This paper presents HAND-JAV, an Internet tool for learning and testing different handover techniques when cellular phones move from one cell to another.
It cannot be denied the importance of cellular phones in today communications. Fifteen years ago, mobile communications where something rare, unusual, but now, almost everyone has one or more cellular phones. But, how many people understand this technology? Every cellular system divides the territory in cells (basic units).Each cell is assigned a range of frequencies for performing the transmissions (incoming or outgoing calls).
This application is intended for use with Computer Science and Telecommunications students. The objective is to try different handover techniques and compare the results.

How is a mobile unit transferred from one cell to another? That is what handover is about. Some of the handover techniques implemented in the tool are:

- Basic handover: a call is transferred from one cell to another only when there are free channels in the second cell.
- Guard band handover: each cell reserve some channels for transferred calls.
- Two level handover: a power margin is used, so no unnecessary handovers are carried out.
- Satellite handover: it arises when there is a hand over from a terrestrial mobile system to a satellite mobile system.

When simulating handover or handoff methods, we are dealing with a discrete event simulation problem. One approach was to work off-line using a software such as ARENA, that is a great program, but as we wanted to offer an Internet application we have to look for a discrete event simulation package, the answer came with SimJava (a process based discrete event simulation package for Java)

Our application has been developed using the Model-View-Controller architecture. The view presents the model in an adequate format, forming the user interface, what will be the applet. The controller represents the system’s events and invokes changes in the model and the view. And, SimJava libraries allow that the communication between entities gives as result changes in the view without the controller, so we apply the MVC active. The model is the mobile phoning system: the business logic/code.

The user’s interface is a Java applet. Simjava uses the graphic library awt, but we decided to modify. The source code to translate awt into swing, the result is a more friendly interface.
The user can introduce the number of calls that will be generated (following some distribution) and the type of handover. Then we can run the simulation. Once the simulation has finished, a report with relevant information is generated and it can be stored or printed.