X-Git-Url: http://git.rohieb.name/skm-ma-ws1314.git/blobdiff_plain/28a82327c7952cf1bad8680ae7b408e57ef70615..3aebd41deecdba7e92d13378f4a30e6103314433:/sec-chatty-things.tex?ds=sidebyside

diff --git a/sec-chatty-things.tex b/sec-chatty-things.tex
index 01f0bb2..25b1426 100644
--- a/sec-chatty-things.tex
+++ b/sec-chatty-things.tex
@@ -1,11 +1,9 @@
 \section{System Architecture of ``Chatty Things''}
 
-After the underlying techniques have been explained, we can have a look at the
-system architecture which Klauck and
+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.
 
-
-\todo
 \pages{3}
 \subsection{Service Provisioning Sublayer}
 
@@ -34,12 +32,12 @@ Furthermore, Klauck and Kirsche implemented new features for uXMPP, which were
 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 item]
+\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 \ref{xep-0175}
+  \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})
   \item XMPP Serverless Messaging (XEP-0174), using \term{uBonjour} as
@@ -50,16 +48,17 @@ The resulting implementation (uXMPP and uBonjour) gets by with 12{.}2\ kBytes of
 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]
+\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
-detected over uBonjour, it is used instead with the ANONYMOUS login method, and the
-XEP-0174 module is disabled. The ANONYMOUS login method is chosen since TLS
-encryption is not yet implemented, and it assigns random JID to the client,
-which do not need to exist on the server. However, a server must exist and must
-be configured in order to use this method.
+detected over uBonjour, it is used instead with the ANONYMOUS login method, and
+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.
 
 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
@@ -69,8 +68,7 @@ devices of a topic, or she can also interact with them 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
 drawback that Multi-User Chats cannot be used for topic filtering, since no
-method is specified to do XEP-0045 and XEP-0174 at the same time. \todo[temporary subscription presence here?]
-In this case,
+method is specified to do XEP-0045 and XEP-0174 at the same time. In this case,
 a user must have an XEP-0174-compliant chat client, but it also gives her the
 opportunity to interact with things spontaneously on an ad-hoc basis (e.~g. when
 entering a room) without need for any additional gateway on the application
@@ -82,11 +80,6 @@ level.
 
 \subsection{Bootstrapping}
 
-In a distributed context like the Internet of Things, devices need to be ready
-to use out of the box. Users often do not want to set up configurations for each
-device they use, and when using several of those devices, it is often not
-reasonable having to configure every single one.
-
 With the given approach, bootstrapping new Chatty Things is easy and no
 configuration is neccessary: on the network layer, IP addresses can simply be
 obtained using IPv4 Link-Local Addressing or IPv6 Stateless Address
@@ -118,10 +111,29 @@ During runtime, a device can then react to changes in network infrastructure:
     Messaging and uBonjour and join topic-based Multi-User Chats.
 \end{itemize}
 
-\todo[short conclusion?]
+\todo{short conclusion?}
 
 \subsection{Temporary Subscription for Presence}\label{sec:tsp}
 
-To further reduce the message overhead
+To further reduce the message overhead and allow more fine-grained control over
+information filtering, \term{Temporary Subscription for Presence} is introduced.
+This technique builds on top of presence stanzas as defined in core XMPP, which
+are sent by default without a \code{to} or \code{from} attribute, and therefore
+fit into a single TCP/IP packet over IEEE~802.15.4. However, a drawback of the
+presence mechanism defined by core XMPP is the fact that a client must manually
+subscribe to presence information of another client in order to receive it,
+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.
+
+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
+join the chat rooms which they are interested in. This allows nodes to inform
+only interested nodes about updates. This has the advantage that existing
+clients supporting Multi-User Chats can be used by a user, but Chatty Things and
+XMPP servers need to be adapted to the new subscription model. Also, this
+mechanism does not work with Serverless Messaging.
 
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