To simulate Software-Defined Wireless Sensor Networks (SD-WSNs) using NS2 has includes to generating a programmable and centralized framework in which the control plane and data plane are decoupled. In SD-WSNs, sensor nodes are handled by a central controller that makes decisions about routing, resource allocation, and network management, since the sensor nodes concentrate on data forwarding.
Here is a step-by-step guide on how to simulate SD-WSN projects using NS2:
Steps to Simulate Software Defined WSN Projects in NS2
- Install NS2
- Download and install NS2 from the official NS2 website.
- Make sure that we have Tcl/Tk and OTcl for executing simulation scripts and NAM for visualization.
- Understand SD-WSN Concepts
- Control Plane: A centralized controller that handle the network’s resources and makes decisions on routing, scheduling, and resource allocation.
- Data Plane: The sensor nodes (data forwarding nodes) that simply forward data according to the instructions delivered by the controller.
- Flow Table: Similar to SDN, sensor nodes sustain a flow table with rules delivered by the central controller for data forwarding.
- Programmability: The network can be reconfigured dynamically according to varying conditions or application requirements.
- Modify NS2 for SD-WSN Support
NS2 does not directly support Software-Defined Networking (SDN) features, so we need to prolong its capabilities to replicate the control and data planes, flow tables, and communication among the central controller and sensor nodes.
- Create the SD-WSN Topology
In an SD-WSN, there are sensor nodes and a central controller. Sensor nodes are shared in the field, and the controller is located centrally or in the cloud. The sensor nodes only manage data forwarding, since the controller is responsible for making routing decisions.
Example OTcl Code to Define SD-WSN Topology:
# Define the simulator instance
set ns [new Simulator]
# Define the topography
set topo [new Topography]
$topo load_flatgrid 1000 1000 ;# Define a flat grid of size 1000×1000
# Create nodes (Sensor Nodes and Controller)
set controller [$ns node] ;# Central Controller
for {set i 0} {$i < 10} {incr i} {
set sensor($i) [$ns node] ;# Sensor Nodes
}
# Establish links between the Controller and Sensor Nodes (Controller sends instructions)
for {set i 0} {$i < 10} {incr i} {
$ns simplex-link $controller $sensor($i) 100Mb 10ms DropTail
}
# Define wireless communication links between sensor nodes (Sensor data forwarding)
for {set i 0} {$i < 9} {incr i} {
$ns simplex-link $sensor($i) $sensor([expr $i+1]) 1Mb 20ms DropTail
}
In this example:
- A central controller is created (controller), that will handle the sensor nodes.
- Sensor nodes (sensor($i)) are generated and associated to the controller through wired links (this represents control signals being sent).
- Sensor nodes are also associated to each other through wireless links, simulating data transmission among sensor nodes.
- Implement Flow Table for Sensor Nodes
Each sensor node sustains a flow table (similar to SDN) that is handled by the central controller. The flow table dictates how packets should be forwarded.
Example OTcl Code for Flow Table:
# Define a flow table for sensor nodes
proc set_flow_table {sensor_id dst_node} {
global flow_table
set flow_table($sensor_id) $dst_node
puts “Flow table set for sensor $sensor_id: Forward to $dst_node”
}
# Controller sets the flow table for each sensor node
for {set i 0} {$i < 10} {incr i} {
set_flow_table $i [expr ($i+1) % 10] ;# Example flow: each sensor forwards to the next sensor
}
In this sample, the controller actively sets flow rules for each sensor node. Sensor node i forwards data to node (i+1) according to the flow table.
- Implement Centralized Control Logic
The centralized controller intermittently gathers network status and makes decisions about how to route the traffic. It installs new flow table entries in the sensor nodes according to the sensed data or application requirements.
Example Central Controller Logic:
# Controller logic to adjust flow table
proc controller_decision {sensor_id} {
global ns flow_table
# Example: Change flow for a specific sensor based on some condition
if {$sensor_id == 5} {
set_flow_table 5 8
puts “Controller changing flow for sensor 5 to forward to sensor 8”
}
}
# Controller making periodic decisions
$ns at 5.0 “controller_decision 5”
$ns at 10.0 “controller_decision 5”
This code simulates the controller periodically checking and adjusting the flow tables of sensor nodes based on network conditions.
- Simulate Data Traffic in SD-WSN
We can create data traffic among sensor nodes that will be forwarded according to the flow rules set by the central controller.
Example UDP Traffic Simulation between Sensors:
# Define UDP traffic from one sensor node to another
set udp [new Agent/UDP]
set null [new Agent/Null]
$ns attach-agent $sensor(0) $udp
$ns attach-agent $sensor(9) $null
$ns connect $udp $null
# Set up a CBR traffic generator
set cbr [new Application/Traffic/CBR]
$cbr set packetSize_ 512
$cbr set rate_ 1Mb
$cbr attach-agent $udp
# Start the traffic from sensor 0 to sensor 9
$ns at 1.0 “$cbr start”
In this sample, data is transmit from sensor node 0 to sensor node 9, following the flow rules set by the controller.
- Run the Simulation
Save OTcl script as sd_wsn_simulation.tcl and execute the simulation in NS2:
ns sd_wsn_simulation.tcl
- Analyse the Results
NS2 creates trace files that we can measure to measure the performance of SD-WSN. Utilize awk, Perl, or Python scripts to process the trace files and extract parameters like:
- Latency: The delay among packets being sent and received.
- Throughput: The amount of data successfully routed over the network.
- Packet Loss: The number of packets dropped because of congestion or errors.
- Flow Table Changes: How usual the flow table changes in the sensor nodes.
Example Trace File Analysis:
awk -f analyze_trace.awk sd_wsn_simulation.tr
- Visualize the Simulation Using NAM
We can utilize Network Animator (NAM) to envision the sensor nodes, flow of data, and the control messages from the controller.
nam sd_wsn_simulation.nam
- Advanced Features in SD-WSN
We can expand the simulation to contain more complex features:
- Dynamic Flow Table Updates: The controller can modify flow rules dynamically according to network load or traffic patterns.
- Fault Tolerance: The controller can identify node or link failures and reroute traffic dynamically.
- Energy Efficiency: Apply the algorithms to minimize power consumption by turning off nodes or adapting transmission power.
Example Simulation Script Outline for SD-WSN
# Simulation script for Software-Defined Wireless Sensor Networks (SD-WSNs)
set ns [new Simulator]
set topo [new Topography]
$topo load_flatgrid 1000 1000 ;# Define a flat grid for the sensor network
# Create the controller and sensor nodes
set controller [$ns node] ;# Central Controller node
for {set i 0} {$i < 10} {incr i} {
set sensor($i) [$ns node] ;# Sensor nodes
}
# Establish links between the controller and sensor nodes
for {set i 0} {$i < 10} {incr i} {
$ns simplex-link $controller $sensor($i) 100Mb 10ms DropTail
}
# Wireless communication links between sensor nodes
for {set i 0} {$i < 9} {incr i} {
$ns simplex-link $sensor($i) $sensor([expr $i+1]) 1Mb 20ms DropTail
}
# Flow table setup
proc set_flow_table {sensor_id dst_node} {
global flow_table
set flow_table($sensor_id) $dst_node
puts “Flow table set for sensor $sensor_id: Forward to $dst_node”
}
# Controller sets flow table rules for each sensor
for {set i 0} {$i < 10} {incr i} {
set_flow_table $i [expr ($i+1) % 10] ;# Forwarding rule example
}
# Define UDP traffic from sensor 0 to sensor 9
set udp [new Agent/UDP]
set null [new Agent/Null]
$ns attach-agent $sensor(0) $udp
$ns attach-agent $sensor(9) $null
$ns connect $udp $null
# Create a CBR traffic generator
set cbr [new Application/Traffic/CBR]
$cbr set packetSize_ 512
$cbr set rate_ 1Mb
$cbr attach-agent $udp
$ns at 1.0 “$cbr start”
# Controller adjusts flow table dynamically
proc controller_decision {sensor_id} {
global ns flow_table
if {$sensor_id == 5} {
set_flow_table 5 8 ;# Change flow for sensor 5 to sensor 8
puts “Controller changing flow for sensor 5 to forward to sensor 8”
}
}
$ns at 5.0 “controller_decision 5”
$ns at 10.0 “finish”
# Run the simulation
$ns run
Key Points:
- Control Plane: The centralized controller handles the sensor nodes, configuring and adjusting flow tables for routing.
- Data Plane: Sensor nodes manage data forwarding according to flow rules.
- Dynamic Control: The controller can adapt routing according to network conditions.
We had successfully and efficiently understand the basic to advanced concepts and ideas on how to install and how to simulate the Software-Defined Wireless Sensor Networks projects using ns2 tool. If you have any query regarding this process feel free to ask.
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