X-Git-Url: http://git.rohieb.name/skm-ma-ws1314.git/blobdiff_plain/f0fb3f3f678d8fe10cad4ff3920a60248a93a077..5d1cfb85e07daea1874f3753ab6ca31437efe869:/sec-discussion.tex?ds=sidebyside

diff --git a/sec-discussion.tex b/sec-discussion.tex
index 3133b6e..0c3838d 100644
--- a/sec-discussion.tex
+++ b/sec-discussion.tex
@@ -1,91 +1,11 @@
-\section{Discussion}
-%\todo
-\pages{3}
-
-\subsection{Future Work}
-
-In addition to the XEPs covered above, there are a few additional XEPs which can
-be implemented to further increase the effictivity of Chatty Things. Especially
-the documents XEP-0323 through XEP-0326 (which are currently in Experimental
-status) are targeted to the Internet of Things.
-
-\paragraph{Concentrators (XEP-0326)~\cite{xep0326}}
-In contrast to sensor nodes which are focused on collecting data, concentrators
-can be used to control and serve as proxy for a subset of the network. The XEP
-defines messages to query a sensor node for data sources, and subscribing to
-them, while subscription is loosely modeled after the Publish-Subscribe
-mechanism (XEP-0060). It also specifies how clients can request data from or
-control certain nodes over a concentrator.
-
-This approach can be practical in large-scale sensor networks, where usually not
-every sensor node can be reached directly, and where sensor nodes only have a
-very limited amount of storage. Individual concentrators can then be equipped
-with larger storage and serve as a facility to aggregate data from sensor nodes.
-This structure can be implemented on several levels, forming a hierarchy. A user
-interested in specific values then only needs to communicate with a single node
-in the network.
-
-\paragraph{Sensor Data (XEP-0323)~\cite{xep0323}}
-%\begin{figure}
-  %\caption{Example stream between a sensor node and a client}
-  %\label{fig:streamexample}
-  %\begin{verbatim}
-%Client               Device
-%<stream>
-
-  %\end{verbatim}
-%\end{figure}
-This XEP specifies a way of reading out values from a
-sensor node. It allows to specify multiple data sources (e.~g. temperature,
-humidity) as well as multiple types of data (e.~g., momentary values, historical
-values, peak values).
-As a simple use case, the client sends an \code{<iq>} stanza containing the request and a
-sequence number used to identify the request. The sensor node then rejects or
-accepts the request by returning a corresponding \code{<iq>} stanza. If it has
-accepted the request, it reads out the requested data and returns it in a
-subsequent \code{<message>} stanza to the client.
-
-\paragraph{Control (XEP-0325)~\cite{xep0325}}
-In this document, a way of controlling sensor nodes is specified, which allows a
-client to get and set control values on the node over
-\code{<message>} or \code{<iq>} stanzas. As an example, in this way a sensor
-node can be instructed to return data in a different unit or range, or can be put
-into power-safe mode.
-
-\paragraph{Provisioning (XEP-0324)~\cite{xep0324}}
-To protect the integrity of a sensor network and securing the data being
-collected, this document specifies a way of implementing access rights and user
-privileges. Since a single sensor node is usually very restricted in user input and
-output, the approach is very simple and can be implemented e.~g. using a button
-and an LED for interaction, while presentation of data takes places on a
-provisioning server with a rich user interface (which can be, for example, a
-concentrator).
-
-When integrating a new sensor node into the network, the user instructs the
-provisioning server to generate a \term{friendship} request for the new node.
-The node can e.~g. symbolize this request by blinking its LED and requesting a
-button press in the next 30 seconds. If the user presses the button, the node
-confirms the friendship to the server. The server then remembers this sensor
-node and generates a token which must be used in all further communication
-between the server and the sensor node or the communication is rejected.
-
-\paragraph{Efficient XML Interchange Format (EXI, XEP-0322)~\cite{xep0322}}
-Finally, EXI describes how XMPP stanzas sent between nodes can be compressed,
-thereby effectively reducing the overhead in message size introduced by XML.
-XMPP nodes can negotiate a compressed stream inside their existing XMPP streams
-and exchange \code{<compress>} stanzas which then contain the payload. However,
-it is to be noted that this requires further implementation of compression
-algorithms as well as additional CPU and memory resources and thus might
-decrease message throughput and increase power consumption on embedded systems.
-
-
-\todo{example XML stream with sensor data}
+\section{Discussion}\label{sec:discussion}
 
 \subsection{Related Approaches}
 
-This section gives a short overview of related protocols for the Internet of
-Things and shows their advantages and disadvantages, which are summarized in
-Table~\ref{tab:comparison}.
+``Chatty Things'' is not the only approach to implement communication in
+embedded networks. This section gives a short overview of related protocols for
+the Internet of Things and shows their advantages and disadvantages, which are
+summarized in Table~\ref{tab:comparison}.
 
 \begin{table}
 \small\centering
@@ -95,7 +15,7 @@ Table~\ref{tab:comparison}.
   \hline
   Feature & Chatty Things & CoAP & MQTT & WS4D \\
   \hline\hline
-  application gateways neccessary & - & yes & yes & - \\ \hline
+  application gateways necessary & - & yes & yes & - \\ \hline
   usable with standard clients & yes & - & - & (yes) \\ \hline
   discovery support & yes & yes & - & yes\\ \hline
   IPv6/6LoWPAN ready & yes & yes & ? & partial \\ \hline
@@ -108,15 +28,16 @@ Table~\ref{tab:comparison}.
 
 The Constrained Application Protocol~\cite{draft-ietf-core-coap-18} focuses on
 machine-to-machine communication and originates from the IETF Constrained
-Resources Working Group, but still has been only in draft status since 2010.\ It
-allows a mapping to HTTP, and is therefore stateless, but it specifies a binary
-protocol, which makes it neccessary to deploy application-level gateways and
-special client software to communicate with its environment. It relies on UDP,
-but emulates congestion control, message confirmation and message IDs, since â
-in contrast to HTTP â messages can be sent asynchronously. Discovery is also
-specified and done over multicast, service discovery is then done over a
-well-known URI on the host. Since it is a binary protocol and mostly
-self-contained, it has low protocol overhead and parsing complexity.
+Resources Working Group\footnote{\url{http://datatracker.ietf.org/wg/core/}},
+but still has been only in draft status since 2010.\ It allows a mapping to
+HTTP, and is therefore stateless, but it specifies a binary protocol, which
+makes it necessary to deploy application-level gateways and special client
+software to communicate with its environment. It relies on UDP, but emulates
+congestion control, message confirmation and message IDs, since â in contrast to
+HTTP â messages can be sent asynchronously. Discovery is also specified and done
+over multicast, service discovery is then done over a well-known URI on the
+host. Since it is a binary protocol and mostly self-contained, it has low
+protocol overhead and parsing complexity.
 
 \paragraph{MQ Telemetry Transport (MQTT)}
 
@@ -136,9 +57,9 @@ Web Services are wide-spread in the business world, this approach can probably
 be used in existing infrastructures, and is also focused on multiple platforms
 like embedded systems and servers. Web Services can be very flexible and
 composable, and discovery is already specified, however, this also comes at a
-cost: web services are enclosed in SOAP, which is enclosed in HTTP, which is
-transported over TCP, which introduces very much overhead, especially with SOAP
-being based on verbose XML. IPv6 support is only partially implemented.
+cost: messages are enclosed in SOAP, which is enclosed in HTTP, which is
+transported over TCP, which introduces a substantial overhead, especially with
+SOAP being based on verbose XML. IPv6 support is only partially implemented.
 For communication, standard APIs can be used.
 
 \subsection{Conclusion}
@@ -147,7 +68,7 @@ For communication, standard APIs can be used.
 protocol, there is the need to implement at least an XML parser on each node,
 which comes with protocol overhead and increased code size. However Klauck and
 Kirsche show that with good optimization (in the code as well as in the
-procotol), a complete stack can be implemented in 12 kByte of ROM, which leaves
+protocol), a complete stack can be implemented in 12 kBytes of ROM, which leaves
 enough space for other applications to be built onto it. As compared to Web
 Services, Chatty Things are probably not as flexible, but they have less
 overhead, even when using XML, while MQTT and CoAP provide less flexibility for
@@ -162,16 +83,18 @@ server in order to use Temporary Subscription for Presence for topic filtering,
 which is caused by the lack of support for Multi-User Chats in XEP-0174
 (Serverless Messaging). If this gap can be closed, or a different way for topic
 filtering in distributed networks is found, the server can be
-eliminated and what remains is truly distributed network without the need for
-any central infrastructure, therefore eliminating most single points of failure
+eliminated and what remains is a highly distributed network without the need for
+much central infrastructure, therefore eliminating most single points of failure
 in the system.
 
 It is always hard to trade flexibility and accessibility for efficiency. The
 Chatty Things approach is probably not one of the most efficient, and not the
 most flexible, but it has the big advantage that users can interact with their
 things using standard chat clients, without the need for application gateways or
-specialized software. In terms of efficiency, it chooses a common ground between
-binary protocols and Web Services, which were originally developed for servers
-with much less resource constraints as embedded systems.
+specialized software. In terms of efficiency, it chooses a compromise between
+binary protocols and Web Services, latter which were originally developed for
+servers with much less resource constraints as embedded systems. However, with
+additional XEPs focusing on the Internet of Things, enough flexibility can be
+achieved for this use case.
 
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