A different physics of scale
Inside a data center, distances are short but counts are enormous and change is constant. Design pillars: structured cabling per ISO/IEC 11801-5 / TIA-942 (MDA/HDA/EDA hierarchy), pre-terminated MPO trunk systems for speed and repeatability, and airtight polarity management (one method site-wide, documented).
Speeds and media choices
Duplex optics (10/25G SR, 100G FR/LR/DR over duplex SM) versus parallel optics (40/100G SR4, 400G DR4 on 8 fibers). Parallel lanes consume MPO trunks; breakouts (1×400G → 4×100G) shape fiber counts. OM4 remains economic in-row; single-mode wins between halls and for 400G+ longevity — many hyperscalers now run SM everywhere.
Loss budgets are brutally tight
100GBASE-SR4 over OM4 allows ~1.9 dB total channel loss; every extra MPO mating (~0.35–0.5 dB) eats reach. Designs count matings per channel explicitly, specify low-loss trunks, and forbid casual cross-patching. Tier 1 test everything; the encircled-flux rules apply.
Enterprise premises notes
Backbone SM between floors/buildings, OM4 or SM horizontals per application life, entrance facilities with listed-cable transitions, and TIA-606 administration from day one. The premises network that grows without records becomes unmaintainable years before it becomes slow.