How to Begin Implement Transport Layer in NS3

To implement a Transport Layer using NS3 that has comprises of creating a network protocol for handling end-to-end interaction, reliability, flow control, and congestion control. Sample contains TCP and UDP by TCP providing reliability and UDP offering lightweight interaction.

Below is a structured mechanism on how to execute a Transport Layer using NS3:

Steps to Begin Implement Transport Layer in NS3

Step 1: Understand the Transport Layer

1. Key Features:
   • Segmentation and Reassembly: Split messages into smaller parts for transmission and reassemble them on receiver.
   • Reliability: Make use of acknowledgments (ACKs) and retransmissions.
   • Flow Control: It avoids sender from devastating the receiver.
   • Congestion Control: Fine-tune sending rate according to the network conditions.
   • Multiplexing/Demultiplexing: Direct sections to the precise application using ports.
2. Applications:
   • Design application-specific transport protocols.
   • Prolong TCP or UDP including new aspects.
   • Replicate a custom transport protocol.

Step 2: Set Up NS3 Environment

1. Create a Protocol Directory:
   • Make a protocol directory in src/, for instance src/transport-layer/.
2. Add Necessary Files:
   • transport-layer.cc: Execution file.
   • transport-layer-helper.h and transport-layer-helper.cc: Helper classes.
   • transport-layer.h: Header file for the transport layer protocol.
3. Update Build System:
   • Adjust the wscript within src/ containing the transport-layer component for updating the system.

Step 3: Design the Transport Layer

Define the Protocol Class

Make a protocol class for handling transport-layer operations with connections, reliability, and flow control.

Header File (transport-layer.h)

#include “ns3/application.h”

#include “ns3/packet.h”

#include <map>

class TransportLayer : public ns3::Object {

public:

static ns3::TypeId GetTypeId (void);

TransportLayer ();

virtual ~TransportLayer ();

void SetNode (ns3::Ptr<ns3::Node> node);

void Send (uint16_t srcPort, uint16_t dstPort, ns3::Ptr<ns3::Packet> packet);

void Receive (ns3::Ptr<ns3::Packet> packet, uint16_t srcPort, uint16_t dstPort);

private:

void HandleSegment (ns3::Ptr<ns3::Packet> segment);

void Retransmit (uint16_t seqNum);

struct ConnectionState {

uint16_t lastAckReceived;

uint16_t nextSeqNum;

std::map<uint16_t, ns3::Ptr<ns3::Packet>> sentSegments; // Retransmission buffer

};

std::map<uint16_t, ConnectionState> m_connections; // Active connections by port

ns3::Ptr<ns3::Node> m_node;                       // Associated node

};

Implement Core Functions

Set Node

Connect the Transport Layer including a certain node.

void TransportLayer::SetNode (ns3::Ptr<ns3::Node> node) {

m_node = node;

}

Send Data

Split the message into segments, allocate sequence numbers, and transmit data to the receiver.

void TransportLayer::Send (uint16_t srcPort, uint16_t dstPort, ns3::Ptr<ns3::Packet> packet) {

uint16_t seqNum = m_connections[srcPort].nextSeqNum++;

m_connections[srcPort].sentSegments[seqNum] = packet;

ns3::Ptr<ns3::Packet> segment = ns3::Create<ns3::Packet> ();

// Serialize headers (srcPort, dstPort, seqNum, etc.)

// …

segment->AddAtEnd(packet);

m_node->GetObject<ns3::Ipv4>()->Send(segment, ns3::Ipv4Address::GetAny(), ns3::Ipv4Address(“destination”), 0);

}

Receive Data

Handle incoming segments and manage the acknowledgments of receiving data.

void TransportLayer::Receive (ns3::Ptr<ns3::Packet> packet, uint16_t srcPort, uint16_t dstPort) {

uint16_t seqNum;

// Deserialize headers to retrieve seqNum, srcPort, dstPort, etc.

// …

if (seqNum == m_connections[dstPort].lastAckReceived + 1) {

m_connections[dstPort].lastAckReceived = seqNum;

// Deliver the payload to the application

ns3::Ptr<ns3::Packet> payload = packet->CreateFragment(sizeof(seqNum), packet->GetSize() – sizeof(seqNum));

// Deliver payload to application layer

}

// Send acknowledgment

ns3::Ptr<ns3::Packet> ack = ns3::Create<ns3::Packet> ();

// Serialize ACK headers

// …

m_node->GetObject<ns3::Ipv4>()->Send(ack, ns3::Ipv4Address::GetAny(), ns3::Ipv4Address(“source”), 0);

}

Handle Retransmissions

Transmit again segments, which have not been known.

void TransportLayer::Retransmit (uint16_t seqNum) {

for (const auto& conn : m_connections) {

auto it = conn.second.sentSegments.find(seqNum);

if (it != conn.second.sentSegments.end()) {

m_node->GetObject<ns3::Ipv4>()->Send(it->second, ns3::Ipv4Address::GetAny(), ns3::Ipv4Address(“destination”), 0);

}

}

}

Step 4: Write a Helper Class

Make a helper class to incorporate the transport layer to replications.

#include “transport-layer.h”

class TransportLayerHelper {

public:

void Install (ns3::NodeContainer nodes) {

for (auto it = nodes.Begin(); it != nodes.End(); ++it) {

ns3::Ptr<TransportLayer> transport = ns3::CreateObject<TransportLayer>();

transport->SetNode(*it);

(*it)->AggregateObject(transport);

}

}

};

Step 5: Write a Simulation Script

Example Simulation Script

#include “ns3/core-module.h”

#include “ns3/network-module.h”

#include “ns3/internet-module.h”

#include “transport-layer-helper.h”

using namespace ns3;

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

NodeContainer nodes;

nodes.Create(2);

PointToPointHelper p2p;

p2p.SetDeviceAttribute(“DataRate”, StringValue(“10Mbps”));

p2p.SetChannelAttribute(“Delay”, StringValue(“2ms”));

NetDeviceContainer devices = p2p.Install(nodes);

InternetStackHelper internet;

internet.Install(nodes);

TransportLayerHelper transportHelper;

transportHelper.Install(nodes);

Simulator::Run();

Simulator::Destroy();

return 0;

}

Step 6: Compile and Run

1. Build the Protocol:

./waf configure

./waf build

1. Run the Simulation:

./waf –run your-script

Step 7: Analyze and Extend

1. Tracing:
   • Examine the segment transmission and acknowledgments leveraging AsciiTraceHelper or PcapHelper.
2. Enhancements:
   • Integrate congestion control such as TCP Reno, TCP Cubic for improvements.
   • Execute further aspects such as Selective Acknowledgment (SACK).
   • Replicate transport-layer protocols for particular use cases such as IoT or streaming.

In this manual, detailed implementation methodology with sample coding for Transport Layer has been conducted using the NS3 environment. Additional insights can be included in an upcoming manual.