How to Calculate Network Gross and Net Bit Rate in NS2

To calculate the Gross Bit Rate and Net Bit Rate are important metrics for estimating the performance of a network, especially how well data is sent over the network. In NS2, these metrics can be derived from the packet transmissions among the nodes.

  • Gross Bit Rate refers to the total amount of bits transmitted that containing all overhead like headers, error correction codes, and control signals.
  • Net Bit Rate refers to the real user data rate, without overhead and accounting only for the payload data.

Key Concepts:

  • Gross Bit Rate (Gbps) is the overall rate at which data is transferred over the network that containing overhead:

Gross Bit Rate (bps)=Total Transmitted BitsSimulation Time\text{Gross Bit Rate (bps)} = \frac{\text{Total Transmitted Bits}}{\text{Simulation Time}}Gross Bit Rate (bps)=Simulation TimeTotal Transmitted Bits​

  • Net Bit Rate (bps) is the effective data rate obtainable to the user after eliminating the overhead, like headers and control information:

Net Bit Rate (bps)=Total Payload BitsSimulation Time\text{Net Bit Rate (bps)} = \frac{\text{Total Payload Bits}}{\text{Simulation Time}}Net Bit Rate (bps)=Simulation TimeTotal Payload Bits​

In the simulation environment NS2, these rates can be estimated by assessing the trace file, which logs packet events.

Steps to Calculate Gross and Net Bit Rate in NS2

  1. Set Up the Wireless or Wired Network in NS2

We require to describe the network configuration, containing nodes, links, and data transmission parameters (e.g., bandwidth, delay).

Example Setup:

# Create a new simulator object

set ns [new Simulator]

# Configure wireless channel and nodes

set val(chan)           Channel/WirelessChannel  ;# Wireless channel

set val(prop)           Propagation/TwoRayGround ;# Propagation model

set val(netif)          Phy/WirelessPhy          ;# PHY Layer

set val(mac)            Mac/802_11               ;# MAC Layer

set val(ifq)            Queue/DropTail/PriQueue  ;# Queue

set val(ll)             LL                       ;# Link Layer

set val(ant)            Antenna/OmniAntenna      ;# Antenna model

# Create base station and user nodes

set node0 [$ns node]

set node1 [$ns node]

# Define a wireless link between nodes with a bandwidth of 10 Mbps

$ns duplex-link $node0 $node1 10Mb 10ms DropTail

Above example configures two nodes are connected by a wireless link including a bandwidth of 10 Mbps.

  1. Generate the Trace File

To compute the Gross Bit Rate and Net Bit Rate, we want to allow the trace generation in NS2 to record all packet events (such as transmission, reception, and drops).

# Enable tracing

set tracefile [open out.tr w]

$ns trace-all $tracefile

# Run the simulation for 100 seconds

$ns at 100.0 “finish”

proc finish {} {

global ns tracefile

close $tracefile

$ns halt

}

It will be generated a trace file (out.tr), which records the packet events during the simulation.

  1. Calculate Gross Bit Rate

The Gross Bit Rate contains all transmitted bits that contains both the payload and overhead (such as headers and error correction bits). In NS2, we can extort the packet size from the trace file and adding all transmitted bits.

AWK Script to Calculate Gross Bit Rate:

awk ‘{

if ($1 == “r” && $4 == “tcp”) {  # Only consider received TCP packets

total_bytes += $6;  # $6 is the packet size in bytes

}

} END {

simulation_time = 100.0;  # Replace with actual simulation time in seconds

total_bits = total_bytes * 8;  # Convert bytes to bits

gross_bitrate = total_bits / simulation_time;  # Gross Bit Rate in bps

print “Gross Bit Rate: ” gross_bitrate ” bps”;

}’ out.tr

This script:

  • Filters received TCP packets.
  • Adds the total bytes received and converts them to bits.
  • Divides the total bits by the simulation time to get the Gross Bit Rate.
  1. Calculate Net Bit Rate

The Net Bit Rate eliminates the overhead and accounts only for the real payload data. In NS2, we may require to exclude headers, like the IP and TCP headers, to focus only on the payload data.

Assume the following overheads:

  • IP header: 20 bytes.
  • TCP header: 20 bytes. Thus, the total overhead is 40 bytes per packet, and the payload size is:

Payload=Packet Size−Overhead\text{Payload} = \text{Packet Size} – \text{Overhead}Payload=Packet Size−Overhead

AWK Script to Calculate Net Bit Rate:

awk ‘{

if ($1 == “r” && $4 == “tcp”) {  # Only consider received TCP packets

total_bytes += $6;  # $6 is the total packet size in bytes

payload_bytes += ($6 – 40);  # Subtract 40 bytes of overhead (IP + TCP headers)

}

} END {

simulation_time = 100.0;  # Replace with actual simulation time in seconds

net_bits = payload_bytes * 8;  # Convert payload bytes to bits

net_bitrate = net_bits / simulation_time;  # Net Bit Rate in bps

print “Net Bit Rate: ” net_bitrate ” bps”;

}’ out.tr

This script:

  • Subtracts the overhead (40 bytes) from each packet to estimate the payload.
  • Adds the payload bytes, converts them to bits, and then divides by the simulation time to acquire the Net Bit Rate.
  1. Calculate and Compare Gross and Net Bit Rates

By running the above scripts, we can be compared the Gross Bit Rate and Net Bit Rate in the NS2 simulation.

For example:

  • If the Gross Bit Rate is 10 Mbps and the overhead is significant then we may discover the Net Bit Rate to be considerably lower (e.g., 9 Mbps, depending on packet sizes and overhead).
  1. Monitor Bit Rates during the Simulation

Also, we can be estimated the Gross Bit Rate and Net Bit Rate actively at regular intervals during the simulation, permitting to track the modifies in the network performance over time.

AWK Script to Calculate Time-Windowed Gross and Net Bit Rate:

awk ‘{

interval = int($2);  # Group events by time intervals (in seconds)

if ($1 == “r” && $4 == “tcp”) {

total_bytes[interval] += $6;  # Total bytes (Gross)

payload_bytes[interval] += ($6 – 40);  # Subtract 40 bytes of overhead for Net Bit Rate

}

} END {

for (interval in total_bytes) {

gross_bits = total_bytes[interval] * 8;

net_bits = payload_bytes[interval] * 8;

gross_bitrate = gross_bits;  # Bits per second in each interval

net_bitrate = net_bits;  # Bits per second in each interval

print “Time Interval: ” interval ” s, Gross Bit Rate: ” gross_bitrate ” bps, Net Bit Rate: ” net_bitrate ” bps”;

}

}’ out.tr

Above script assesses and prints the Gross Bit Rate and Net Bit Rate per second of the simulation and permitting to monitor the differences in bit rates over time.

Utilising AWK script and some concepts to estimate and assess the Network Gross and Net Bit rate through basic computation method within NS2 simulation tool. We will also be offered further informations depending on your requests.

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