TL;DR: A fixed RJ45 copper jack (8P8C 母座) and an SFP fiber cage solve different problems. RJ45 wins on cost, power (PoE) and density; SFP wins on reach, rate and field flexibility. VOOHU makes both, and the most common right answer is: put both on the board.
At a glance
- RJ45 jack (copper 8P8C socket): twisted-pair Cat5e/6/6A, 10/100M–10GBASE-T, up to 100 m (TIA-568/ISO 11801), carries PoE (802.3af/at/bt), ~1.5 kV magnetics isolation. Medium is fixed at design time.
- SFP cage (pluggable MSA): hosts an optical module or DAC; 5G–400G (up to QSFP112); ~100 m DAC, ~300–400 m MMF, 10–80 km SMF (per IEEE 802.3 optics); no power over fiber; galvanic isolation inherent; swap the module to change reach/medium with no board respin.
Where each wins
- RJ45: cost per port, powering the far end (cameras, APs), and port density.
- SFP: long reach, higher rates, and future-proofing (change optics, not the board).
The decision path
- Does the far end need power over the cable? -> RJ45 (PoE).
- How far is the link? >100 m -> fiber/SFP.
- What rate? >10G -> SFP.
- Need medium flexibility or isolation over distance? -> SFP.
The pattern most designs land on
Put an RJ45 jack and an SFP cage on the same board: copper for powered/short links, an SFP uplink for reach and rate. VOOHU supplies both sides.
Full guide + comparison table + FAQ: https://voohuelectronic-ux.github.io/voohu-rj45-guide/resources/rj45-jack-vs-sfp-copper-vs-fiber.html
VOOHU Electronics | https://www.voohuele.com | olivia@voohuele.com
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