\begin{tikzpicture}[->,auto,x=1.5cm, y=1.5cm]

\foreach \i in {1,2,3,4,5,6}
  \node [state] (input-\i) at (0,2.5-\i) {};

\foreach \i in {1,2,3}
  \node [state] (hidden-\i) at (3,2-\i*1.25) {};

\foreach \i in {1,2,3,4,5,6}
  \node [state] (output-\i) at (6,2.5-\i) {};

\foreach \i in {1,2,3}
  \foreach \j in {1,2,3,4,5,6}
    \draw  (hidden-\i) -- (output-\j);

\foreach \i in {1,2,3,4,5,6}
  \foreach \j in {1,2,3}
    \draw (input-\i) -- (hidden-\j);


\foreach \i in {1,2,3,4,5,6}
  \draw [<-] (input-\i) -- ++(-1,0)
    node [above, midway] {Ch \i};

\foreach \i in {1,2,3,4,5,6}
  \draw [->] (output-\i) -- ++(1,0)
    node [above, midway] {Ch \i};

\end{tikzpicture}