How to Implement Network Relay Selection in NS2

To implement Network Relay Selection in NS2 has includes to mimic the scenarios in which the nodes or devices enthusiastically select relays to frontward data to their destination. This is usually in multi-hop wireless networks, ad-hoc networks, and relay-assisted communication systems such as cooperative communication.

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Here is a protocol is implementing the Network Relay Selection in ns2:

Step-by-Step Implementation:

  1. Understand Network Relay Selection

In a network with relay selection, the source node can use intermediate relay nodes to forward data to the destination. The selection of relay nodes can be based on numerous parameters such as:

  • Signal quality (SNR/BER) between the nodes.
  • Distance between nodes.
  • Energy efficiency of the relays.
  • Link capacity or bandwidth.
  • Packet delay and queue length at the relay.

our implementation of relay selection can contain one or more of these parameters.

  1. Set up Network Topology

Initiate by describing the nodes in simulation that contain source, destination, and relay nodes.

# Create NS2 Simulator instance

set ns [new Simulator]

# Create nodes (source, destination, and relays)

set src [$ns node]

set relay1 [$ns node]

set relay2 [$ns node]

set dst [$ns node]

# Create wired or wireless links between nodes

$ns duplex-link $src $relay1 2Mb 10ms DropTail

$ns duplex-link $src $relay2 2Mb 10ms DropTail

$ns duplex-link $relay1 $dst 2Mb 10ms DropTail

$ns duplex-link $relay2 $dst 2Mb 10ms DropTail

This generates a basic relay-based topology with two possible relays (relay1 and relay2) among the source (src) and destination (dst).

  1. Define Relay Selection Criteria

Now, describe the relay selection logic according to particular criteria. For instance, we can use:

  • Distance-based selection: Select the relay closest to the destination.
  • Signal strength: choose the relay with the strongest signal.
  • Delay-based selection: prioritize the relay with the lowest end-to-end delay.

Here’s an example of distance-based selection:

proc select_relay {src dst relay1 relay2} {

# Calculate distance between source and relays

set dist1 [$ns get-dist $src $relay1]

set dist2 [$ns get-dist $src $relay2]

# Select the relay with the shortest distance

if { $dist1 < $dist2 } {

puts “Relay1 selected (closer to source)”

return $relay1

} else {

puts “Relay2 selected (closer to source)”

return $relay2

}

}

In this code, select_relay estimates the distances among the source and the relays, then prioritize the relay with the shortest distance.

  1. Implement Relay Selection Based on Signal Strength

We can also choose the relay based on signal strength or SNR (Signal-to-Noise Ratio). Here’s how we might mimic signal strength among nodes:

proc get_signal_strength {src relay} {

# Simulate signal strength based on a simple function (e.g., inverse of distance)

set dist [$ns get-dist $src $relay]

set signal_strength [expr 1.0 / $dist]

return $signal_strength

}

proc select_best_relay {src relay1 relay2} {

set signal1 [get_signal_strength $src $relay1]

set signal2 [get_signal_strength $src $relay2]

if { $signal1 > $signal2 } {

puts “Relay1 selected (higher signal strength)”

return $relay1

} else {

puts “Relay2 selected (higher signal strength)”

return $relay2

}

}

Here, get_signal_strength returns simulated signal strength, and select_best_relay choose the relay with the highest signal strength.

  1. Simulate Traffic Flow through the Selected Relay

Once a relay is chosen, we need to forward traffic through it. Use agents such as UDP or TCP to replicate the flow of packets through the relay node.

# Create a UDP agent on the source

set udp [new Agent/UDP]

$ns attach-agent $src $udp

# Create a Null agent on the destination

set null [new Agent/Null]

$ns attach-agent $dst $null

$ns connect $udp $null

# Choose the relay based on the selection criteria

set selected_relay [select_best_relay $src $relay1 $relay2]

# Set up forwarding from source to selected relay, then to the destination

$ns connect $udp [$ns attach-agent $selected_relay [new Agent/UDP]]

In this sample, traffic from the source (src) is forwarded via the selected relay, which then transferred the traffic to the destination.

  1. Implement Cooperative Communication (Optional)

If we want to mimic cooperative communication, in which both the source and the relay transmit the same message to enhance the reliability, we can adjust the above procedure to contain both the source and relay in transmission.

# Cooperative communication: both source and relay transmit

proc cooperative_relay {src relay dst} {

puts “Both source and relay are transmitting to the destination.”

# Source and relay send data to the destination cooperatively

set udp_src [new Agent/UDP]

$ns attach-agent $src $udp_src

set udp_relay [new Agent/UDP]

$ns attach-agent $relay $udp_relay

set null [new Agent/Null]

$ns attach-agent $dst $null

# Send data from both source and relay

$ns connect $udp_src $null

$ns connect $udp_relay $null

}

This replicates a scenario in which both the source and relay nodes instantaneously transmit information to the destination, that enhance the reliability through diversity.

  1. Trace and Analyse Relay Selection

We can use NS2’s trace functionality to log relay selections and packet flows for analysis.

# Open a trace file

set tracefile [open “relay_selection_trace.tr” w]

$ns trace-all $tracefile

# Log relay selection

proc log_relay_selection {relay} {

global tracefile

puts $tracefile “Selected relay: $relay at time [$ns now]”

}

log_relay_selection $selected_relay

This permits to evaluate the relay selection process and see how well criteria perform.

  1. Run the Simulation

Once everything is set up, execute the simulation:

# Run the simulation for 10 seconds

$ns at 10.0 “finish”

proc finish {} {

global ns tracefile

$ns flush-trace

close $tracefile

exec nam out.nam &

exit 0

}

$ns run

  1. Analyse Results

Once the simulation is done, measure the trace file or envision outcomes using xgraph or NAM. Key parameters are to evaluate include:

  • End-to-end delay: How long it takes for packets to reach the destination.
  • Throughput: The rate of successfully delivered packets.
  • Packet delivery ratio: Ratio of packets successfully delivered to the destination.
  • Relay selection accuracy: How well the selection technique performs according to the chosen parameters such as signal strength, distance.

Through this approach we will able to learn and gain knowledge about how to configure the network scenario and to select the relay based on the criteria that were deploys in ns2 simulator. More information regarding the network relay selection will be provided in further manual.