\subsection{Objectives}
%1, 2
The objective of this document is to provide an approach for testing a
particular implementation of \textit{Transmission Control Protocol} (TCP). TCP
is a host-to-host protocol that provides a reliable communication.

This testing approach can be used by either an internal test team or an
independent testing team. The test effort's goal is to become confident about
the conformance of an existing implementation to the specification created by
\textit{The Internet Engineering Task Force}
(IETF)\footnote{\url{http://www.ietf.org}} as document
\textit{RFC793}~\cite{rfc793}. This document is explicitly \emph{not} intended
to serve as guideline for testing during the development phase, but for testing
conformity to the specification of an \emph{existing} implementation.

\subsection{SUT}
%3,4
\includegraphics[width=\linewidth]{SUTsetup.eps}

The \textit{System under test} (SUT) is the TCP implementation of a system
running a Linux kernel\footnote{\url{http://www.kernel.org}} version $3.13$.
TCP is not a program that runs on its own and therefore we have to make use of
some tools to be able to test the protocol. This is further described in
Section~\ref{section:testenv}.

The specification of TCP is too big to be tested in one go so we focus on
specific sections from \textit{RFC793}.
\begin{itemize}
	\item Sequence numbers~\cite[Section~3.3]{rfc793}.
	\item Setting up a connection via the 
		``Three-way handshake''~\cite[Section~3.4]{rfc793}.
	\item Closing a connection~\cite[Section~3.5]{rfc793}.
	\item Data communication~\cite[Section~3.7]{rfc793}.
\end{itemize}

\subsection{Risks}
\label{sec:risks}
%5. Risks
Risks can be divided into two categories. Project risks and product risks.
Because an existing implementation is tested the project risks are non
applicable. Product risks however are very important since it is unknown if the
product has been tested during development.

The product risks for the SUT are significant because misbehaviour of the SUT
could have potential large consequences. The key characteristics of TCP are
integrity and reliability~\cite[Section~1]{rfc793}, these characteristics cease
to exist when the implementation is faulty.

Because TCP is a core functionality of a networking capable system it is
crucial that the TCP implementation functions according to the specification.
Several critical systems could rely on the correct functionality of the TCP
implementation. A failure in the SUT could therefore have extensive
consequences. Even more so since TCP is a computer-to-computer protocol, which
leaves no room for ambiguity, which could be solved in a computer-to-human
protocol. Another effect of the SUT being a computer-to-computer protocol
without a standalone program is the fact that we can only observe the SUT
indirectly. With the use of tools we can see what the output is for a given
input but there is always the risk that the tools give an incomplete or faulty
view of the output.
