在NS2中增加自己的协议模块一般分一下几个步骤:
(1) 添加协议类
(2) 定义协议分组头结构
(3) 编译代码
其实在ns3.35版本中已经有ping协议,此步骤只是为了了解ns2添加协议的一般步骤。
1、 在ping协议中,需要定义自己的控制分组,因此首先需要在ping.h头文件中定义ping的分组头结构,C++代码如下:
//在ping协议中定义自己的控制分组
struct hdr_ping {
char ret; //0:从发送者到接收者,1:从接受者到发送者
double send_time; //发送时间,为了计算RTT
};
class PingAgent : public Agent {
public:
PingAgent();
int command(int argc, const char*const* argv);
void recv(Packet*, Handler*);
protected:
int off_ping_;
};
2、ping需要被NS-2所接受并且可以在OTcl代码中使用,需要在ping.cc中定义如下代码:
static class PingHeaderClass : public PacketHeaderClass {
public:
PingHeaderClass() : PacketHeaderClass("PacketHeader/Ping",
sizeof(hdr_ping)) {}
} class_pinghdr;
本代码实现了OTcl中的PingHead/ping类与C++中的hdr_ping绑定在一起,这样定义出的分组头为Ping。
2、 在~ns/tcl/lib/ns-packet.tcl中包含了系统中所有已实现的协议分组头名字,我们也需要在其中添加包头的名字Ping。
Foreach {
IVS
QS
…
Ping
}
3、 为了创建ping分组,需要定义ping的分组类型。需要修改ns/common/packet.h文件:首先在emun packet中新增包类型:PT_PING;
Enum packet_t {
PT_TCP,
PT_UDP,
…
PT_PING
}
然后在class p_info类的构造函数中定义新增包类型的名字:
Class p_info {
Public:
P_info {
name_[PT_TCP]=”tcp”;
……
name_[PT_PIING]="ping";
}
……
}
4、 需要从TclCL继承一个PingClass类,其构造函数通过调用基类的构造函数“TclClass(”Agent/Ping”)”指定其对应的OTcl对象为Agent/Ping,这实际是做了登记工作,在ping.cc中定义:
static class PingClass : public TclClass {
public:
PingClass() : TclClass("Agent/Ping") {}
TclObject* create(int, const char*const*) {
return (new PingAgent());
}
} class_ping;
OTcl代码:
set p0 [new Agent/Ping]
$ns attach-agent $n0 $p0
当执行set p0 [new Agent/Ping]时,就会调用父类的构造函数(init方法),父类SplitObject调用create-shadow方法来登记OTcl对象p0和被创建的C++对象class_ping的关系。根据登记关系去调用TclObject* create(int, const char*const*)创建并返回对象指针:return (new PingAgent());
5、 需要在PingAgent的构造函数中,需要将新创建的分组类型传递给Agent类的构造函数,因为PingAgent父类的构造函数中就需要定制分组类型作为参数。在PingAgent构造函数中实现C++和OTcl之间成员变量的绑定。
PingAgent::PingAgent() : Agent(PT_PING)
{
bind("packetSize_", &size_);
bind("off_ping_", &off_ping_);
}
变量绑定后,Agent/Ping类对象p0的成员变量packetSize_和off_ping_的变量在任何时候都和C++对象的成员变量保持一致。为了给这些变量初始化,需要在~ns/tcl/lib/ns-default.tcl中添加以下代码:
Agent/Ping set packetSize 0
Agent/Ping set off_ping_ 0
ns-default.tcl这个文件是在Tcl脚本运行之前被执行的,所以在创建对象并在绑定变量时,变量已经进行了初始化。
6、当执行
$ns at 0.2 "$p0 send"
C++对象的指针根据过程函数名去调用command函数,如下:
int PingAgent::command(int argc, const char*const* argv)
{
if (argc == 2) {
if (strcmp(argv[1], "send") == 0) {
// Create a new packet
Packet* pkt = allocpkt();
// Access the Ping header for the new packet:
hdr_ping* hdr = (hdr_ping*)pkt->access(off_ping_);
// Set the ‘ret‘ field to 0, so the receiving node knows
// that it has to generate an echo packet
hdr->ret = 0;
// Store the current time in the ‘send_time‘ field
hdr->send_time = Scheduler::instance().clock();
// Send the packet
send(pkt, 0);
// return TCL_OK, so the calling function knows that the
// command has been processed
return (TCL_OK);
}
}
// If the command hasn‘t been processed by PingAgent()::command,
// call the command() function for the base class
return (Agent::command(argc, argv));
}
6、 完成ping协议的定义和实现后,把ping.hh和ping.cc放在~ns/ping下,然后重新编译NS-2,把ping协议嵌入到NS-2代码中去,我们需要修改~ns/Makefile文件。
在Makefile的OBJ_CC中,增加以下代码:ping/ping.o
在ns目录下:make clean和make,完成编译。
7、 ping.cc中的recv函数代码如下:
void PingAgent::recv(Packet* pkt, Handler*)
{
// Access the IP header for the received packet:
hdr_ip* hdrip = (hdr_ip*)pkt->access(off_ip_);
// Access the Ping header for the received packet:
hdr_ping* hdr = (hdr_ping*)pkt->access(off_ping_);
// Is the ‘ret‘ field = 0 (i.e. the receiving node is being pinged)?
if (hdr->ret == 0) {
// Send an ‘echo‘. First save the old packet‘s send_time
double stime = hdr->send_time;
// Discard the packet
Packet::free(pkt);
// Create a new packet
Packet* pktret = allocpkt();
// Access the Ping header for the new packet:
hdr_ping* hdrret = (hdr_ping*)pktret->access(off_ping_);
// Set the ‘ret‘ field to 1, so the receiver won‘t send another echo
hdrret->ret = 1;
// Set the send_time field to the correct value
hdrret->send_time = stime;
// Send the packet
send(pktret, 0);
} else {
// A packet was received. Use tcl.eval to call the Tcl
// interpreter with the ping results.
// Note: In the Tcl code, a procedure ‘Agent/Ping recv {from rtt}‘
// has to be defined which allows the user to react to the ping
// result.
char out[100];
// Prepare the output to the Tcl interpreter. Calculate the round
// trip time
sprintf(out, "%s recv %d %3.1f", name(),
hdrip->src_ >> Address::instance().NodeShift_[1],
(Scheduler::instance().clock()-hdr->send_time) * 1000);
Tcl& tcl = Tcl::instance();
tcl.eval(out);
// Discard the packet
Packet::free(pkt);
}
}
8、TCL测试脚本如下:
#Create a simulator object
set ns [new Simulator]
#Open a trace file
set nf [open out.nam w]
$ns namtrace-all $nf
#Define a ‘finish‘ procedure
proc finish {} {
global ns nf
$ns flush-trace
close $nf
exec nam out.nam &
exit 0
}
#Create three nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
#Connect the nodes with two links
$ns duplex-link $n0 $n1 1Mb 10ms DropTail
$ns duplex-link $n1 $n2 1Mb 10ms DropTail
#Define a ‘recv‘ function for the class ‘Agent/Ping‘
Agent/Ping instproc recv {from rtt} {
$self instvar node_
puts "node [$node_ id] received ping answer from \
$from with round-trip-time $rtt ms."
}
#Create two ping agents and attach them to the nodes n0 and n2
set p0 [new Agent/Ping]
$ns attach-agent $n0 $p0
set p1 [new Agent/Ping]
$ns attach-agent $n2 $p1
#Connect the two agents
$ns connect $p0 $p1
#Schedule events
$ns at 0.2 "$p0 send"
$ns at 0.4 "$p1 send"
$ns at 0.6 "$p0 send"
$ns at 0.6 "$p1 send"
$ns at 1.0 "finish"
#Run the simulation
$ns run
http://www.cnblogs.com/ManMonth/archive/2011/03/15/1985518.html