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Difficulty: MediumTroubleshooting Physical Cabling and Connectors

A network technician is troubleshooting a newly installed Category 6 UTP cable drop connecting a desktop computer to a wall outlet. The workstation successfully connects at 100 Mbps Fast Ethernet, but fails to establish a 1000BASE-T (Gigabit Ethernet) link. A basic wiremap continuity tester indicates that all eight conductor pins match correctly end-to-end (pins 1 through 8 are straight-through). Which of the following diagnostic findings or testing methods would most likely identify the root cause of this failure? (Select TWO)

  1. A split pair condition is present on the termination points, allowing DC continuity to pass while causing severe high-frequency crosstalk.Answer
  2. Using a cable certifier to measure Near-End Crosstalk (NEXT) and attenuation parameters across all four pairs.Answer
  3. C
    Tracing the cable run using a tone generator and inductive probe to locate an open circuit along the wire path.
  4. D
    Configuring the connected switch port speed and duplex settings to auto-negotiate Half-Duplex mode to resolve late collisions.

Answer

The physical failure is identified by recognizing a split pair condition at the termination points and utilizing a cable certifier to measure Near-End Crosstalk (NEXT) and attenuation.
Gigabit Ethernet (1000BASE-T) relies on all four pairs working with tight differential noise rejection. A split pair retains pin-to-pin continuity (passing simple wiremap devices) but breaks pair pairing, generating excessive Near-End Crosstalk (NEXT). A cable certifier evaluates NEXT, attenuation, and frequency compliance to accurately diagnose this condition.

Step-by-Step Solution

1
Analyze the reported symptoms and test results.
100BASE-TX operates on two pairs (pins 1, 2, 3, and 6), whereas 1000BASE-T requires all four pairs (pins 1-8). Basic continuity testers verify DC pin-to-pin connectivity but cannot test high-frequency signal integrity or pair pairing consistency.
Passing a basic continuity test proves electrical connection, but does not guarantee that wires are paired according to T568A/T568B color standards.
2
Identify the physical impairment cause.
Split pairs maintain 1-to-1 pin connections across both ends (passing basic continuity checks), but separate the twisted pairs. This leads to severe crosstalk at high frequencies, preventing 1 Gbps speed negotiation.
Ethernet twisted pairs rely on balanced differential signaling to reject cross-talk; untwisting or splitting pairs disrupts differential cancellation.
3
Select the appropriate diagnostic tool for confirmation.
A advanced cable certifier tests RF performance indicators such as NEXT, FEXT, return loss, and attenuation.
Advanced parameter measurement is required to pinpoint physical layer faults that simple continuity or tone testing tools miss.

Key Concept

Identifying Split Pairs and Cable Certification Testing
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Topics

Troubleshooting Physical Cabling and Connectors

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