Data mules in ns2

For doing this, you can write a “hello Like” protocol or a beacon protocol.

If a mobile agent(data mules) starts to move, it should send a “hello” or “beacon” message. A sensor node which hears that “hello” or “beacon” message will start to send data to that mobile agent.

You can see a similar project in the following link :

http://www.projectguideline.com/a-simple-vanet-protocol-simulation-using-tcl-level-functions-of-ns-2/

In that VANET project, the stationary nodes will do something while recieving the beacon of the moving node(vehicle).

You may design your protocol based on this model.