unison/examples/tcp/tcp-variants-comparison.cc

/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * Copyright (c) 2013 ResiliNets, ITTC, University of Kansas
 *
 * 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
 *
 * Authors: Justin P. Rohrer, Truc Anh N. Nguyen <annguyen@ittc.ku.edu>, Siddharth Gangadhar <siddharth@ittc.ku.edu>
 *
 * James P.G. Sterbenz <jpgs@ittc.ku.edu>, director
 * ResiliNets Research Group  https://resilinets.org/
 * Information and Telecommunication Technology Center (ITTC)
 * and Department of Electrical Engineering and Computer Science
 * The University of Kansas Lawrence, KS USA.
 *
 * Work supported in part by NSF FIND (Future Internet Design) Program
 * under grant CNS-0626918 (Postmodern Internet Architecture),
 * NSF grant CNS-1050226 (Multilayer Network Resilience Analysis and Experimentation on GENI),
 * US Department of Defense (DoD), and ITTC at The University of Kansas.
 *
 * “TCP Westwood(+) Protocol Implementation in ns-3”
 * Siddharth Gangadhar, Trúc Anh Ngọc Nguyễn , Greeshma Umapathi, and James P.G. Sterbenz,
 * ICST SIMUTools Workshop on ns-3 (WNS3), Cannes, France, March 2013
 */

#include <iostream>
#include <fstream>
#include <string>

#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"
#include "ns3/error-model.h"
#include "ns3/tcp-header.h"
#include "ns3/udp-header.h"
#include "ns3/enum.h"
#include "ns3/event-id.h"
#include "ns3/flow-monitor-helper.h"
#include "ns3/ipv4-global-routing-helper.h"
#include "ns3/traffic-control-module.h"

using namespace ns3;

NS_LOG_COMPONENT_DEFINE ("TcpVariantsComparison");

static std::map<uint32_t, bool> firstCwnd;    //!< First congestion window.
static std::map<uint32_t, bool> firstSshThr;  //!< First SlowStart threshold.
static std::map<uint32_t, bool> firstRtt;     //!< First RTT.
static std::map<uint32_t, bool> firstRto;     //!< First RTO.
static std::map<uint32_t, Ptr<OutputStreamWrapper>> cWndStream;     //!< Congstion window outut stream.
static std::map<uint32_t, Ptr<OutputStreamWrapper>> ssThreshStream; //!< SlowStart threshold outut stream.
static std::map<uint32_t, Ptr<OutputStreamWrapper>> rttStream;      //!< RTT outut stream.
static std::map<uint32_t, Ptr<OutputStreamWrapper>> rtoStream;      //!< RTO outut stream.
static std::map<uint32_t, Ptr<OutputStreamWrapper>> nextTxStream;   //!< Next TX outut stream.
static std::map<uint32_t, Ptr<OutputStreamWrapper>> nextRxStream;   //!< Next RX outut stream.
static std::map<uint32_t, Ptr<OutputStreamWrapper>> inFlightStream; //!< In flight outut stream.
static std::map<uint32_t, uint32_t> cWndValue;      //!< congestion window value.
static std::map<uint32_t, uint32_t> ssThreshValue;  //!< SlowStart threshold value.

/**
 * Get the Node Id From Context.
 *
 * \param context The context.
 * \return the node ID.
 */
static uint32_t
GetNodeIdFromContext (std::string context)
{
  std::size_t const n1 = context.find_first_of ('/', 1);
  std::size_t const n2 = context.find_first_of ('/', n1 + 1);
  return std::stoul (context.substr (n1 + 1, n2 - n1 - 1));
}

/**
 * Congestion window tracer.
 *
 * \param context The context.
 * \param oldval Old value.
 * \param newval New value.
 */
static void
CwndTracer (std::string context,  uint32_t oldval, uint32_t newval)
{
  uint32_t nodeId = GetNodeIdFromContext (context);

  if (firstCwnd[nodeId])
    {
      *cWndStream[nodeId]->GetStream () << "0.0 " << oldval << std::endl;
      firstCwnd[nodeId] = false;
    }
  *cWndStream[nodeId]->GetStream () << Simulator::Now ().GetSeconds () << " " << newval << std::endl;
  cWndValue[nodeId] = newval;

  if (!firstSshThr[nodeId])
    {
      *ssThreshStream[nodeId]->GetStream ()
          << Simulator::Now ().GetSeconds () << " " << ssThreshValue[nodeId] << std::endl;
    }
}

/**
 * Slow start threshold tracer.
 *
 * \param context The context.
 * \param oldval Old value.
 * \param newval New value.
 */
static void
SsThreshTracer (std::string context, uint32_t oldval, uint32_t newval)
{
  uint32_t nodeId = GetNodeIdFromContext (context);

  if (firstSshThr[nodeId])
    {
      *ssThreshStream[nodeId]->GetStream () << "0.0 " << oldval << std::endl;
      firstSshThr[nodeId] = false;
    }
  *ssThreshStream[nodeId]->GetStream () << Simulator::Now ().GetSeconds () << " " << newval << std::endl;
  ssThreshValue[nodeId] = newval;

  if (!firstCwnd[nodeId])
    {
      *cWndStream[nodeId]->GetStream () << Simulator::Now ().GetSeconds () << " " << cWndValue[nodeId] << std::endl;
    }
}

/**
 * RTT tracer.
 *
 * \param context The context.
 * \param oldval Old value.
 * \param newval New value.
 */
static void
RttTracer (std::string context, Time oldval, Time newval)
{
  uint32_t nodeId = GetNodeIdFromContext (context);

  if (firstRtt[nodeId])
    {
      *rttStream[nodeId]->GetStream () << "0.0 " << oldval.GetSeconds () << std::endl;
      firstRtt[nodeId] = false;
    }
  *rttStream[nodeId]->GetStream () << Simulator::Now ().GetSeconds () << " " << newval.GetSeconds () << std::endl;
}

/**
 * RTO tracer.
 *
 * \param context The context.
 * \param oldval Old value.
 * \param newval New value.
 */
static void
RtoTracer (std::string context, Time oldval, Time newval)
{
  uint32_t nodeId = GetNodeIdFromContext (context);

  if (firstRto[nodeId])
    {
      *rtoStream[nodeId]->GetStream () << "0.0 " << oldval.GetSeconds () << std::endl;
      firstRto[nodeId] = false;
    }
  *rtoStream[nodeId]->GetStream () << Simulator::Now ().GetSeconds () << " " << newval.GetSeconds () << std::endl;
}

/**
 * Next TX tracer.
 *
 * \param context The context.
 * \param old Old sequence number.
 * \param nextTx Next sequence number.
 */
static void
NextTxTracer (std::string context, [[maybe_unused]] SequenceNumber32 old, SequenceNumber32 nextTx)
{
  uint32_t nodeId = GetNodeIdFromContext (context);

  *nextTxStream[nodeId]->GetStream () << Simulator::Now ().GetSeconds () << " " << nextTx << std::endl;
}

/**
 * In-flight tracer.
 *
 * \param context The context.
 * \param old Old value.
 * \param inFlight In flight value.
 */
static void
InFlightTracer (std::string context, [[maybe_unused]] uint32_t old, uint32_t inFlight)
{
  uint32_t nodeId = GetNodeIdFromContext (context);

  *inFlightStream[nodeId]->GetStream () << Simulator::Now ().GetSeconds () << " " << inFlight << std::endl;
}

/**
 * Next RX tracer.
 *
 * \param context The context.
 * \param old Old sequence number.
 * \param nextRx Next sequence number.
 */
static void
NextRxTracer (std::string context, [[maybe_unused]] SequenceNumber32 old, SequenceNumber32 nextRx)
{
  uint32_t nodeId = GetNodeIdFromContext (context);

  *nextRxStream[nodeId]->GetStream () << Simulator::Now ().GetSeconds () << " " << nextRx << std::endl;
}

/**
 * Congestion window trace connection.
 *
 * \param cwnd_tr_file_name Congestion window trace file name.
 * \param nodeId Node ID.
 */
static void
TraceCwnd (std::string cwnd_tr_file_name, uint32_t nodeId)
{
  AsciiTraceHelper ascii;
  cWndStream[nodeId] = ascii.CreateFileStream (cwnd_tr_file_name);
  Config::Connect ("/NodeList/" + std::to_string (nodeId) + "/$ns3::TcpL4Protocol/SocketList/0/CongestionWindow",
                   MakeCallback (&CwndTracer));
}

/**
 * Slow start threshold trace connection.
 *
 * \param ssthresh_tr_file_name Slow start threshold trace file name.
 * \param nodeId Node ID.
 */
static void
TraceSsThresh (std::string ssthresh_tr_file_name, uint32_t nodeId)
{
  AsciiTraceHelper ascii;
  ssThreshStream[nodeId] = ascii.CreateFileStream (ssthresh_tr_file_name);
  Config::Connect ("/NodeList/" + std::to_string (nodeId) + "/$ns3::TcpL4Protocol/SocketList/0/SlowStartThreshold",
                   MakeCallback (&SsThreshTracer));
}

/**
 * RTT trace connection.
 *
 * \param rtt_tr_file_name RTT trace file name.
 * \param nodeId Node ID.
 */
static void
TraceRtt (std::string rtt_tr_file_name, uint32_t nodeId)
{
  AsciiTraceHelper ascii;
  rttStream[nodeId] = ascii.CreateFileStream (rtt_tr_file_name);
  Config::Connect ("/NodeList/" + std::to_string (nodeId) + "/$ns3::TcpL4Protocol/SocketList/0/RTT",
                   MakeCallback (&RttTracer));
}

/**
 * RTO trace connection.
 *
 * \param rto_tr_file_name RTO trace file name.
 * \param nodeId Node ID.
 */
static void
TraceRto (std::string rto_tr_file_name, uint32_t nodeId)
{
  AsciiTraceHelper ascii;
  rtoStream[nodeId] = ascii.CreateFileStream (rto_tr_file_name);
  Config::Connect ("/NodeList/" + std::to_string (nodeId) + "/$ns3::TcpL4Protocol/SocketList/0/RTO",
                   MakeCallback (&RtoTracer));
}

/**
 * Next TX trace connection.
 *
 * \param next_tx_seq_file_name Next TX trace file name.
 * \param nodeId Node ID.
 */
static void
TraceNextTx (std::string &next_tx_seq_file_name, uint32_t nodeId)
{
  AsciiTraceHelper ascii;
  nextTxStream[nodeId] = ascii.CreateFileStream (next_tx_seq_file_name);
  Config::Connect ("/NodeList/" + std::to_string (nodeId) + "/$ns3::TcpL4Protocol/SocketList/0/NextTxSequence",
                   MakeCallback (&NextTxTracer));
}

/**
 * In flight trace connection.
 *
 * \param in_flight_file_name In flight trace file name.
 * \param nodeId Node ID.
 */
static void
TraceInFlight (std::string &in_flight_file_name, uint32_t nodeId)
{
  AsciiTraceHelper ascii;
  inFlightStream[nodeId] = ascii.CreateFileStream (in_flight_file_name);
  Config::Connect ("/NodeList/" + std::to_string (nodeId) + "/$ns3::TcpL4Protocol/SocketList/0/BytesInFlight",
                   MakeCallback (&InFlightTracer));
}

/**
 * Next RX trace connection.
 *
 * \param next_rx_seq_file_name Next RX trace file name.
 * \param nodeId Node ID.
 */
static void
TraceNextRx (std::string &next_rx_seq_file_name, uint32_t nodeId)
{
  AsciiTraceHelper ascii;
  nextRxStream[nodeId] = ascii.CreateFileStream (next_rx_seq_file_name);
  Config::Connect ("/NodeList/" + std::to_string (nodeId) +
                       "/$ns3::TcpL4Protocol/SocketList/1/RxBuffer/NextRxSequence",
                   MakeCallback (&NextRxTracer));
}

int main (int argc, char *argv[])
{
  std::string transport_prot = "TcpWestwood";
  double error_p = 0.0;
  std::string bandwidth = "2Mbps";
  std::string delay = "0.01ms";
  std::string access_bandwidth = "10Mbps";
  std::string access_delay = "45ms";
  bool tracing = false;
  std::string prefix_file_name = "TcpVariantsComparison";
  uint64_t data_mbytes = 0;
  uint32_t mtu_bytes = 400;
  uint16_t num_flows = 1;
  double duration = 100.0;
  uint32_t run = 0;
  bool flow_monitor = false;
  bool pcap = false;
  bool sack = true;
  std::string queue_disc_type = "ns3::PfifoFastQueueDisc";
  std::string recovery = "ns3::TcpClassicRecovery";


  CommandLine cmd (__FILE__);
  cmd.AddValue ("transport_prot", "Transport protocol to use: TcpNewReno, TcpLinuxReno, "
                "TcpHybla, TcpHighSpeed, TcpHtcp, TcpVegas, TcpScalable, TcpVeno, "
                "TcpBic, TcpYeah, TcpIllinois, TcpWestwood, TcpWestwoodPlus, TcpLedbat, "
		"TcpLp, TcpDctcp, TcpCubic, TcpBbr", transport_prot);
  cmd.AddValue ("error_p", "Packet error rate", error_p);
  cmd.AddValue ("bandwidth", "Bottleneck bandwidth", bandwidth);
  cmd.AddValue ("delay", "Bottleneck delay", delay);
  cmd.AddValue ("access_bandwidth", "Access link bandwidth", access_bandwidth);
  cmd.AddValue ("access_delay", "Access link delay", access_delay);
  cmd.AddValue ("tracing", "Flag to enable/disable tracing", tracing);
  cmd.AddValue ("prefix_name", "Prefix of output trace file", prefix_file_name);
  cmd.AddValue ("data", "Number of Megabytes of data to transmit", data_mbytes);
  cmd.AddValue ("mtu", "Size of IP packets to send in bytes", mtu_bytes);
  cmd.AddValue ("num_flows", "Number of flows", num_flows);
  cmd.AddValue ("duration", "Time to allow flows to run in seconds", duration);
  cmd.AddValue ("run", "Run index (for setting repeatable seeds)", run);
  cmd.AddValue ("flow_monitor", "Enable flow monitor", flow_monitor);
  cmd.AddValue ("pcap_tracing", "Enable or disable PCAP tracing", pcap);
  cmd.AddValue ("queue_disc_type", "Queue disc type for gateway (e.g. ns3::CoDelQueueDisc)", queue_disc_type);
  cmd.AddValue ("sack", "Enable or disable SACK option", sack);
  cmd.AddValue ("recovery", "Recovery algorithm type to use (e.g., ns3::TcpPrrRecovery", recovery);
  cmd.Parse (argc, argv);

  transport_prot = std::string ("ns3::") + transport_prot;

  SeedManager::SetSeed (1);
  SeedManager::SetRun (run);

  // User may find it convenient to enable logging
  //LogComponentEnable("TcpVariantsComparison", LOG_LEVEL_ALL);
  //LogComponentEnable("BulkSendApplication", LOG_LEVEL_INFO);
  //LogComponentEnable("PfifoFastQueueDisc", LOG_LEVEL_ALL);

  // Calculate the ADU size
  Header* temp_header = new Ipv4Header ();
  uint32_t ip_header = temp_header->GetSerializedSize ();
  NS_LOG_LOGIC ("IP Header size is: " << ip_header);
  delete temp_header;
  temp_header = new TcpHeader ();
  uint32_t tcp_header = temp_header->GetSerializedSize ();
  NS_LOG_LOGIC ("TCP Header size is: " << tcp_header);
  delete temp_header;
  uint32_t tcp_adu_size = mtu_bytes - 20 - (ip_header + tcp_header);
  NS_LOG_LOGIC ("TCP ADU size is: " << tcp_adu_size);

  // Set the simulation start and stop time
  double start_time = 0.1;
  double stop_time = start_time + duration;

  // 2 MB of TCP buffer
  Config::SetDefault ("ns3::TcpSocket::RcvBufSize", UintegerValue (1 << 21));
  Config::SetDefault ("ns3::TcpSocket::SndBufSize", UintegerValue (1 << 21));
  Config::SetDefault ("ns3::TcpSocketBase::Sack", BooleanValue (sack));

  Config::SetDefault ("ns3::TcpL4Protocol::RecoveryType",
                      TypeIdValue (TypeId::LookupByName (recovery)));
  // Select TCP variant
  if (transport_prot == "ns3::TcpWestwoodPlus")
    {
      // TcpWestwoodPlus is not an actual TypeId name; we need TcpWestwood here
      Config::SetDefault ("ns3::TcpL4Protocol::SocketType", TypeIdValue (TcpWestwood::GetTypeId ()));
      // the default protocol type in ns3::TcpWestwood is WESTWOOD
      Config::SetDefault ("ns3::TcpWestwood::ProtocolType", EnumValue (TcpWestwood::WESTWOODPLUS));
    }
  else
    {
      TypeId tcpTid;
      NS_ABORT_MSG_UNLESS (TypeId::LookupByNameFailSafe (transport_prot, &tcpTid), "TypeId " << transport_prot << " not found");
      Config::SetDefault ("ns3::TcpL4Protocol::SocketType", TypeIdValue (TypeId::LookupByName (transport_prot)));
    }

  // Create gateways, sources, and sinks
  NodeContainer gateways;
  gateways.Create (1);
  NodeContainer sources;
  sources.Create (num_flows);
  NodeContainer sinks;
  sinks.Create (num_flows);

  // Configure the error model
  // Here we use RateErrorModel with packet error rate
  Ptr<UniformRandomVariable> uv = CreateObject<UniformRandomVariable> ();
  uv->SetStream (50);
  RateErrorModel error_model;
  error_model.SetRandomVariable (uv);
  error_model.SetUnit (RateErrorModel::ERROR_UNIT_PACKET);
  error_model.SetRate (error_p);

  PointToPointHelper UnReLink;
  UnReLink.SetDeviceAttribute ("DataRate", StringValue (bandwidth));
  UnReLink.SetChannelAttribute ("Delay", StringValue (delay));
  UnReLink.SetDeviceAttribute ("ReceiveErrorModel", PointerValue (&error_model));


  InternetStackHelper stack;
  stack.InstallAll ();

  TrafficControlHelper tchPfifo;
  tchPfifo.SetRootQueueDisc ("ns3::PfifoFastQueueDisc");

  TrafficControlHelper tchCoDel;
  tchCoDel.SetRootQueueDisc ("ns3::CoDelQueueDisc");

  Ipv4AddressHelper address;
  address.SetBase ("10.0.0.0", "255.255.255.0");

  // Configure the sources and sinks net devices
  // and the channels between the sources/sinks and the gateways
  PointToPointHelper LocalLink;
  LocalLink.SetDeviceAttribute ("DataRate", StringValue (access_bandwidth));
  LocalLink.SetChannelAttribute ("Delay", StringValue (access_delay));

  Ipv4InterfaceContainer sink_interfaces;

  DataRate access_b (access_bandwidth);
  DataRate bottle_b (bandwidth);
  Time access_d (access_delay);
  Time bottle_d (delay);

  uint32_t size = static_cast<uint32_t>((std::min (access_b, bottle_b).GetBitRate () / 8) *
    ((access_d + bottle_d) * 2).GetSeconds ());

  Config::SetDefault ("ns3::PfifoFastQueueDisc::MaxSize",
                      QueueSizeValue (QueueSize (QueueSizeUnit::PACKETS, size / mtu_bytes)));
  Config::SetDefault ("ns3::CoDelQueueDisc::MaxSize",
                      QueueSizeValue (QueueSize (QueueSizeUnit::BYTES, size)));

  for (uint32_t i = 0; i < num_flows; i++)
    {
      NetDeviceContainer devices;
      devices = LocalLink.Install (sources.Get (i), gateways.Get (0));
      tchPfifo.Install (devices);
      address.NewNetwork ();
      Ipv4InterfaceContainer interfaces = address.Assign (devices);

      devices = UnReLink.Install (gateways.Get (0), sinks.Get (i));
      if (queue_disc_type == "ns3::PfifoFastQueueDisc")
        {
          tchPfifo.Install (devices);
        }
      else if (queue_disc_type == "ns3::CoDelQueueDisc")
        {
          tchCoDel.Install (devices);
        }
      else
        {
          NS_FATAL_ERROR ("Queue not recognized. Allowed values are ns3::CoDelQueueDisc or ns3::PfifoFastQueueDisc");
        }
      address.NewNetwork ();
      interfaces = address.Assign (devices);
      sink_interfaces.Add (interfaces.Get (1));
    }

  NS_LOG_INFO ("Initialize Global Routing.");
  Ipv4GlobalRoutingHelper::PopulateRoutingTables ();

  uint16_t port = 50000;
  Address sinkLocalAddress (InetSocketAddress (Ipv4Address::GetAny (), port));
  PacketSinkHelper sinkHelper ("ns3::TcpSocketFactory", sinkLocalAddress);

  for (uint32_t i = 0; i < sources.GetN (); i++)
    {
      AddressValue remoteAddress (InetSocketAddress (sink_interfaces.GetAddress (i, 0), port));
      Config::SetDefault ("ns3::TcpSocket::SegmentSize", UintegerValue (tcp_adu_size));
      BulkSendHelper ftp ("ns3::TcpSocketFactory", Address ());
      ftp.SetAttribute ("Remote", remoteAddress);
      ftp.SetAttribute ("SendSize", UintegerValue (tcp_adu_size));
      ftp.SetAttribute ("MaxBytes", UintegerValue (data_mbytes * 1000000));

      ApplicationContainer sourceApp = ftp.Install (sources.Get (i));
      sourceApp.Start (Seconds (start_time * i));
      sourceApp.Stop (Seconds (stop_time - 3));

      sinkHelper.SetAttribute ("Protocol", TypeIdValue (TcpSocketFactory::GetTypeId ()));
      ApplicationContainer sinkApp = sinkHelper.Install (sinks.Get (i));
      sinkApp.Start (Seconds (start_time * i));
      sinkApp.Stop (Seconds (stop_time));
    }

  // Set up tracing if enabled
  if (tracing)
    {
      std::ofstream ascii;
      Ptr<OutputStreamWrapper> ascii_wrap;
      ascii.open ((prefix_file_name + "-ascii").c_str ());
      ascii_wrap = new OutputStreamWrapper (prefix_file_name + "-ascii",
                                            std::ios::out);
      stack.EnableAsciiIpv4All (ascii_wrap);

      for (uint16_t index = 0; index < num_flows; index++)
        {
          std::string flowString ("");
          if (num_flows>1)
            {
              flowString = "-flow" + std::to_string (index);
            }

          firstCwnd[index+1] = true;
          firstSshThr[index+1] = true;
          firstRtt[index+1] = true;
          firstRto[index+1] = true;

          Simulator::Schedule (Seconds (start_time * index + 0.00001), &TraceCwnd,
                               prefix_file_name + flowString + "-cwnd.data", index+1);
          Simulator::Schedule (Seconds (start_time * index + 0.00001), &TraceSsThresh,
                               prefix_file_name + flowString + "-ssth.data", index+1);
          Simulator::Schedule (Seconds (start_time * index + 0.00001), &TraceRtt,
                               prefix_file_name + flowString + "-rtt.data", index+1);
          Simulator::Schedule (Seconds (start_time * index + 0.00001), &TraceRto,
                               prefix_file_name + flowString + "-rto.data", index+1);
          Simulator::Schedule (Seconds (start_time * index + 0.00001), &TraceNextTx,
                               prefix_file_name + flowString + "-next-tx.data", index+1);
          Simulator::Schedule (Seconds (start_time * index + 0.00001), &TraceInFlight,
                               prefix_file_name + flowString + "-inflight.data", index+1);
          Simulator::Schedule (Seconds (start_time * index + 0.1), &TraceNextRx,
                               prefix_file_name + flowString + "-next-rx.data", num_flows+index+1);
        }
    }

  if (pcap)
    {
      UnReLink.EnablePcapAll (prefix_file_name, true);
      LocalLink.EnablePcapAll (prefix_file_name, true);
    }

  // Flow monitor
  FlowMonitorHelper flowHelper;
  if (flow_monitor)
    {
      flowHelper.InstallAll ();
    }

  Simulator::Stop (Seconds (stop_time));
  Simulator::Run ();

  if (flow_monitor)
    {
      flowHelper.SerializeToXmlFile (prefix_file_name + ".flowmonitor", true, true);
    }

  Simulator::Destroy ();
  return 0;
}