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\subsection{Identification (0x00)}
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As an example of CATS' extreme flexibility, even the packet's identification exists in a whisker. When using CATS as intended, this whisker will likely always be included. There are some situations where it may not be, however. For example, to save data it could be omitted in some packets, as long as it is included often enough for legal station identification. It could also be omitted if CATS is being used outside of amateur frequencies. \textbf{A valid CATS packet contains a maximum of one identification whisker.}
The callsign is an arbitrary string of UTF-8 up to 252 bytes long. In most cases, it should be much shorter. One remaining byte at the end is for the SSID. This allows up to 255 different stations to share a single callsign.
The identification whisker also has 2 bytes which specify an icon. CATS icons are loosely equivalent to APRS symbols. Two bytes allows a maximum of 65536 different icons. For now, only a handful are defined, though this list will evolve with the standard. All icon IDs are valid, even those that don't currently correspond with an icon. This property is essential to allow the icon list to grow while ensuring backwards-compatibility with older nodes.
\subsubsection{Structure}
\begin{tabularx}{\textwidth}{|l|l|l|X|}
\hline
\textbf{Byte offset} & \textbf{Length} & \textbf{Value} & \textbf{Description} \\
\hline
0 & 1 & 0x00 & Whisker type \\
\hline
1 & 1 & $N$ & Whisker length in bytes \\
\hline
2 & 2 & & Icon ID \\
\hline
4 & $N - 3$ & & Callsign data \\
\hline
$N + 1$ & 1 & & SSID \\
\hline
\end{tabularx}
\subsubsection{Icon Table}
\begin{tabular}{|l|l|}
\hline
\textbf{Icon ID} & \textbf{Icon Name} \\
\hline
0 & [No Icon] \\
\hline
1 & Cat \\
\hline
2 & Car \\
\hline
3 & House \\
\hline
4 & Office building \\
\hline
5 & Truck \\
\hline
6 & Van \\
\hline
7 & Red Square \\
\hline
8 & Orange Square \\
\hline
9 & Yellow Square \\
\hline
10 & Green Square \\
\hline
11 & Blue Square \\
\hline
12 & Purple Square \\
\hline
13 & Balloon \\
\hline
14 & Airplane \\
\hline
15 & Helicopter \\
\hline
16 & Bus \\
\hline
17 & Train \\
\hline
18 & Person \\
\hline
19 & Warning \\
\hline
20 & Error \\
\hline
21 & Satellite \\
\hline
22 & Computer \\
\hline
23 & Bicycle \\
\hline
24 & Motorcycle \\
\hline
\end{tabular}