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+\chapter{Networks}
+
+A \textit{network} is a system involving two or more computers that are
+connected, allowing them to \textbf{communicate}. A computer not
+connected to a network is a \textit{stand alone computer}.
+
+Networks allows the easy sharing of data, file, backups, and
+peripherals (such as printers). Networks also allow for efficient and
+high volume communication and can reduce the cost of computing.
+However, a network can also allow hacking and the spread of viruses.
+Networks require additional security measures and potentially
+specialist equipment or staff at additional expense.
+
+We typically identify three classes of network:
+
+\begin{itemize}
+    \item A personal area network (PAN) exists in the range of a
+        single person. This may include an individuals devices that
+        are networked such as a computer, mobile phone, or tablet and
+        other devices connected by network such as Bluethooth
+        headphones or USB devices.
+    \item A large area network (LAN) covers a small geographical area.
+        This could be anything from a single home to a university and
+        thereby can vary in complexity and scale. Twisted pair cables
+        (Ethernet) and Wi-Fi are commonplace in a LAN.
+    \item A wide area network (WAN) covers a large geographical area.
+        The Internet is a very large WAN through the use of fibre
+        optic cables, often undersea, reaching every continent other
+        than Antarctica
+        \footnote{\url{https://en.wikipedia.org/wiki/Submarine_communications_cable}}
+        (which is nonetheless served by satellite Internet links).
+        Organisations with significant sums of money may also
+        create a WAN for the transfer of large amounts of data or
+        speed critical transfer.
+\end{itemize}
+
+\section{Wired networks}
+
+In a wired network the \textit{communication media} is a physical
+cable that transmits a signal. A \textit{coaxial cable} is a single
+copper cable with shielding. A twisted pair cable is also copper but
+can transmit data at a higher \textit{bandwidth} and is flexible
+whilst coaxial cable is not. Fibre optic cables are made of glass and
+transmit light.
+
+Copper cables are cheap and generally compatible with existing
+hardware, but are easy to \textit{eavesdrop} on and cannot transmit
+data at longer distances. Fibre optic cables are better for long
+distance communications and are much higher bandwidth than copper.
+They are also lightweight and hard to eavesdrop on. However fibre
+optic cables are very expensive and often require new infrastructure
+in order to use.
+
+\section{Wireless networks}
+
+Wireless networks send data by transmitting and receiving
+\textit{electromagnetic radiation} (generally radio waves). A wireless
+access point (WAP) transmits and receives this data for many devices
+and is often built into modern household routers. Wi-Fi removes the
+need for cables which are expensive and inconvinient. However the
+range, speed, and bandwidth of Wi-Fi are limited. Transmission is 
+limited by interference (such as thick walls or metal construction)
+and the signal can be easily intercepted causing the need for further
+security measures.
+
+\section{Network topology}
+
+The topology of a network describes the layout of network devices and
+allow the planning of suitable network infrastructure.
+
+\subsection{Bus topology}
+
+\begin{center}
+\begin{tikzpicture}
+    \draw (0,0) edge[*-*] (12,0);
+    \draw [-o] (2,0) -- (2,-2);
+    \draw [-o] (4,0) -- (4,2);
+    \draw [-o] (6,0) -- (6,-2);
+    \draw [-o] (8,0) -- (8,2);
+    \draw [-o] (10,0) -- (10,-2);
+\end{tikzpicture}
+\end{center}
+
+In the bus topology, nodes (devices or computers) are connected along
+the \textit{backbone}, each sending and receiving data.
+\textit{Terminators} are positioned at each end of the backbone to
+prevent the signal \textit{bouncing} and transmitting to the devices
+again.
+
+A bus topology is cheap and scalable, but the backbone is a single
+point of failure and can be eavesdropped on, leading to the compromise
+of all data. Data sent by one device is received by all other devices
+thus compromising privacy and only one device can send data on the
+backbone at a time, thus slowing the network.