GCSE · Computer Science · Edexcel · Spec 1CP2

Network speeds and transmission calculations

Everyone's online and your download crawls. Nothing is broken: the link is shared, and one division tells you how long a file will take.

Computer Science · Structure

Who is sharing this network?

Tap a device to see the link that joins it. Which link can carry the most data? Then tap the router.

Copper Ethernet cableOptical fibre cableWi-FiWi-FiBluetooth

Tap any part of the diagram to see what it does.

Bandwidth or latency?

Which one is it?

You are explaining to a friend why the network feels slow.

Which statement is closest to what you think right now?
How sure are you?

Range

How far can the signal go?

Rank the four media by typical range: the maximum effective distance a signal can travel before its quality begins to drop. Put your guess for the longest range at the top.

1 · Longest range4 · Shortest range

  1. Wi-Fi

  2. Optical fibre cable

  3. Bluetooth

  4. Copper Ethernet cable

Transmission time

Finish the working

A 90,000-bit file is sent across a network that moves 3,000 bits per second. How long does it take?

  1. time (seconds) = size of file in bits ÷ network speed in bits per secondStart from the formula. It tells you which two numbers you need.
  2. Size of file = 90,000 bitsAlready in bits, so nothing to convert.
  3. missing step
Which line is step 3?

Check someone else's working

Where did the answer go wrong?

A 12,000-bit file is sent across a network that moves 4,000 bits per second. How long does it take?

A classmate's answer — which line goes wrong?

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

What makes a network fast or slow, and how long a file really takes to arrive.

What you need to know

  • Bandwidth is how much data can be transferred in a set amount of time, typically measured in Mbps or Gbps.
  • Higher bandwidth means the transmission media can transmit more data at once.
  • Latency is the delay between a signal being sent and received. Lower latency means quicker responses and less lag.
  • Have a goMaya groans: 'Our bandwidth is awful! I press play and there's a huge gap before anything happens.' Which idea is she actually describing?

    Latency: the delay between sending and receiving.

    Bandwidth is about how much data moves in a given time. A gap before anything responds is a delay, which is latency.

  • Every type of transmission media has a maximum bandwidth, and optical fibre has the highest of the four in this lesson.
  • Range is the maximum effective distance a signal can travel before its quality begins to drop.
  • Have a goPriya's Bluetooth speaker plays perfectly beside her, then cuts out down the hall. Is that more likely a bandwidth problem or a range problem?

    Range, most likely.

    Range is how far a signal can travel before its quality begins to drop. Bandwidth is how much data can be transferred in a given time.

  • Network performance, meaning the speed and reliability of data transfer, is affected by bandwidth, latency, range and the number of devices connected.
  • The more devices connected, the more they share the available bandwidth and add traffic, so each device's data transfer rate falls.
  • Transmission time in seconds = size of file in bits ÷ network speed in bits per second.
  • Have a goA 2,000-bit file crosses a link at 500 bits per second. How many seconds will it take? Work it out before you look.

    4 seconds.

    2,000 ÷ 500 = 4. The file size in bits goes on top and the speed in bits per second goes underneath.

  • Units check: bits ÷ bits per second leaves seconds, so the file size goes on top and the speed underneath.

The big picture

Bandwidth is how much data can be transferred in a given time, and latency is the delay before it arrives. Each transmission medium has its own maximum bandwidth and range, more devices on a network means each device's transfer rate falls, and transmission time is the size of the file in bits divided by the network speed in bits per second.

Key points

1Bandwidth is how much data can be transferred in a given time, typically in Mbps or Gbps. Latency is the delay between sending and receiving.
2Each type of transmission media has a maximum bandwidth, and optical fibre has the highest of the four here.
3Range is the maximum effective distance a signal can travel before its quality begins to drop.
4More devices connected means they share the available bandwidth, so each device's data transfer rate falls.
5Transmission time (seconds) = size of file in bits ÷ network speed in bits per second.

Worked example

Problem

A 50,000-bit file is sent across a network that moves 1,000 bits per second. How many seconds does it take?

⚠ Watch out

Dividing the wrong way round: network speed ÷ file size. The file size in bits always goes on top, the network speed in bits per second underneath.

🧠

Memory hook

A pile of bits divided by the bits each second leaves seconds. The pile goes on top.

✓

Check yourself

Cover the page and say the transmission-time formula. Then use it: how long does a 100-bit file take at 2 bits per second, and in what unit?

Flashcards

(12)
What is bandwidth?
How much data can be transferred in a specific amount of time. Typically measured in Mbps or Gbps.
What does higher bandwidth let the transmission media do?
Transmit more data at once.
What is latency?
The delay from the time a signal is sent to when it is received.
What does lower latency mean for the user?
Quicker responses and less lag.
Which of copper Ethernet, optical fibre, Wi-Fi and Bluetooth has the highest maximum bandwidth?
Optical fibre cable: 1 Gbps up to 100 Gbps.
Copper Ethernet cable: typical maximum bandwidth?
100 Mbps to 1 Gbps, or up to 10 Gbps with Cat 6, 7 or 8 cable.
Wi-Fi and Bluetooth: typical maximum bandwidth?
Wi-Fi up to 9.6 Gbps (Wi-Fi 6 or 6E). Bluetooth up to 2 to 3 Mbps.
What is range?
The maximum effective distance a signal can travel before its quality begins to drop.
Put the typical ranges in order for copper Ethernet, optical fibre, Wi-Fi and Bluetooth.
Optical fibre 40 km, copper Ethernet 100 m, Wi-Fi 50 m, Bluetooth 10 m.
Which factors affect network performance?
Bandwidth, latency, range and the number of devices connected.
Why does a device slow down when more devices join the network?
The devices share the available bandwidth and add to network traffic, so each device's data transfer rate falls.
How do you calculate the time to transmit a file?
time (seconds) = size of file in bits ÷ network speed in bits per second. Bits ÷ bits per second leaves seconds.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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