This tool is an essential part of the planning process of network design and structure. it allows you to see each process of encapsulation the packets go through a built network. It would be so helpful to have a portable version of this to show people your designed network and operation without having to priorly install the software
here is a link to the software (free download for cisco netacad students);
http://www.megaupload.com/?d=N7A11S83
here is the page from the cisco site:
https://www.cisco.com/web/learning/netacad/course_catalog/PacketTracer.html