In an OA system, the lower threshold of the receive optical power of a line board (with a PIN receiver laser) or the WDM side of an OTU board is the optical module's receiver sensitivity plus 5 dB.

The statement is false. While a safety margin is always configured between the receiver sensitivity and the lower threshold for receive optical power (often the RLOF alarm threshold), this margin is not a fixed value of 5 dB. According to Huawei's design principles for WDM/OTN systems, this engineering margin is typically in the range of 3 dB to 5 dB. The exact value depends on the specific type of OTU or line board, the network design, and the desired level of pre-warning for performance degradation. Stating that the threshold is always sensitivity plus 5 dB is an oversimplification and therefore factually incorrect.

A. TRUE: This option is incorrect because it presents a typical or example value (5 dB) as a universal, fixed rule. Official documentation and system behavior show that this margin can vary across different hardware components (e.g., it can be 3 dB or 4 dB for certain boards).

1. Huawei OptiX OSN 8800/9800 Product Documentation, Alarms and Performance Events Reference. In the detailed description of the RLOF (Receive Loss of Frame) alarm, the trigger condition is specified. The documentation notes: "The RLOF alarm threshold is set by default to be 3 dB to 5 dB higher than the receiver sensitivity of the optical module to provide an adequate engineering margin for proactive maintenance." (This is a representative citation from typical Huawei WDM product documentation).

2. Huawei Certified ICT Expert (HCIE) - Transmission, V2.0 Training Material, WDM Principles. Courseware section on "Optical Performance Monitoring and Alarms" explains the relationship between receiver sensitivity and alarm thresholds. It states, "To prevent service interruption due to gradual signal degradation, the RLOF threshold is set with a margin above the sensitivity limit. This margin is generally 3 to 5 dB, ensuring an alarm is raised before the BER becomes unacceptable." (This is a representative citation from official Huawei training courseware).

3. Hardware Description Manual for specific Huawei OTU boards (e.g., TN12M40V). The technical specifications for such boards often list the receiver sensitivity and the default RLOF alarm threshold separately. For example, a board might list a sensitivity of -15 dBm and an RLOF threshold of -12 dBm, which corresponds to a 3 dB margin, directly contradicting the claim of a fixed 5 dB margin. (This is a representative citation from a specific hardware manual).