220-1101 Question 195
Single answerT568A/T568B standardsA technician is replacing a damaged RJ-45 connector on a horizontal cable run between a wall jack and a patch panel in an office. The existing building cabling was terminated using the T568B standard, and the technician wants to preserve proper Ethernet connectivity and avoid introducing wiring problems. Which action should the technician take?
- A
Terminate the replacement connector using T568B so both ends of the cable run remain pinned the same way
- B
Terminate the replacement connector using T568A because it is electrically superior for Gigabit Ethernet
- C
Terminate one end using T568A and the other using T568B to improve compatibility with modern switches
- D
Use either T568A or T568B on the replacement connector because Ethernet auto-negotiation corrects pair order automatically
Show answer and explanation
Correct answer: A
Explanation
T568A and T568B are both valid ANSI/TIA-568 pinout standards for twisted-pair Ethernet termination. In structured cabling, the key best practice is consistency: both ends of a standard cable run should use the same scheme unless a crossover cable is specifically required. In this scenario, the building is already using T568B, so the correct repair is to terminate the replacement connector as T568B. Mixing T568A on one end and T568B on the other creates a crossover cable, which is not appropriate for a typical horizontal office run between a wall jack and patch panel. Although many modern devices support auto MDI-X, technicians should still terminate cabling according to the documented cabling standard rather than relying on device features to compensate for incorrect wiring.
- A. Correct.
Correct. For a standard straight-through Ethernet link, both ends of the cable segment should use the same wiring scheme. Since the existing structured cabling is already terminated as T568B, the replacement should also be terminated as T568B to maintain correct pin-to-pin continuity and pair placement. This preserves compatibility and avoids creating an unintended crossover.
- B. Incorrect.
Incorrect. T568A is not electrically superior to T568B. Both standards support the same Ethernet performance when properly terminated. The difference is the placement of the green and orange pairs, not signal quality. Choosing T568A here would also create a mismatch with the existing T568B termination on the other end.
- C. Incorrect.
Incorrect. Terminating one end as T568A and the other as T568B creates a crossover cable, not a standard straight-through cable run. While crossover cables have specific uses, that is not appropriate when repairing an existing in-wall office run intended to match the building's structured cabling standard.
- D. Incorrect.
Incorrect. Auto-negotiation can determine speed and duplex settings, but it does not fix incorrect pair termination or convert a mismatched pinout into the intended cable type. Proper pair order and consistent termination standard are still required for reliable Ethernet operation.