Network Speeds
Measuring Network Speed
Network speed (bandwidth) is the rate at which data is transmitted across a network. It is measured in bits per second (bps).
| Unit | Value |
|---|---|
| Kbps | 1,000 bits per second |
| Mbps | 1,000,000 bits per second |
| Gbps | 1,000,000,000 bits per second |
SI vs Binary
Network speeds use SI (decimal) units, 1 kilobit = 1,000 bits. Storage sizes use binary units, 1 kibibyte = 1,024 bytes. Never confuse the two in a calculation.
Transmission Time Formula
Transmission time (seconds) = File size (bits) ÷ Network speed (bits per second)
Both values must be in bits before dividing.
Converting File Size to Bits
File sizes are often given in bytes or kibibytes. Convert using:
bytes → bits: × 8
KiB → bytes: × 1,024
MiB → bytes: × 1,024 × 1,024
Full chain:
File size in MiB → × 1,024 → KiB → × 1,024 → bytes → × 8 → bits
Worked Examples
Example 1
Q: A 5 MiB file is transferred at 40 Mbps. How long does it take?
File size in bits = 5 × 1,024 × 1,024 × 8 = 41,943,040 bits
Network speed = 40 × 1,000,000 = 40,000,000 bps
Time = 41,943,040 ÷ 40,000,000 ≈ 1.05 seconds
Example 2
Q: Write an expression for the transmission time of a 200 KiB file at 2 Mbps.
Time = (200 × 1,024 × 8) ÷ (2 × 1,000,000) seconds
Exam Style
Exams often ask you to construct an expression rather than calculate the exact answer. Write out all the conversion steps clearly.
Factors Affecting Network Speed
| Factor | Effect |
|---|---|
| Bandwidth | Higher bandwidth = faster transmission |
| Number of users | More users sharing the connection = slower for each |
| Interference (wireless) | Weakens signal, reduces effective speed |
| Distance from router | Further = weaker signal (wireless) |
| Type of connection medium | Fibre optic > UTP cable > Wi-Fi (generally) |
Key Terms
| Term | Definition |
|---|---|
| Network speed | The rate at which data is transmitted, measured in bits per second |
| Bandwidth | The maximum amount of data transferable per second |
| Transmission time | Time to send a file = file size (bits) ÷ network speed (bps) |
Exam Questions
Q: What formula is used to calculate transmission time?
Transmission time = file size in bits ÷ network speed in bits per second.
Q: Why must file size be converted into bits?
Because network speed is measured in bits per second, both values must use the same unit for the calculation to be valid.
Q: State the difference between 1 kilobit and 1 kibibyte.
1 kilobit = 1,000 bits (SI decimal unit for network speed). 1 kibibyte = 1,024 bytes = 8,192 bits (binary unit for storage).
Exam Tip
The most common mistake is mixing bits and bytes. Network speed is in bits per second; file sizes are usually given in bytes. Always multiply by 8 to convert bytes to bits before dividing.