ping.cc

NS的教程

/*
 * File: Code for a new 'Ping' Agent Class for the ns
 *       network simulator
 * Author: Marc Greis ([e-mail]), May 1998
 *
 */


#include "ping.h"


static class PingHeaderClass : public PacketHeaderClass {
public:
  PingHeaderClass() : PacketHeaderClass("PacketHeader/Ping", 
					sizeof(hdr_ping)) {}
} class_pinghdr;


static class PingClass : public TclClass {
public:
  PingClass() : TclClass("Agent/Ping") {}
  TclObject* create(int, const char*const*) {
    return (new PingAgent());
  }
} class_ping;


PingAgent::PingAgent() : Agent(PT_PING)
{
  bind("packetSize_", &size_);
  bind("off_ping_", &off_ping_);
}


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));
}


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);
  }
}