The Real Experiment eXecution approach to Networking courseware
A networking courseware deals with instruments that are mostly software applications (such as Telnet or FTP clients and WWW browsers); it is worth noting that the nature of the instruments is substantially the same as the REX interface, since both of them are software applications. The REX interface is no more forced to directly connect with an external instrument, but it can limit itself to sniff the network traffic produced by the student's activity. In this way the REX interface becomes independent from the instrument: for instance, a Virtual Teacher that knows the FTP protocol is able to deal with any kind of FTP client/server application. This feature enlarges the range of applicability with comparable complexity and development costs.
Figure 3- The REX Model applied to the Networking Protocols Domain
We conclude with an example drawn from
the REX Networking Courseware: we will describe a sketch
of a lesson in which REX teaches TCP/IP, FTP, DNS and ARP
protocols to the student. In Figure 4 a detailed picture
of the REX architecture for the Networking Courseware is
given; the small Java cup designates components written
in Java language.
Thanks to the Java language dynamic
nature, the REX interface can be easily enhanced without
making changes to existing parts of the software. For
instance, to support the SMTP protocol it is enough to
add the proper plug-in modules in the Protocol Analyser
and in the Virtual Teacher.
In the TCP Window all the generated packets appear in iconic form. The student can freely inspect them analysing all their fields, for instance learning how different level packets are encapsulated according to the OSI definitions.
When the first step is over, the Virtual Teacher invites the student to enter the login and the password. Now a sufficient amount of TCP traffic has been generated. The Virtual Teacher analyses the packets and displays a graphic showing how sequential TCP packets are linked together by means of the sequence and acknowledgement numbers, as well as other concepts such as fragmentation and the push function.
It is important to stress the student's freedom when playing with the real thing. While it is true that the Virtual Teacher often provides hints to proceed, the student is really free to do what (s)he wants (of course staying in the FTP environment).
Unlike canned drills, that look always the same, this sketch of lesson could be replayed many times and it might exhibit some slight differences, giving the "feel" of the real world. For instance:
Here is a snapshot of what you will see when the courseware starts:
REX provides some tools to analyse network packets:
REX collects the network packets as they are generated and prepares their graphical representation in the network map. At the beginning, the first packet is selected and displayed. When you have completed the analysis of the current packet, you can move forward in the packet sequence by pressing the NEXT button, until you reach the latest generated packet. If you would like to step back, you can use the PREV button to have REX displaying again the previous stages of the experiment. The FIRST and the LATEST buttons are shortcuts for the first and the latest packet in the experiment.
You can experiment both the real version of the courseware and the demo.
In the real world, the experiment is performed in the following way: the student fires up REX, launches a FTP client program (such as ftp.exe in Windows 95/NT or similar commands in the UNIX world) then issues some FTP commands.
The demo describes a sketch of the lesson where the protocols involved in a FTP transaction are explained; it is based upon a data file which was previously recorded using the complete version of the courseware. In this way REX can be operated locally without any network connection and avoiding the installation of all the modules included in the courseware.
If you want download and install the real Ftp Courseware click here.
If you want try the demo of the Ftp Courseware click here.