Planning, Techno-Economics, Security and Governance

Introduction

Optical communication networks are no longer planned only as collections of fibres, transmitters, receivers, and switching platforms. They are strategic infrastructure supporting cloud services, financial transactions, industrial control, public administration, healthcare, scientific research, and increasingly critical national functions. A technically excellent optical system can nevertheless fail as an investment if demand is overestimated, lifecycle costs are ignored, interoperability is weak, security is treated as an afterthought, or regulatory and environmental obligations are neglected.

This chapter presents an integrated approach to planning and governing optical communication systems. It connects traffic forecasting, architecture selection, techno-economic analysis, procurement, risk management, migration, optical-layer security, laser safety, privacy, regulation, interoperability, ethics, and sustainability. The central argument is that optical-network decisions should be evaluated over their complete lifecycle and against multiple objectives: capacity, availability, security, affordability, adaptability, compliance, and social responsibility.

Learning Objectives

After studying this chapter, the reader should be able to:

1. Forecast demand and translate it into optical-network capacity requirements.

2. Compare architectures, technologies, and vendors using technical and economic criteria.

3. Calculate lifecycle cost and interpret investment, operating, and risk-related costs.

4. Construct a risk register for optical infrastructure and plan migration from legacy systems.

5. Explain optical-layer threats and appropriate preventive, detective, and corrective controls.

6. Apply principles of laser safety, privacy, regulation, interoperability, ethical procurement, and sustainability.

7. Formulate a governance framework for accountable and resilient optical-network operation.

1. Planning as a Multidimensional Decision Problem

Network planning begins with a service requirement and ends with an implementable, governed system. The planning process normally includes:

• defining service objectives and users;
• forecasting traffic, geographic coverage, and performance requirements;
• selecting topology and technology;
• sizing fibre, wavelengths, ports, amplifiers, and protection capacity;
• evaluating capital and operating expenditure;
• assessing risk, compliance, and environmental impact;
• preparing procurement and implementation plans; and
• establishing monitoring, review, and retirement policies.

The planner must distinguish between capacity, throughput, and service availability. Installed fibre capacity is the physical potential of the plant; provisioned capacity is the capacity equipped with active systems; and delivered throughput is the usable service after protocol overhead, protection reservations, congestion, and failures. These quantities should not be used interchangeably.

A useful planning principle is modularity. A network should be capable of expansion through additional wavelengths, higher-order modulation, new coherent transponders, or additional fibre pairs without requiring complete reconstruction. However, modularity has a cost. Empty ducts, diverse routes, spare ports, and compatible passive infrastructure may appear uneconomic initially but can substantially reduce future disruption and deployment time.

1.1 Demand Forecasting

Demand forecasting combines historical measurements, customer commitments, market analysis, and scenario assumptions. Common demand drivers include subscriber growth, access speed, cloud adoption, video traffic, data-centre interconnection, mobile backhaul and fronthaul, machine-to-machine traffic, and enterprise digitisation.

A simple compound-growth model is

\[

D_t=D_0(1+g)^t

\]

where \(D_0\) is demand in the base year, \(g\) is the annual fractional growth rate, and \(t\) is the number of years. The model assumes a constant growth rate and is suitable for an initial estimate, not for markets approaching saturation.

For a saturated market, a logistic model is more realistic:

\[

D(t)=\frac{K}{1+A e^{-rt}}

\]

where \(K\) is the asymptotic demand ceiling, \(r\) is the growth parameter, and \(A\) is determined by the initial condition. The logistic model assumes that growth slows as penetration, affordability, or available customers approach a limit. In practice, planners often use low, central, and high scenarios rather than relying on one forecast.

The required installed capacity should include engineering margins. If forecast peak traffic is \(D\), a reserve factor \(m\), and a protection or restoration allowance \(p\) are used, a planning estimate may be expressed as

\[

C_{plan}=D(1+m)(1+p).

\]

Here, \(m\) and \(p\) must be defined consistently. If protection capacity is already included in the measured demand or in a dedicated design rule, it must not be counted twice. The formula is a planning approximation; detailed wavelength assignment must additionally account for channel granularity, guard bands, reach, spectrum continuity, and failure scenarios.

Forecast quality should be evaluated using historical back-testing. The mean absolute percentage error is commonly defined as

\[

MAPE=\frac{100}{n}\sum_{i=1}^{n}\left|\frac{A_i-F_i}{A_i}\right|,

\]

where \(A_i\) is actual demand, \(F_i\) is forecast demand, and \(n\) is the number of observations. MAPE is problematic when actual values are zero or very small; in such cases, mean absolute error or scaled errors are preferable. Forecast uncertainty should be represented explicitly because a network designed only for the central estimate may fail under rapid adoption.

2. Architecture and Technology Evaluation

Architecture evaluation compares not merely equipment but complete operating models. Important choices include point-to-point versus ring or mesh topology, dedicated versus shared access, centralised versus distributed control, fixed-grid versus flexible-grid wavelength systems, and protection versus restoration.

2.1 Topology and Resilience

A point-to-point system is simple and easy to troubleshoot but may provide limited alternative routing. Rings can offer rapid protection for certain failure patterns, while mesh networks provide greater route diversity and restoration flexibility at the cost of more complex control and planning. Physical route diversity is distinct from logical diversity: two services may use different logical paths while sharing the same duct, bridge, power system, or building entrance.

Availability is often approximated by

\[

A=\frac{MTBF}{MTBF+MTTR},

\]

where MTBF is mean time between failures and MTTR is mean time to repair. This steady-state approximation assumes statistically stable failure and repair processes and should not be applied uncritically to correlated failures, disasters, or planned maintenance. For independent series components, system availability is approximately the product of component availabilities. For a parallel redundant arrangement, unavailability may be reduced, but only if the components, power supplies, routes, and control systems are genuinely independent.

Resilience planning must consider fibre cuts, amplifier failures, power loss, software faults, misconfiguration, cyberattack, extreme weather, construction activity, and common-cause failures. A route labelled “diverse” should be verified through geographic information, civil records, and physical inspection.

2.2 Technology Selection

Technology evaluation should cover:

• fibre type, attenuation, dispersion, and installed condition;
• optical line systems and amplifier compatibility;
• coherent transponders, modulation, forward-error correction, and reach;
• wavelength or spectrum efficiency;
• open interfaces and disaggregation options;
• telemetry, automation, and software support;
• power consumption and thermal requirements;
• vendor lifecycle and software-maintenance policy; and
• upgrade, repair, and recycling arrangements.

Higher spectral efficiency may increase capacity but can reduce reach or tolerance to impairments. A nominal line rate does not establish end-to-end service performance. The engineering decision must consider optical signal-to-noise ratio, nonlinear effects, chromatic dispersion, polarization effects, amplifier spacing, connector losses, and interoperability.

An open architecture can reduce vendor lock-in and enable multi-vendor procurement, but it may introduce integration responsibility, more complex troubleshooting, and uncertain accountability when faults cross vendor boundaries. “Open” should therefore be evaluated through tested profiles, information models, conformance evidence, support processes, and contractual responsibility rather than marketing claims.

2.3 Vendor Evaluation

A balanced vendor scorecard may allocate weighted criteria such as technical compliance, lifecycle cost, cybersecurity, interoperability, delivery capability, service support, financial stability, sustainability, and ethical conduct. Weights should reflect the mission. For a national backbone, resilience and security may dominate initial price; for a short-lived private deployment, rapid delivery and operating simplicity may have greater weight.

A weighted score can be calculated as

\[

S=\sum_{j=1}^{k} w_j s_j,

\]

where \(s_j\) is the normalised score for criterion \(j\), \(w_j\) is its weight, and \(\sum w_j=1\). Scores must be based on evidence and accompanied by sensitivity analysis. A vendor ranking that changes when a reasonable weight changes is not a robust decision and should trigger further investigation.

3. Techno-Economic Analysis

Techno-economics evaluates whether a proposed system creates sufficient value relative to its total cost and risk. Capital expenditure includes fibre construction, ducts, rights of way, buildings, optical equipment, power systems, installation, commissioning, and initial software. Operating expenditure includes energy, leases, maintenance, field support, licences, monitoring, security operations, insurance, and regulatory fees. Indirect costs include outages, migration, training, inventory, stranded assets, and management effort.

3.1 Lifecycle Costing

The present value of a cost occurring in year \(t\) is

\[

PV_t=\frac{C_t}{(1+r)^t},

\]

where \(C_t\) is the nominal cost in year \(t\) and \(r\) is the discount rate per period. If costs escalate with inflation or another index, the escalation should be modelled separately and consistently with the selected discount rate. Lifecycle present cost is

\[

LCC=C_0+\sum_{t=1}^{N}\frac{C_t}{(1+r)^t}+\frac{C_{ret}}{(1+r)^N},

\]

where \(C_0\) is initial cost, \(N\) is the analysis horizon, and \(C_{ret}\) is the net retirement or residual-value term. A negative retirement cost may represent salvage value; the sign convention must be stated.

For comparing alternatives with different capacity or service output, cost per delivered capacity may be useful, but it can mislead if one option provides greater resilience or coverage. Total cost of ownership should therefore be accompanied by service-level, risk, and sustainability indicators.

Worked Example: Present Value of Maintenance

An optical system requires an initial investment of $1,000,000 and maintenance of $120,000 at the end of each year for three years. Using a 5% annual discount rate and ignoring residual value,

\[

LCC=1,000,000+\frac{120,000}{1.05}+\frac{120,000}{1.05^2}+\frac{120,000}{1.05^3}.

\]

The discounted maintenance costs are approximately $114,286, $108,844, and $103,661. Thus,

\[

LCC\approx 1,326,791\text{ dollars}.

\]

This result is not a prediction of cash expenditure; it is a comparison value under the stated discount and timing assumptions. If one alternative has higher energy use, shorter support life, or greater outage exposure, those effects should be added rather than ignored.

3.2 Investment Decisions and Real Options

A project may be evaluated using net present value, internal rate of return, payback period, or benefit-cost ratio. NPV is conceptually strong because it compares discounted benefits and costs, but benefits such as resilience, public safety, and strategic autonomy may be difficult to monetise. In such cases, multi-criteria analysis is appropriate.

Phased deployment creates a real option: the organisation can defer later investment until demand becomes clearer. This flexibility has value, but only if the initial architecture preserves future choices. Conversely, premature commitment to proprietary platforms can create switching costs and reduce the value of waiting.

4. Risk Analysis and Migration Planning

Risk is commonly assessed as a combination of likelihood and consequence, but a numerical product should not conceal uncertainty. A risk register should record the asset, threat or hazard, vulnerability, consequence, likelihood basis, existing controls, owner, treatment, trigger, and residual risk.

Relevant risks include:

• civil works delay and right-of-way disputes;
• inaccurate demand forecasts;
• fibre cuts and common-route failures;
• component obsolescence and vendor withdrawal;
• software vulnerabilities and credential compromise;
• inadequate spares or specialist skills;
• energy-price and supply-chain volatility;
• non-compliance with safety or privacy requirements; and
• environmental or community opposition.

Risk treatment may involve avoidance, reduction, transfer, acceptance, or contingency planning. Insurance transfers only selected financial consequences; it does not remove operational responsibility.

Migration Strategy

Migration from legacy synchronous, wavelength, or proprietary systems should begin with inventory and dependency mapping. The planner should identify services, protection states, optical budgets, timing dependencies, customer contracts, management systems, licences, and physical constraints. A migration that considers only equipment replacement may interrupt services that were not documented.

A controlled migration commonly uses:

1. discovery and baseline measurement;

2. target architecture and coexistence design;

3. laboratory and interoperability testing;

4. pilot deployment on a low-risk route;

5. parallel operation or protected cutover;

6. staged service migration with rollback criteria;

7. performance and security validation; and

8. decommissioning, data sanitisation, recycling, and contract closure.

Rollback must be technically feasible, time-bounded, and rehearsed. “Backout” is not a plan if old equipment, licences, staff, or route capacity have already been removed.

5. Optical-Layer Security and Resilience

Security is often associated with encryption and higher-layer authentication, but the optical layer also presents important risks. Threats include fibre tapping, deliberate bending or insertion loss, high-power injection, rogue optical signals, wavelength abuse, amplifier manipulation, management-channel compromise, unauthorised patching, and denial of service through physical damage.

Controls should be layered:

• Physical: secure buildings, locked cabinets, route surveillance, tamper evidence, diverse paths, controlled patch panels, and documented access.
• Optical: power thresholds, spectrum monitoring, optical time-domain reflectometry where suitable, alarm correlation, automatic shutdown policies, and isolation of abnormal channels.
• Control plane: authenticated management, least privilege, network segmentation, secure logging, configuration backup, change approval, and independent recovery access.
• Service layer: encryption, key management, traffic validation, and customer-specific security controls.
• Operational: incident response, supplier notification, exercises, spare equipment, and restoration procedures.

Optical monitoring must be interpreted carefully. A sudden loss may indicate a cut, connector problem, dirty interface, amplifier fault, or malicious intervention. Monitoring systems themselves are security-sensitive because they reveal topology, traffic conditions, and alarm states.

Encryption does not prevent physical disruption, traffic analysis, or metadata exposure. Conversely, physical security does not replace cryptographic protection. Security architecture should therefore apply defence in depth and assume that any single control can fail.

Resilience and Recovery

Resilience includes resistance, absorption, adaptation, and recovery. Protection switching can restore service rapidly but may consume reserved capacity. Restoration can use resources more efficiently but normally requires more control coordination. Recovery objectives should specify maximum acceptable interruption, data impact, service priority, and restoration order.

Exercises should include realistic faults: simultaneous route and power failures, loss of management access, corrupted configuration, unavailable vendors, and compromised credentials. The objective is not merely to verify that a protection ring switches, but to determine whether the organisation can operate safely under degraded information and staffing conditions.

6. Laser Safety and Occupational Practice

Optical transmitters and amplifiers may emit invisible infrared radiation capable of damaging the eye. Safety depends on wavelength, accessible power, exposure duration, beam geometry, enclosure, and applicable classification standards. Personnel must never inspect a live fibre end directly or with unauthorised optical instruments.

Good practice includes automatic laser shutdown where appropriate, connector inspection and cleaning, warning labels, interlocks, controlled work permits, safe inspection equipment, training, and documented procedures for dark-fibre and amplified systems. A system that is safe at a customer interface may not be safe at an amplifier output or disconnected patch point. Safety assessments should consider maintenance states, reflected power, accidental reconnection, and contractor activity.

Laser safety is both an engineering and governance responsibility. Procurement specifications should require compliance evidence, safety documentation, training, and incident reporting rather than assuming that product conformity alone ensures safe workplace practice.

7. Privacy, Regulation, and Governance

Optical networks carry information that may be personal, commercially confidential, or safety-critical. Privacy governance should address data minimisation, purpose limitation, access control, retention, lawful processing, breach response, and cross-border transfer. Network telemetry can itself become personal or sensitive data when linked to users, locations, or behaviour.

Regulatory obligations vary by jurisdiction but commonly involve spectrum and telecommunications licensing, rights of way, construction permits, electromagnetic and electrical safety, occupational health, lawful access requirements, data protection, competition, critical-infrastructure protection, environmental impact, and electronic waste. The responsible organisation must identify applicable national and sectoral rules rather than assuming that equipment certification covers the complete deployment.

Governance assigns decision rights and accountability. A practical governance model includes:

• a technical authority for architecture and engineering standards;
• a security authority for threat assessment and incident response;
• a safety authority for occupational and laser controls;
• procurement and legal review for contracts and compliance;
• an operations authority for change and outage management; and
• independent assurance through audits, tests, and performance reviews.

Key performance indicators should include availability, mean time to repair, forecast error, change-failure rate, patch latency, energy per delivered bit, incident closure time, supplier concentration, and unresolved high risks. Metrics must not encourage unsafe behaviour, such as suppressing alarms to improve apparent availability.

8. Interoperability and Ethical Procurement

Interoperability has technical, semantic, operational, and contractual dimensions. Technical interoperability concerns optical characteristics and interfaces. Semantic interoperability concerns common models for alarms, inventory, topology, and performance. Operational interoperability concerns provisioning, fault isolation, upgrades, and responsibility. Contractual interoperability concerns support obligations and remedies when multiple suppliers are involved.

Standards compliance should be demonstrated through profiles, test results, and multi-vendor trials. A published interface does not guarantee interoperable behaviour under all line conditions. Acceptance tests should cover nominal and degraded states, alarms, protection switching, software upgrade, restoration, telemetry, and security controls.

Ethical procurement requires transparent evaluation, avoidance of conflicts of interest, fair treatment of suppliers, respect for labour and human rights, anti-corruption controls, responsible mineral sourcing, and attention to the social effects of route construction. Lowest purchase price is not necessarily value for money. Procurement should consider supplier security practices, vulnerability disclosure, support geography, environmental declarations, repairability, and end-of-life responsibility.

9. Sustainability and Emerging Tools

Sustainability analysis includes embodied carbon in fibre, ducts, electronics, buildings, and transport; operational energy; cooling; battery and material use; land disturbance; and end-of-life treatment. Efficiency should be measured against useful service, for example energy per delivered bit or per transported traffic unit, while recognising that boundaries must be stated. A low-power device may not yield a lower lifecycle impact if it fails early or requires frequent replacement.

Sustainable design practices include sharing ducts and civil infrastructure, extending equipment life through software and modular upgrades, improving power and cooling efficiency, using renewable electricity where credible, reducing unnecessary truck rolls, recovering materials, and requiring supplier environmental data. Resilience and sustainability can conflict: additional routes and spare equipment improve availability but increase embodied impact. Multi-criteria evaluation is therefore preferable to a single environmental score.

Artificial intelligence can assist with demand forecasting, anomaly detection, predictive maintenance, route-risk analysis, and energy optimisation. However, AI outputs may inherit biased data, generate false alarms, or make unsafe recommendations. Human oversight, explainability appropriate to the decision, data governance, model monitoring, and safe fallback modes are essential. AI should support—not replace—engineering judgement and accountable change control.

10. Illustrative Case: Regional Research and Public-Service Backbone

Background

A regional consortium operates a 500-km optical backbone connecting universities, hospitals, emergency-service centres, and data facilities. The network uses ageing proprietary wavelength equipment, has two locations with shared duct routes, and experiences increasing demand from scientific data transfer and telemedicine.

Problem

Traffic has grown unpredictably, two vendors have announced product end-of-support dates, and a previous fibre cut interrupted several services simultaneously. The consortium must expand capacity while preserving critical services, controlling cost, and improving security.

Analysis

The planning team collects five years of traffic data, customer commitments, construction records, outage logs, power consumption, and equipment support information. It develops low, central, and high traffic scenarios rather than extrapolating a single trend. The risk review identifies common-route exposure, inadequate spare transponders, shared administrative credentials, and incomplete laser-safety documentation.

Three alternatives are compared: replacing the proprietary system with another closed platform; adopting a multi-vendor coherent system over the existing fibre; and constructing a new physically diverse route before upgrading equipment. Lifecycle analysis shows that the first option has lower initial integration effort but higher lock-in and support risk. The second offers better modularity but requires stronger testing and operations capability. The third gives the greatest resilience but cannot be delivered within the required schedule and budget.

Approach and Solution

The consortium selects a phased, multi-vendor architecture. It first secures critical sites, separates management networks, replaces shared credentials, and installs monitoring at route-diverse locations. A laboratory validates optical power ranges, alarms, protection behaviour, telemetry, and software upgrades. A pilot is deployed on a non-critical span. Critical services are migrated in protected windows, with the legacy system retained until acceptance criteria are met.

A contract establishes interface compliance, vulnerability disclosure, support response, spare-part obligations, software escrow or continuity measures where appropriate, and responsibilities for multi-vendor faults. The consortium also introduces annual route-diversity verification, laser-safety training, supplier sustainability reporting, and an incident exercise involving simultaneous fibre and management-plane failure.

Outcome

The phased approach increases capacity without a disruptive “big bang” replacement. It reduces vendor concentration, improves visibility of physical faults, and exposes a previously undocumented shared route. Although integration and testing costs are higher than in the closed-platform alternative, the consortium gains better migration flexibility and reduces the probability of a prolonged future outage.

Learning Points

The case demonstrates that the lowest initial price is not equivalent to lowest lifecycle cost. Physical diversity must be verified, not assumed. Migration is a socio-technical activity involving people, contracts, safety, and operating procedures. Interoperability requires evidence and accountability. Security improvements often begin with basic governance—inventory, identity management, logging, and change control—rather than advanced equipment alone.

Challenges and Limitations

Forecasts remain uncertain because technology adoption can change abruptly. Economic comparisons depend on discount rates, cost boundaries, residual values, and the treatment of risk. Availability models may fail under correlated disasters or common-cause faults. Vendor scores can create false precision when evidence is weak. Open architectures can transfer integration cost to the operator. Security controls may create operational complexity, while extensive monitoring can raise privacy concerns. Sustainability metrics are difficult to compare when suppliers use different lifecycle boundaries. Finally, regulation changes over time, so compliance must be maintained as an ongoing capability rather than treated as a one-time approval.

Best-Practice Decision Process

A defensible optical-network decision should:

1. Define services, stakeholders, safety constraints, and regulatory obligations.

2. Establish measured baseline data and explicit demand scenarios.

3. Compare architectures using technical, economic, risk, and sustainability criteria.

4. Verify physical diversity and lifecycle support claims.

5. Test interoperability and security before production deployment.

6. Include migration, rollback, training, spares, and retirement in the business case.

7. Assign accountable owners for risks, controls, and decisions.

8. Review performance, forecasts, supplier health, and emerging threats periodically.

Chapter Summary

Strategic optical-network planning integrates demand forecasting, architecture selection, lifecycle economics, resilience, security, safety, governance, and sustainability. Forecasts should use measured data and scenarios, while capacity plans must distinguish demand from engineering reserve and protection requirements. Architecture and vendor decisions should consider reach, interoperability, support life, operating capability, and route diversity—not merely nominal data rate or purchase price.

Lifecycle costing discounts future costs and should include energy, maintenance, support, migration, risk, and retirement. Risk management requires explicit ownership, treatment, residual-risk review, and realistic exercises. Migration should be staged, tested, reversible, and supported by complete service and dependency inventories.

Optical-layer security requires physical, optical, control-plane, service-layer, and operational controls. Laser safety, privacy, regulation, ethical procurement, interoperability, and environmental responsibility are core engineering obligations. Governance converts these principles into decision rights, assurance, metrics, and accountability. The most robust network is therefore not simply the fastest network; it is one that remains safe, adaptable, supportable, secure, and socially responsible throughout its lifecycle.

Key Terms

Demand forecasting: Estimating future traffic, users, and service requirements.

Lifecycle cost: Total discounted cost from acquisition through operation and retirement.

Capital expenditure: Initial investment in infrastructure and equipment.

Operating expenditure: Recurring cost of operating and maintaining a system.

Present value: Current value of a future monetary amount after discounting.

Common-cause failure: A failure mechanism that disables supposedly independent elements.

Route diversity: Physical separation of communication paths to reduce shared risk.

Protection switching: Automatic transfer to reserved resources after a fault.

Restoration: Re-establishment of service using available network resources after failure.

Interoperability: Ability of different systems to work together technically and operationally.

Vendor lock-in: Dependence that makes changing supplier or technology costly or impractical.

Risk register: Structured record of risks, controls, owners, and treatments.

Optical-layer attack: Malicious action targeting fibre, optical signals, amplifiers, or optical control functions.

Laser safety: Practices controlling hazardous exposure to optical radiation.

Residual risk: Risk remaining after controls are applied.

Governance: Allocation of authority, accountability, oversight, and decision rights.

Ethical procurement: Purchasing that considers integrity, human rights, fairness, and sustainability.

Embodied carbon: Emissions associated with manufacture, construction, transport, and installation.

Multi-criteria analysis: Evaluation using several weighted technical, economic, and social criteria.

Migration rollback: Planned restoration to the previous system after an unsuccessful change.

Review Questions

Short Answer Questions

1. Distinguish installed capacity, provisioned capacity, and delivered throughput.

2. Why should optical-network demand be represented using multiple scenarios?

3. Identify four categories of cost included in lifecycle analysis.

4. Name three threats that directly affect the optical layer.

5. Why is physical route diversity important even when logical paths are different?

Long Answer Questions

1. Explain a complete demand-forecasting and capacity-planning process for a regional optical backbone.

2. Discuss how lifecycle costing can alter the choice between a closed vendor platform and a multi-vendor architecture.

3. Describe a staged migration methodology, including testing, rollback, and decommissioning.

4. Explain the relationship among optical-layer security, encryption, physical security, and operational governance.

5. Discuss the ethical, regulatory, and sustainability responsibilities of an organisation procuring optical-network infrastructure.

Analytical / Application Questions

1. A network has forecast peak demand of 80 Gb/s, a 25% engineering reserve, and a 20% separately required protection allowance. Estimate the planning capacity using the stated planning model, and explain when the calculation could double-count capacity.

2. Compare two five-year network alternatives using lifecycle cost, route diversity, vendor support, energy use, and migration risk. Recommend a decision method and identify which assumptions require sensitivity analysis.

3. Design a risk register and migration plan for replacing a legacy wavelength system while maintaining hospital and emergency-service connectivity. Include at least five risks, controls, acceptance criteria, and rollback triggers.

Multiple Choice Questions with Answers

Question 1

Which expression represents a constant-growth demand forecast?

A. D_t = D_0(1 + g)^t

B. D_t = D_0 + g/t

C. D_t = D_0(1 - g)^t

D. D_t = t/(D_0 + g)

Correct Answer: A. D_t = D_0(1 + g)^t

Question 2

What does lifecycle cost primarily include?

A. Only the purchase price of equipment

B. Only annual maintenance expenditure

C. Costs from acquisition through operation and retirement

D. Only the cost of energy consumption

Correct Answer: C. Costs from acquisition through operation and retirement

Question 3

Which factor most directly indicates a common-cause failure?

A. Two services use different wavelengths

B. Two physically separate buildings use different vendors

C. Two logical paths share the same duct

D. Two transponders use different modulation formats

Correct Answer: C. Two logical paths share the same duct

Question 4

In the availability approximation A = MTBF/(MTBF + MTTR), MTTR denotes:

A. Maximum transmission time rate

B. Mean time to repair

C. Mean traffic transfer rate

D. Minimum technical test requirement

Correct Answer: B. Mean time to repair

Question 5

Which control is primarily a physical optical-layer security measure?

A. Route surveillance and secured patch panels

B. Customer password expiry only

C. Application-level input validation

D. Financial auditing

Correct Answer: A. Route surveillance and secured patch panels

Question 6

Why is a rollback plan important during network migration?

A. It eliminates the need for interoperability testing

B. It permits controlled return to the previous system if acceptance criteria fail

C. It guarantees that no outage can occur

D. It removes the need for service inventory

Correct Answer: B. It permits controlled return to the previous system if acceptance criteria fail

Question 7

What is a limitation of MAPE?

A. It cannot be expressed as a percentage

B. It is unsuitable when actual values are zero or very small

C. It always overestimates demand

D. It requires a discount rate

Correct Answer: B. It is unsuitable when actual values are zero or very small

Question 8

Which statement best describes ethical procurement?

A. Selecting the lowest purchase price regardless of consequences

B. Selecting the supplier with the most advertising

C. Considering integrity, human rights, fairness, and sustainability

D. Avoiding all multi-vendor solutions

Correct Answer: C. Considering integrity, human rights, fairness, and sustainability

Question 9

Why must encryption and physical security be used together?

A. Encryption prevents every form of fibre cut

B. Physical security replaces the need for key management

C. Each addresses different classes of threats and neither is sufficient alone

D. They are alternative names for the same control

Correct Answer: C. Each addresses different classes of threats and neither is sufficient alone

Question 10

For a forecast demand of 80 Gb/s, a 25% reserve, and a 20% protection allowance applied multiplicatively as C_plan = D(1+m)(1+p), what is the planning capacity?

A. 96 Gb/s

B. 100 Gb/s

C. 120 Gb/s

D. 125 Gb/s

Correct Answer: C. 120 Gb/s