A structured lesson workspace with readable content, hands-on examples, and a clean path to completion.
Office moved desks over the weekend. Monday: one PC that was 1 Gbps is now 100 Mbps. No config changed. You look under the desk: someone used a flat 4-wire decorative patch cable. Swap it for a real Cat6, back to 1 Gbps. Cables cause 30% of real tickets.
Copper Ethernet is twisted pairs in a jacket. Twists cancel noise. More twists + better shielding = higher speed. That's all Cat5e vs Cat6 vs Cat6a is. Fiber is glass/plastic using light — for long runs and uplinks between floors, not to your laptop.
| Cable | Max speed | Max run | Use it for |
|---|---|---|---|
| Cat5e | 1 Gbps | 100 m | Old offices, still OK for PCs |
| Cat6 | 1 Gbps / 10 Gbps up to 55 m | 100 m / 55 m | New offices, best value |
| Cat6a | 10 Gbps | 100 m | New uplinks, APs, data rooms |
| Fiber OM3/OM4 | 10/40 Gbps+ | 300 m+ | Between floors/buildings |
100 meters = 90 m in walls + 10 m patch cords total. Go longer and it works sometimes and fails when it gets hot or busy — the worst kind of fault.
Both ends wired T568B = straight-through (PC to switch). One end T568A, other T568B = crossover (old switch-to-switch). Today almost all ports do auto-MDIX and accept either. On the exam you still must identify them by pinout.
# Straight-through T568B both ends - PC to switchPin1 white-orange <-> Pin1 white-orangePin2 orange <-> Pin2 orangePin3 white-green <-> Pin3 white-greenPin6 green <-> Pin6 green# Only pins 1,2,3,6 needed for 100 Mbps# All 8 pins needed for 1 Gbps + PoE
If 1 Gbps drops to 100 Mbps after a move: suspect pins 4,5,7,8 broken. Cheap 4-wire cables do 100 Mbps fine and never do Gigabit. Swap cable first, don't touch config.
No light = no link (power, cable, disabled port). Amber = 100 Mbps or error. Green blinking = traffic, normal. If one end has light and other doesn't, cable or SFP is half-dead. Reseat both ends before anything else.
You can now blame the cable correctly. Next: the boxes that cables plug into — switch vs router vs AP vs firewall.
Finish the lesson once you have worked through the material. This awards ★ 25 XP.