How to Implement Massive Channel Access in NS2

To implement the Massive Channel Access using the simulation environment NS2 that encompasses simulating a network including a large number of nodes (devices) are attempting to access a distributed communication channel concurrently. This situation is general in the wireless networks like sensor networks, 5G networks, and IoT, that numerous devices contend for the channel access to transfer the data. We present the simple stepwise method to execute it in NS2:

Step-by-Step Implementation:

Key Steps:

  1. Configure a huge number of nodes to replicate the massive access.
  2. Set up the MAC (Medium Access Control) protocols like 802.11 (Wi-Fi) or CSMA/CA to handle the channel access.
  3. Make traffic from every node to mimic simultaneous transmission attempts.
  4. Observe the collision, throughput, and delay that are vital metrics to estimate how effectively the network manages the massive channel access.
  1. NS2 Setup for Massive Channel Access

Primarily, configure the NS2 and describe the network properties. We will want to make a huge number of nodes and state a wireless channel for communication.

# Create an NS2 simulator instance

set ns [new Simulator]

# Open trace file and NAM file for logging the simulation

set tracefile [open “massive_channel_access.tr” w]

set namfile [open “massive_channel_access.nam” w]

$ns trace-all $tracefile

$ns namtrace-all-wireless $namfile 1000 1000

# Define the wireless channel for communication

set chan_1_ [new Channel/WirelessChannel]

# Define the topography (e.g., a 1000×1000 grid)

set topo [new Topography]

$topo load_flatgrid 1000 1000

# Define propagation, MAC, and queue parameters

set prop [new Propagation/TwoRayGround]   ;# Propagation model for wireless communication

set netif [new Phy/WirelessPhy]

set mac [new Mac/802_11]                  ;# 802.11 MAC protocol to simulate CSMA/CA

set ll [new LL]

set ifq [new Queue/DropTail/PriQueue]     ;# Priority queue

set ant [new Antenna/OmniAntenna]

# Configure node settings

$ns node-config -llType $ll \

-macType $mac \

-ifqType $ifq \

-ifqLen 50 \

-antType $ant \

-propType $prop \

-phyType $netif \

-channel $chan_1_ \

-topoInstance $topo

  1. Creating a Massive Number of Nodes

Describe a large number of nodes to replicate the massive access. For instance, we can mimic the 100 nodes that will all attempt to access the channel concurrently.

# Create 100 mobile nodes (devices)

set num_nodes 100

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

set node($i) [$ns node]

# Randomly place nodes in the simulation space

$node($i) set X_ [expr rand() * 1000]

$node($i) set Y_ [expr rand() * 1000]

$node($i) set Z_ 0

}

  1. Defining Traffic for Massive Channel Access

Set up each node to make traffic to emulate simultaneous channel access attempts. CBR (Constant Bit Rate) traffic can be used to replicate the continuous data transmission.

Example: Creating UDP Traffic

# Create UDP agents and CBR traffic between random nodes

for {set i 0} {$i < $num_nodes/2} {incr i} {

set udp($i) [new Agent/UDP]

set null($i) [new Agent/Null]

# Attach UDP agent to a source node and Null agent to a destination node

$ns attach-agent $node($i) $udp($i)

$ns attach-agent $node([expr $i + $num_nodes/2]) $null($i)

# Connect the source and destination

$ns connect $udp($i) $null($i)

# Create a CBR application and attach it to the UDP agent

set cbr($i) [new Application/Traffic/CBR]

$cbr($i) attach-agent $udp($i)

$cbr($i) set packetSize_ 512   ;# 512-byte packets

$cbr($i) set rate_ 256Kb       ;# Data rate of 256 Kbps

# Start and stop traffic at random times to simulate contention

set start_time [expr 0.5 + rand() * 5]  ;# Start traffic randomly between 0.5 and 5 seconds

set stop_time [expr 10.0 + rand() * 5]  ;# Stop traffic between 10 and 15 seconds

$ns at $start_time “$cbr($i) start”

$ns at $stop_time “$cbr($i) stop”

}

  1. MAC Protocol (CSMA/CA)

The 802.11 MAC protocol (used in Wi-Fi) that executes CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) that is important for managing the contention for a shared channel within the wireless networks.

The MAC protocol will make sure that nodes are listen before transferring to minimise the collisions. In a massive channel access scenario, this may even the outcomes in collisions because of the high number of simultaneous transmission attempts.

  1. Running the Simulation

Place the simulation duration and run the simulation. Finally, complete the simulation then close the trace files.

# Set the simulation end time

$ns at 20.0 “finish”

# Finish procedure to close trace files and end simulation

proc finish {} {

global ns tracefile namfile

$ns flush-trace

close $tracefile

close $namfile

exit 0

}

# Run the simulation

$ns run

  1. Analysing the Results

We can estimate the trace files and network animation (NAM), after running the simulation that to assess the performance of the massive channel access. Some vital parameters to analyse contain:

6.1 Throughput

Compute how much data is well transmitted despite contention. We can extract throughput data from the trace files by straining for the packet delivery events.

6.2 Packet Loss

Verify for dropped packets by reason of the collisions or full queues. High contention may lead to maximise packet loss.

6.3 Latency

Estimate how long it obtains for packets to attain their end. Contention and collisions might cause delays in the packet delivery.

6.4 Collision Count

The 802.11 MAC protocol supports to minimise the collisions using CSMA/CA, however while many nodes attempts to access the channel simultaneously, and collisions may still happen. We can observe how frequently collisions occur by evaluating the trace logs.

In the above procedure established the comprehensive process to execute and evaluate the Massive Channel Access in ns2 simulation tool. Additional specific details regarding this topic will also be provided.

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