longtable: hline doesn't display on the first page

Question

table head and \hline do not display on the first page, as shown the red line below.

Here is the source code.

\documentclass[twoside,12pt]{article}
\usepackage{longtable}

\begin{document}

\begin{longtable}{|c|c|r|r|r|r|r|r|r|l|}
    \caption{The throughput improvements achieved by network coding in Toulouse}
    \label{table:throughput improvement 2}
    \endfirsthead
    \hline
    line1   &   line2   &   $t_1$       &   $t_{12}$    &   $t_2$       &   $r$(\%)&    $D$(GB)&    $D_{nc}(GB)$&$G_t$(\%)&Station\\    % table head
    \hline
    \endhead % all the lines above this will be repeated on every page
    \hline
    \endfoot %  to appear at the bottom of each page
    10  &   2       &   0:22:00 &   9:46:00 &   2:00:00 &   80.49   &   159.18  &   302.25  &   89.88   &   Cours Dillon    \\
    10  &   109 &   1:19:00 &   8:55:00 &   1:40:00 &   74.93   &   188.48  &   319.09  &   69.3    &   Malepère    \\
    % more data is here
\end{longtable}

\end{document}

If I remove \endfirsthead, it raised the following error.

Answer 1

You should add content of the head also to the firsthead:

\documentclass[twoside,12pt]{article}
\usepackage{longtable}

\begin{document}
    \begin{longtable}{|c|c|r|r|r|r|r|r|r|l|}
    \caption{The throughput improvements achieved by network coding in Toulouse}
    \label{table:throughput improvement 2}\\ %<-- added
\hline%<-- added
line1 & line2 & $t_1$ & $t_{12}$ & $t_2$  & $r$(\%) & $D$(GB) & $D_{nc}(GB)$ & $G_t$(\%) & Station\\  %<-- added
\hline%<-- added
    \endfirsthead
    \hline
    line1   &   line2   &   $t_1$       &   $t_{12}$    &   $t_2$       &   $r$(\%)&    $D$(GB)&    $D_{nc}(GB)$&$G_t$(\%)&Station\\    % table head
    \hline
    \endhead % all the lines above this will be repeated on every page
    \hline
    \endfoot %  to appear at the bottom of each page
    10  &   2       &   0:22:00 &   9:46:00 &   2:00:00 &   80.49   &   159.18  &   302.25  &   89.88   &   Cours Dillon    \\
    10  &   109 &   1:19:00 &   8:55:00 &   1:40:00 &   74.93   &   188.48  &   319.09  &   69.3    &   Malepère    \\
% more data is here
    \end{longtable}
\end{document}

Note: The code, as it is, will not repeat caption on the new page.

Answer 2

Put \\\hline before \endfirsthead:

\documentclass[twoside,12pt]{article}
\usepackage{longtable}

\begin{document}

\begin{longtable}{|c|c|r|r|r|r|r|r|r|l|}
    \caption{The throughput improvements achieved by network coding in Toulouse}
    \label{table:throughput improvement 2}
    \\\hline
    \endfirsthead
    \hline
    line1   &   line2   &   $t_1$       &   $t_{12}$    &   $t_2$       &   $r$(\%)&    $D$(GB)&    $D_{nc}(GB)$&$G_t$(\%)&Station\\    % table head
    \hline
    \endhead % all the lines above this will be repeated on every page
    \hline
    \endfoot %  to appear at the bottom of each page
    10  &   2       &   0:22:00 &   9:46:00 &   2:00:00 &   80.49   &   159.18  &   302.25  &   89.88   &   Cours Dillon    \\
    10  &   109 &   1:19:00 &   8:55:00 &   1:40:00 &   74.93   &   188.48  &   319.09  &   69.3    &   Malepère    \\
    % more data is here
\end{longtable}

\end{document}