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Description of Example System
The SDL System
Functional Description
The example system is a model of a GSM system. The implementation is restricted to the high-level layers of the GSM standard. The following functionality is implemented:
- User PIN code verification (PIN code is one digit only)
- Tracking of mobile phones through VLR and HLR databases
- Freedom of movement for mobile phones by base station switching
- Control of the IMEI code of a mobile phone
- Billing service to keep track of elapsed time and cost for phone calls
Implementation Description
The system is implemented in a modular way. Each functional entity is implemented as a block type. The block types are organized in a package, called "GSM".
The SDL system uses the GSM package and instantiates its block types. The "Mobile" system has four MobileStation block instances, four BaseTransceiverStation block instances and two MobileSwitchingCenter block instances. The MobileStation instances are named as mobile phone owners. The names are Marie, John, ParisPizza and LyonPizza. The BaseTransceiverStation instances are named Lyon11, Lyon12, Paris11 and Paris12, indicating their location.
The Target Application
Deployment
The Mobile system is partitioned into five executable files. Each MobileStation block instance is built as an executable and the remaining block instances (Proxy, BaseTranscieverStation, BaseStationController, MobileSwitchingCenter and Database) execute together in one executable.
The Graphical User Interface
A graphical user interface (GUI) is provided for the MobileStation block. It is delivered as C source code to be compiled and linked when building each of the four mobile phone executable files. The interface resembles that of a typical mobile phone. A simple menu system, containing a phone book and a billing report, is provided. The user can switch base station from the option menu in the bottom of the window. The GUI is shown in Figure 204.
TCP/IP Communication
The executable files of the target application communicate by sending signals via TCP/IP. The communication is handled by the SDL Suite TCP/IP communication module, which is delivered as C source code. It is compiled and linked into each of the executables.
To be able to locate the receiver of a signal, the TCP/IP module needs the host name and TCP port number of the receiving executable. This information must be supplied through a routing function, which is manually implemented in C.
The mobile system is delivered with default routing functions. This will enable you to run all executables on your computer without giving any routing information manually.
Figure 205 shows a UML component diagram of the executable files in the deployed mobile system. Each executable file sets up a TCP/IP server, listening on a specific TCP port number. This number is used by remote executables for addressing SDL signals. The TCP/IP server is illustrated by the interface on each component. The dashed arrows indicate a flow of signals from one component to another.
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