在NS2（ns-allione-2.34）中加入bing协议

  今天开始沉下心来好好搞项目，我们小组的任务是完成利用网络编码技术改进传统TCP协议，我主要是负责进行ns仿真。今天上午回顾了一下以前进行的工作，下午试验在ns2中植入了一个小协议Bing（其实就是Ping协议，由于在现有ns源代码中已经有了Ping协议，故改名为Bing协议）。以下是植入的过程：

First Step:    编写bing.h文件

#ifndef ns_bing_h
#define ns_bing_h

#include "agent.h"
#include "tclcl.h"
#include "packet.h"
#include "address.h"
#include "ip.h"

/*
 * 定义Bing协议的分组头结构
 */
struct hdr_bing {
	char ret;                                // 用来判断是否发送pktret响应包
	double send_time;                        // 包传送时间
 	int seq;		// sequence number


	// Header access methods
	static int offset_; // required by PacketHeaderManager       // 分组头在整个包头中的偏移量。 疑问：何时确定的这个偏移量的值？？？
	inline static int& offset() { return offset_; }
	inline static hdr_bing* access(const Packet* p) {
		return (hdr_bing*) p->access(offset_);
	}
};

class BingAgent : public Agent {
public:
	BingAgent();
 	int seq;	// a send sequence number like in real ping
	virtual int command(int argc, const char*const* argv);            // 重写父类的command函数，在这里实际就是传送包的函数
	virtual void recv(Packet*, Handler*);
};

#endif // ns_ping_h

Second Step:  编写bing.cc文件

#include "bing.h"
#include <iostream>;

/*
 * bing协议需要被NS-2所接受并且，可以在OTcl代码中使用，需要定义如下代码：
 * 以下代码使得OTcl中的bingHead/Ping类与C++中的hdr_bing绑定在一起,这样定义出的分组头为Bing
 */

int hdr_bing::offset_;
static class BingHeaderClass : public PacketHeaderClass {
public:
	BingHeaderClass() : PacketHeaderClass("PacketHeader/Bing",
					      sizeof(hdr_bing)) {
		bind_offset(&hdr_bing::offset_);
	}
} class_binghdr;


/*
 *  以下代码从TclCL继承一个BingClass类，其构造函数通过调用基类的构造函数TclClass("Agent/Bing")指定其
 *  对应的OTcl对象为Agent/Bing,这实际是做了登记工作。
 */

static class BingClass : public TclClass {
public:
	BingClass() : TclClass("Agent/Bing") {}
	TclObject* create(int, const char*const*) {
		return (new BingAgent());
	}
} class_bing;


BingAgent::BingAgent() : Agent(PT_BING), seq(0)
{
	bind("packetSize_", &size_);
}

int BingAgent::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_bing* hdr = hdr_bing::access(pkt);
      // Set the 'ret' field to 0, so the receiving node
      // knows that it has to generate an echo packet
      hdr->ret = 0;
      hdr->seq = seq++;
      // Store the current time in the 'send_time' field
      hdr->send_time = Scheduler::instance().clock();

      std::cout << Agent::size_ << endl;
      // 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));
}


void BingAgent::recv(Packet* pkt, Handler*)
{
  // Access the IP header for the received packet:
  hdr_ip* hdrip = hdr_ip::access(pkt);
  
  // Access the Ping header for the received packet:
  hdr_bing* hdr = hdr_bing::access(pkt);
  

  // 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;
    int rcv_seq = hdr->seq;
    // Discard the packet
    Packet::free(pkt);
    // Create a new packet
    Packet* pktret = allocpkt();
    // Access the Ping header for the new packet:
    hdr_bing* hdrret = hdr_bing::access(pktret);
    // 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;
    // Added by Andrei Gurtov for one-way delay measurement.
    hdrret->seq = rcv_seq;
    // 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_.addr_ >> Address::instance().NodeShift_[1],
	    (Scheduler::instance().clock()-hdr->send_time) * 1000);
    Tcl& tcl = Tcl::instance();
    tcl.eval(out);
    // Discard the packet
    Packet::free(pkt);
  }
}

Third Step:
  (1) 在lib/ns-packet.tcl中添加包头名字Bing;
  (2) 在common/packet.h中新增包类型:PT_BING; 并定义新增包类型的名字name_[PT_BING]= "bing";
  (3)在lib/ns-default.tcl中增加定义变量初始值的语句。这里的变量只包括通过bind函数进行OTcl与C++语言绑定的变量：
       Agent/Bing set packetSize_ 64;

Fourth Step:
   最后，修改ns/Makefile文件,并编译。

Bing协议植入过程就此结束！