To simulate Optical Communication projects in NS2 can be a difficult task because NS2 was mainly intended for traditional wireless and wired networks such as TCP/IP, Wi-Fi, and MANETs instead of optical fibre networks or free-space optical (FSO) communication. But, it is possible to prolong NS2 to design optical communication systems by using custom modules or replicates optical behaviour with existing NS2 capabilities.
Here is an approach to simulate the optical communication projects using ns2
Steps to Simulate Optical Communication Projects in NS2
- Components of Optical Communication
Optical communication involves:
- Optical Transmitter: usually a laser or LED that emits light signals modulated to carry information.
- Optical Receiver: A photodetector that converts received optical signals back into electrical signals.
- Optical Fiber or Free-Space Optical (FSO) Channel: The medium through which the light signals propagate.
- Wavelength Division Multiplexing (WDM): A approaches utilized in optical communication to send multiple signals over different wavelengths on a single optical fiber.
- Signal Loss and Dispersion: As light propagates, it experiences attenuation and dispersion that impacts the signal quality.
- Extending NS2 for Optical Communication
Since NS2 does not directly support optical communication, we can expand it by:
- Emulating optical fiber or free-space communication channels using custom-defined high-speed wired links.
- Modifying the bandwidth, latency, and signal loss to represent features of optical communication.
- Executing WDM (Wavelength Division Multiplexing) by generating an isolate logical links for diverse wavelengths.
- Optical Fiber Communication Setup in NS2
We will emulate a simple optical fiber communication system by design an optical link as a high-bandwidth wired link. The transmitter and receiver will signify optical transceivers, and the link will denote an optical fiber.
Example: Simulating Optical Fiber Communication
# Create the NS2 simulator instance
set ns [new Simulator]
# Define a high-speed optical fiber link with low latency
set transmitter [$ns node] ;# Optical Transmitter
set receiver [$ns node] ;# Optical Receiver
# Create a high-bandwidth duplex link (100 Gbps bandwidth, 1 ms delay)
$ns duplex-link $transmitter $receiver 100Gb 1ms DropTail
# Set up TCP agents to simulate data transmission over the optical link
set tcp_sender [new Agent/TCP]
set tcp_receiver [new Agent/TCPSink]
$ns attach-agent $transmitter $tcp_sender
$ns attach-agent $receiver $tcp_receiver
# Connect the TCP sender to the receiver
$ns connect $tcp_sender $tcp_receiver
# Set up FTP application to simulate data transfer
set ftp [new Application/FTP]
$ftp attach-agent $tcp_sender
# Start the FTP traffic at time 1 second
$ns at 1.0 “$ftp start”
$ns at 5.0 “$ftp stop”
# Enable tracing for analysis
set tracefile [open optical_trace.tr w]
$ns trace-all $tracefile
# Define finish procedure
proc finish {} {
global ns tracefile
$ns flush-trace
close $tracefile
exit 0
}
# End the simulation after 6 seconds
$ns at 6.0 “finish”
$ns run
Explanation:
- Nodes as Optical Transmitter and Receiver: The nodes transmitter and receiver denote the optical transceivers.
- High-Speed Link: We describe an optical fiber link with a high bandwidth of 100 Gbps and a latency of 1 ms, signify a long-distance optical fiber network.
- Traffic Generation: A TCP connection is configures among the transmitter and receiver, and FTP traffic simulates data transmission.
- Trace File: The simulation creates a trace file (optical_trace.tr) for performance evaluation.
- Adding Signal Loss and Dispersion in Optical Fiber
Optical communication is impacted by attenuation and dispersion that trigger signal degradation. We can replicate these effects by establishing packet loss or increasing delay in terms of the length of the optical fiber.
Example: Simulating Signal Loss in Optical Fiber
# Function to simulate optical signal loss based on distance
proc signal_loss_model {distance} {
# Define the attenuation coefficient (in dB/km)
set attenuation_coefficient 0.2 ;# Typical for optical fiber
# Calculate signal loss (in dB)
set signal_loss [expr $distance * $attenuation_coefficient]
# Determine if packet should be dropped based on signal loss threshold
if {$signal_loss > 10} { ;# Example threshold of 10 dB
return 1 ;# Packet should be dropped
} else {
return 0 ;# Packet should not be dropped
}
}
# Example usage: Simulate signal loss for a 50 km optical link
set distance 50
if {[signal_loss_model $distance] == 1} {
puts “Packet dropped due to high signal loss.”
} else {
puts “Packet successfully transmitted.”
}
In this example, we replicate signal loss over an optical fiber according to the distance and attenuation coefficient. If the signal loss exceeds a threshold, the packet is dropped.
- Wavelength Division Multiplexing (WDM) Simulation
Wavelength Division Multiplexing (WDM) is a key approch in optical communication that enable multiple data streams to be routed over the same optical fiber by using different wavelengths (channels).
In NS2, we can simulate WDM by generating multiple logical links signify different wavelengths among the same transmitter and receiver.
Example: Simulating WDM with Multiple Logical Links
# Create separate links for different wavelengths (wavelength1, wavelength2, etc.)
set wavelength1_link [$ns duplex-link $transmitter $receiver 40Gb 1ms DropTail]
set wavelength2_link [$ns duplex-link $transmitter $receiver 40Gb 1ms DropTail]
# Set up TCP agents for each wavelength (channel)
set tcp_sender1 [new Agent/TCP]
set tcp_sender2 [new Agent/TCP]
set tcp_receiver1 [new Agent/TCPSink]
set tcp_receiver2 [new Agent/TCPSink]
$ns attach-agent $transmitter $tcp_sender1
$ns attach-agent $transmitter $tcp_sender2
$ns attach-agent $receiver $tcp_receiver1
$ns attach-agent $receiver $tcp_receiver2
# Connect TCP agents for each wavelength
$ns connect $tcp_sender1 $tcp_receiver1 ;# Wavelength 1
$ns connect $tcp_sender2 $tcp_receiver2 ;# Wavelength 2
# Set up FTP applications for each wavelength
set ftp1 [new Application/FTP]
set ftp2 [new Application/FTP]
$ftp1 attach-agent $tcp_sender1
$ftp2 attach-agent $tcp_sender2
# Start FTP traffic on different wavelengths at different times
$ns at 1.0 “$ftp1 start”
$ns at 2.0 “$ftp2 start”
# Stop the traffic after 5 seconds
$ns at 5.0 “$ftp1 stop”
$ns at 6.0 “$ftp2 stop”
Explanation:
- Wavelength Channels: We replicate multiple wavelengths (WDM channels) by generating isolate logical links for different wavelengths (wavelength1_link and wavelength2_link).
- Separate Traffic Flows: Each wavelength carries its own data traffic, characterized by diverse TCP connections and FTP applications.
- Free-Space Optical (FSO) Communication Simulation
Free-Space Optical (FSO) Communication is a form of optical communication in which the transmitter and receiver are not linked by an optical fiber however it interacts via free space such as lasers communicating across buildings. To replicate FSO communication in NS2, we can utilize wireless nodes and customize the parameters to signify optical transmission.
Example: Simulating Free-Space Optical Communication
# Create FSO Transmitter and Receiver nodes
set fso_transmitter [$ns node]
set fso_receiver [$ns node]
# Set initial positions for FSO transmitter and receiver (line of sight)
$fso_transmitter set X_ 0.0
$fso_transmitter set Y_ 0.0
$fso_transmitter set Z_ 10.0
$fso_receiver set X_ 500.0
$fso_receiver set Y_ 0.0
$fso_receiver set Z_ 10.0
# Create a high-speed wireless link to emulate FSO communication (10 Gbps, 1 ms delay)
$ns duplex-link $fso_transmitter $fso_receiver 10Gb 1ms DropTail
# Set up TCP agents and FTP traffic similar to optical fiber simulation
In this instance, the FSO transmitter and receiver interact via a wireless link that signify free-space optical communication.
- Analysing Optical Communication Performance
After processing the simulation, we can measure several parameters:
- Throughput: The rate of successful data transfer over the optical link.
- End-to-End Delay: The time taken for a packet to travel from the transmitter to the receiver.
- Packet Loss: The percentage of packets lost because of signal attenuation or dispersion.
Example: Parsing Trace File for Throughput
We need to utilize AWK or Python scripts to parse the trace file and estimate throughput or packet delivery ratio.
awk ‘{ if ($1 == “r” && $4 == “AGT” && $7 == “tcp”) count++; } END { print “Packets received: “, count; }’ optical_trace.tr
This script counts the number of TCP packets successfully received at the optical receiver.
- Visualizing Optical Communication in NAM
We can envision the optical communication simulation using NAM (Network Animator):
# Enable NAM trace file for visualization
set namfile [open optical_comm_simulation.nam w]
$ns namtrace-all $namfile
# Open NAM after the simulation ends
proc finish {} {
global ns namfile
$ns flush-trace
close $namfile
exec nam optical_comm_simulation.nam &
exit 0
}
Overall, we had clearly obtainable the detailed description to perform the Optical Communication projects with sample code snippets were given above that were evaluated in ns2 implementation tool. We also further provide the detailed information that related to Optical Communication.
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