Cabling Media and Components
Copper
Balanced twisted-pair is 100-ohm cable rated by category: Cat 3 (16 MHz), Cat 5e (100 MHz), Cat 6 (250 MHz), Cat 6A (500 MHz). Cat 6A supports 10GBASE-T to 100 m; Cat 6 is limited to about 55 m for 10GBASE-T. 1000BASE-T uses all four pairs. Shielded variants (F/UTP, S/FTP) require proper bonding. The 8-position modular jack (often called RJ-45) is the standard data connector; T568A and T568B are the two pin/pair assignments, and both ends of a horizontal cable must use the same one. Coaxial cable for video is 75 ohm.
Fiber
Multimode: OM1 (62.5/125), OM2–OM5 (50/125), used with LED or VCSEL sources for shorter runs. Singlemode: OS1/OS2 (9/125) for long distance. Common connectors: LC (small form factor), SC (square), ST (bayonet), FC (threaded). Connector endfaces are polished (PC, UPC, APC); APC is angled and must not be mated with UPC.
Traps
Memorizing distances without the category context; assuming a cable's category guarantees a passing link (installation quality matters); confusing T568A/B with crossover or rollover wiring; and mixing multimode types or APC/UPC endfaces.
Worked example
T568B pin order: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown. A straight-through patch cord uses T568B on both ends; a crossover swaps transmit and receive pairs.