To simulate Metropolitan Area Networks (MANs) in NS2 has includes to design the communication infrastructure of a large urban area in which the nodes like routers, switches, and base stations interconnect various parts of the city. A MAN usually covers a geographic area larger than a LAN however smaller than WAN, usual using high-speed connections like fibre optics or wireless technologies such as WiMAX or LTE.
This guide provides a step-by-step explanation of how to simulate a MAN using NS2.
Steps to Simulate Metropolitan Area Networks Projects in NS2
- Install NS2
- Download and install NS2.
- Make sure all dependencies (Tcl/Tk, OTcl, NAM) are installed properly for executing simulations and envision outcomes.
- Understand MAN Topology Components
- Core Routers: These high-capacity routers form the backbone of the MAN and interconnect numerous parts of the city.
- Access Routers: These lower-capacity routers connect end users such as homes, businesses to the core routers.
- End Devices: Denotes end-user devices like computers, smartphones, or IoT devices associated to access routers.
- High-Speed Links: MANs usually utilize high-bandwidth links (fiber optics, microwave, etc.) among core routers, and medium-speed links between access routers and end devices.
- Define the MAN Topology
In this step, we will configure a hierarchical topology in which multiple access routers associate to core routers. Core routers are interconnected, forming the backbone of the MAN, since access routers deliver connections to end devices.
Example OTcl Code to Define MAN Topology:
# Create a simulator instance
set ns [new Simulator]
# Define the topography (flat grid for the metropolitan area)
set topo [new Topography]
$topo load_flatgrid 5000 5000 ;# Flat grid with 5000×5000 meter area
# Define core routers (high-capacity backbone nodes)
set core_router_1 [$ns node]
set core_router_2 [$ns node]
set core_router_3 [$ns node]
# Define access routers (connecting end devices to core routers)
set access_router_1 [$ns node]
set access_router_2 [$ns node]
set access_router_3 [$ns node]
set access_router_4 [$ns node]
# Create end devices (users connected to access routers)
set end_device_1 [$ns node]
set end_device_2 [$ns node]
set end_device_3 [$ns node]
set end_device_4 [$ns node]
# Set up links between core routers (high-speed backbone)
$ns duplex-link $core_router_1 $core_router_2 1000Mb 10ms DropTail
$ns duplex-link $core_router_2 $core_router_3 1000Mb 10ms DropTail
$ns duplex-link $core_router_3 $core_router_1 1000Mb 10ms DropTail
# Set up links between access routers and core routers
$ns duplex-link $access_router_1 $core_router_1 100Mb 5ms DropTail
$ns duplex-link $access_router_2 $core_router_1 100Mb 5ms DropTail
$ns duplex-link $access_router_3 $core_router_2 100Mb 5ms DropTail
$ns duplex-link $access_router_4 $core_router_2 100Mb 5ms DropTail
# Set up links between end devices and access routers
$ns duplex-link $end_device_1 $access_router_1 10Mb 2ms DropTail
$ns duplex-link $end_device_2 $access_router_2 10Mb 2ms DropTail
$ns duplex-link $end_device_3 $access_router_3 10Mb 2ms DropTail
$ns duplex-link $end_device_4 $access_router_4 10Mb 2ms DropTail
In this example:
- Core routers form the backbone of the MAN, associated by high-speed links such as 1000 Mbps.
- Access routers associate to core routers and deliver connections to end-user devices, using medium-speed links such as 100 Mbps.
- End devices denote users connected to the access routers through lower-speed links (e.g., 10 Mbps).
- Configure Routing
To replicate on how data is transmit via the MAN, we can enable dynamic routing protocols like OSPF, AODV, or Distance Vector routing.
Example: Enable Dynamic Routing
# Enable dynamic routing protocol
$ns rtproto DV ;# Enable Distance Vector routing protocol
# Alternatively, you can enable a different routing protocol like OSPF or AODV
- Simulate Traffic in the MAN
We can simulate numerous kinds of traffic such as HTTP, VoIP, video streaming, file transfers using UDP or TCP agents.
Example: Simulate UDP Traffic
# Define UDP agents and attach them to end devices
set udp0 [new Agent/UDP]
set null0 [new Agent/Null]
$ns attach-agent $end_device_1 $udp0
$ns attach-agent $end_device_3 $null0
$ns connect $udp0 $null0
# Create a Constant Bit Rate (CBR) traffic generator
set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 512
$cbr0 set rate_ 1Mb
$cbr0 attach-agent $udp0
# Start the CBR traffic at time 1.0 seconds
$ns at 1.0 “$cbr0 start”
This sample simulates constant bit rate (CBR) traffic among end_device_1 and end_device_3.
- Run the Simulation
Save OTcl script as man_simulation.tcl and execute it using the NS2 command:
ns man_simulation.tcl
- Analyse the Results
NS2 create trace files that record all network events in the period of the simulation. We can utilize these trace files to measure network parameters like:
- Throughput: The rate at which data is successfully routed over the network.
- Delay: The time taken for packets to travel among nodes.
- Packet Loss: The number of packets dropped because of congestion or link failure.
Example: Analyze Trace Files Using Awk
awk -f analyze_trace.awk man_simulation.tr
- Visualize the Simulation Using NAM
We can utilize Network Animator (NAM) to envision the network topology and packet flows in the MAN.
nam man_simulation.nam
- Advanced Features in MAN Simulation
We can prolong the simulation to contain more advanced characteristics like:
- Quality of Service (QoS): Apply traffic prioritization and bandwidth allocation to make sure QoS for specific kinds of traffic such as VoIP or video streaming.
- Multicast Routing: Utilize multicast routing protocols to replicate group communication services such as video conferencing via the MAN.
- Link Failures and Recovery: Replicate link or node failures to validate the fault tolerance and flexibility of the network.
Example Simulation Script Outline for MAN
# Simulation script for Metropolitan Area Network (MAN) in NS2
set ns [new Simulator]
set topo [new Topography]
$topo load_flatgrid 5000 5000 ;# Define the area for the MAN
# Create core routers (backbone)
set core_router_1 [$ns node]
set core_router_2 [$ns node]
set core_router_3 [$ns node]
# Create access routers (connecting users to core routers)
set access_router_1 [$ns node]
set access_router_2 [$ns node]
set access_router_3 [$ns node]
set access_router_4 [$ns node]
# Create end devices (connected to access routers)
set end_device_1 [$ns node]
set end_device_2 [$ns node]
set end_device_3 [$ns node]
set end_device_4 [$ns node]
# Set up links between core routers (high-speed backbone)
$ns duplex-link $core_router_1 $core_router_2 1000Mb 10ms DropTail
$ns duplex-link $core_router_2 $core_router_3 1000Mb 10ms DropTail
$ns duplex-link $core_router_3 $core_router_1 1000Mb 10ms DropTail
# Set up links between access routers and core routers
$ns duplex-link $access_router_1 $core_router_1 100Mb 5ms DropTail
$ns duplex-link $access_router_2 $core_router_1 100Mb 5ms DropTail
$ns duplex-link $access_router_3 $core_router_2 100Mb 5ms DropTail
$ns duplex-link $access_router_4 $core_router_2 100Mb 5ms DropTail
# Set up links between end devices and access routers
$ns duplex-link $end_device_1 $access_router_1 10Mb 2ms DropTail
$ns duplex-link $end_device_2 $access_router_2 10Mb 2ms DropTail
$ns duplex-link $end_device_3 $access_router_3 10Mb 2ms DropTail
$ns duplex-link $end_device_4 $access_router_4 10Mb 2ms DropTail
# Enable dynamic routing (Distance Vector Routing Protocol)
$ns rtproto DV
# Define UDP traffic from end device 1 to end device 3
set udp0 [new Agent/UDP]
set null0 [new Agent/Null]
$ns attach-agent $end_device_1 $udp0
$ns attach-agent $end_device_3 $null0
$ns connect $udp0 $null0
# CBR traffic generator
set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 512
$cbr0 set rate_ 1Mb
$cbr0 attach-agent $udp0
# Start CBR traffic at 1.0 seconds
$ns at 1.0 “$cbr0 start”
# End the simulation at 20 seconds
$ns at 20.0 “finish”
# Run the simulation
$ns run
Key Points:
- Core and Access Routers: Core routers form the backbone of the MAN, and access routers deliver user connectivity.
- Dynamic Routing: Enable routing protocols such as OSPF, AODV, or DV to handle communication among nodes.
- Traffic Simulation: Use UDP/TCP to create traffic among nodes and evaluate network performance.
- Visualization: Utilize NAM to envision the MAN simulation and monitor the traffic flow and routing decisions.
Using ns2 tool, we illustrated the fundamental approach with the sample coding for metropolitan area network project that were simulated and visualized the outcomes. We plan to deliver more information regarding the metropolitan area network.
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