CompTIA Review

Core 1 · Chapter 6

Cabling and Connectors

Twisted pair categories and speeds, 100 m limit, T568A/B, fiber vs copper, coax, PoE, and cabling tools.

Twisted pair (copper)

  • UTP (unshielded) is the default LAN cable; STP adds shielding against EMI.
  • RJ-45 is the 8P8C connector for Ethernet twisted pair.
  • Cat 5e: 1 Gb/s at 100 m. Cat 6: 10 Gb/s but only to 55 m (100 m at 1 Gb/s). Cat 6a: 10 Gb/s at 100 m. Cat 7: 10 Gb/s, shielded, 100 m.
  • All Ethernet twisted pair: maximum run 100 m before signal attenuation.
  • T568A and T568B are the two wiring orders for the 8 wires; use one standard on both ends (straight-through).
  • Crossover cable (T568A on one end, B on the other) is legacy — modern NICs auto-detect with Auto-MDIX.

Fiber and coax

  • Fiber uses light: immune to EMI, no crosstalk, longest distances, highest cost.
  • Single-mode fiber (SMF): laser, long distance (campus/ISP backbone), small core (about 9 micron).
  • Multimode fiber (MMF): LED/VCSEL, shorter runs inside buildings, larger core (50/125 or 62.5/125 micron), orange/aqua jacket.
  • Fiber connectors: LC (small, latching — most common today), SC (push-pull square), ST (bayonet twist, legacy).
  • Coaxial (RG-6 for TV/satellite/internet drops, RG-59 legacy video): F-connector screws on; BNC twists/locks (older networks, CCTV).

Power over Ethernet (PoE)

  • PoE delivers DC power over the same Ethernet cable that carries data.
  • 802.3af (PoE): up to 15.4 W at the switch.
  • 802.3at (PoE+): up to 30 W.
  • 802.3bt (PoE++/4PPoE): up to about 60 W (Type 3) / 100 W (Type 4).
  • Powers APs, IP cameras, VoIP phones — no outlet needed at the device.

Tools and common problems

  • Crimper attaches RJ-45 ends; punch-down tool terminates cable into patch panels/keystone jacks (110 block).
  • Cable tester verifies pinout; wire map tester catches split/incorrect pairs. Tone generator + probe traces a cable in a bundle.
  • Loopback plug tricks a NIC into thinking it is connected — quick port test.
  • Common faults: wrong pinout (T568 mismatch), bent/broken cable, runs over 100 m, EMI near motors/fluorescent lights (use STP or fiber), crosstalk from untwisted pairs left too long at the connector.