/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation;
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <iostream>
#include "ns3/core-module.h"
#include "ns3/network-module.h"
#include "ns3/internet-module.h"
#include "ns3/point-to-point-module.h"
#include "ns3/applications-module.h"

using namespace std;
using namespace ns3;

NS_LOG_COMPONENT_DEFINE ("FirstExercise");

int
main (int argc, char *argv[])
{
  Time::SetResolution (Time::NS);
  LogComponentEnable ("UdpEchoClientApplication", LOG_LEVEL_INFO);
  LogComponentEnable ("UdpEchoServerApplication", LOG_LEVEL_INFO);

  int clientAmount;
  cout << "Amount of client: ";
  cin >> clientAmount;

  NodeContainer nodes;
  nodes.Create (clientAmount + 1); // Additional one for the server node.

  UdpEchoServerHelper echoServer (9);
  // Node 0 is reserved for the server.
  ApplicationContainer serverApps = echoServer.Install (nodes.Get (0));
  serverApps.Start (Seconds (1.0));
  serverApps.Stop (Seconds (10.0));

  InternetStackHelper stack;
  stack.Install (nodes);

  PointToPointHelper pointToPoint;
  pointToPoint.SetDeviceAttribute ("DataRate", StringValue ("10Mbps"));
  pointToPoint.SetChannelAttribute ("Delay", StringValue ("4ms"));

  Ipv4AddressHelper address;
  address.SetBase ("10.1.1.0", "255.255.255.0");

  for (int client = 1; client <= clientAmount; client++)
  {
    NetDeviceContainer devices;
    devices = pointToPoint.Install (nodes.Get (0), nodes.Get (client));

    Ipv4InterfaceContainer interfaces;
    interfaces = address.Assign (devices);
    // Due to the implementation of PointToPointHelper, 
    // each p2p link should be established on its unique subnet, 
    // in order to make sure that each client can receive the packet 
    // returning from the server. (If receiving is not required, 
    // then we are done here.)
    //
    // Otherwise, only the last client registered to the network
    // will be able to receive the packet back.
    //
    // I think it's probably caused by the routing policy in ns-3,
    // under the situation that multiple interfaces (of the server node, 
    // in this case) are assigned into the same subnet, that
    // may raise routing problem of which interface should be used,
    // to send echo packet back to the client.
    //
    // For a simple example, consider the situtation of 2 clients.
    // The network topology is as follows:
    //
    // Subnet: 10.1.1.0/30
    //
    //             p2p link 1   10.1.1.1 (link 1)              10.1.1.4
    //    n1     --------------       n0           -------------- n2
    // 10.1.1.2                 10.1.1.3 (link 2)    p2p link 2    
    //
    // We assume that link 2 is established (assigned IP addresses) 
    // after link 1.
    //
    // Now when the server (n0) tries to send echo packet back to n1 
    // (or n2), it's reasonable to use either the interface on link 1
    // (10.1.1.1) or the one on link 2 (10.1.1.3), since all IPs are in
    // the same subnet (10.1.1.0/30).
    //
    // However, n1 will never receive the packet if n0 selects interface
    // on the link 2 (10.1.1.3). It's similar for n2 if 10.1.1.1 is used.
    //
    // It seems more likely, in ns-3, to use the last interface attached,
    // that is 10.1.1.3 on link 2 in this case.
    //
    // Therefore, address.NewNetwork() is called to create a new subnet
    // for the next p2p link.
    address.NewNetwork ();

    UdpEchoClientHelper echoClient (interfaces.GetAddress (0), 9);
    echoClient.SetAttribute ("MaxPackets", UintegerValue (4));
    echoClient.SetAttribute ("Interval", TimeValue (Seconds (1.0)));
    echoClient.SetAttribute ("PacketSize", UintegerValue (4096));

    ApplicationContainer clientApps = echoClient.Install (nodes.Get (client));
    clientApps.Start (Seconds (2.0));
    clientApps.Stop (Seconds (10.0));
  }

  Simulator::Run ();
  Simulator::Destroy ();
  return 0;
}