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# How to Calculate Buffer Rate in ns3

To calculate buffer rate in ns3, we have to monitor the buffer occupancy over time and determining the rate at which packets are being added to the buffer. In scenarios such as streaming applications or network congestion studies, this concept is very useful. Here is a complete guide to calculate buffer rate in ns3.

Steps for calculating buffer rate

1. Set up the simulation :
• To simulate the network, create a network topology with nodes, protocols and links configured.
1. Monitor the buffer :
• To monitor the buffer occupancy at regular intervals, use ns3 tracing capabilities.
1. Calculate buffer rate :
• Calculate the rate at which packets are added to the buffer over time.

Example of a simple buffer rate calculation

Create a basic network topology and calculate the buffer rate.

set up the simulation

#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/queue-disc-module.h”

#include <iostream>

#include <fstream>

using namespace ns3;

NS_LOG_COMPONENT_DEFINE(“BufferRateExample”);

// Global variables to store buffer occupancy data

std::vector<uint32_t> bufferOccupancy;

std::vector<double> timeStamps;

void

QueueMonitor(Ptr<QueueDisc> queue, double interval) {

// Record the current buffer occupancy and time stamp

bufferOccupancy.push_back(queue->GetInternalQueue(0)->GetNPackets());

timeStamps.push_back(Simulator::Now().GetSeconds());

// Schedule the next monitoring event

Simulator::Schedule(Seconds(interval), &QueueMonitor, queue, interval);

}

int main(int argc, char *argv[]) {

// Set up the default simulation parameters

Time::SetResolution(Time::NS);

LogComponentEnable(“BufferRateExample”, LOG_LEVEL_INFO);

// Create nodes

NodeContainer nodes;

nodes.Create(2);

// Set up the point-to-point link

PointToPointHelper pointToPoint;

pointToPoint.SetDeviceAttribute(“DataRate”, StringValue(“5Mbps”));

pointToPoint.SetChannelAttribute(“Delay”, StringValue(“2ms”));

NetDeviceContainer devices;

devices = pointToPoint.Install(nodes);

// Install the Internet stack

InternetStackHelper stack;

stack.Install(nodes);

// Set up a UDP server

uint16_t port = 9;

UdpServerHelper server(port);

ApplicationContainer serverApps = server.Install(nodes.Get(1));

serverApps.Start(Seconds(1.0));

serverApps.Stop(Seconds(10.0));

// Set up a UDP client

uint32_t packetSize = 1024; // 1 KB

uint32_t maxPacketCount = 320; // 320 KB total data

Time interPacketInterval = Seconds(0.05); // 50 ms interval

client.SetAttribute(“MaxPackets”, UintegerValue(maxPacketCount));

client.SetAttribute(“Interval”, TimeValue(interPacketInterval));

client.SetAttribute(“PacketSize”, UintegerValue(packetSize));

ApplicationContainer clientApps = client.Install(nodes.Get(0));

clientApps.Start(Seconds(2.0));

clientApps.Stop(Seconds(10.0));

// Set up QueueDisc

TrafficControlHelper tch;

tch.SetRootQueueDisc(“ns3::PfifoFastQueueDisc”);

Ptr<QueueDisc> queue = tch.Install(devices.Get(1)).Get(0);

// Monitor the buffer occupancy every 0.1 seconds

Simulator::Schedule(Seconds(0.1), &QueueMonitor, queue, 0.1);

Simulator::Stop(Seconds(10.0));

Simulator::Run();

// Calculate buffer rate

std::ofstream outFile;

outFile.open(“buffer_rate.txt”);

outFile << “Time (s)\tBuffer Occupancy (packets)\tBuffer Rate (packets/s)\n”;

for (size_t i = 1; i < bufferOccupancy.size(); ++i) {

double rate = static_cast<double>(bufferOccupancy[i] – bufferOccupancy[i – 1]) / (timeStamps[i] – timeStamps[i – 1]);

outFile << timeStamps[i] << “\t” << bufferOccupancy[i] << “\t” << rate << “\n”;

}

outFile.close();

Simulator::Destroy();

return 0;

}

Explanation

1. Simulation setup :

Two nodes are created. Those nodes are connected using a point-to-point link. Install the Internet stack on both nodes and assign IP addresses.

1. Application setup :

On destination node (Node 1), a UDP server is installed. and On source node (Node 0), a UDP echo client is installed.

1. Queue disc setup :

To install a queue discipline (e.g., PfifoFastQueueDisc) on the device, use TrafficControlHelper.

1. Monitoring Buffer Occupancy:

To record buffer occupancy and timestamps at regular intervals, define the QueueMonitor. Schedule the QueueMonitor function to run periodically.

1. Running the Simulation :

The simulation runs for a specified period of time.

1. Calculating buffer rate :

The simulation runs by calculating the buffer rate by computing the difference in buffer occupancy between consecutive time points and dividing by the time interval.  Save the results to a file.

Overall, we had successfully learned on calculating buffer rate in ns3 by monitoring the buffer occupancy over time and determining the rate at which packets are being added to the buffer.

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