[Tex/LaTex] Drawing a packet layout with TikZ

Question

I'm new to TikZ, and I'm having a terrible time figuring out how to create an image similar to this.

So far I am able to create all the rectangles, but there are two things I cannot figure out how to do:

1. I'd like to replace the B symbols region with an ellipses in the center to show continuation, and
2. Is there an elegant way to specify positioning for the labels, beyond just coordinates, so that moving around the rectangle regions moves the associated labels?

Answer 1

Here's one possibility (I wasn't sure of the desired layout for the central region):

\documentclass{article}
\usepackage{graphicx}
\usepackage{tikz}
\usetikzlibrary{calc,positioning,shapes,decorations.pathreplacing}

% the styles for short and long nodes
\tikzset{
short/.style={draw,rectangle,text height=3pt,text depth=13pt,
  text width=7pt,align=center,fill=gray!30},
long/.style={short,text width=1.5cm}
}

\begin{document}

% the short nodes \shnode{<label>}{<right of>}{<text>}
\def\shnode#1#2#3{%
  \node[short,right=of #1] (#2) {\rotatebox{270}{#3}}}

% the long nodes \lnode{<label>}{<right of>}
\def\lnode#1#2{%
  \node[long,right=of #1] (#2) {}}

\noindent\begin{tikzpicture}[node distance=-\pgflinewidth]

\node[short,fill=black] (a) {};
\shnode{a}{b}{src};
\shnode{b}{c}{dst};
\shnode{c}{d}{len};
\lnode{d}{e};
\lnode{e}{f};
\node[long,draw=none,fill=none,right=of f,text height=0pt,text depth=0pt,text width=1cm] (g) {$\ldots$};
\node[long,right=of g,label=center:$b$ bits] (h) {};
\lnode{h}{i};
\shnode{i}{j}{len};
\shnode{j}{k}{dst};
\shnode{k}{l}{src};
\node[short,fill=black,right=of l] (m) {};

\node[above right=1cm of a] (ppre) {Packet preamble};
\node[above left=1cm of m] (ppos) {Packet postamble};

\draw[decorate,decoration={brace,raise=2pt}] (b.north west) -- node[above=4pt] {Header} (d.north east);
\draw[decorate,decoration={brace,raise=2pt}] (j.north west) -- node[above=4pt] {Trailer} (l.north east);
\draw[decorate,decoration={brace,raise=2pt}] (h.north west) -- node[above=4pt] {Codeword} (h.north east);
\draw (ppre.west) -- +(-20pt,0pt) -- (a.north);
\draw (ppos.east) -- +(20pt,0pt) -- (m.north);
\draw (a.south east) -- +(0,-1.2cm);
\draw (m.south west) -- +(0,-1.2cm);
\draw[<->] ( $ (a.south east) +(0,-0.6cm) $ ) -- node[fill=white] {$S/B$ Codewords} ( $ (m.south west) +(0,-0.6cm) $ );
\draw[,dotted] (f.north east) -- (h.north west);
\draw[dotted] (f.south east) -- (h.south west);

\end{tikzpicture}

\end{document}