How to Implement Cross Layer in NS2

To execute a Cross-Layer Design using NS2 which requires to include, enabling communication among various layers of the OSI model, like the physical, MAC, network, and transport layers. It breaks the old OSI model’s strict layer separation to permit the layers to distribute the information, thus enhancing the overall network performance, like developing the throughput, latency, and energy efficiency. In the simulation environment NS2, cross-layer interaction can be executed by interchanging data among the various protocols, influencing the parameters over the layers, or making new mechanisms which leverage information from several layers to enhance the performance.

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Step-by-Step Implementation:

  1. Understand Cross-Layer Concept

Cross-layer design normally includes:

  • Physical and MAC layer interaction: Modifying the transmission power, rate adaptation, or link quality information according on the state of the physical layer.
  • MAC and Network layer interaction: These routing protocols can be used data from the MAC layer, like link status or queue length, to make better routing decisions.
  • Network and Transport layer interaction: TCP can modify its performance rely on the network conditions such as congestion or packet loss observed at lower layers.
  1. Modify NS2 for Cross-Layer Communication

The simulation environment NS2 is modular and permits the customization, however executing cross-layer design usually contains:

  • Creating custom protocols that permits communication among various layers.
  • Modifying existing protocols to enable cross-layer information interchange.
  1. Step-by-Step Implementation

Example: Cross-Layer Interaction between the MAC and Network Layer

Now, we make a basic cross-layer implementation in which the network layer (routing) uses information from the MAC layer (e.g., current queue length) helps to make better routing decisions. It can help prevent the congested routes.

  1. a) Modify the MAC Layer to Expose Queue Length

In the simulation environment NS2, the MAC layer uses a queue to buffer packets before transmission. We can change the MAC layer to deliver the queue length within the network layer.

  1. Edit the MAC layer source code (mac-802_11.cc or mac-802_11.h depending on which MAC protocol you are using). Append a function to show the current queue length:

int Mac802_11::get_queue_length() {

return ifq_->length();

}

This technique will return the recent length of the MAC queue.

  1. Recompile NS2 to apply the changes:

make clean

make

  1. b) Modify the Network Layer (Routing Protocol) to Use MAC Information

For this instance, consider we are adapting the AODV routing protocol to assume the MAC layer queue length in route decisions.

  1. Edit the AODV source code (aodv.cc or aodv.h). Inside the AODV route discovery process, add logic to check the MAC queue length.

Append a function to recover the MAC queue length:

int AODV::get_mac_queue_length(nsaddr_t node_id) {

MobileNode *node = (MobileNode *)Node::get_node_by_address(node_id);

Mac802_11 *mac = (Mac802_11 *)node->mac();

return mac->get_queue_length();

}

  1. Modify the route selection process to consider the MAC queue length:

void AODV::choose_route() {

// Existing route discovery code…

// Example: Add logic to avoid nodes with large MAC queues

if (get_mac_queue_length(current_node_id) > MAX_QUEUE_THRESHOLD) {

// Skip this route, as the MAC queue is full

continue;

}

// Continue with normal routing logic

}

  1. Recompile NS2 to apply the changes:

make clean

make

  1. c) Create a TCL Script to Test Cross-Layer Implementation

Below is an instance TCL script to replicate the network with cross-layer routing:

# Create a new simulator

set ns [new Simulator]

# Open trace and nam files

set tracefile [open cross_layer.tr w]

$ns trace-all $tracefile

set namfile [open cross_layer.nam w]

$ns namtrace-all $namfile

# Define the topology

set num_nodes 4

set x_dim 500

set y_dim 500

# Create a topography object

set topo [new Topography]

$topo load_flatgrid $x_dim $y_di

# Configure wireless channel

set chan [new Channel/WirelessChannel]

set prop [new Propagation/TwoRayGround]

set netif [new Phy/WirelessPhy]

set mac [new Mac/802_11]

set ll [new LL]

set ant [new Antenna/OmniAntenna]

set ifq [new Queue/DropTail/PriQueue]

set ifqlen 50

set bw 2Mb

set delay 10ms

# Configure the nodes

$ns node-config -adhocRouting AODV \

-llType $ll \

-macType $mac \

-ifqType $ifq \

-ifqLen $ifqlen \

-antType $ant \

-propType $prop \

-phyType $netif \

-channelType $chan \

-topoInstance $topo \

-agentTrace ON \

-routerTrace ON \

-macTrace ON

# Create nodes and set positions

for {set i 0} {$i < $num_nodes} {incr i} {

set node($i) [$ns node]

}

$node(0) set X_ 50

$node(0) set Y_ 100

$node(0) set Z_ 0

$node(1) set X_ 100

$node(1) set Y_ 200

$node(1) set Z_ 0

$node(2) set X_ 150

$node(2) set Y_ 150

$node(2) set Z_ 0

$node(3) set X_ 200

$node(3) set Y_ 100

$node(3) set Z_ 0

# Create traffic flow

set tcp [new Agent/TCP]

set sink [new Agent/TCPSink]

$ns attach-agent $node(0) $tcp

$ns attach-agent $node(3) $sink

$ns connect $tcp $sink

# Attach FTP application to generate traffic

set ftp [new Application/FTP]

$ftp attach-agent $tcp

$ftp start

# Set simulation end time

$ns at 20.0 “finish”

# Finish procedure

proc finish {} {

global ns tracefile namfile

$ns flush-trace

close $tracefile

close $namfile

exec nam cross_layer.nam &

exit 0

}

# Run the simulation

$ns run

  1. Explanation of Key Components
  • MAC Layer Queue Exposure: Now, the MAC layer shows its queue length to higher layers.
  • Routing Protocol Modification: The AODV routing protocol now takes into account the MAC queue length while choosing routes, aiding to prevent the congested nodes.
  • Cross-Layer Decision Making: The routing decisions at the network layer are manipulated by real-time information from the MAC layer (queue length).
  1. Analyse the Simulation
  1. Run the simulation by saving the above script as cross_layer.tcl and implementing:

ns cross_layer.tcl

  1. Visualize the network behavior using NAM to observe how the network adjusts to congestion or overload conditions according to the cross-layer interaction:

nam cross_layer.nam

  1. Examine the trace file (cross_layer.tr) to compute the routing behaviour and packet delivery. We can verify whether the nodes with high MAC queue lengths are prevented in the route selection procedure.
  1. Extend the Implementation
  • Cross-Layer between PHY and MAC Layer: We can execute the cross-layer optimization for adaptive power control or rate adaptation at the MAC layer depending on the signal-to-noise ratio (SNR) from the physical layer.
  • Energy-Aware Routing: We can integrate energy levels from the physical layer into the routing decisions at the network layer.
  • QoS-aware Cross-Layer Design: Execute the QoS-aware cross-layer interactions in which the MAC layer queue lengths or delays influence transport layer performance such as TCP congestion control.
  1. Advanced Considerations
  • Optimization Algorithms: We can execute the optimization algorithms such as Machine Learning or Game Theory at the application layer to create the intelligent decisions rely on the cross-layer information.
  • Protocol Stack Modification: If we want more flexibility, we can create the own cross-layer protocol by adapting the NS2 stack to permit the greater freedom in how information is exchanged among the layers.
  • Metrics: Examine metrics like throughput, delay, energy consumption, or packet delivery ratio under various cross-layer optimization approaches.

As above, we completely explained about how to follow the procedure that support to implement and examine the Cross layer in the simulation environment NS2. We will presented further insights in another materials based on your needs.