Specifying Source and Destination of Messages

One of the frequently asked questions in the community is how to specify which particular nodes would act as source(s) and destination(s) of the messages created in the ONE simulator. The simulator, in fact, provides a pair of settings (shown below in bold face) aimed for this particular purpose.

Let us consider that there are $n + 1$ nodes in an OMN.  Further, let the nodes with addresses from $x$ to $y$, both inclusive, would create messages. The nodes in the range $w$ to $z$, both inclusive, would be the destinations of those messages, where $0 \le x \le y \le n$, and $0 \le w \le z \le n$. Then, the corresponding simulation scenario can be configured as follows.

## Message creation parameters

# How many event generators
Events.nrof = 1
# Class of the first event generator
Events1.class = MessageEventGenerator
# (Following settings are specific for the MessageEventGenerator class)
# Creation interval in seconds (one new message every 25 to 35 seconds)
Events1.interval = 25,35
# Message sizes (500kB - 1MB)
Events1.size = 500k,1M
# The source nodes -- nodes that create the messages
# Lower bound is inclusive; upper bound is exclusive
Events1.hosts = x, y+1
# The destinations of the messages created
# Lower bound is inclusive; upper bound is exclusive
Events1.tohosts = w, z+1
 # Message ID prefix
Events1.prefix = M

Note that the expressions $y + 1$ and $z+ 1$ should be replaced with their actual values. For example, if nodes $10$ to $20$ would create messages (both inclusive), and node $25$ is their destination, then the settings would like the following.

Events1.hosts = 10, 21
Events1.tohosts = 25, 26

Update: An alternative approach toward message creation is discussed in Juliano's blog.