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S4 ICT: Computer Networks and Internet Protocols (Paper 4 (error clinic))
Tutor Prep Guide · LAN versus WAN, IPv4 and IPv6 address length, the 8-bit range of each octet, subnet masks and usable hosts, HTTP/HTTPS/FTP/SMTP with their ports, TCP versus UDP, and bandwidth to download time
S4 ICT: Computer Networks and Internet Protocols (Paper 4 (error clinic))
Paper 4 (error clinic): ten questions on networks and internet protocols, with answers and notes.
Direct answers Level: S4 ICT; format: IP addresses, subnet masks, usable hosts, ports, TCP and UDP, bandwidth arithmetic.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S4 ICT: Computer Networks and Internet Protocols |
| Level | S4 |
02 Questions (10 items)
- FoundationThe ping command uses ICMP. Does it use a TCP or UDP port number?
- FoundationHow many seconds does a 300 MB file need at 150 Mbps?
- FoundationWhich of 192.168.1.5 and 8.8.8.8 is a private address?
- IntermediateAn IPv4 octet has 8 bits. Why is the maximum 255 rather than 256?
- IntermediateWhat is the main difference between HTTP on 80 and HTTPS on 443?
- IntermediateA MAC address is 48 bits. How many bytes is that?
- ChallengeHow many usable host addresses does a /30 subnet (common for point-to-point links) provide?
- ChallengeHow many seconds does a 5 GB (take it as 5 000 MB) backup need at 20 Mbps?
- ChallengeWith a round-trip time of 30 ms, how long does the TCP three-way handshake take?
- Error redoA student claims Wi-Fi is always faster than wired LAN. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | No, ICMP uses no port numbers | ICMP sits at the network layer inside IP packets with no notion of ports, which is why firewalls must allow it separately. |
| 2 | 16 seconds | 300 MB times 8 is 2 400 Mb, and dividing by 150 Mbps gives 16 seconds. |
| 3 | 192.168.1.5 | Anything starting 192.168 is private and stays inside a network, while 8.8.8.8 is public and routable on the internet. |
| 4 | Counting starts at 0, so the 256 values run from 0 to 255 | Eight bits give 256 combinations, but counting from 0 the last one is 255, so 256 is already out of range. |
| 5 | HTTPS is encrypted, HTTP is not | HTTPS wraps the traffic in TLS so it cannot easily be eavesdropped, while HTTP is plain text, which is why logins and payments need HTTPS. |
| 6 | 6 bytes | 48 divided by 8 is 6, which is why a MAC address is written as six pairs of hexadecimal digits. |
| 7 | 2 | A /30 leaves 2 host bits: 2 to the power 2 is 4, and minus 2 gives 2, exactly enough for the two routers. |
| 8 | 2000 seconds | 5 000 MB times 8 is 40 000 Mb, and dividing by 20 Mbps gives 2000 seconds, about 33 minutes. |
| 9 | 45 ms | The handshake takes one and a half round trips, so 30 times 1.5 is 45 ms; the further the peer, the slower the setup. |
| 10 | Wired LAN is usually more stable and lower latency, so it is often faster in practice | Wireless shares a channel and suffers walls and interference, so real throughput is often below a comparable cable; you must compare the actual standard and environment. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
First ask how many bits the address has and how many host bits remain, then decide between 2 to the power minus two and a plain subtraction; name both the protocol and its port, and convert MB to Mb before dividing by bandwidth.Tutor Registration →
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