✍ 05: Cabling — Exercises¶
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Practice — try each question first, then expand the answer to check your reasoning.
Work through each question, then click ▶ Show answer to check yourself. Review the notes if you get stuck.
💡 Q1. You need 10 Gbps over 100 m of copper. Which category is the minimum, and why not Cat 6?¶
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**Cat 6a** — it supports 10GBASE-T over the full 100 m. **Cat 6** only reaches 10 Gbps to ~55 m, so it fails at 100 m.🔹 Q2. Two buildings are 800 m apart and need a 10 Gbps link. Copper or fiber? Which fiber type and a suitable standard?¶
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Copper can't span 800 m (100 m limit) → **fiber**. Use **single-mode fiber (SMF)**; standard **10GBASE-LR** (~10 km). Multimode 10GBASE-SR only reaches a few hundred meters.💡 Q3. Why are the pairs in twisted-pair cable twisted?¶
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Twisting causes interference to affect both wires of a pair equally so it **cancels out** (common-mode rejection), reducing **crosstalk** and susceptibility to **EMI**.🔹 Q4. Define attenuation and crosstalk, and give one mitigation for each.¶
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- **Attenuation** — signal loss over distance → stay within length limits or use fiber. - **Crosstalk** — one pair interfering with an adjacent pair → maintain proper twists / quality terminations (or use shielded cable).🔹 Q5. A run near large industrial motors keeps getting errors. Give two mitigations.¶
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Use **shielded cable (STP)** or **fiber**, and **reroute** the cable away from the motors/power lines.🔹 Q6. Match the connector to its media: RJ-45, LC, BNC.¶
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- **RJ-45 → twisted-pair copper (Ethernet)** - **LC → fiber** (small form factor, often duplex) - **BNC → coaxial**🔹 Q7. Compare single-mode and multimode fiber (core size, light source, distance).¶
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- **Single-mode (SMF):** ~9 µm core, **laser**, very long distance (km). - **Multimode (MMF):** 50/62.5 µm core, **LED/VCSEL**, shorter distance. Mnemonic: **S**ingle-mode = **S**maller core, **S**tretches further.💡 Q8. A department needs to power 8 APs at ~25 W each from the switch. Which PoE standard, and why not 802.3af?¶
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Each AP needs ~30 W → **802.3at (PoE+)**. **802.3af** supplies only ~15.4 W, insufficient for a 25 W AP.🔹 Q9. Which tool verifies a cable's wiremap (opens/shorts/miswires), and which traces a specific cable in a bundle?¶
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- **Cable tester / wiremap tester** — verifies pin-to-pin correctness (opens, shorts, miswires). - **Toner probe** (tone generator + probe) — traces/identifies a specific cable.🔹 Q10. In 1000BASE-T, what do "1000," "BASE," and "T" mean, and what's the max distance?¶
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- **1000** = 1 Gbps - **BASE** = baseband (whole medium carries one digital signal) - **T** = twisted-pair copper Max distance = **100 m**.💡 Q11. What does Auto-MDIX do, and why does it make crossover cables largely unnecessary?¶
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Auto-MDIX auto-detects the cable type and swaps transmit/receive pairs as needed, so either a straight-through or crossover cable works — you no longer need to hand-pick a crossover for like-device connections.❓ Q12. What is a fiber's minimum bend radius, and what happens if you exceed it?¶
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The tightest radius a cable can be bent safely. Bending tighter causes **macrobend loss** (light escaping the core) or physical damage, raising insertion loss or breaking the link.⬅️ Prev: Module 04 · 📚 All Exercises · Next: Module 06 — Wireless Networking ➡️
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