% ------------------------------------------------------------------------------
% Copyright (c) 2010, 2020 Contributors to the Eclipse Foundation
%
% See the NOTICE file(s) distributed with this work for additional
% information regarding copyright ownership.
%
% This program and the accompanying materials are made available under the terms
% of the MIT License which is available at https://opensource.org/licenses/MIT
%
% SPDX-License-Identifier: MIT
% ------------------------------------------------------------------------------
\documentclass{article}
\usepackage{tikz}
\usepackage{verbatim}

\usepackage[paperwidth=40in, paperheight=20in]{geometry}

\usetikzlibrary{arrows, automata, positioning, shapes.geometric}
\begin{document}
\pagestyle{empty}

\definecolor{se-blue}{HTML}{D0D5FF}

\newcommand{\state}[2]{\begin{tabular}{@{}c@{}}#1\\#2\end{tabular}}

\begin{tikzpicture}[
  ->,>=stealth',auto,node distance=3cm,thick,
  every node/.style={font=\sffamily\small},
  every state/.style={draw=se-blue,thick,top color=white,ellipse,
                      bottom color=se-blue!75,initial text=},
  accepting/.style={accepting by arrow,accepting text=\ldots},
  every edge/.style={draw=black!50}]

  \node[state, initial] (s01) [                               ] {p/s};
  \node[state]          (s02) [                   right of=s01] {i/s};
  \node[state]          (s03) [                   right of=s02] {i/a};
  \node[state]          (s05) [above =1cm of s03, right of=s03] {p/a};
  \node[state]          (s06) [below =1cm of s03, right of=s03] {p/b};
  \node[state]          (s04) [below =1cm of s05, right of=s05] {i/b};

  \path[every node/.style={font=\sffamily\normalsize,outer sep=-1pt}]
    (s01) edge[             ] node[                   ] {produce   } (s02)
    (s02) edge[bend left =20] node[sloped,anchor=south] {provide\_a} (s05)
    (s02) edge[bend right=20] node[sloped,anchor=north] {provide\_b} (s06)
    (s03) edge[             ] node[sloped,anchor=north] {provide\_b} (s06)
    (s04) edge[             ] node[sloped,anchor=south] {provide\_a} (s05)
    (s05) edge[             ] node[sloped,anchor=south] {produce   } (s03)
    (s06) edge[             ] node[sloped,anchor=north] {produce   } (s04)
  ;

\end{tikzpicture}
\end{document}