\draw[thick, {Latex[round]}-{Latex[round]}] (0,3.5) -- (0,0) -- (13,0);

\draw[thin,dotted] (0.5,0) -- (0.5,3);
\draw[thin,dotted] (2.5,0) -- (2.5,3);
\draw[thin,dotted] (4.5,0) -- (4.5,3);
\draw[thin,dotted] (6.5,0) -- (6.5,3);
\draw[thin,dotted] (8.5,0) -- (8.5,3);
\draw[thin,dotted] (10.5,0) -- (10.5,3);

\draw[thin,dotted] (0,0.5) -- (12,0.5);
\draw[thin,dotted] (0,2.5) -- (12,2.5);

\draw (0.5,0)  --++(0,-0.1) 
  node[below,inner sep=2pt] {$0$};
\draw (2.5,0)  --++(0,-0.1) 
  node[below,inner sep=2pt] {$\nicefrac{f_{\mathrm{S}}}{2}$};
\draw (4.5,0)  --++(0,-0.1) 
  node[below,inner sep=2pt] {$f_{\mathrm{S}}$};
\draw (6.5,0)  --++(0,-0.1) 
  node[below,inner sep=2pt] {$\nicefrac{3f_{\mathrm{S}}}{2}$};
\draw (8.5,0)  --++(0,-0.1) 
  node[below,inner sep=2pt] {$2f_{\mathrm{S}}$};
\draw (10.5,0) --++(0,-0.1)
  node[below,inner sep=2pt] {$\nicefrac{5f_{\mathrm{S}}}{2}$};

\draw (0,0.5) --++(-0.1,0) 
  node[left, inner sep=2pt] {$0$};  
\draw (0,2.5) --++(-0.1,0) 
  node[left, inner sep=2pt] {$\nicefrac{f_{\mathrm{S}}}{2}$}; 

\draw[semithick] (0.5,0.5) -- (2.5,2.5) -- (4.5,0.5) -- (6.5,2.5) --
                 (8.5,0.5) -- (9.5,1.5);

\draw[semithick,densely dashed] (9.5,1.5) --   (10.5,2.5) -- (11.5,1.5); 

\node[anchor=south] at (12.9,0  )  {$f_{\mathrm{i}}$};
\node[anchor=west]  at (0   ,3.4) {$f_{\mathrm{o}}$};