How to Implement Network Blockage Mitigation in NS2

To implement the Network Blockage Mitigation in ns2, we have to simulate an environment with signal propagation amongst nodes congested by hindrances (like buildings or other objects) and accomplishing strategies to mitigate the influence of the jamming. It is especially vital in mmWave and 5G networks that have the important line-of-sight (LoS) communication and blockages can severely degrade network performance.

In ns2, we can replicate the impacts of network congestion by altering propagation models, launching packet loss, maximizing delays or redirecting traffic depends on the identified blockage. We have to expand its potential by modeling blockages when packet loss or signal degradation events because ns2 can’t directly replicate physical hindrances.

In this demonstration, we have provided the technique to implement the network blockage mitigation using ns2:

Steps to Implement Network Blockage Mitigation in NS2

  1. Simulate Blockage Effects: Launch blockage as a condition that degrades communication amongst nodes. This can be modeled as:
    • Increased packet loss: When a blockage happens, maximize the packet error rate.
    • Increased delay: Raise the transmission delays to replicate the impacts of obstructions.
    • Signal degradation: Minimize the transmission power or reception signal quality because of blockage.
  2. Mitigation Strategies:
    • Rerouting: If a blockage is identified, redirect the communication via other existed nodes.
    • Beam Steering: Bypass the blockage by modifying the transmission direction or antenna orientation.
    • Power Adjustment: Raise transmission power to overcome the blockage, if possible.

Example: Simulating Network Blockage and Mitigation in NS2

Below is an example that mimics network blockage amongst two nodes and executes a rerouting strategy to mitigate the blockage.

Step 1: Simulate Blockage by Increasing Packet Loss

You can simulate a blockage event by dynamically raising the packet loss rate among the two nodes.

# Define a simulator object

set ns [new Simulator]

# Define trace and nam files for output

set tracefile [open out.tr w]

set namfile [open out.nam w]

$ns trace-all $tracefile

$ns namtrace-all $namfile

# Define a ‘finish’ procedure to end the simulation and visualize in NAM

proc finish {} {

global ns tracefile namfile

$ns flush-trace

close $tracefile

close $namfile

exec nam out.nam &

exit 0

}

# Set up the topography for the simulation area

set topo [new Topography]

$topo load_flatgrid 1000 1000

# Define the wireless channel

set chan [new Channel/WirelessChannel]

# Configure wireless nodes with the IEEE 802.11 MAC protocol

$ns node-config -adhocRouting DSDV \

-llType LL \

-macType Mac/802_11 \

-ifqType Queue/DropTail/PriQueue \

-ifqLen 50 \

-antType Antenna/OmniAntenna \

-propType Propagation/TwoRayGround \

-phyType Phy/WirelessPhy \

-channel $chan

# Create three nodes to simulate a rerouting scenario

set node1 [$ns node]

set node2 [$ns node]

set node3 [$ns node]

# Set node positions (node1 and node2 are directly connected, node3 is a possible alternative route)

$node1 set X_ 200; $node1 set Y_ 200; $node1 set Z_ 0

$node2 set X_ 800; $node2 set Y_ 800; $node2 set Z_ 0

$node3 set X_ 500; $node3 set Y_ 500; $node3 set Z_ 0

# Create a duplex wireless link between node1 and node2

$ns duplex-link $node1 $node2 2Mb 10ms DropTail

# Define TCP traffic between node1 and node2

set tcp [new Agent/TCP]

set sink [new Agent/TCPSink]

$ns attach-agent $node1 $tcp

$ns attach-agent $node2 $sink

$ns connect $tcp $sink

# Create FTP traffic over TCP

set ftp [new Application/FTP]

$ftp attach-agent $tcp

$ftp start 1.0

$ftp stop 4.5

# Step 2: Introduce a blockage event between node1 and node2 by increasing packet loss

# Introduce a packet loss model (simulating signal degradation due to blockage)

set em [new ErrorModel]

$em unit packet

$em set rate_ 0.3  ;# Set a 30% packet loss rate due to blockage

$ns at 2.0 “$ns lossmodel $em $node1 $node2”  ;# Blockage occurs at 2 seconds

# Step 3: Mitigation strategy – reroute traffic through node3

proc reroute_traffic {src dst new_route} {

global ns

# Stop the current FTP traffic

$ns at 3.0 “$ftp stop”

# Detach current agents

$ns detach-agent $src $tcp

$ns detach-agent $dst $sink

# Reconfigure to route traffic through the new route (node3)

set new_tcp [new Agent/TCP]

set new_sink [new Agent/TCPSink]

$ns attach-agent $src $new_tcp

$ns attach-agent $new_route $new_sink

# Reconnect via the new route

$ns connect $new_tcp $new_sink

# Start FTP traffic over the new route

set new_ftp [new Application/FTP]

$new_ftp attach-agent $new_tcp

$new_ftp start 3.5  ;# Restart traffic at 3.5 seconds

}

# Schedule the rerouting after blockage is detected

$ns at 3.0 “reroute_traffic $node1 $node2 $node3”

# Schedule the end of the simulation

$ns at 6.0 “finish”

# Run the simulation

$ns run

  1. Explanation of the Script
  • Blockage Simulation: A blockage is simulated by maximizing the packet loss rate amongst node1 and node2 at 2.0 seconds. This indicates a physical obstruction that interrupts communication.
  • Rerouting Strategy: When the blockage is identified, the traffic is redirected over node3 at 3.0 seconds to bypass the blockage. The rerouting is accomplished by detaching the current agents and reconfiguring the traffic flow through node3.
  • Traffic: TCP traffic is primarily sent directly between node1 and node2, but after the blockage, it is redirected through node3.
  1. Run the Simulation

Save the script as blockage_mitigation.tcl and execute it using the given command:

ns blockage_mitigation.tcl

This will produce a trace file (out.tr) and a NAM file (out.nam). Authenticate the blockage effect and redirecting activities by analyzing the trace file.

  1. Visualize the Network in NAM

To visualize the simulation in the NAM tool, use the following command:

nam out.nam

In the NAM visualization, you can see:

  • Initial packet transmission amongst node1 and node2.
  • Packet loss or degradation after the blockage happens.
  • Rerouting of traffic through node3 after blockage mitigation.
  1. Advanced Mitigation Strategies

Here are a few latest mitigation techniques you can establish:

  • Dynamic Power Adjustment: Rather than rerouting, you can raise the transmission power of the nodes to overcome the blockage.

Example:

proc increase_power_due_to_blockage {node} {

# Increase the transmission power

$node set txPower_ 0.5  ;# Increase power

puts “Increased power to mitigate blockage”

}

# Schedule the power increase due to blockage

$ns at 2.5 “increase_power_due_to_blockage $node1”

  • Beam Steering: Simulate beam steering by altering the direction of transmission to evade the blockage. This can be modeled by modifying node locations or orientations over time.

Example:

proc steer_beam {node} {

# Adjust the node’s position to simulate beam steering

set current_x [$node set X_]

set new_x [expr $current_x + 100]

$node set X_ $new_x

puts “Steered beam by adjusting position”

}

# Schedule the beam steering after blockage

$ns at 2.5 “steer_beam $node1”

  • Multi-path Communication: Execute multi-path communication where packets are delivered sideways several paths to escape blockages.

Through the above manual, you can obtain and learn how to configure the simulation environment, how to replicate the network blockages and mitigation techniques into it including example snippets for the implementation of Network Blockage Mitigation using ns2 tool. You can also include their modern strategies for future enhancements.

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