HOSN-app/thesis/content/05-proof-of-concept/technology-decisions.tex

In order to implement the concept in the best possible way, some technology decisions had to be made. These included the implementation of the data exchange on a peer-to-peer basis and the choice of a framework for the development of the app. In the following, different technologies and libraries are presented that were considered for the implementation.

\subsection{Peer 2 Peer Network}
\label{sec:p2p-network-technology}
Basically, there are two conceivable approaches for the P2P network:

\begin{itemize}
	\item Creation of a separate P2P network between the hybrid clients
	\item Use of an existing P2P network for own purpose
\end{itemize}

In the following, solutions for both ways are presented and compared with each other.

\subsubsection{Creation of a P2P Network}
\label{sec:create-p2p-network}
The advantage of having an extra P2P network is that it is completely under control. Accordingly, it can be designed to fit exactly to the use case and require little or no compromise. However, setting up a P2P network is a big challenge and some hurdles must be overcome. These challenges include peer discovery (how peers find each other), global data exchange over the Internet and data storage, and availability of the stored data. And of course, all these requirements must scale. It should work for P2P networks with only a few peers and also for a few thousand or even more peers. Two approaches are conceivable here: the use of an established standard such as Wi-Fi Dircet or WebRTC or the use of a library (for example Hive2Hive, Y-Js) to create a dedicated P2P network.

\subsubsection*{Wi-Fi Direct}
Wi-Fi Direct is a standard (IEEE 802.11) for data transmission between two WLAN terminals. There is no need for an access point between the two devices. However, the distance that may lie between the two peers is thus limited. Without obstacles, which contribute to the attenuation of the signal, a distance of up to 95m is possible. In buildings, it sinks to 32m or less. However, the requirement for the P2P network to expand Twitter is different. Users can be scattered around the world and may be online through the mobile network. There is no P2P connection via Wi-Fi Dircet in this case.

\subsubsection*{WebRTC}
WebRTC (Web Real-Time Communication) is an open standard that provides various communication protocols for real-time communication between two or more peers. Above all, WebRTC is popular for its ability to easily perform video calls, as known from Skype, in the browser without a server. But also the file transfer between peers is possible. In a separate P2P network, data could be exchanged between the clients. However, the connection between the clients is complex, since in addition to the two peers also a STUN server and optionally a TURN server is involved. Furthermore, it is unclear whether the system scales. At least for Google Chrome browser is known that a maximum of 265 connections to other peers can be maintained in parallel.

\subsubsection*{Y-JS}
The JavaScript library Y-JS describes itself as \enquote{a framework for offline-first P2P shared editing on structured data-like text, richtext, json, or XML.} The library takes care of solving synchronization conflicts when editing distributed files. By choosing a connector, you can set the protocol for the communication between the peers.There is the possibility to use WebRTC, XMPP or Websockets, but with some connectors running a server is a prerequisite. Further extensions can be used to supplement a database and data types, but the focus here is on the joint editing of data by multiple peers. For all connectors, the authors of the library recommend using an own server.

\subsubsection*{Hive2Hive}
Hive2Hive is a Java library for \enquote{secure, distributed, P2P-based file synchronization and sharing}. There is no less promise than \enquote{a free and open-sourced, distributed and scalable solution that focuses on maximum security and privacy of both users and data}. In order to be able to use Hive2Hive globally via the Internet, it is necessary to operate at least one relay peer - five are recommended\footnote{https://github.com/Hive2Hive/Android/wiki/Guide-for-System-Admins}. Since a permanent TCP connection between peer and relay peer is maintained, the power consumption is quite high. Constant TCP connection can be avoided by using Google Cloud Messaging (GCM). However, Google has already discontinued this service. And since the development of Hive2Hive was discontinued in March 2015 too, there is currently no solution to this problem.

\subsubsection*{GUN}
GUN is a graph database that keeps a state in sync across multiple instances. GUN is written in JavaScript and unlike Hive2Hive and Y-JS, the project is still being worked on.

\textit{todo...}

\subsubsection{Using an Existing P2P Network}
\label{sec:using-existing-p2p-network}
As mentioned in the previous section, setting up your own P2P network involves a number of challenges. If you use an already existing P2P network for your own purpose, these challenges can be elegantly avoided. For this purpose, however, a suitable P2P network must be found whose properties and possible uses meet the requirements of the hybrid OSN client.

In the following, various P2P networks are considered and examined for their usability for a potential deployment to extend an OSN.

\subsubsection*{Filesharing P2P Networks}

\subsubsection*{Blockchain}

\subsubsection*{IPFS}

\subsubsection{Conclusion}

\subsection{Application Framework}
\label{sec:application-framework}

[Standard Android Java App vs. Ionic]