what program should i use to simulate WSN?

Hi
I'm a master student from Syria .
I'm doing my master thesis about wireless sensor network and I'm having a problem getting the right program to do the simulation.
I 'm trying to develop a data aggregation protocol based on the clustering approach.
Since I'm from Syria, I cannot get any program that can serve my purpose because of the penalties imposed on my country. Lots of things are not available including programs and there is no credit card either to buy online and what I could get is only the educational versions of programs that can be available on the net and it's not helping .
I need a program that can allow me to simulate a wireless sensor network and can make me do the following:
1- To be able to change the message structure and to create three types of messages .
2- To be able to program the transmission in the node ( like in tinyos ) so i can decide when and where to do the transmission and to change the receiver address as I wish. In other words , I need the node to be programmable to decide what is the destination and what type of message to use
Note.
_ I worked on Tiny OS before and I'm familiar with NesC . The only problem is that in Tiny Os 2, I don't know how to visualize the results. Since in TinyOS1, there was TinyViz but it's no longer supported in TinyOS2 and it seems like the TinyOS is refusing to be installed on my laptop the right way , so that's a problem
- I tried OPnet 14.5 the educational version but it seems like I can't change the message structure and I didn't even know how to change the data within the message .
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So if anyone can help me or advise me please about what program should I use that supports WSN and can do what I mentioned earlier
and please let it be available online so i can download it easily.
Thanks

Have a look at this I think you will find this interesting
http://www.zdnet.com/build-your-own-supercomputer-out-of-raspberry-pi-boards-7000015831/

Also check this out all about beowolf (building Clusters from used macinesand utilising free operating systems such as Linux ) Very Interesting

http://yclept.ucdavis.edu/Beowulf/aboutbeowulf.html

Here are some other notes with reference to software free for download etc plus of course links inside ( Not that i know an awful lot about Clusters but it didn’t take me too long to understand the jist of what they are doing here Nice simple explanations here which make this easy to understand and also implement )

Here are some other notes with reference to sofwtare free for download etc plus of course links inside ( Not that i know an awfull lot about Clusters but it didnt take me too long to understand the jist of what they are doing here Nice simple explanations here which make this easy to understand and also implement )

As far as software is concerened i guess its write your own using whats available to you in the form of Open Source and free IDE's Good news is linux also includes many different compilers from what Ive read so far

Looks as though you can do all of this yourself with the only limitation being your interest to do so

Here is another link I think you will find usefull very good explanations plus diagrams network diagrams etc

Have you tried Contiki it is an opensource realtime OS written for wsn with possibility to simulate . Free to download so it might be intresting for you.
http://www.contiki-os.org/

thank you sir I will check it out , but may i ask if there is a programme that is supported by Windows ?

thank you so much i will check it out