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The Test System


This section describes the system that is going to be tested and what roles the SDL and TTCN Integrated Simulator and SDL simulator play in the test.

An SDL system called ABP will be used in this tutorial. The ABP system implements a small OSI stack containing a network layer, a data-link layer and a physical layer. The network component on one side is handled by the TTCN Suite and on the other side by an SDL process.

The data-link layer implements a very simple protocol known as the Alternating Bit Protocol (ABP).

The network protocol is very simple protocol, where all messages are echoed back as an acknowledgment that they have been received.

This setup gives us the ability to send messages from the TTCN Suite to the network peer simulated by the SDL Suite, and to receive acknowledgments in return. If the answer is identical to the message, we have managed to communicate successfully.

What we want to test is the ability of the Data-Link layer's protocol to deliver, even when messages are lost on the way. To enable this, we have introduced an extra channel between the SDL and TTCN Integrated Simulator and the SDL simulator, on which commands can be sent to make the physical layer lose messages.

The ABP system is stored in the TTCN Suite installation, in the sub-directory examples/bitprotocol. If you have set up the $telelogic environment variable, the complete path is $telelogic/examples/bitprotocol.


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