Unit 5 · Session 2
Data Communication Media and Transmission
🎯 Learning Objectives
By the end of this session, you will be able to:
- ✅ Differentiate between guided (wired) and unguided (wireless) transmission media.
- ✅ Identify common types of wired media, such as twisted-pair and fiber optic cable.
- ✅ Define bandwidth and its importance in data transmission.
The Physical Path of Data
Transmission Media: The physical channel connecting a sender and receiver in a network.
Think of it as the "highway" that data travels on. 🛣️
Sender 💻 ➡️ Channel (Media) ➡️ Receiver 🖥️
📶 Turning Data into Signals
A computer's data is just 1s and 0s. To travel, every bit is turned into a signal the medium can carry:
⚡ Copper cable
Changes in electrical voltage
💡 Fibre optic
Very fast flashes of light
📡 Wireless
Changes in radio waves
Every signal faces two enemies:
- Attenuation: the signal gets weaker the further it travels.
- Noise: unwanted signals, such as from motors or other cables, mix in and corrupt the data.
Choosing a medium is really about how far, how fast and how cleanly the signal can travel.
Two Main Categories
1. Guided (Wired) Media
Signals are physically guided along a solid medium.
- Twisted-Pair Cable
- Coaxial Cable
- Fiber Optic Cable
2. Unguided (Wireless) Media
Signals are broadcast through the air or space without a physical path.
- Radio Waves (Wi-Fi, Bluetooth)
- Microwaves (Satellite)
Guided Media: Twisted-Pair Cable
The Everyday Cable
- Pairs of insulated copper wires twisted together.
- Why twist? To reduce electronic interference (crosstalk). 🔍
- Common Uses:
- Ethernet (LAN) cables
- Traditional telephone lines
This is the most common, cost-effective type of wired media for local networks.
Inside a twisted-pair cable
🎬 Why Twist? Listen to the Noise
Guided Media: Coaxial & Fiber Optic
Coaxial Cable
- Single copper conductor at the center.
- Insulated and shielded for better protection against interference.
- Uses: Cable TV, older network setups.
⚡ Fiber Optic Cable
- Transmits data as pulses of light!
- Made of thin glass or plastic strands (fibers).
- Uses: Internet backbone, high-speed business/home connections.
📊 Wired Media Comparison
Twisted-Pair
Speed: Good
Cost: Low
Interference: Susceptible
Coaxial
Speed: Better
Cost: Medium
Interference: More Resistant
Fiber Optic
Speed: Best 🚀
Cost: High
Interference: Immune
Key Takeaway: Fiber optic is the fastest and most reliable, but also the most expensive to install.
🎬 Copper vs. Fibre in 90 Seconds
📏 How Far Can Each Medium Go?
| Medium | Typical distance before the signal needs a boost |
|---|---|
| Twisted-pair Ethernet | 100 m per cable run |
| Fibre optic | Tens of kilometres. Undersea cables add a repeater about every 50–100 km. |
| Wi-Fi | Tens of metres indoors, since walls weaken it |
| Bluetooth | About 10 m for most devices |
| Microwave link | Tens of kilometres between towers that can see each other |
Quick check: Your new office desk is 150 m of cable away from the server room. Can you use one Ethernet cable?
No. 150 m is over the 100 m limit. Add a switch part-way, or run fibre.
Unguided Media (Wireless)
Radio Waves 📡
Travel in all directions from the source (omnidirectional).
Easily pass through walls, making them great for indoor use.
Uses: Wi-Fi, Bluetooth, Cellular (4G/5G), FM Radio.
Microwaves
Travel in a straight line (unidirectional).
Requires a clear line-of-sight between transmitter and receiver.
Uses: Satellite communication, long-distance point-to-point links.
Microwave links need line of sight
🛰️ Satellites: High and Slow, or Low and Fast?
Geostationary (GEO)
- About 35,786 km up, so it seems to stay still over one spot
- Three satellites can cover most of the Earth
- Signals take about half a second to go up, come down and return, which makes video calls lag
- Used for TV broadcasting and remote links
Low Earth Orbit (LEO)
- About 500–1,200 km up, circling Earth in about 90–110 minutes
- Needs thousands of satellites working together, as in Starlink
- Much shorter delay, usually well under a tenth of a second
- Used for fast internet in remote areas, ships and planes
The delay is called latency. Distance adds latency, even at the speed of light.
Key Concept: Bandwidth
Bandwidth: The maximum data transfer capacity of a network connection in a given amount of time.
Analogy: Think of it as the width of a highway.
- A narrow, one-lane road = Low Bandwidth
- A wide, multi-lane highway = High Bandwidth
Measured in bits per second (bps), e.g., Mbps, Gbps.
🧮 Worked Example: How Long Will It Take to Download?
Internet plans are sold in megabits per second (Mbps), but files are measured in bytes. As in Session 3.8, 1 byte = 8 bits.
Task: Download a 1.5 GB movie on a 100 Mbps fibre plan.
- Convert to megabytes: 1.5 GB = 1,500 MB
- Convert to megabits: 1,500 × 8 = 12,000 Mb
- Divide by the speed: 12,000 ÷ 100 = 120 seconds, so 2 minutes
That's the best case. Real downloads are slower, because the connection is shared and the server may be busy.
🎯 Your Turn: Bandwidth in Real Life
Work it out in pairs, then reveal the answer.
- A 600 MB app update on a 20 Mbps 4G connection
600 × 8 = 4,800 Mb, and 4,800 ÷ 20 = 240 s, so 4 minutes - A 25 MB PowerPoint file over a 1 Gbps (1,000 Mbps) office LAN
25 × 8 = 200 Mb, and 200 ÷ 1,000 = 0.2 seconds - A 4K movie stream needs about 15 Mbps. How many 4K streams can a 50 Mbps home plan carry at once?
50 ÷ 15 ≈ 3.3, so 3 streams, with a little left over
Bandwidth is shared. Every extra device or user takes a slice of the "highway".
🎬 Bandwidth vs. Latency
Practical Application in Nepal
Connecting a Nation
Nepal's internet backbone heavily relies on fiber optic cables connecting to India and China for international bandwidth.
In cities like Kathmandu, ISPs like WorldLink and Vianet use Fiber-to-the-Home (FTTH) for high-speed internet.
In remote, hilly regions, microwave and radio wave (wireless) links are crucial for providing connectivity where laying cables is difficult and expensive.
Wireless reaches where cable can’t
🌋 Case Study: The Country That Lost Its Internet
- On 15 January 2022, an undersea volcano erupted near Tonga, a Pacific island nation.
- The eruption cut Tonga's only undersea fibre cable to the rest of the world.
- For about five weeks, until the cable was repaired, the country relied on limited satellite links. Phone calls, bank transfers and money from relatives abroad were badly disrupted.
Discuss: Nepal is landlocked, and its international bandwidth comes through fibre links to India and China.
- Why is it important to have more than one route out of the country?
- Which medium could act as a backup if the main cables failed?
Tonga, 2022: the eruption that cut a cable
🎯 Activity: Choose the Medium
Pick the best transmission medium for each job, and give one reason.
| 1. Wiring 30 desks on one office floor | Twisted pair: cheap, easy, and every run is under 100 m |
| 2. Linking two office buildings 2 km apart | Fibre: long distance at high speed |
| 3. A factory floor full of heavy electric motors | Fibre: light is immune to electrical noise |
| 4. A mountain village 25 km away, across a valley with a clear view | Microwave link: no cable to lay, and the towers can see each other |
| 5. Customers using phones in a café | Radio waves (Wi-Fi): no cables, and they pass through walls |
| 6. A research ship in the middle of the ocean | Satellite: the only option far from land |
Now look back at the village from Session 1. Which would you choose?
Summary & Key Takeaways 📝
- Transmission media is the physical path for data, either guided (wired) or unguided (wireless).
- Fiber optic cable offers the highest speed and capacity for wired connections and forms the internet's backbone.
- Radio waves are the foundation for modern wireless technologies like Wi-Fi and 5G cellular networks.
- Bandwidth measures the maximum data rate of a network connection—the "width of the pipe".
Image & Video Credits
Images
- "Satellite Orbits Drawn to Scale": diagram made for this course (IT231)
- "Network utp unshielded twisted pair cable": Leon Brooks, public domain — https://commons.wikimedia.org/wiki/File:Network_utp_unshielded_twisted_pair_cable.jpg
- "Coaxial cable cutaway": Tkgd2007, CC BY 3.0 — https://commons.wikimedia.org/wiki/File:Coaxial_cable_cutaway.svg
- "Fiber optic illuminated": Hustvedt, CC BY-SA 3.0 — https://commons.wikimedia.org/wiki/File:Fiber_optic_illuminated.jpg
- "BNSF Communications Tower with Andrew Corporation-CommScope Terrestrial Point-to-Point Microwave Antennas": Tony Webster, CC BY-SA 2.0 — https://commons.wikimedia.org/wiki/File:BNSF_Communications_Tower_with_Andrew_Corporation-CommScope_Terrestrial_Point-to-Point_Microwave_Antennas_-_Lafayette,_Iowa_(24700229995).jpg
- "A view of Satpokharee Valley with its solar power mobile tower": Mohan Singh BK, CC BY-SA 3.0 — https://commons.wikimedia.org/wiki/File:A_view_of_Satpokharee_Valley_with_its_solar_power_mobile_tower.jpg
- "ISS-66 Atmospheric plume from 2022 Hunga Tonga eruption": NASA / Kayla Barron, public domain — https://commons.wikimedia.org/wiki/File:ISS-66_Atmospheric_plume_from_2022_Hunga_Tonga_eruption_-_edited.jpg
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Videos (YouTube)
- Audio University, "Twisted vs. Untwisted Wires" (0:00 to 1:21)
- CodeAI (Code.org), "The Internet: Wires, Cables & Wifi" (3:42 to 5:11, and 2:53 to 3:42)
Exam Practice 📝
Short answer
- List the five components of data communication.
- Differentiate between guided and unguided media.
- Differentiate between simplex, half-duplex, and full-duplex with examples.
Long answer
- Compare twisted-pair, coaxial, and fiber optic cables.
- Explain unguided transmission media and their uses, with examples from Nepal.
Revise the answers in the full note linked on the last slide.
Thank You
Questions before we wrap this hour?
Next: Unit 5 · Session 3 — Network Types and Topologies