {
// If there exists a loop, must drop the packet
if (ch->num_forwards() > 0) {
drop(p, DROP_RTR_ROUTE_LOOP);
return;
}
// else if this is a packet I am originating, must add IP header
else if (ch->num_forwards() == 0)
ch->size() += IP_HDR_LEN;
}
// If it is a Emur packet, must process it
if (ch->ptype() == PT_EMUR)
recv_emur_pkt(p);
// Otherwise, must forward the packet (unless TTL has reached
zero)
else {
ih->ttl_--;
if (ih->ttl_ == 0) {
drop(p, DROP_RTR_TTL);
return;
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}
Emur Send Packet – Step - 7
Void Emur::send_emur_pkt() {
Packet* p = allocpkt();
struct hdr_cmn* ch = HDR_CMN(p);
struct hdr_ip* ih = HDR_IP(p);
struct hdr_Emur_pkt* ph = HDR_Emur_PKT(p);
ph->pkt_src() = ra_addr();
ph->pkt_len() = 7;
ph->pkt_seq_num() = seq_num_++;
ch->ptype() = PT_Emur;
ch->direction() = hdr_cmn::DOWN;
ch->size() = IP_HDR_LEN + ph->pkt_len();
ch->error() = 0;
ch->next_hop() = IP_BROADCAST;
ch->addr_type() = NS_AF_INET;
ih->saddr() = ra_addr();
ih->daddr() = IP_BROADCAST;
ih->sport() = RT_PORT;
ih->dport() = RT_PORT;
ih->ttl() = IP_DEF_TTL;
Scheduler::instance().schedule(target_, p, JITTER);
}
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Emur Scheduling Packets –
Step 8
void Emur_PktTimer::expire(Event* e) {
agent_->send_emur_pkt();
resched((double)5.0);
}
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Emur Tracing – Step 9
//trace/cmu-trace.h
trace/cmu-trace.h
class CMUTrace : public Trace {
/* ... definitions ... */
private:
/* ... */
void format_aodv(Packet *p, int offset);
void format_emur(Packet *p, int offset);
};
//trace/cmu-trace.cc
Void CMUTrace::format_emur(Packet *p, int
offset)
{
struct hdr_emur_pkt* ph = HDR_EMUR_PKT(p);
…
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}
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Add Method to TCL library –
Step 10
//tcl/lib/ns-lib.tcl
Simulator instproc create-Emur-agent {
node } {
# Create Emur routing agent
set ragent [new Agent/Emur [$node nodeaddr]]
$self at 0.0 "$ragent start"
$node set ragent_ $ragent
return $ragent
}
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EMUR Final Step
• Change Makefile.in to add your source
files
• Run Configure
• Run make
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Summary
• Internals of NS2
• How to add new component in ns2
– Queue
– Routing
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