DCI Testing & Troubleshooting 5 — Questions and Answers
Question 1: Which reference method for fiber insertion loss testing includes the loss of the launch cord in the measurement?
- One-cord (Method B) (Correct answer)
- Two-cord (Method A)
- Three-cord (Method C)
- Bidirectional OTDR
Correct answer: One-cord (Method B)
The one-cord reference method sets a reference using only the launch cord, so the launch connector's loss is included in the final link measurement.
Question 2: A copper channel test fails for ELFEXT (Equal-Level Far-End Crosstalk). At which end of the cable is ELFEXT measured?
- The far end, opposite to the signal transmitter (Correct answer)
- The near end, at the signal transmitter
- Both ends simultaneously
- The midpoint of the cable run
Correct answer: The far end, opposite to the signal transmitter
FEXT (and ELFEXT, which normalizes for attenuation) is measured at the far end of the cable, opposite to where the disturbing signal is injected.
Question 3: A technician suspects a high-resistance fault on a copper pair. Which test parameter would best confirm this?
- DC loop resistance (Correct answer)
- NEXT
- Propagation delay
- ACR-F
Correct answer: DC loop resistance
DC loop resistance measures the total resistance of the conductor loop and will be elevated if there is a poor connection, corrosion, or a partial break in the conductor.
Question 4: When using a visual fault locator (VFL) on a fiber, a bright red glow is visible through the jacket. What does this indicate?
- A tight bend, break, or macro-bend causing light to escape at that location (Correct answer)
- The fiber is correctly transmitting signal at full power
- The wrong wavelength is being injected into the fiber
- The connector at the far end is disconnected
Correct answer: A tight bend, break, or macro-bend causing light to escape at that location
A VFL emits visible red light; if it escapes through the jacket it means the fiber is losing light at that point due to a bend, break, or mechanical fault.
Question 5: What does it mean when a copper cable tester reports 'PASS*' (pass with an asterisk)?
- The cable passed but one or more measurements were within the tester's measurement uncertainty margin (Correct answer)
- The cable failed and must be replaced
- The cable passed all tests without any marginal results
- The tester detected a split pair but it does not affect performance
Correct answer: The cable passed but one or more measurements were within the tester's measurement uncertainty margin
A PASS* result means the cable technically passed all limits but at least one parameter fell within the uncertainty band of the test instrument, indicating a marginal link.
Question 6: Which fiber type requires an encircled flux (EF) compliant launch condition for accurate multimode testing per TIA-526-14-C?
- OM3 and OM4 laser-optimized multimode fiber (Correct answer)
- OS2 single-mode fiber
- OM1 62.5/125 multimode fiber
- All fiber types equally
Correct answer: OM3 and OM4 laser-optimized multimode fiber
OM3 and OM4 fibers are designed for VCSEL laser sources, and encircled flux launch conditions are required to accurately measure their bandwidth and loss per TIA-526-14-C.
Question 7: A technician tests a newly installed Cat 6A shielded (F/UTP) link and finds the shield is not continuous end-to-end. What is the primary performance risk?
- Reduced alien crosstalk (AXT) protection and potential EMI susceptibility (Correct answer)
- Increased propagation delay skew
- Higher DC loop resistance beyond category limits
- Failure of the wire map continuity test
Correct answer: Reduced alien crosstalk (AXT) protection and potential EMI susceptibility
A broken shield defeats the alien crosstalk and EMI shielding that F/UTP relies on, potentially degrading 10GBASE-T performance and causing EMI issues.
DCI Testing & Troubleshooting 5
Which reference method for fiber insertion loss testing includes the loss of the launch cord in the measurement?