The Nokia power commissioning system, as implemented in platforms like the 1830 PSS, is an automated procedure designed to discover network topology and set optical power levels. This system is engineered to support the most common optical network configurations, which include both linear (chain) and ring topologies. The commissioning process operates over the Optical Supervisory Channel (OSC), which establishes communication between adjacent nodes. A "through connection" refers to a data wavelength that passes through a node's equipment (e.g., a ROADM) without being terminated. This does not affect the OSC link, which is terminated at each node. Therefore, the commissioning process is not halted and continues to discover the next node in the sequence.

A. The commissioning process is not stopped by a through connection, as it relies on the node-to-node OSC link, which is independent of data wavelength paths.

B. The system is not limited to ring topologies; linear (chain) configurations are also fully supported by the automated power commissioning procedure.

C. While it is correct that a through connection does not stop the system, the statement that the system must be a ring only is inaccurate.

1. Nokia 1830 PSS Engineering and Planning Guide, Release 11.2 (Document ID: 3KC-13003-AAAA-TCZZA), Section 3, "Network configurations and topologies". This section details the support for various network structures, explicitly including linear chain and ring topologies for WDM systems.

2. Nokia 1830 PSS Commissioning Guide, Release 11.2 (Document ID: 3KC-13005-AAAA-TCZZA), Chapter 4, "System commissioning procedures". This chapter describes the automated power commissioning process, explaining that it uses the OSC to sequentially discover and configure adjacent nodes. The procedure is designed to progress along the entire line system (linear or ring) and is not impeded by the presence of through-connected service wavelengths at intermediate nodes.

The diagram illustrates a link power budget for an optical communication system. Location 2 represents the receiver's dynamic range, which is the difference between the maximum input power the receiver can tolerate without overloading (top line) and the minimum input power required to achieve a specific Bit Error Rate (BER), known as receiver sensitivity (bottom line). This operational window is also referred to as the receiver's power range. The received signal power must fall within this range for the link to function correctly.

B. OSNR margin: OSNR (Optical Signal-to-Noise Ratio) margin is a measure of signal quality relative to noise, not a range of acceptable power levels at the receiver.

C. Minimum attenuation: Attenuation is the signal loss over the fiber link, represented by the slope of the main diagonal line, not a characteristic of the receiver's power handling capability.

D. System aging margin: This is a specific allowance for component degradation over time and is a component of the overall system margin (represented at location 3), not the receiver's entire operational range.

1. Nokia Optical Networking Fundamentals, Student Guide (Course Number: TTP32001V3.0), Module 3: Link Engineering. This guide explains that the receiver dynamic range is the difference in power (dB) between the receiver overload level and the receiver sensitivity. The diagram in the question is a standard representation used in this context, where the bracketed area '2' denotes this power range.

2. Gerd Keiser, "Optical Fiber Communications," 5th Edition, McGraw-Hill, 2015. Chapter 6, Section 6.8.2, "Receiver Dynamic Range," states: "The dynamic range of an optical receiver is the range of received optical power levels over which the receiver can operate and produce a specified BER. The upper limit is set by the receiver saturation or overload level... The lower limit is determined by the receiver sensitivity." (p. 329). This directly corresponds to the region marked '2'.

3. Rajiv Ramaswami, Kumar N. Sivarajan, Galen H. Sasaki, "Optical Networks: A Practical Perspective," 3rd Edition, Morgan Kaufmann, 2010. Chapter 5, Section 5.2, "Power Budget," describes the key parameters in a link power budget. It defines the receiver's dynamic range as the difference between the maximum and minimum receivable power levels, which is precisely what is depicted at location 2 in the exhibit.

The exhibit displays a single Optical Transponder (OT) card with two line-side ports. This hardware configuration is designed to support an intra-card line protection scheme, commonly referred to as "Y-cable protection". In this scheme, the client signal is internally bridged to both line-side transmitter ports. To make this protection functional, an external 1x2 Optical Protection Switch (OPS) is required. The OPS is placed between the two line ports of the OT and the single line fiber, where it selects the signal from either the working or the protection port for transmission. The diagram shows the prerequisite hardware (the OT with dual line ports) for this type of protection but lacks the switching component, making the statement that an OPS is required the only correct conclusion.

A. OCH (Optical Channel) protection is a path protection mechanism that requires two physically diverse fiber routes between the endpoints, which is not shown in the exhibit.

B. O-SNCP (Optical Sub-Network Connection Protection) is another form of path protection that also mandates two diverse optical paths, which are not present in the diagram.

C. E-SNCP (Electrical SNCP) is a protection mechanism that operates on the electrical client-side signal, not the optical line side as depicted in the diagram's focus.

1. Nokia 1830 PSS Engineering and Planning Guide (Release 11.1), Document ID: 3KC-13891-AAAA-TCZZA, Chapter 4: "Protection and restoration", Section: "1+1 OTM-internal line-side protection". This section explicitly describes the "Y-cable" protection scheme, stating: "1+1 OTM-internal line-side protection uses a single OTM with two line ports and an external 1x2 optical switch... The OTM internally bridges the signal from the client port to the two line ports." This confirms that an external switch (OPS) is a mandatory component for this configuration to provide protection.

2. Nokia 1830 PSS Optical Layer Guide (Release 11.1), Document ID: 3KC-13893-AAAA-TCZZA, Chapter 3: "Optical protection switching". This chapter details the functionality of OPS cards (like the OPSB) and their application in various protection schemes, including line-side protection for transponders, which aligns with the scenario requiring an OPS for the OT shown. The guide clarifies that OCH and O-SNCP protection schemes involve path-level switching between diverse routes, which is fundamentally different from the hardware setup in the exhibit.

The network topology is a ring, which inherently provides two link-disjoint paths between any two nodes. The displayed routing shows one of these paths being used for each demand (the working path). For example, the demand from A to C uses the path A-B-C. A second, disjoint path, A-E-D-C, is available on the other side of the ring. This structure is the fundamental requirement for implementing 1+1 protection, where a dedicated protection path is available to take over if the working path fails. The design, therefore, supports the 1+1 protection requirement.

B. Minimum cost design: The design is not minimum cost because it forgoes using the more direct "candidate" links (e.g., A-C), opting instead for multi-hop paths around the ring perimeter.

C. Minimum latency: Latency is proportional to distance. Routing around the ring (e.g., A-B-C is 160 km) results in higher latency than a potential direct candidate link would provide.

D. Resilience against two link faults: A simple ring topology is not inherently resilient to two link faults. The failure of two non-adjacent links (e.g., A-B and C-D) would partition the ring into disconnected segments.

1. Nokia Network Services Platform (NSP) 23.10 NFM-P Transport Network Design and Optimization Guide, Chapter: "Optical network design", Section: "Protection and restoration". This guide details protection mechanisms, stating: "1+1 protection provides dedicated protection where a protection path is configured for a specific working path. The working and protection paths are typically disjoint." The ring topology in the exhibit provides this required path disjointness.

2. Pioro, M., & Medhi, D. (2004). Routing, Flow, and Capacity Design in Communication and Computer Networks. Morgan Kaufmann. Chapter 7, "Survivable Network Design". Section 7.2 discusses how 2-connected topologies, such as a ring, can survive any single link failure by rerouting traffic, which is the basis for 1+1 protection. It also clarifies that two link failures can disconnect the network.

3. Nokia Service Routing Architect (SRA) Self-Study Guide: Preparing for the 4A0-200 Exam Series, (Internal Nokia Courseware). The principles of network survivability are covered, emphasizing that ring topologies are a common and simple method to achieve path diversity for protection against single points of failure, but not multiple simultaneous failures.

The statement that is false is that Hard Decision Forward Error Correction (HDFEC) provides a higher coding gain than Soft Decision FEC (SDFEC). In fact, the opposite is true. SDFEC provides a significantly higher net coding gain (NCG) than HDFEC. This is because SDFEC utilizes more information from the received analog signal. Instead of making a simple binary ('0' or '1') decision based on a single threshold (as HDFEC does), SDFEC quantizes the signal into multiple levels, preserving "soft" information about the reliability or probability of each bit. This additional information allows the SDFEC decoder to perform more effective error correction, resulting in a performance improvement of 1.5 to 2 dB over HDFEC.

A. This statement is true. HDFEC involves a simpler decoding algorithm with less computational complexity compared to SDFEC, which results in lower processing time and therefore less latency.

C. This statement is true. HDFEC uses a single decision threshold to distinguish between a '0' and a '1'. SDFEC uses multiple thresholds to quantize the received signal into several "soft" values.

D. This statement is true. HDFEC makes an irreversible binary decision at the very first stage of receiving the signal, thereby discarding all analog "soft" information (e.g., how strong the signal was) immediately.

1. Nokia Application Note: "Forward error correction for high-speed optical transmission systems" (Doc ID: AN-FEC-HS-OPT-TRANS-EN).

Section 3.2, "Soft-decision FEC": This document states, "Soft-decision FEC (SD-FEC) decoders can provide a coding gain improvement of up to 2 dB over hard-decision decoders for the same code rate and overhead." This directly contradicts option B, confirming it is the false statement. The same section also describes the increased complexity of SDFEC, which supports why option A is true.

2. Essiambre, R. J., & Tkach, R. W. (2012). "Capacity trends and limits of optical communication networks." Proceedings of the IEEE, 100(5), 1035-1055.

Section III-B, "Forward Error Correction": The paper explains, "Soft-decision decoding... provides a substantial improvement in performance of about 2 dB in required OSNR compared to hard-decision decoding." This academic source validates that SDFEC has a superior coding gain, making statement B false.

3. ITU-T Recommendation G.975.1 (10/2020), "Forward error correction for high bit-rate DWDM submarine-cable systems."

Appendix I, "FEC codes for high bit-rate line systems": This standard discusses various FEC schemes. It details that soft-decision decoding, by using more information from the channel output, provides a significant performance gain over hard-decision decoding. This supports the conclusion that SDFEC's coding gain is higher than HDFEC's.

Protection and Restoration Combined (PRC) is a resilience mechanism in GMPLS-controlled networks. It leverages a pre-computed, pre-signaled protection path to provide very fast recovery for the first network failure. This initial recovery action is a protection switchover, which is designed to be as fast as traditional protection schemes like Sub-Network Connection Protection (SNCP) or 1+1 protection, typically completing within 50 milliseconds. For subsequent or concurrent failures, PRC then relies on slower, dynamic restoration mechanisms to establish new paths. Therefore, its initial recovery speed is comparable to SNCP.

B. PRC is as fast as restoration mechanisms.

This is incorrect. The primary advantage of PRC's protection component is that it is significantly faster than dynamic restoration, which involves signaling and path computation after a failure.

C. PRC has a recovery time that depends on the broken links.

This is misleading. While failure detection is a prerequisite, the initial protection switchover time is largely pre-determined and not dependent on the specific link that failed, unlike dynamic restoration.

D. PRC has a typical recovery time greater than 50 ms.

This is incorrect. The protection phase of PRC is specifically designed to meet the carrier-grade requirement of sub-50 ms recovery, which is a key performance indicator for protection switching.

1. Nokia 7750 SR and 7950 XRS GMPLS and ASON Guide, Release 21.10.R1, Document ID: 3HE 17489 AAAC TQZZA, Edition 01. In the "Protection and Restoration Combined (PRC)" section, it is explained that PRC provides fast protection for the first failure. The document states: "PRC provides fast protection for the first failure (within 50 ms) and restoration for subsequent failures." This directly supports that PRC's initial recovery is not greater than 50ms (refuting D) and is on par with fast protection schemes like SNCP (supporting A).

2. Martini, B., et al. (2005). "On the Integration of Protection and Restoration in GMPLS-based Networks." In Proceedings of the First International Conference on Quality of Service in Heterogeneous Wired/Wireless Networks (QSHINE'04). This academic paper discusses hybrid approaches like PRC. It highlights that the goal is to combine the "fast recovery time of protection schemes" with the "high resource efficiency of restoration schemes." This confirms that the protection aspect of PRC is designed for speed, comparable to standalone protection mechanisms. (DOI not readily available for this specific older conference proceeding, but the concept is foundational in GMPLS literature).

3. RFC 4427, "Recovery (Protection and Restoration) Terminology for Generalized Multi-Protocol Label Switching (GMPLS)," Section 3. This RFC defines the terminology. It distinguishes "Protection" as using a pre-computed and often pre-provisioned recovery path, enabling very fast switching times (typically < 50ms). "Restoration" involves computing a path after failure detection, which is inherently slower. PRC combines these, using the fast protection mechanism first.

The viability of transporting alien wavelengths at 10 Gb/s is fundamentally based on the high degree of standardization for that technology. ITU-T recommendations, such as G.959.1, defined the physical layer interfaces for 10G DWDM systems. This resulted in transponders from various vendors exhibiting very similar optical performance characteristics, including the use of Non-Return-to-Zero (NRZ) modulation, comparable Optical Signal-to-Noise Ratio (OSNR) requirements, and chromatic dispersion tolerance. This interoperability is a hallmark of the 10G era and is the primary enabler for the alien wavelength use case, allowing a third-party signal to be successfully transported over a Nokia optical line system.

A. An alien wavelength is a desired, data-carrying optical service signal, not an unwanted signal generated by the Four-Wave Mixing (FWM) non-linear impairment.

C. A VAC (Variable Attenuator Channel) card is used for power equalization by attenuating signals. Comprehensive measurement is performed by an Optical Channel Monitor (OCM).

D. This statement is factually correct; alien wavelengths do not support Nokia's proprietary Wavelength Tracker. However, this is a vendor-specific operational detail, whereas option B describes the fundamental technological principle that enables 10G alien wavelengths in the first place.

1. ITU-T Recommendation G.959.1 (2012-03), "Optical transport network physical layer interfaces": This standard specifies the physical layer characteristics for various optical interfaces, including 10G DWDM. Section 8, "Transverse compatibility," details the parameters required for multi-vendor interoperability, which is the basis for the "similar optical performance" described in the correct answer.

2. Nokia 1830 PSS Product Information and Planning Guide, 3KC-01111-KAAA-TCZZA: This document describes the features of the Nokia optical transport platform. The sections on Wavelength Tracker specify that it requires Nokia transponders to embed a pilot tone, confirming that alien wavelengths (from third-party equipment) would not support this feature. This supports the reasoning for why option D is factually correct but less fundamental than B.

3. Nokia Application Note: "1830 PSS Alien Wavelengths": Documents of this nature detail the process for qualifying third-party signals. The need for a qualification process highlights that while performance is similar, it must be verified to ensure compatibility with the Nokia line system's transmission requirements (e.g., launch power, OSNR). This reinforces that performance characteristics are the central issue for alien wavelength transport.

The statement is false because Recovery Point Objective (RPO) defines the maximum acceptable age of the data that can be lost, which is a measure of time (e.g., 15 minutes of data), not a quantity of data measured in bits. Recovery Time Objective (RTO) is the target time to restore a service after a failure and is unrelated to the amount of data lost. Therefore, the statement incorrectly defines both RTO and RPO.

A. This is a true statement. RTO and RPO are fundamental metrics used to quantify and define the business continuity and disaster recovery requirements for applications and services within a data center.

C. This is a true statement. Synchronous data center mirroring is a solution designed to achieve the most stringent (near-zero) RTO and RPO for mission-critical applications that cannot tolerate data loss or downtime.

D. This is a true statement. In application tiering models, Tier 1 and Tier 2 applications are the most critical to business operations and are therefore assigned the strictest (lowest) RTO and RPO values compared to less critical Tier 3 and Tier 4 applications.

1. Nokia Data Center Fabric Solution Guide, Release 2.0, Section 2.3.2 "Business continuity and disaster recovery." This section explains that RTO and RPO are the key parameters that drive the design of a disaster recovery solution. It defines RPO as the "maximum amount of data, measured in time, that can be lost" and RTO as the "maximum amount of time that an application can be unavailable." This confirms that RPO is a time-based metric, not a volume-based one (bits), making statement B false.

2. Nokia Application Note: "Data Center Interconnect with the Nokia 7750 Service Router and 7950 Extensible Routing System," Section: "Disaster Recovery Solutions." This document details how different DCI technologies map to RTO/RPO requirements. It describes synchronous replication (mirroring) as the solution for "mission-critical applications with zero or near-zero RTO and RPO," which validates statement C. It also implicitly supports statement D by categorizing solutions based on application criticality.

3. Patterson, D. A., & Hennessy, J. L. (2017). Computer Organization and Design RISC-V Edition: The Hardware Software Interface. Morgan Kaufmann. Chapter 6, "Parallel Processors from Client to Cloud." University-level texts on computer architecture and cloud computing often discuss dependability and business continuity. These texts define RTO and RPO as time-based metrics that are essential for designing resilient systems, aligning with the reasoning that statement B is incorrect. RPO is consistently defined in terms of the time interval of potential data loss.

An Optical Time Domain Reflectometer (OTDR) is a fundamental tool for characterizing and troubleshooting optical fibers. For security purposes, it operates by sending high-powered light pulses down a fiber and analyzing the backscattered and reflected signal. A physical intrusion, such as an attempt to tap the fiber, requires bending it, which induces a measurable, localized power loss (attenuation). The OTDR detects this attenuation event and, by measuring the round-trip time of the light pulse, can pinpoint the exact location of the intrusion along the fiber. This makes it a primary tool for detecting physical tampering with the fiber optic plant.

B. Power injection one channel: This type of attack, also known as jamming, is detected by monitoring power per wavelength. The correct tool for this is an Optical Spectrum Analyzer (OSA) or Optical Channel Monitor (OCM), not an OTDR.

C. Hacking of L1 encryption: This is a cryptographic attack on the data itself. It occurs at a logical layer and does not create a physical change in optical power that an OTDR could detect.

D. Intrusions in the cryptographic keys: This is a data security breach involving the compromise of encryption keys. Like hacking, it is a logical attack with no corresponding physical layer event for an OTDR to measure.

1. Nokia White Paper: "Protecting critical infrastructure with a secure optical foundation" (2021).

Page 4, Section: "Physical intrusion detection": "Physical intrusion detection can identify and locate a fiber-tapping attempt in real time. It works by monitoring fiber attenuation, which increases when a fiber is bent to install a tap. An optical time-domain reflectometer (OTDR) can be used to pinpoint the location of the tap." This reference directly supports that OTDRs are used to detect physical intrusions (A).

2. Nokia Application Note: "Ultra-fast data protection for the cloud era" (2017).

Page 5, Section: "Multi-layer protection": "The 1830 PSS can also detect attempts to jam the fiber with a foreign light source. This is accomplished by monitoring the optical spectrum for unexpected signals." This confirms that power injection/jamming attacks (B) are detected by monitoring the optical spectrum (using an OSA/OCM), not with an OTDR.

3. Nokia Courseware: "Nokia Optical Networking Fundamentals" Student Guide.

Module on Optical Layer Security: The course material explains that Layer 0 (photonic layer) security involves protecting the physical fiber. It explicitly details the use of OTDRs to detect and locate fiber taps by measuring attenuation changes, while identifying jamming (power injection) as a separate threat detected by spectrum analysis. This distinguishes the use cases for OTDRs versus other monitoring tools.

Raman amplification is a nonlinear optical effect that provides distributed gain along the length of a transmission fiber. This is achieved by transferring energy from a high-power pump laser to the signal. This process does not alter the fundamental linear properties of the fiber itself. Chromatic dispersion is a linear property determined by the fiber's material composition and waveguide structure, which dictates how different wavelengths travel at different speeds. Raman amplification provides gain but does not change this intrinsic fiber characteristic. Therefore, the statement that chromatic dispersion is increased is false.

A. Raman amplification is, by definition, a distributed amplification scheme where the transmission fiber itself acts as the gain medium along its length.

C. The Raman gain spectrum is determined by the pump wavelength(s). Using multiple pumps allows for the creation of a broad, flat gain profile in any desired band (C, L, S, etc.).

D. By amplifying the signal throughout the span, Raman amplification prevents the signal power from dropping to very low levels, resulting in a superior Optical Signal-to-Noise Ratio (OSNR) compared to discrete EDFAs.

1. Nokia Application Note: "Unleashing the full potential of optical networks with Raman amplification" (2018).

Reference for A, C, D: Page 3, Figure 1, illustrates the principle of distributed amplification along the fiber (supports A). Page 4, "The main benefit of distributed Raman amplification is OSNR improvement," directly supports D. Page 5, Figure 3, shows how multiple pumps are used to achieve a flat gain profile, supporting C. The document makes no mention of Raman amplification affecting chromatic dispersion.

2. Agrawal, G. P. (2010). Fiber-Optic Communication Systems (4th ed.). Wiley.

Reference for B: Chapter 2, Section 2.3, "Chromatic Dispersion," describes dispersion as a fundamental, linear property of the fiber. Chapter 6, Section 6.4, "Raman Amplifiers," describes the gain mechanism. The text treats these as separate, independent physical phenomena. The process of stimulated Raman scattering does not alter the fiber's group-velocity dispersion parameter. (ISBN: 978-0-470-50511-3).

3. Nokia Data Sheet: "1830 Photonic Service Switch (PSS) portfolio."

Reference for A, D: Product descriptions for Raman amplifier cards (e.g., RA2P) consistently highlight their use for "distributed Raman amplification" (supporting A) in long-haul and unrepeatered systems to improve OSNR and extend reach (supporting D).