FOA CFOS/D flashcards

31 cards. Read the term and the definition here. The deck at the top of this page is optional.

Link power budget

Difference between minimum transmitter output power and receiver sensitivity, minus design margin. Must cover fiber attenuation, splice loss, connector loss, and splitter loss for the link to work.

Insertion loss formula

Total loss = (fiber dB/km × length km) + (splice count × splice dB) + (connector pairs × connector dB) + splitter dB. Compare result to available budget minus margin.

Splitter loss 1×N

Ideal loss is 10·log10(N) dB; practical loss adds about 0.3–0.5 dB excess per stage. A 1×32 splitter is roughly 15 dB ideal and 16–17 dB real.

OM3 vs OM4 reach

At 10GBASE-SR, OM3 supports about 300 m and OM4 about 400 m. At 40/100GBASE-SR4, OM3 reaches about 100 m and OM4 about 150 m.

Single-mode wavelength windows

1310 nm is the zero-dispersion window; 1550 nm has lowest attenuation near 0.2 dB/km and supports EDFA amplification. OS2 attenuation limits are 0.35 and 0.25 dB/km.

APC vs UPC connectors

APC uses an 8-degree angled polish with reflectance ≤ −60 dB, used in PON and RFoG. UPC is flat polish ≤ −50 dB. Never mate APC to UPC; loss and damage result.

Bend-insensitive fiber

Multimode fiber designed for a 7.5 mm minimum bend radius instead of 10× cable OD. Reduces macrobend loss in tight cabinets and high-density patch panels.

PON power budget classes

ITU-T PON classes: B+ 28 dB, C+ 32 dB, D 35 dB. Split ratio and reach must fit within the class budget after splitters and fiber loss.

PON wavelengths

Downstream 1490 nm, upstream 1310 nm, video overlay 1550 nm. Each wavelength has a separate budget and must be tested at its operating wavelength.

MPO polarity method B

Straight-through key-up-to-key-down MPO trunk with reversed pair order at each end. Default for parallel optics such as 40/100GBASE-SR4 using 12- or 24-fiber MPO.

PMD and chromatic dispersion

PMD is in ps/√km and grows with distance; chromatic dispersion is in ps/(nm·km). Both must be budgeted for 10G+ single-mode spans to avoid pulse spreading.

OTDR dead zones

Event dead zone is about 1 m and attenuation dead zone about 4 m for standard modules. Short pulse widths reduce dead zones for closely spaced splices.

Tier 1 vs Tier 2 test

Tier 1 uses an OLTS to measure insertion loss and length. Tier 2 adds an OTDR trace to locate events. Specify Tier 2 for backbone and high-count links.

Design margin

Reserve of at least 3 dB in the link budget for aging, repairs, temperature, and future splices. Never consume the full transceiver budget.

Return loss definition

Return loss in dB = −10·log10(reflected/incident). A larger positive value means less reflection; 55 dB is better than 40 dB.

Spare fiber provisioning

Design rule to provision at least 25–50% spare strands per cable and at least one spare tube per closure for growth, repairs, and future services.

Critical path and float

Float = late start − early start = late finish − early finish. The critical path has zero float and sets the minimum project duration.

Earned value core formulas

CV = EV − AC; SV = EV − PV; CPI = EV/AC; SPI = EV/PV. Positive CV/SV is favorable; index above 1 is favorable.

EAC forecast formulas

EAC = BAC/CPI when current variance persists; EAC = AC + (BAC − EV) for atypical variance; EAC = AC + bottom-up ETC when the original estimate is flawed.

PERT three-point estimate

Expected = (O + 4M + P)/6 and standard deviation = (P − O)/6. Used for schedule and cost uncertainty in splicing and termination labor.

Scope baseline components

Scope statement plus WBS plus WBS dictionary. Any change to these requires integrated change control and CCB approval before work proceeds.

Contingency vs management reserve

Contingency reserve covers identified risks and sits inside the cost baseline. Management reserve covers unknown-unknowns, sits above baseline, and needs sponsor approval.

TCPI meaning

To-complete performance index = (BAC − EV)/(BAC − AC). A value above 1 means remaining work must be more efficient than planned to hit budget.

WBS 100% rule

Children sum exactly to parent scope. Work packages are typically 8–80 hours and decompose into activities for scheduling and estimating.

Crashing vs fast-tracking

Crashing adds resources and cost, such as a second splice crew. Fast-tracking overlaps phases and adds risk. Apply only to critical path activities.

Resource leveling vs smoothing

Leveling may change start and finish dates and extend the critical path. Smoothing uses existing float without changing the critical path.

Parametric estimating

Uses unit rates such as dollars per km or per splice from historical data. Faster than bottom-up and more accurate than analogous estimating.

Project charter purpose

Formally authorizes the project and names the sponsor. Without it there is no budget authority, baseline, or project manager assignment.

RACI accountability rule

Each work package or activity has exactly one Accountable owner. Responsible, Consulted, and Informed roles may have multiple people.

One-call locate lead time

Utility locate requests (811/one-call) are typically submitted 2–3 business days before excavation. Missed locates are a common schedule risk in buried OSP work.

Long-lead procurement

Fiber cable 6–12 weeks, OLT/ONT 4–12 weeks, permits and pole attachments 60–120 days. Order these before design freeze to protect the schedule.