How to Calculate Network Maximum Transfer Unit in NS2

To calculate the network maximum transfer unit (MTU) using NS2 (Network Simulator 2), which refers to the largest size of a packet (in bytes) that can send across the network interface without requiring to be fragmented. The MTU is normally set at the network interface level (e.g., Ethernet, wireless, etc.), and it determines the maximum size of the payload, which can transmit in one packet.

In the simulation environment NS2, the MTU is typically described at the link layer that specifically for wired or wireless interfaces, however it is not something we can be estimated during the simulation. As an alternative, it is a value which setup in the simulation script. The following is a brief approach on how to configure and compute the MTU in NS2:

Steps to Set and Calculate the MTU in NS2

The MTU value is described when we set up the network interface properties in the NS2 simulation. It is normally predefined rely on the kind of network link we are replicating. For sample, Ethernet networks are normally use an MTU of 1500 bytes, whereas wireless networks may be used a various MTU rely on the protocol.

  1. Set MTU in NS2

When setting up the network in NS2 then we normally describe the metrics such as bandwidth, delay, and queue size, however the MTU is connected with the packet size and link properties.

  • For TCP or UDP packets, the packet size is normally set when we make a traffic generator (e.g., TCP, CBR, or FTP traffic), and it must be less than or equal to the MTU.

Given below how we can set the packet size that is normally constrained by the MTU:

# Create a TCP source and a TCP sink

set tcp [new Agent/TCP]

set sink [new Agent/TCPSink]

# Attach the TCP source to node 0 and the sink to node 1

$ns attach-agent $node(0) $tcp

$ns attach-agent $node(1) $sink

# Create a traffic source (FTP) and attach it to the TCP agent

set ftp [new Application/FTP]

$ftp attach-agent $tcp

# Set the packet size (less than or equal to the MTU)

$tcp set packetSize_ 1400  ;# Set packet size in bytes (MTU-dependent)

Above instance, the packet size is set to 1400 bytes that is within the MTU limit of a standard Ethernet network (1500 bytes).

  1. MTU and Link Properties

We can be replicated various kinds of links by setting up their delay and bandwidth that indirectly impacts how packet fragmentation may happen if the packet size exceeds the MTU.

Here’s how we configure a link among the nodes in NS2:

# Create a link between node 0 and node 1 with bandwidth 10Mbps and delay 10ms

$ns duplex-link $node(0) $node(1) 10Mb 10ms DropTail

# Optionally, set the queue size (which might influence packet fragmentation)

$ns queue-limit $node(0) $node(1) 50

But, NS2 does not explicitly describe the MTU for the link. As an alternative, we manage the packet size through the traffic generator, and also the network will be managed the packet fragmentation if the packet size exceeds the underlying network’s MTU.

  1. Packet Fragmentation

If the packet size exceeds the MTU, the network might fragment the packet then based on the link properties and transport protocol. In the simulation environment packet fragmentation is managed internally by the simulator.

We can set the packet size to exceed the expected MTU and observe how the simulator manages the fragmentation:

# Set a large packet size (larger than typical MTU)

$tcp set packetSize_ 3000  ;# Packet size larger than 1500 bytes (typical Ethernet MTU)

If the packet size exceeds the MTU of the link then NS2 will mimic the fragmentation procedure, though it doesn’t deliver comprehensive visibility into MTU behaviour in the trace file. Still we can be monitor the effect of large packet sizes via packet drops or delays.

  1. Check for Packet Fragmentation in Trace File

While NS2 does not clearly log MTU-related fragmentation then we can manage the packet fragmentation by looking at the trace file for changes in packet size.

If the packet size exceeds the MTU then fragmentation or drops may happen. We can be used an AWK script to observe the packet sizes and verify whether packets are being fragmented:

awk ‘{

if ($1 == “+” && $4 == “tcp”) {

print “Packet Size: ” $6 ” bytes at time ” $2;

}

}’ out.tr

This script will be printed out the sizes of sent TCP packets ($6 is the packet size). If we monitor the large packet sizes, which exceed usual MTU values then we can imply that fragmentation is possible happening.

  1. MTU Impact on Network Performance

The MTU setting can importantly affect network performance:

  • Larger MTU: Fewer packets are want to be transmitted the similar amount of data, reducing overhead, however large packets may experience higher delays or packet loss if there is congestion or a lower MTU on the middle links.
  • Smaller MTU: More packets are made for the similar amount of data then increasing overhead, however packets are less likely to fragment or drop.

We can run simulations including various packet sizes to monitor how performance parameters such as throughput and delay are influenced by the MTU.

  1. Handling MTU in Wireless Networks

For wireless networks, the MTU may differ based on the hardware and protocol. Fror instance, within a Wi-Fi network, the MTU is normally 2304 bytes for 802.11 frames.

We can be replicated a wireless network in NS2 and set suitable packet sizes, which align with the wireless MTU:

# Define wireless parameters

set val(chan)           Channel/WirelessChannel   ;# Channel type

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

set val(netif)          Phy/WirelessPhy           ;# Network interface type

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

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

set val(ll)             LL                        ;# Link layer type

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

# Set packet size for wireless simulation

$tcp set packetSize_ 2000  ;# Packet size for wireless link

The procedure for Network Maximum Transfer was configured and calculated methodically using the simulation tool ns2. We will explore this topic in depth using various simulation tools as required providing a comprehensive analysis.

It is best to seek professional assistance when calculating the Network Maximum Transfer Unit in the NS2 tool. Contact us, and we will assist you with timely delivery and optimal outcomes.