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Difficulty: HardTroubleshooting Physical Cabling and Connectors

A network technician deploys a 65-meter Category 6A UTP cable run between a core switch and a distribution switch. A basic continuity cable tester indicates proper 1-to-1 pin alignment across all eight conductors (Pin 1 to Pin 1, Pin 2 to Pin 2, etc.). However, when the link is connected to 10GBASE-T ports, the connection frequently drops, exhibits excessive frame errors, and fails to sustain 10Gbps throughput. During physical termination, individual wires from different twisted pairs were incorrectly paired together on adjacent pins (such as pairing pin 3 with pin 4 and pin 5 with pin 6) at both ends of the run. Which physical cabling fault is present in this installation, and which diagnostic tool is required to identify and measure the extent of this failure?

  1. A split pair condition; a cable certifier capable of measuring Near-End Crosstalk (NEXT)Answer
  2. B
    An open pair fault; a tone generator and inductive probe tracking signal propagation
  3. C
    A switch duplex mismatch; a network device CLI analyzing port interface error counters
  4. D
    A Layer 2 PDU encapsulation mismatch; a software packet analyzer capturing data frames

Answer

A split pair condition is present in the installation, requiring a cable certifier capable of measuring Near-End Crosstalk (NEXT) to detect and quantify the fault.
The correct answer identifies a split pair condition and selects a cable certifier. In twisted-pair Ethernet cabling standards (such as T568A/T568B), specific pins form differential pairs (Pins 1-2, 3-6, 4-5, and 7-8). When an installer connects wires from different pairs to pins intended for a single pair at both ends, DC continuity remains 1-to-1 straight-through, so basic wiremap tools report no errors. However, because the positive and negative signals of a differential pair no longer travel along the same twisted pair of wires, mutual electromagnetic shielding is lost, producing catastrophic Near-End Crosstalk (NEXT) at high signaling rates such as 10GBASE-T. A cable certifier evaluates RF signaling performance, including NEXT, across the frequency spectrum of Category 6A.

Step-by-Step Solution

1
Analyze the reported symptom and continuity test results
The continuity tester shows straight-through pin-to-pin alignment (1-to-1), ruling out simple opens, shorts, or transposed pins (reversed wiremap).
Standard continuity testers only measure DC electrical continuity and wire alignment, not high-frequency signal integrity.
2
Evaluate the physical termination details
Wires from separate pairs were placed onto adjacent pin positions (e.g., pin 3 with pin 4, pin 5 with pin 6) at both ends of the cable run.
Twisted pair cabling (such as T568A/T568B) relies on specific pair groupings (pins 1-2, 3-6, 4-5, 7-8) to ensure electromagnetic interference and crosstalk cancel out along the run. Splitting pairs destroys this differential signaling protection.
3
Identify the cabling anomaly and appropriate testing tool
This fault is defined as a split pair, which causes severe Near-End Crosstalk (NEXT) and attenuation-to-crosstalk ratio (ACR) failure under high frequencies. A cable certifier is required to measure RF parameters like NEXT.
Simple continuity testers or tone probes cannot measure RF parameters or detect split pairs when DC continuity is preserved.

Key Concept

Split Pair Faults and NEXT Measurement
Estimated Time:2m 0s
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Topics

Troubleshooting Physical Cabling and Connectors

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