How to Implement Data Link Layer in NS2

To implement the Data Link Layer (DDL) in Network Simulator 2 (NS2), start by understanding how ns2 manages the link-layer functions. This layer is accountable for tasks like framing, error control and Medium Access Control (MAC). For optimal implementation guidance, please reach out to ns2project.com.We can simulate various characteristics of the Data Link Layer by using or altering the available protocols include MAC protocols (for instance: 802.11) or designing custom link-layer implementations:

Below is a guide on how to implement or customize the Data Link Layer in NS2.

Components of the Data Link Layer in NS2

NS2 already presents support for numerous frequent data link layer elements:

  1. Link Layer (LL): Offers basic link-layer functions like framing.
  2. MAC Layer: Executes protocols like 802.11, TDMA, CSMA/CA.
  3. Interface Queue (IFQ): Handles the queue of packets at each node’s interface.
  4. Logical Link Control (LLC): Offers a logical link service to the network layer.

Step-by-Step Implementation:

  1. Basic Configuration of the Data Link Layer in NS2

Use Tcl script to set up and replicate the Data Link Layer. NS2 has built-in modules for the Link Layer (LL) and MAC Layer that you can straightly use it in your simulation.

Example TCL Script to Configure the Data Link Layer:

Here’s an example TCL script that simulates a wireless network using the 802.11 MAC protocol and set up the data link layer:

# Create a new simulator instance

set ns [new Simulator]

# Open trace file and NAM file for visualization

set tracefile [open “datalink_trace.tr” w]

$ns trace-all $tracefile

set namfile [open “datalink.nam” w]

$ns namtrace-all-wireless $namfile

# Define the topology and grid

set topo [new Topography]

$topo load_flatgrid 500 500

# Configure the nodes with link-layer and MAC settings

$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 \

-channelType Channel/WirelessChannel \

-topoInstance $topo \

-agentTrace ON \

-routerTrace ON \

-macTrace ON

# Create nodes

set n0 [$ns node]

set n1 [$ns node]

# Create a duplex link between the nodes to simulate the data link layer

$ns duplex-link $n0 $n1 10Mb 10ms DropTail

# Set up UDP agents and traffic

set udp0 [new Agent/UDP]

set null [new Agent/Null]

$ns attach-agent $n0 $udp0

$ns attach-agent $n1 $null

$ns connect $udp0 $null

# Set up a CBR traffic generator and attach it to UDP

set cbr [new Application/Traffic/CBR]

$cbr set packetSize_ 512

$cbr set rate_ 1Mb

$cbr attach-agent $udp0

# Start traffic

$ns at 1.0 “$cbr start”

# Define finish procedure

proc finish {} {

global ns tracefile namfile

$ns flush-trace

close $tracefile

close $namfile

exec nam datalink.nam &

exit 0

}

# Schedule simulation end

$ns at 5.0 “finish”

# Run the simulation

$ns run

Key Components of the Script:

  • LL (Link Layer): The -llType LL option fix the link layer to LL, which is accountable for basic data link layer functions like framing.
  • MAC (Medium Access Control): The -macType Mac/802_11 option states the use of the 802.11 MAC protocol, which manages channel access and collision avoidance (CSMA/CA).
  • IFQ (Interface Queue): The -ifqType Queue/DropTail/PriQueue option develops the interface queue, which manages packets waiting to be transmitted at the link layer.

This simplified script build a simulation where two nodes communicate using the 802.11 MAC protocol, with standard link-layer and interface queue configurations.

  1. Customizing the Data Link Layer in NS2

Customize or execute new activities at the Data Link Layer by adjusting the NS2’s C++ source code. The vital files for the link layer are placed in the ns-2.35 directory.

  • LL: This class offers the basic functionality of the link layer.
    • Files: ll.cc and ll.h.
    • Accountable for handling link-level packets and deliver them to the MAC layer.
  • MAC Layer: To execute custom MAC behavior, you can alter available MAC protocols or generate a new MAC protocol.
    • Files: mac-802_11.cc, mac-tdma.cc, etc.
    • These files had the logic for MAC protocols like CSMA/CA, TDMA, etc.

Example: Modifying MAC Layer Behavior (C++ Code)

Suppose you want to accomplish a basic backoff mechanism in the 802.11 MAC protocol. You can fine-tune the mac-802_11.cc file:

  1. Navigate to the mac-802_11.cc file:

cd ns-allinone-2.35/ns-2.35/

  1. Locate the MAC Backoff Logic: Within mac-802_11.cc, the function responsible for managing backoff is send(). You can include or alter the backoff algorithm here.

Example modification:

void Mac802_11::send(Packet *p, Handler *h) {

// Add custom backoff behavior

if (backoff_enabled_) {

// Perform custom backoff logic

schedule(send_timer_, backoff_time);

} else {

// Normal packet sending behavior

…

}

}

  1. Recompile NS2: After making alterations to the C++ code, recompile NS2 by executing the below commands:

./configure

make clean

make

  1. Visualizing and Analyzing the Data Link Layer

You can evaluate the activities of the Data Link Layer by inspecting the trace file (datalink_trace.tr), after the simulation is done. The trace file contains entries for packet transmissions at the MAC layer, collisions, and other link-layer events.

Visualize the communication amongst nodes and see how packets are managed at the data link layer by using the NAM (Network Animator) file.

  1. Advanced Customization: New Data Link Layer Protocols

If you want to establish a completely new Data Link Layer protocol, follow these steps:

  1. Create New Protocol Files:
    • Develop new C++ files (e.g., my_mac.cc and my_mac.h) depends on the available MAC layer protocols.
    • Execute the new protocol logic in these files.
  2. Modify Makefile.in:
    • Attach your new protocol files to the Makefile.in to make sure they are compiled with NS2.

Example:

mac/my_mac.o: mac/my_mac.cc

$(CC) $(CFLAGS) -c mac/my_mac.cc

  1. Register the New Protocol in NS2:
    • In the tcl/lib/ns-default.tcl file, register your new protocol so that it can be used in TCL scripts.

Example:

Mac/MyMac set bandwidth_ 11Mb

  1. Test the New Protocol:
    • Set up a TCL script that uses your new protocol by stating it in the node-config section of the script:

$ns node-config -macType Mac/MyMac

This procedure will walk you through the whole implementation and customization process of Data link layer including their examples using ns2 tool. We will also offer the extra information on data link layer or their advanced feature attachments, if you needed for the future enhancements.