\begin{figure}[!h]
\label{ttcn3_overview}
\begin{center}

\begin{psmatrix}[rowsep=-0.06]
\psframebox[]{\parbox{9cm}{\centering \ttcn{} Test System \\[5pt]
	\begin{psmatrix}[rowsep=0.12,colsep=0]
	[name=D0] \pnode{x} & [name=MTC]  \psbox{7cm}{Main Test Component (MTC)} \\[0pt]
	[name=D1] \pnode{x} & [name=PTC1] \psbox{7cm}{Parallel Test Component (PTC)} \\[0pt]
	[name=D2] \pnode{x} & [name=PTC2] \psbox{7cm}{Parallel Test Component (PTC)} \\[0pt]
	\end{psmatrix}
}} \\
\psframebox[]{\parbox{9cm}{\centering Abstract Test System Interface}} \\
\\[10pt]
\psframebox[]{\parbox{9cm}{\centering
	\begin{psmatrix}[rowsep=0,colsep=0.1]
	[name=D4] \pnode{x} & \parbox{5cm}{\centering Real Test System Interface} \\
	\end{psmatrix}
}} \\
\psframebox[fillstyle=solid,fillcolor=lightgray]{\parbox{9cm}{\centering System Under Test (SUT)}} \\
\end{psmatrix}

\ncbar[angle=180]{o->}{D0}{D4}
\ncbar[angle=180]{o->}{D1}{D4}
\ncbar[angle=180]{o->}{D2}{D4}
\end{center}
\caption[Overview of the \ttcn{} architecture]{Overview of the \ttcn{} architecture: ports are used for the communication between test components and the SUT}
\end{figure}
