220-1101 Question 199
Single answerUnshielded twisted pairA technician is installing new Ethernet drops in a small office using unshielded twisted pair (UTP) cable. After termination, several workstations only negotiate at 100 Mbps instead of 1 Gbps, even though the switch ports support Gigabit Ethernet. The cable runs are under 90 meters and pass a basic continuity test. Which issue is the MOST likely cause of the reduced link speed?
- A
The installer untwisted too much of each wire pair when punching down the cable
- B
The cable jacket is blue instead of plenum-rated white
- C
The patch panel was mounted in a vertical rack instead of a horizontal rack
- D
The technician used RJ11 connectors instead of keystone jacks at the patch panel
Show answer and explanation
Correct answer: A
Explanation
This scenario tests practical troubleshooting of UTP terminations. With Gigabit Ethernet over copper, proper pair integrity is critical because 1000BASE-T uses all four twisted pairs, unlike 100BASE-TX, which uses only two pairs. A cable can pass a simple continuity test yet still fail certification for performance issues such as excessive untwist, split pairs, or poor punch-down technique. Industry best practices from TIA/EIA structured cabling standards recommend maintaining pair twists as close as possible to the point of termination to minimize near-end crosstalk (NEXT) and preserve signal quality. In real-world environments, a workstation negotiating at 100 Mbps on a known-good Gigabit switch port often points to a cabling or termination issue rather than a problem with rack orientation or cable jacket color.
- A. Correct.
Correct. UTP relies on the twists in each pair to reduce crosstalk and maintain signal integrity. If the technician untwists too much of the conductor pairs during termination, the cable may still show continuity but fail to meet performance requirements for Gigabit Ethernet. 1000BASE-T uses all four pairs and is more sensitive to pair quality and proper termination than 100BASE-TX.
- B. Incorrect.
Incorrect. Jacket color does not affect link speed. Plenum rating relates to fire-safety requirements for installation spaces such as air-handling areas, not Ethernet negotiation performance. A candidate might choose this if confusing building-code compliance with data transmission quality.
- C. Incorrect.
Incorrect. The orientation of the rack or patch panel does not determine whether the cable can support Gigabit Ethernet. Poor cable management can create maintenance issues, but vertical versus horizontal mounting is not a likely cause of negotiation dropping to 100 Mbps.
- D. Incorrect.
Incorrect. RJ11 connectors are for telephone wiring and would be physically and functionally inappropriate for an Ethernet patch panel termination. If RJ11 had actually been used, the connection would likely fail entirely rather than consistently negotiate at 100 Mbps. This distractor targets confusion between telephone and Ethernet connectors.