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diff --git a/exercise01/exercise01.tex b/exercise01/exercise01.tex index d581704..075a12a 100644 --- a/exercise01/exercise01.tex +++ b/exercise01/exercise01.tex @@ -2,6 +2,133 @@ \addcontentsline{toc}{section}{Exercise 1} \section*{Exercise 1} -\begin{question} +\begin{question}[subtitle={Shannon-Weaver Model}] + Illustrate the process of sending an e-mail using the Shannon-Weaver model! Describe all nodes and edges shortly! +\end{question} + +\begin{solution} + Person A send an e-mail to person B: + \begin{itemize} + \item Information source: Brain of person A + \item Signal: Impulses on nerve cells + \item Transducer: Keyboard, converts keystrokes to electronic signals + \item Signal: Electronic signals + \item Modem: PC, Receives keystrokes and decodes them into the e-mail + \item Signal: Data + \item Transmission channel: Internet + \item Signal: Data + \item Modem: PC, decodes e-mail, generates text + \item Signal: Electronic signals + \item Transducer: Screen, displays text + \item Signal: Impulses on nerve cells + \item Information source: Brain of person B + \end{itemize} +\end{solution} + +\begin{question}[subtitle={Classes of Signals}] + Assign the following signals to the categories: time-continuous vs. time-discrete, value-continuous vs. value-discrete! + \begin{tasks} + \task + $\cos\left(2 \pi \cdot \SI{50}{Hz} \cdot t\right)$ + \task + Letters: a, B, F, f + \task + \begin{equation*} + f(x) = \begin{cases} + -1 & \qquad \forall \; x \leq 0 \\ + 1 & \qquad \forall \; x > 0 + \end{cases} + \end{equation*} + \end{tasks} +\end{question} + +\begin{solution} + \begin{tasks} + \task + time-continuous, value-continuous + \task + time-discrete, value-discrete + \task + time-continuous, value-discrete + \end{tasks} +\end{solution} + +\begin{question}[subtitle={Frequency Allocation}] + An LTE (4G cell phone) signal can occupy a bandwidth of up to \SI{20}{MHz}. One of the bands allocated to LTE is, amongst others, the band 1 (uplink: \SIrange{1920}{1980}{MHz}, uplink: \SIrange{2110}{2170}{MHz}). The range of one LTE base station is a few kilometres. + + However, the HF band (\SIrange{3}{30}{MHz}) has the advantage that waves are reflected by the ionosphere and can propagate over longer distances or even across the whole world. Mostly, narrow-band services like AM broadcasting or amateur radio are allocated to the HF band. + + Why is it pointless to use the HF band for LTE? +\end{question} + +\begin{solution} + Reasons: + \begin{enumerate} + \item Band capacity: + \begin{itemize} + \item HF band is only \SI{27}{MHz} wide. + \item In contrast, the UHF band is \SI{2700}{MHz} wide. + \item One LTE base station would occupy the whole HF band. + \item LTE base stations should only have a limited range. One base station can only service a limited number of users. + \item Increasing the cell coverage will decrease the number of users and the data rate. + \item \textbf{That's why high data rate services use higher frequencies.} + \end{itemize} + \item Antenna size + \begin{itemize} + \item The antenna size is proportional to the wave length. For example, a $\lambda/2$-dipole measures the half of the wave length. + \item HF band wave length: \SI{10}{100}{m} + \item UHF band wave length: \SI{0.1}{1}{m} + \item UHF antennas are much smaller. They must fit into a cell phone. + \item \textbf{The higher the frequencies, the more compact the antennas and devices.} + \end{itemize} + \end{enumerate} +\end{solution} + +\begin{question}[subtitle={OSI Layers}] What is the difference between a \emph{digital communication system} and a \emph{service}? To which OSI layers are they associated? -\end{question}
\ No newline at end of file +\end{question} + +\begin{solution} + \begin{itemize} + \item Digital communication system (in our understanding): collection of technologies for conveying information + \item Implemented in lower layers (1 - 4), we consider with layers 1 and 2 + \item Services provide user applications (e.g. video-on-demand, social media, etc.). A service uses communication systems. + \item Services are located in layer 5 - 7. + \end{itemize} +\end{solution} + +\begin{question}[subtitle={Networks}] + \begin{tasks} + \task + What is the major difference between OSI layers 2 and 3? + \task + Give one example for each layer! + \task + What is routing? + \end{tasks} +\end{question} + +\begin{solution} + \begin{tasks} + \task + \begin{itemize} + \item Layer 2: Connection of two devices + \item Layer 3: Data transfer across multiple nodes (creating a network) + \end{itemize} + \task + \begin{itemize} + \item Layer 2: IEEE\,802.11 (WiFi) + \item Layer 3: Internet Protocol (IP) + \end{itemize} + \task + \begin{itemize} + \item Routing is used in layer 3 + \item A network consists of devices interconnected using layer 2 protocols. + \item If one device sends a layer 3 packet, it is wrapped into a layer 2 frame and sent to the next node. + \item The next node unpacks the layer 3 packet. + \item The next node has to decide to which next node the layer 3 packet should be relayed. + \item \textbf{This is routing.} Routing means findig the best way to the destination route. + \item The node packs the layer 3 packet into a layer 2 frame and sends to it the node it has selected. + \end{itemize} + \end{tasks} +\end{solution} |