FOA CFOS/W flashcards

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

PON splitter loss 1:32

A 1:32 PLC splitter introduces roughly 16.6 dB of insertion loss including excess loss. This value is subtracted from the optical link budget before fiber and connector losses are considered.

GPON downstream rate

GPON carries 2.488 Gbit/s downstream at 1490 nm and 1.244 Gbit/s upstream at 1310 nm, using TDM downstream and TDMA upstream bursts scheduled by the OLT.

FTTB versus FTTH

FTTH runs fiber all the way to the living unit. FTTB terminates fiber at the building and distributes inside over copper or LAN, so subscribers share a building-side conversion point.

Feeder and distribution cable

The feeder spans OLT to splitter, the distribution cable spans splitter to access terminal, and the drop cable runs from terminal to subscriber. Each segment uses different fiber counts and protection.

XGS-PON wavelengths

XGS-PON uses 1577 nm downstream and 1270 nm upstream at symmetric 9.953 Gbit/s, coexisting with GPON on the same feeder through WDM coexistence filters.

PON link budget formula

Link loss equals fiber attenuation in dB per km times length, plus connector and splice losses, plus splitter insertion loss. The total must stay below the PON class budget with margin.

Upstream TDMA ranging

Each ONT measures its round-trip delay; the OLT assigns an equalization delay so all upstream bursts arrive in their assigned time slots without colliding at the OLT receiver.

OLT functions

The optical line terminal terminates PON ports, schedules upstream bandwidth, encrypts downstream traffic, aggregates uplinks, and provisions ONTs through OMCI management channels.

SC/APC connector

An SC/APC connector uses an 8-degree angled endface, typically green, giving return loss of 60 dB or better. APC and UPC endfaces must never be mated because the air gap causes high loss.

PLC versus FBT splitter

PLC splitters use planar waveguides and work broadband from 1:2 to 1:64 with uniform outputs. FBT splitters are fused couplers, cheaper for 1:2 and 1:4 but wavelength sensitive.

Optical distribution frame

The ODF is the cross-connect point where OLT ports are patched to feeder cables. It holds splice trays, pigtails and adapters, and provides a test access point.

Fiber access terminal

A FAT is a street or pole-mounted closure housing splices and splitter outputs, serving typically four to sixteen subscribers through individual drop ports.

ONT service interfaces

An ONT terminates the PON and delivers Ethernet data, VoIP POTS lines, RF video overlay, and Wi-Fi. SFU, MDU and MTU variants differ in port count and mounting.

Drop cable construction

Drop cable is flat or round, one or two fibers, with steel strength members and LSZH jacket. Aerial versions are often self-supporting figure-8; indoor versions must meet fire ratings.

Splitter module placement

Splitters sit in the central office ODF, street cabinets, or FAT closures. Placing them closer to subscribers shortens drop distances but increases splitter count and cost.

Cable bend radius rule

During installation the bend radius must be at least twenty times the cable diameter; in service at least ten times. Bare 250-micron fiber needs 30 mm minimum radius.

Fusion splice loss target

A good fusion splice has loss of 0.1 dB or less, with 0.15 dB accepted in the field. Mechanical splices typically show 0.3 to 0.5 dB and are used only for temporary repair.

Duct fill ratio

Conduit should not exceed roughly 40 to 50 percent fill by cable cross-section. Subducts inside a main duct allow additional cables to be pulled later without excavation.

Laser safety at 1550 nm

Infrared light at 1310, 1490 and 1550 nm is invisible and can damage the retina. Never look into a fiber or connector; use an IR viewer card and cap unused ports.

Aerial FTTH construction

Aerial plant uses messenger strand with lashing or self-supporting ADSS cable. Span sag, clearance above roads and power lines, and separation from electrical plant follow local code.

Field-installable connector

A field-installable connector is cleaved and terminated on site. Quality depends on cleave angle and assembly, targeting 0.3 dB insertion loss and at least 50 dB return loss for UPC.

Cable pulling tension

Typical limits are about 600 N for outdoor drop cable and 270 N for indoor drop. Exceeding the rating stretches fiber, causing permanent bend loss and possible breakage.

As-built documentation

As-built records capture actual cable routes, splice closures, splitter legs, port assignments and labeling. They are handed over at acceptance and used for later fault isolation.

OLTS insertion loss test

An optical loss test set uses a light source and power meter at 1310, 1490 and 1550 nm. Results depend on the reference method chosen: one, two or three jumper.

OTDR launch cable purpose

A launch reel of known length moves the OTDR's blind zone away from the first connector, so the near-end connector and first splice can be measured accurately.

Reflectance limits APC UPC

APC connectors must show reflectance of -60 dB or better; UPC connectors -50 dB or better. Excess reflectance causes upstream burst errors and unstable ranging in the PON.

Optical power in dBm

dBm is an absolute power referenced to one milliwatt; dB is a relative ratio. Link loss in dB equals input power in dBm minus output power in dBm.

Endface inspection standard

IEC 61300-3-35 defines pass and fail zones for scratches, pits and contamination on connector endfaces. Every connector is inspected and cleaned before mating.

Macrobend detection

Testing at 1625 or 1650 nm reveals macrobends that show little loss at 1310 nm. A bend shows as elevated loss or a reflective event without a splice.

GPON ONT power window

Class B+ ONTs typically receive between about -8 and -27 dBm. Below sensitivity causes loss of signal; above overload the receiver saturates and errors appear.

ONT LOS indicator

A loss-of-signal LED on the ONT means no valid downstream optical signal. Causes include fiber break, dirty or disconnected connector, splitter port swap, or OLT port failure.

Troubleshooting escalation order

Isolate faults from subscriber CPE to drop cable, access terminal, splitter and feeder, then OLT. Swap patch cords and test at the FAT before escalating to outside plant.