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diff --git a/ex09/kn09.tex b/ex09/kn09.tex
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 	\item SONET is called a synchronous network because it uses STS (\textbf{synchronous} transport signal) multiplexing and demultiplexing. That means the receiver has to be synchronized with the sender to interpret the signal correctly.
 \end{enumerate}
 \Aufgabe{ATM}{10+5}
-
+\begin{enumerate}
+    \item One cell has 53byte. So at most we have to wait for he transmission of 53byte at each switch. With a transmission rate of 43 Mbit/s we get:\\
+    $\frac{5\cdot2\cdot(53\cdot8)}{43 Mbit/s}=9.86\cdot 10^{-5}s$\\
+    Minimal is half of the time (no waiting but only transmission at each switch):\\
+    $\frac{5\cdot(53\cdot8)}{43 Mbit/s}=4.93\cdot 10^{-5}s$
+    %TODO: maybe 43Mbit/s in the whole network?
+    \item $20byte+20byte+8byte=48byte$ which is exactly the payload of an ATM cell, so we need one cell.
+\end{enumerate}
 \end{document}