One server and multiple clients in NS-3 - server

Question

I want to simulate a server that receives packets from multiple clients and process the data of these packets simultaneously together in NS-3. I have simulated one single server and client in NS-3 by modifying udp-echo-server and udp-echo-client applications in NS-3. Now, for implementing multiple clients, I modified the end lines of StartApplication function in udp-echo-server application as follows:
if((childpid=fork())==0)
{
m_socket->SetRecvCallback (MakeCallback(&UdpEchoServer::HandleRead, this));
m_socket6->SetRecvCallback (MakeCallback(&UdpEchoServer::HandleRead, this));
}
But it does not work. Actually, by connecting two clients, it just reads the first client and ignores the second client. It just runs StartApplication function once. Can anyone help me with this?
Thanks

Answer 1

The fundamental problem with what you're trying to do is that ns-3 is a single threaded simulator. You should not use fork to simulate forking. If you want multiple clients, you have to explicitly create them. I have quickly whipped up a simple example:
/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
// simple udp multi-client, single-server simulation to answer
// https://stackoverflow.com/q/59632211/13040392
#include "ns3/core-module.h"
#include "ns3/internet-module.h"
#include "ns3/point-to-point-module.h"
#include "ns3/ipv4-global-routing-helper.h"
#include "ns3/applications-module.h"
#include "ns3/point-to-point-grid.h"
#include "ns3/flow-monitor-module.h"
using namespace ns3;
NS_LOG_COMPONENT_DEFINE("UdpMultiClient");
int
main(int argc, char *argv[]) {
// create grid structure of network
// not necessary. Could just create topology manually
PointToPointHelper p2pLink;
PointToPointGridHelper grid (2, 2, p2pLink);
InternetStackHelper stack;
grid.InstallStack(stack);
// assign IP addresses to NetDevices
grid.AssignIpv4Addresses (Ipv4AddressHelper ("10.1.1.0", "255.255.255.0"),
Ipv4AddressHelper ("10.2.1.0", "255.255.255.0"));
Ipv4GlobalRoutingHelper::PopulateRoutingTables();
// configure and install server app
int serverPort = 8080;
UdpEchoServerHelper serverApp (serverPort);
serverApp.Install(grid.GetNode(0,0));
Address serverAddress = InetSocketAddress(grid.GetIpv4Address(0,0), serverPort);
// configure and install client apps
UdpEchoClientHelper clientApp (serverAddress);
clientApp.Install(grid.GetNode(0,1));
clientApp.Install(grid.GetNode(1,0));
clientApp.Install(grid.GetNode(1,1));
// install FlowMonitor to collect simulation statistics
FlowMonitorHelper flowHelper;
Ptr<FlowMonitor> flowMonitor = flowHelper.InstallAll();
// configure and run simulation
Simulator::Stop(Seconds(10));
NS_LOG_UNCOND("Starting simulation.");
Simulator::Run();
Simulator::Destroy();
NS_LOG_UNCOND("Simulation completed.");
// simulation complete
// get statistics of simlation from FlowMonitor
flowMonitor->CheckForLostPackets();
std::map<FlowId, FlowMonitor::FlowStats> stats = flowMonitor->GetFlowStats();
uint64_t txPacketsum = 0;
uint64_t rxPacketsum = 0;
uint64_t DropPacketsum = 0;
uint64_t LostPacketsum = 0;
double Delaysum = 0;
for (std::map<FlowId, FlowMonitor::FlowStats>::const_iterator i = stats.begin(); i != stats.end(); ++i) {
txPacketsum += i->second.txPackets;
rxPacketsum += i->second.rxPackets;
LostPacketsum += i->second.lostPackets;
DropPacketsum += i->second.packetsDropped.size();
Delaysum += i->second.delaySum.GetSeconds();
}
NS_LOG_UNCOND(std::endl << " SIMULATION STATISTICS");
NS_LOG_UNCOND(" All Tx Packets: " << txPacketsum);
NS_LOG_UNCOND(" All Rx Packets: " << rxPacketsum);
NS_LOG_UNCOND(" All Delay: " << Delaysum / txPacketsum);
NS_LOG_UNCOND(" All Lost Packets: " << LostPacketsum);
NS_LOG_UNCOND(" All Drop Packets: " << DropPacketsum);
NS_LOG_UNCOND(" Packets Delivery Ratio: " << ((rxPacketsum * 100) / txPacketsum) << "%");
NS_LOG_UNCOND(" Packets Lost Ratio: " << ((LostPacketsum * 100) / txPacketsum) << "%");
// flowMonitor->SerializeToXmlFile("test.xml", true, true);
return 0;
}
As a quick note, in
UdpEchoClientHelper clientApp (serverAddress);
clientApp.Install(grid.GetNode(0,1));
clientApp.Install(grid.GetNode(1,0));
clientApp.Install(grid.GetNode(1,1));
we installed the UdpEchoClient on three Nodes. According to the documentation for this Application, UdpEchoClient sends a packet every 1000000000 ns = 1 s by default. Since we set the length of the simulation to 10 seconds using Simulator::Stop(Seconds(10));, we expect that each client will send 10 packets to the server. So, a total of 30 packets should be sent by clients. Also, since we are using UdpEchoServerHelper on the server, each packet will be echoed back by the server. Therefore, a total of 30 x 2 = 60 packets should be transmitted on the network.
The output of the script is
Starting simulation.
Simulation completed.
SIMULATION STATISTICS
All Tx Packets: 60
All Rx Packets: 60
All Delay: 0.0423177
All Lost Packets: 0
All Drop Packets: 0
Packets Delivery Ratio: 100%
Packets Lost Ratio: 0%
This answer actually demonstrates several features of ns-3, so feel free to ask any followup questions. I highly encourage you to check out the ns-3 documentation for classes you haven't encountered yet.