-\section{System Architecture of ``Chatty Things''}
+\section{System Architecture of ``Chatty Things''}\label{sec:arch}
After the underlying techniques have been explained, we can now have a look at
the system architecture which Klauck and
Kirsche~\cite{Klauck:2012:BCC:2352852.2352881} use to build Chatty Things.
-\pages{3}
\subsection{Service Provisioning Sublayer}
Considering the application in deeply embedded systems and the special needs of
the Internet of Things on the one hand, the protocol stack needs to fulfil
certain technical requirements.
-First, memory, computing resources and bandwith on embedded systems are limited,
+First, memory, computing resources and bandwidth on embedded systems are limited,
which demands for a lightweight protocol stack without too much overhead and
predictable memory consumption, while also retaining enough flexibility for
future development. The authors therefore provide only the most essential
realized as separate modules to allow enabling and disabling them at runtime,
thus further reducing the memory footprint of a running system:
-\todo{minimize space between list items}
\begin{itemize}
\item support for IPv6
\item support for Multi-User Chats (XEP-0045), which are used for information
filtering
\item support for SASL ANONYMOUS login for XMPP servers \cite{xep0175}
\item a new publish-subscribe mechanism called Temporary Subscription for
- Presence (see \ref{sec:tsp})
+ Presence (see Section~\ref{sec:tsp})
\item XMPP Serverless Messaging (XEP-0174), using \term{uBonjour} as
underlying mDNS/DNS-SD implementation for Contiki.
\end{itemize}
ROM and 0{.}63\ kBytes of RAM, which was about the size of the original,
unoptimized uXMPP implementation while also implementing new features.
-\todo{figure of example network structure with and without central server}
-
In order to react to different network infrastructures, their implementation
allows both communication with a central XMPP server as well as peer-to-peer
communication over XMPP Serverless Messaging. When a central XMPP server is
the XEP-0174 module is disabled. The ANONYMOUS login method is chosen since TLS
encryption is not yet implemented, and with this method, the server assigns a
random JID to the client, which does not need to exist on the server. However, a
-server must exist and must be configured to use this login method in order to
-use this method.
+server must exist and must be configured to supply this login method in order
+for this approach to work.
With a server, information filtering is achieved by creating topic-based
Multi-User Chats where multiple devices can be grouped. A user can then simply
join the chat with a standard XMPP client on her machine and interact with all
-devices of a topic, or she can also interact with them directly.
+devices of a topic, or she can also interact with single devices directly.
In scenarios without an XMPP server, the XEP-0174 module is activated and
devices talk directly with the user or with other devices. This method has the
Bootstrapping a Chatty Thing therefore incorporates three steps:
\begin{enumerate}
- \item Activate uBonjour and try to discover an XMPP server
+ \item Activate uBonjour and try to discover an XMPP server.
\item If a server is found, connect to it using ANONYMOUS login, join
topic-based Multi-User Chats, deactivate the uBonjour client
- \term(Infrastructure mode).
- \item If no server is found, activate the XEP-0174 client \term{Ad-hoc mode}.
+ \term{(Infrastructure mode).}
+ \item If no server is found, activate the XEP-0174 client \term{(Ad-hoc
+ mode)}.
\end{enumerate}
-During runtime, a device can then react to changes in network infrastructure:
+During runtime, a device can then react to changes in network infrastructure by
+changing from one mode to the other:
\begin{itemize}
\item In Infrastructure mode: when connection to the server is lost, enable
Messaging and uBonjour and join topic-based Multi-User Chats.
\end{itemize}
-\todo{short conclusion?}
-
\subsection{Temporary Subscription for Presence}\label{sec:tsp}
To further reduce the message overhead and allow more fine-grained control over
which requires further communication between the clients. Since the network can
change rapidly, and clients can frequently join and leave the network,
subscriptions would often be outdated and must be renewed, leading to overhead
-of subscriptions and unsubscription packets, which would inhibit the flow of the
-actual information.
+of subscriptions and unsubscription messages, which would inhibit the flow of
+the actual information.
To solve this problem, a dynamic, topic-based roster is implemented on top of
Multi-User Chats (XEP-0045). Every topic corresponds with a chat room, and nodes
projects / skm-ma-ws1314.git / blobdiff