title: How to create two BulkSendApplications?
body: <p>I want to use two BulkSendApplications to send from node_0 to node_1 and from node_2 to node_3.
  My code for creating the applications looks the following:</p>
  
  <pre><code>  // node_0 to node_1
  
    uint16_t rcv_port = 50000;
    PacketSinkHelper sink1 ("ns3::TcpSocketFactory",
                           Address (InetSocketAddress (Ipv4Address::GetAny (), rcv_port)));
    ApplicationContainer sinkApps1 = sink1.Install (node_1);
    sinkApps1.Start (MilliSeconds (0));
    sinkApps1.Stop (MilliSeconds (start_sending_traffic + traffic_duration));
  
    BulkSendHelper source1 (
        "ns3::TcpSocketFactory",
        Address (InetSocketAddress (node_1, rcv_port)));
    ApplicationContainer sourceApps1 = source1.Install (node_0);
    source.SetAttribute ("MaxBytes", UintegerValue (0));
    sourceApps1.Start (MilliSeconds (start_sending_traffic));
    sourceApps1.Stop (MilliSeconds (start_sending_traffic + traffic_duration));
  
    // node_2 to node_3
  
    uint16_t rcv_port2 = 50001;
    PacketSinkHelper sink2 ("ns3::TcpSocketFactory",
                            Address (InetSocketAddress (Ipv4Address::GetAny (), rcv_port2)));
    ApplicationContainer sinkApps2 = sink2.Install (node_3);
    sinkApps2.Start (MilliSeconds (0));
    sinkApps2.Stop (MilliSeconds (start_sending_traffic + traffic_duration));
  
    BulkSendHelper source2 (
        "ns3::TcpSocketFactory",
        Address (InetSocketAddress (node_3, rcv_port2)));
    ApplicationContainer sourceApps2 = source2.Install (node_2);
    source2.SetAttribute ("MaxBytes", UintegerValue (0));
    sourceApps2.Start (MilliSeconds (start_sending_traffic));
    sourceApps2.Stop (MilliSeconds (start_sending_traffic + traffic_duration));
  </code></pre>
  
  <p>The code is the same for both, just with the correct nodes. If I run this code, node_0->node_1 is transmitting the correct amount of traffic while node_2->node_3 is not transmitting anything.
  I am checking the amount of bits received with the following code snippet:</p>
  
  <pre><code>  Ptr&lt;PacketSink&gt; s1 = DynamicCast&lt;PacketSink&gt; (sinkApps1.Get (0));
    std::cout &lt;&lt; "Total Bits Received: " &lt;&lt; s1-&gt;GetTotalRx () * 8 &lt;&lt; std::endl;
    Ptr&lt;PacketSink&gt; s2 = DynamicCast&lt;PacketSink&gt; (sinkApps2.Get (0));
    std::cout &lt;&lt; "Total Bits Received: " &lt;&lt; s2-&gt;GetTotalRx () * 8 &lt;&lt; std::endl;
  </code></pre>
  
  <p>Does anyone know what is going wrong here? Am I using the constructors the wrong way?</p>