FOA CFOS/DAS cheat sheet

Link loss budget: total budget (dB) = transmitter output power (dBm) − receiver sensitivity (dBm); the design must keep worst-case connector, splice, and fiber losses plus margin below this value.

Fiber attenuation is wavelength dependent: OS2 single-mode is typically ≤0.4 dB/km at 1310 nm and ≤0.3 dB/km at 1550 nm; OM4 multimode is roughly 3.0 dB/km at 850 nm and 1.0 dB/km at 1300 nm.

Connector loss allowance is commonly 0.5 dB per mated pair for field-terminated connectors and 0.3 dB for factory pigtails; splice loss allowance is typically 0.1–0.3 dB for fusion splices.

Design margin: add at least 3 dB for aging, repairs, temperature cycling, and future splices; systems with many field terminations or harsh environments use 5 dB or more.

Multimode distance is limited by modal dispersion: 1000BASE-SX reaches about 550 m on OM2, 300 m on OM1; 10GBASE-SR reaches about 300–400 m on OM3/OM4 depending on the standard revision.

Single-mode reach is limited by loss and dispersion: 1000BASE-LX about 10 km, 10GBASE-LR about 10 km, 10GBASE-ER about 40 km; check the transceiver's published link budget rather than assuming.

Bend radius rule: installed cable must not be bent tighter than 10× the cable outside diameter under load and 20× when pulled; bend-insensitive fiber allows tighter radii but only per the manufacturer's rating.

Choose fiber type by reach and upgrade path: OM4/OM5 for in-building and data-center backbones up to ~400 m at 10G/25G, OS2 for campus and metro links beyond multimode reach; polarity method (A, B, or C) must match the transceiver pairing scheme.

Work breakdown structure (WBS) decomposes the install into deliverable-oriented packages (survey, pathway, pulling, splicing, testing, documentation); every task must map to one WBS element.

Critical path method: the critical path is the longest-duration chain of dependent tasks; its float is zero, so any delay on it delays the project completion date.

Float (slack) = late start − early start = late finish − early finish; tasks with positive float can slip without moving the end date.

Earned value metrics: CV = EV − AC, SV = EV − PV, CPI = EV/AC, SPI = EV/PV; CPI or SPI below 1.0 signals cost or schedule overrun.

Estimate-to-complete (ETC) = (BAC − EV) / CPI; variance at completion (VAC) = BAC − EAC, where EAC = AC + ETC.

Cost of quality: prevention and appraisal costs are cheaper than failure costs; rework from failed OTDR or loss tests is an internal failure cost that erodes margin.

Risk register entries need probability, impact, owner, and response (avoid, mitigate, transfer, accept); schedule risk from weather, permits, and fiber lead times is common on outside-plant work.

Change control: any scope change (route change, added splice closures, higher fiber count) requires documented approval and a revised baseline before work proceeds.

Acceptance and closeout: punch list, as-built drawings, OTDR/loss test reports, and warranty documentation must be delivered before final payment and retention release.