\subsection{XMPP}
-\todo
\pages{3-4}
The \term{Extensible Messaging and Presence Protocol (XMPP)} is a distributed,
the resource is only needed for routing between client and server.
\subsubsection{Architecture}
-\begin{wrapfigure}{r}{0.4\textwidth}
-%\begin{figure}[htop]
+\begin{wrapfigure}{r}{0.5\textwidth}
+ \tikzstyle{iconlabel}=[text width=3cm, align=center, font=\footnotesize]
+ \begin{tikzpicture}[node distance=0pt,scale=1.5,>=stealth,thick]
+ \def\nodelist{
+ juliet/{(-1,-1)}/XMPP client \code{juliet@example.net}/below/computer,
+ examplenet/{(-1,1)}/XMPP server \code{example.net}/above/server,
+ imexampleorg/{(1,1)}/XMPP server \code{im.example.org}/above/server,
+ romeo/{(1,-1)}/XMPP client \code{romeo@im.example.org}/below/computer%
+ }
+ \foreach \name/\pos/\text/\tpos/\icon in \nodelist {
+ \node (\name) at \pos { \includegraphics[width=1.2cm]{icon-\icon.pdf} };
+ \node[\tpos=of \name,iconlabel] (\name text) { \text };
+ }
+ \draw[<->,dashed] (juliet) -- node[anchor=east]{s2c} (examplenet);
+ \draw[<->] (examplenet) -- node[anchor=south]{s2s} (imexampleorg);
+ \draw[<->,dashed] (imexampleorg) -- node[anchor=west]{s2c} (romeo);
+ \end{tikzpicture}
\centering
- \includegraphics[width=0.4\textwidth]{fig-xmpp-architecture-mock.jpg}
- \caption{XMPP architecture}
+ \caption{XMPP architecture, showing server-to-server (s2s) and
+ server-to-client (s2c, dashed) connection types}
\label{fig:xmpparch}
-%\end{figure}
\end{wrapfigure}
The original architecture underlying XMPP strongly leans on the established
\todo[Example stream]
-\subsubsection{Multi-User Chats}
+\subsubsection{Publish/Subscribe and Presence}
+
+Typically, a user wants to chat with a more or less fixed set of other users,
+whose JIDs she needs to know, so she needs some kind of ``address book'' that
+remembers the JIDs for her. In XMPP, this is address book is called
+\term{roster}, and it also shows the users' willingness to chat (``presence'').
+In order to see their chat status (which can be one of ``online'', ``offline'',
+and several ``away'' or ``do not disturb'' states), a user needs to subscribe to
+the other user's status. The mechanism behind this is called
+\term{Publish-Subscribe} and is specified in XEP-0060~\cite{xep0060}. It can
+be used to notify interested users about changes in personal information, and
+implements the classic Observer pattern.
-\cite{xep-0045}
+A user publishes information by creating a \term{node} on the XMPP server, which
+acts as a handle for the data. Interested users can then query the server for
+nodes, and request subscription to them. When the owner of the node confirms the
+subscription request, subscribers get notified whenever the owner updates the
+respective node.
-\subsubsection{Publish/Subscribe, Presence and the Roster}
+All communication takes place between the client and the server over \code{<iq>}
+(``information query'') stanzas.
-\cite{xep-0060}
+\subsubsection{Multi-User Chats}
+Besides one-to-one messaging, XMPP also allows users to create multi-user
+chat rooms, which is specified in \cite{xep0045}. Each chat room is given a
+unique JID to which the users send their messages to. Each incoming message is
+then dispatched to all users which have joined the room.
-\cite{rfc6121}
+To join a room, the user sends a \code{<presence>} stanza to the room JID, where
+the resource part of the room JID specifies the desired nick name.
\subsubsection{XMPP Serverless Messaging}\label{sec:xsm}
-\todo
+\pages{1}
To overcome the need for a central server and authentication, XMPP Serverless
-Messaging~\cite{xep-0174} allows XMPP clients on a network to build a
+Messaging~\cite{xep0174} allows XMPP clients on a network to build a
peer-to-peer mesh network and chat directly with each other. This feature was
first introduced by Apple as part of their \term{Bonjour} project, and nowadays
it is also available in many other XMPP clients.
over the corresponding TXT record in the mDNS. To go offline, a client
announces the deletion of its mDNS records.
-\pages{1}
-
% vim: set ft=tex et ts=2 sw=2 :