You take the Unit 6 test in class today. This page is everything you can do before it — what’s on it, the traps, and practice that isn’t on the real test. There are no test questions here.
No new reading. Everything on the test comes from 6.1–6.14. The fastest revision is the 6.14 vocabulary rapid-fire and the 6.12 speedup drill, not re-reading.
A checkpoint on the Internet region. Nothing here is new. After the test: redraw the internet, then Unit 7.
What it covers — study to this map:
| What it tests | From |
|---|---|
| Protocols: what they are, why open and layered matters | 6.2 |
| IP addresses, IPv4 vs IPv6, DNS | 6.3 |
| Packets: metadata, out-of-order arrival, reassembly, TCP | 6.4 |
| Routing, redundancy, fault tolerance — network diagrams | 6.6–6.7 |
| Bandwidth vs latency | 6.8 |
| Sequential, parallel, distributed; speedup calculations | 6.9–6.10 |
| Internet vs the web; HTTP | 6.11 |
1. Say the unit in a breath (2 min). From 6.14.
2. Run the six traps (5 min). Below.
3. Five speedup problems (5 min). The 6.12 drill.
4. Take the practice set (8 min). Section 4 — fresh questions, none on the real test.
| Don’t confuse | The one-line difference |
|---|---|
| internet vs web | The internet is the network. The web is linked pages that run on it. Email isn’t the web. |
| bandwidth vs latency | How much per second vs. how long the delay. Big downloads care about the first; games and calls about the second. |
| bytes vs bits | Speeds are in bits per second. Multiply megabytes by 8 before dividing. |
| redundancy vs fault tolerance | Redundancy is the extra paths. Fault tolerance is what they produce: it keeps working. |
| total vs longest | Parallel time is the sequential part plus the longest processor’s time — not the sum, not the average. |
| more processors vs proportionally faster | The sequential portion never shrinks, so speedup flattens. |
Six mixed questions in AP format. None is on the real test — they’re for calibration.
Prompt. A student sends a 2 MB file to a friend in another state. It is split into packets. The packets take different routes, arrive out of order, and one is lost on the way.
(a) Explain why packets from the same file can take different routes. (b) Explain how the friend’s computer ends up with the complete file in the right order. (c) Give one advantage of sending the file as packets instead of as one piece.
□ (a) Names hop-by-hop routing. Each router chooses the next hop for each packet as it arrives, based on current conditions; there’s no fixed path chosen in advance, and there are many possible paths.
□ (b) Names the metadata and the protocol. Each packet carries a sequence number; the receiver (TCP) uses them to put packets in order, notices one is missing, and the missing packet is sent again.
□ (c) Names a specific advantage. Only the lost packet is resent, not the whole file — or packets can use whatever paths are available, so one busy or broken link doesn’t stop the transfer.
□ Explains, doesn’t just name. “TCP fixes it” earns little. Say what TCP does with what information.
You get back the drawing you made in 6.1. Draw the internet again, on a fresh page, next to it. Label at least six things you couldn’t have labeled three weeks ago. Then write one sentence: what was the biggest thing your first drawing got wrong?