Table Of Contents
Table Of Contents

Step 9. Configuring node movements

Goals

In this step, we make the model more interesting by adding node mobility. Namely, we make the intermediate nodes travel north during simulation. After a while, they will move out of the range of host A (and B), breaking the communication path.

The model

Mobility

In the INET Framework, node mobility is handled by the mobility submodule of hosts. Several mobility module type exist that can be plugged into a host. The movement trail may be deterministic (such as line, rectangle or circle), probabilistic (e.g. random waypoint), scripted (e.g. a “turtle” script) or trace-driven. There are also individual and group mobility models.

Here we install LinearMobility into the intermediate nodes. LinearMobility implements movement along a line, where the heading and speed are parameters. We configure the nodes to move north at the speed of 12 m/s.

Other changes

So far, L2 queues (the queues in the wireless interfaces) have been unlimited, that is, no packet would be dropped due to congestion. Meanwhile, there was indeed a congestion in host R1 and host A, because the the application in host A was generating packets at a higher rate that the netwok could carry.

From this step on, we limit the queue lengths at 10 packets. This allows the network to react faster to topology changes caused by node movements, because queues will not be clogged up by old packets. However, as a consequence of packet drops, we expect that the sequence numbers of packets received by host B will no longer be continuous.

We also update the visualization settings, and turn on an option that will cause mobile nodes to leave a trail as they move. We also enable a visualizer option that will display the velocity vector of the moving nodes.

The configuration:

[Config Wireless09]
description = Configuring node movements
extends = Wireless08

*.hostR*.mobility.typename = "LinearMobility"
*.hostR*.mobility.speed = 12mps
*.hostR*.mobility.initialMovementHeading = 270deg

*.host*.wlan[0].mac.maxQueueSize = 10

*.visualizer.mobilityVisualizer.displayVelocities = true
*.visualizer.mobilityVisualizer.displayMovementTrails = true

Results

It is advisable to run the simulation in Fast mode, because the nodes move very slowly if viewed in Normal mode.

It can be seen in the animation below as host R1 leaves host A’s communication range at around 11 seconds. After that, the communication path is broken. Traffic could be routed through R2 and R3, but that does not happen because the routing tables are static and have been configured according to the initial positions of the nodes. When the communication path breaks, the blue arrow that represents successful network layer communication paths fades away, because there are no more packets to reinforce it.

As mentioned before, a communication path could be established between host A and B by routing traffic through hosts R2 and R3. To reconfigure routes according to the changing topology of the network, an ad-hoc routing protocol is required.

Number of packets received by host B: 547

Sources: omnetpp.ini, WirelessB.ned

Discussion

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