In the U1900 connecting to PSTN with the El trunk, the Tx and Rx indicators are off but the call service still fails. To locate the fault, which of the following operations are required? (Multiple…

Question

Options

• APerform the CRC check.
• BCheck the position parameter.
• CCheck the clock source.
• DCheck the El cable.

• A
  80% (33)
• C
  12% (5)
• D
  7% (3)

Explanation

When Tx and Rx indicators are off, it signals the E1 physical layer is up with no line alarm - meaning the cable and clock synchronization are functioning normally, so the fault lies above the physical layer. A (CRC check) is correct because CRC errors reveal framing or data integrity problems on an otherwise physically connected E1 link, which would silently break call signaling. B (position parameter check) is correct because misconfigured parameters (such as timeslot mapping or channel assignments) are a common logical-layer cause of call failure when the physical link is healthy.

C (clock source) is incorrect because clock problems typically produce physical alarms that would show up as active Tx/Rx indicators - since those are off, clock sync is not the culprit. D (E1 cable) is incorrect for the same reason: a faulty cable would trigger physical layer alarms visible on the indicators, which are confirmed off.

Memory tip: Think in layers - indicators off = physical layer clear, so always look up the stack (framing integrity → CRC, configuration → parameters). If indicators were on, you'd look down (cable, clock).

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