Year 9 · Computing

Lesson 2
Connectivity

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Objectives

By the end of this lesson you will be able to…

  • Understand different types of network media: twisted-pair copper, fibre optic, coaxial and wireless.
  • Explain what bandwidth is and how it affects file transfer time.
  • Calculate the time taken to download files of different sizes at different bandwidths.
  • Understand why streaming video and audio uses buffering.

Starter

The first communication cable from the UK to the USA was installed in 1858. Discuss with a partner, then click each card to reveal the answer.

🎲 Fun fact

Submarine cables today

Internet cables now contain fibre-optic strands. The newest cables can transmit up to 160 terabits per second.

160
Terabits / second

Maximum bandwidth of the newest submarine cables.

70million
HD films streamed at once

That's how much data 160 Tb/s could carry.

550+
Cables under the sea

Connecting countries and continents around the world.

🌍 Almost all international internet traffic travels through submarine cables on the seabed, not through satellites.
🗺️ Explore the live submarine cable map ↗

Cable types

Click each cable to find out what it is and where it's used.

❓ What other medium can data travel through without using a cable? Click below.
📝 Now complete Task 1 on Worksheet 2.

Wireless connections

✅ Advantages

⚠️ Disadvantages

Bandwidth

The amount of data which can be transferred through a cable each second is called its bandwidth.

Click an analogy to expand it.

💧 Analogy 1: Water pipe

A thin pipe only lets a small amount of water through each second.
A wide pipe lets a lot more water through in the same time.

Bandwidth works the same way. It's the "width" of the cable. The wider it is, the more data can flow through each second.

Thin pipe
(low bandwidth)
💧 a little water
Medium pipe
(medium bandwidth)
💧💧 more water
Wide pipe
(high bandwidth)
💧💧💧 lots of water
🛣️ Analogy 2: Motorway lanes

Now let's put numbers on it. Data is made of bits (1s and 0s). Each row below has to deliver the same 48 bits, and every bit travels at the same speed.

The road with more lanes finishes first because more bits move in parallel. That's exactly what bigger bandwidth means: more bits per second.

1 lane
(low bandwidth)
48 bits
3 lanes
(medium bandwidth)
48 bits
6 lanes
(high bandwidth)
48 bits
Year 2000 modem 56 kb/s
Modern home internet 100 Mb/s
Submarine fibre 160 Tb/s

Modern home internet is more than 1,750 times faster than a year 2000 modem.
📏 The bars use a squashed (logarithmic) scale — drawn to true scale, the modem's bar would be far too thin to see!

⚠️ Watch the units!
Mb/s = megabits per second (lower-case b)
MB/s = megabytes per second (upper-case B)

Remember: 1 byte = 8 bits, so MB/s is 8 times bigger than Mb/s.

Calculating download time

When calculating the time to download a file, remember the units.

8 bits (b) = 1 byte (B)
1,000 bytes = 1 kilobyte (kB)
1,000,000 bytes = 1 megabyte (MB)
1,000,000,000 bytes = 1 gigabyte (GB)

Worked example

A home network has a bandwidth of 100 Mb/s. How long will it take to download a 300 MB file?

Try it yourself

Change the file size and bandwidth. The calculator will show every step.

Buffering

When streaming video or music, the first few seconds are stored in a buffer. If the connection slows or drops, the buffer keeps the video playing.

⚖️ The key idea: if data downloads slower than the video plays, the buffer empties and the video has to stop and wait. That's buffering.
A larger bandwidth means data arrives faster, so the download can stay ahead of playback and the video plays smoothly.
▶
Ready
Played Buffered ahead Not loaded
💡 If the internet connection isn't fast enough, the video will keep pausing while the buffer fills up again.
📝 Now complete Task 2 on Worksheet 2.

Plenary

Click a media type on the left, then click the matching label on the right.

Matched 0 / 4

Key terms

Click each term to reveal its definition.

🎉 End of Lesson 2