Exercises: Telecommunications

In all communication, there are three parts: the one sending (sender), the path through which the signal travels (medium), and the one receiving it (receiver). Identify these three parts in each situation: (a) sending a message on a cell phone; (b) watching a video on a laptop; (c) playing online on a console.

The figure shows the diagram of any communication: a sender transmits a message that reaches a receiver, but the central element is covered with a question mark, as shown in the diagram.

Which element of the diagram is covered? Give two examples of this element, one wired and one wireless, and explain what would happen to the message if that element disappeared.

Classify these transmission media into "wired" and "wireless": twisted pair, Wi-Fi, fiber optic, Bluetooth, coaxial cable, 4G cellular networks. Explain in one sentence what difference there is between the two groups.

True or false? Justify each answer: (a) fiber optics transmit information as light pulses; (b) Bluetooth is designed for very short distances; (c) Wi-Fi travels through the air as radio waves; (d) the television remote control can work from kilometers away.

Match each device to the medium it uses to communicate: (a) the TV remote control, (b) wireless headphones, (c) your cell phone when you are out on the street, (d) the classroom computer connected to the router. Media: 1. Bluetooth; 2. infrared; 3. network cable (twisted pair); 4. 4G or 5G cellular network.

When subscribing to an internet connection "of $600$ megs", those megs are megabits per second ($\text{Mbps}$). Using the analogy of a pipe or a road, explain what it means for one connection to have more megs than another and what a family notices when using it.

Order these media from shortest to longest typical range and explain the criterion you followed: infrared, satellite, Wi-Fi, Bluetooth, 4G cellular networks.

Connections advertise a download speed and an upload speed. Explain what downloading and uploading data mean, and give an everyday example of each action: one where you use downloading and another where you use uploading.

The figure shows a table comparing several transmission media, but some cells remain to be completed, as shown in the diagram.

Complete the three cells marked with "?" by reasoning from the other rows. Then explain which medium from the table you would choose to connect two school buildings separated by $300\ \text{m}$ using a cable, and why.

Your home Wi-Fi works much worse in the room furthest from the router. Explain this by considering what happens to radio waves over distance and when passing through walls, and reason why this loss does not occur with a network cable.

Fiber optics have replaced old copper ADSL in many homes. Explain the difference between transmitting information as light pulses or as electric current, and reason why fiber achieves much higher speeds and degrades less over distance.

The TV remote control does not work if you stand behind the door, but the games console controller keeps working even inside a backpack. Relate this to the medium used by each (infrared versus Bluetooth), explain what "line of sight" is, and in what situations it is a problem.

Your family pays for $300\ \text{Mbps}$ fiber, but the speed test shows $280\ \text{Mbps}$ with the computer connected by cable and only $60\ \text{Mbps}$ with the laptop on Wi-Fi at the back of the house. Analyse where those megs are "lost" and suggest two ways to recover them.

In a village without fiber or copper cable, the only option is satellite internet. Explain how data travels in that case (from the home dish to the satellite and back), what great advantage this medium has, and what drawbacks you can imagine: the time it takes for the signal to travel up and down, storms...

The figure compares typical speeds of four transmission media, as shown in the chart.

Order the four media from slowest to fastest and choose the most suitable one for each situation, justifying your choice: (a) wireless headphones; (b) watching a high-quality movie; (c) a home desktop computer; (d) a cell phone on the bus. Notice that the Bluetooth bar is barely visible: what does that tell you about what that medium is used for (and what it is not)?

Your cell phone automatically connects to home Wi-Fi and uses cellular data (4G) when you are outdoors. Explain the difference between both media in terms of range and who "pays" for the data traffic, and reason why it is advisable to download large files while connected to Wi-Fi.

In a home there is $600\ \text{Mbps}$ fiber, but the computer in the attic, connected via Wi-Fi, only reaches $30\ \text{Mbps}$. Analyse where the bottleneck is (the fiber or the wireless link?) and suggest two different technical solutions (wiring the room, installing an access point, or a Powerline/PLC adapter using the electrical installation), comparing them.

A family is hesitating between two offers: fixed fiber of $100\ \text{Mbps}$ or a 4G router of $50\ \text{Mbps}$ that "you can take to any home". Compare both options thinking about speed, stability, potential data limits, and what would happen with four people connected at the same time, and make a reasoned recommendation.

You are on a video call with your uncle, who lives in another city: your cell phone connects via Wi-Fi, your house has fiber to the exchange, and he receives the signal on his cell phone via 4G. Describe the complete sender, media, and receiver chain through which your voice travels and count how many times it changes medium along the way.

Your Bluetooth headphones cut out if you leave your cell phone in the bedroom and go to the kitchen, but the home Wi-Fi speaker plays everywhere. Explain the difference in range and battery consumption between both media, what role walls play, and reason what would happen if the headphones used Wi-Fi instead of Bluetooth.

A country house without fiber wants internet for daily work. Evaluate three alternatives (a 4G router if there is coverage, a satellite connection, or a radio link antenna with the nearby village) by comparing range, speed, and installation difficulty, and recommend one with arguments.

Aboard a cruise ship on the high seas, it is impossible to connect to terrestrial 4G cell towers or run a direct cable. The ship uses a $50\ \text{Mbps}$ satellite connection, but passengers notice that it is impossible to maintain smooth video calls or play online games due to the massive signal delay (latency exceeding $600\ \text{ms}$), and that the service cuts out during storms. Justify why terrestrial mobile towers do not work on the high seas, explain the path of the signal to the ground justifying the cause of this high delay compared to terrestrial fiber optics, and explain why heavy rain blocks the satellite's microwaves.

A video game takes up $60\ \text{GB}$ and your connection downloads at $100\ \text{Mbps}$. Remember that $1$ byte is $8$ bits: first convert megabits per second to megabytes per second, then calculate the theoretical download time of the game (use the school convention $1\ \text{GB} = 1024\ \text{MB}$), and explain why in reality it will take somewhat longer.

A friend claims: 'In the future, cables will disappear and everything will be wireless.' Argue for and against using what you know about the range, speed and stability of each medium, think about what carries traffic between cities, and end with your reasoned conclusion.