X-Git-Url: http://git.rohieb.name/skm-ma-ws1314.git/blobdiff_plain/28a82327c7952cf1bad8680ae7b408e57ef70615..bbf634a989779b4193d927a3f0046ba61e19f1c7:/sec-chatty-things.tex?ds=sidebyside

diff --git a/sec-chatty-things.tex b/sec-chatty-things.tex
index 01f0bb2..fe69f94 100644
--- a/sec-chatty-things.tex
+++ b/sec-chatty-things.tex
@@ -4,8 +4,6 @@ After the underlying techniques have been explained, we can 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}
 
@@ -69,8 +67,7 @@ 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
@@ -122,6 +119,23 @@ During runtime, a device can then react to changes in network infrastructure:
 
 \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 controls over
+information filtering, \term{Temporary Subscription for Presence} is introduced.
+This technique builds on top of presence stanzas as defined in core XMPP. These
+presence stanzas are sent without a \code{to} or \code{from} attribute, and
+therefore fit into a single TCP/IP packet over IEEE~802.15.4. However, to be
+able to receive these stanzas, a client must manually subscribe to those
+information in their roster, which requires further communication between nodes. As the network
+can change rapidly, subscriptions would be often outdated, and there would be
+much 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.
 
 % vim: set ft=tex et ts=2 sw=2 :