Media and connectors

July 12, 2025 · in CompTIA Network+ (Dion Training)

Copper media

802.3 defines wired Ethernet. Twisted pair fights EMI and crosstalk by twisting the conductors. UTP is cheap and flexible; STP adds shielding at the cost of bulk and price.

Coax is a single copper core with insulation and shield. RG-6 is the modern residential standard, RG-59 legacy. DAC (direct attach copper) is fixed-assembly cabling for short switch, router, and server links; twinax (two conductors) rides inside DAC for SFP+/QSFP.

Plenum cable is fire-retardant for air-handling spaces (NFPA/NEC); non-plenum goes where fire risk is lower.

The speed and distance ladder:

CAT 5: 100 Mbps, 100 m
CAT 5e: 1 Gbps, 100 m
CAT 6: 1 Gbps at 100 m, 10 Gbps at 55 m
CAT 6a: 10 Gbps, 100 m
CAT 7: 10 Gbps, 100 m
CAT 8: 25-40 Gbps, 30 m
RG-6: 1 Gbps, about 300 m
Twinax: 10+ Gbps, 10 m
DAC: 100 Gbps, 15 m active / 7 m passive

Copper connectors

RJ-11: telephone, 6P2C, too small for high-speed data.
RJ-45: Ethernet, 8P8C, works with CAT 5 through CAT 8.
F-type: screw-on coax connector for cable TV, satellite, and cable internet (RG-6/RG-59).
BNC: bayonet push-and-twist coax connector, pro video and RF work (and no, it’s not “British Naval Connector”).

Fiber media

Data as light: immune to EMI, spans hundreds of miles, speeds past 10 Gbps. It costs more and needs specialized tools and training.

Single-mode (SMF) has a tiny 8.3-10 micron core, one light path, a yellow sheath, and handles long-haul backbone runs. Multimode (MMF) has a 50-100 micron core, multiple light paths, an aqua or orange sheath, reaches up to about 2 km, and covers building and campus links.

Fiber connectors and polish

SC: square push-pull, common on single-mode and FTTH.
LC: compact push-pull, the high-density datacenter favorite, ships in transmit/receive pairs.
ST: round twist-lock, holds under vibration, common on multimode and outdoors.
MTRJ: small rectangular, transmit + receive in one, RJ-style latch, space-constrained LANs.
MPO: multi-fiber in a single connector for high-density, high-speed builds.

Back reflection is light bouncing back toward the source and degrading signal. Polish styles, weakest to strongest suppression: PC (slight curve), UPC (dome), APC (8-degree angle, best for long-haul and undersea).

Transceivers

A transmitter and receiver in one module; converts between protocols (Ethernet to Fibre Channel) and between media (copper to fiber). Ethernet is the LAN/MAN/WAN family; Fibre Channel is high-throughput, low-latency SAN storage connectivity (see my SAN notes).

The form factors:

SFP: 4.25 Gbps
SFP+: 16 Gbps
QSFP: 40 Gbps
QSFP+: 41.2 Gbps
QSFP28: 100 Gbps
QSFP56: 200 Gbps

All hot-pluggable, no need to power down the switch.