Simulation of Mixed TCP and UDP Traffic and Their Performance Impact Using ns3 | NS3 Project 16

Simulation of Mixed TCP and UDP Traffic and their Performance Impact Using ns-3

The objective of this experiment is to simulate a network with both TCP and UDP traffic using ns-3 and analyze how they affect each other’s performance in terms of throughput. In computer networks, TCP (Transmission Control Protocol) is a reliable and congestion-controlled protocol, while UDP (User Datagram Protocol) is faster but does not implement congestion control. When both protocols share the same network, their behavior differs significantly. This experiment studies their interaction and performance impact.

A network topology with multiple nodes connected using point-to-point links is created in ns-3. TCP traffic is generated using BulkSendApplication and UDP traffic is generated using OnOffApplication. FlowMonitor is used to collect performance metrics such as throughput. NetAnim is used to visualize packet transmission.

Source Code

#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/flow-monitor-module.h"
#include "ns3/netanim-module.h"

using namespace ns3;

int main () {
    NodeContainer nodes;
    nodes.Create(4);

    // Point-to-Point links
    PointToPointHelper p2p;
    p2p.SetDeviceAttribute("DataRate", StringValue("10Mbps"));
    p2p.SetChannelAttribute("Delay", StringValue("2ms"));

    NetDeviceContainer d1 = p2p.Install(nodes.Get(0), nodes.Get(1));
    NetDeviceContainer d2 = p2p.Install(nodes.Get(1), nodes.Get(2));
    NetDeviceContainer d3 = p2p.Install(nodes.Get(2), nodes.Get(3));

    // Internet stack
    InternetStackHelper stack;
    stack.Install(nodes);

    // IP addressing
    Ipv4AddressHelper address;

    address.SetBase("10.1.1.0", "255.255.255.0");
    Ipv4InterfaceContainer i1 = address.Assign(d1);

    address.SetBase("10.1.2.0", "255.255.255.0");
    Ipv4InterfaceContainer i2 = address.Assign(d2);

    address.SetBase("10.1.3.0", "255.255.255.0");
    Ipv4InterfaceContainer i3 = address.Assign(d3);

    Ipv4GlobalRoutingHelper::PopulateRoutingTables();

    // ---------------- TCP TRAFFIC ----------------
    uint16_t tcpPort = 8080;

    BulkSendHelper tcpSource("ns3::TcpSocketFactory",
                             InetSocketAddress(i3.GetAddress(1), tcpPort));
    tcpSource.SetAttribute("MaxBytes", UintegerValue(0));

    ApplicationContainer tcpApp = tcpSource.Install(nodes.Get(0));
    tcpApp.Start(Seconds(1.0));
    tcpApp.Stop(Seconds(10.0));

    PacketSinkHelper tcpSink("ns3::TcpSocketFactory",
                             InetSocketAddress(Ipv4Address::GetAny(), tcpPort));
    tcpSink.Install(nodes.Get(3));

    // ---------------- UDP TRAFFIC ----------------
    uint16_t udpPort = 9090;

    OnOffHelper udpSource("ns3::UdpSocketFactory",
                          InetSocketAddress(i3.GetAddress(1), udpPort));
    udpSource.SetAttribute("DataRate", StringValue("5Mbps"));
    udpSource.SetAttribute("PacketSize", UintegerValue(1024));

    ApplicationContainer udpApp = udpSource.Install(nodes.Get(1));
    udpApp.Start(Seconds(2.0));
    udpApp.Stop(Seconds(10.0));

    PacketSinkHelper udpSink("ns3::UdpSocketFactory",
                             InetSocketAddress(Ipv4Address::GetAny(), udpPort));
    udpSink.Install(nodes.Get(3));

    // ---------------- FLOW MONITOR ----------------
    FlowMonitorHelper flowmon;
    Ptr<FlowMonitor> monitor = flowmon.InstallAll();

    // ---------------- NETANIM ----------------
    AnimationInterface anim("anim.xml");

    Simulator::Stop(Seconds(10.0));
    Simulator::Run();

    // Save results
    monitor->SerializeToXmlFile("results.xml", true, true);

    Simulator::Destroy();
    return 0;
}

Simulation Setup Details

• LLM Used: ChatGPT (GPT-5.3)
• Prompt: “Generate ns-3 code to simulate mixed TCP and UDP traffic and analyze their performance using FlowMonitor.”

Network Animation

The animation shows packet transmission between nodes. Both TCP and UDP flows are visible. UDP transmits continuously, while TCP adapts its rate. This demonstrates how both protocols share network resources.

Throughput Analysis

Explanation:

The graph was generated using Gnuplot based on throughput values obtained from FlowMonitor. Both TCP and UDP achieve nearly equal throughput (~6.9 Mbps), indicating that the network is not congested. TCP maintains its transmission rate even in the presence of UDP traffic.

FlowMonitor Output & Calculations

Throughput is calculated using the formula:

Throughput (Mbps) = (rxBytes × 8) / (time × 1,000,000)

For TCP:
= (8,693,408 × 8) / (10 × 1,000,000) ≈ 6.95 Mbps

For UDP:
Throughput = (8,649,896 × 8) / (10 × 1,000,000) ≈ 6.91 Mbps

Conclusion

The experiment demonstrates that both TCP and UDP can achieve similar throughput under low congestion conditions. However, UDP does not adjust its rate, whereas TCP adapts based on network conditions. This highlights the importance of congestion control in network performance.

Increasing UDP traffic can reduce TCP throughput due to congestion, showing unfair bandwidth sharing.