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Open Submarine Cable Systems
1. Introduction to Open Submarine Cable Systems
Open submarine cable systems represent a fundamental shift in how global telecommunications infrastructure is procured, deployed, and operated. This approach decouples wet plant infrastructure (undersea cables, repeaters, branching units) from dry plant equipment (Submarine Line Terminal Equipment or SLTE), enabling operators to select best-in-breed components from different vendors while maintaining full interoperability.
The open cable model addresses critical business and technical challenges in modern submarine networks, including vendor lock-in elimination, technology refresh alignment with faster terrestrial innovation cycles, and support for emerging multi-owner fiber pair models prevalent in hyperscaler-driven deployments.
Key Concept: In traditional turnkey systems, a single vendor provides both wet plant (submarine infrastructure) and dry plant (terminal equipment). Open cables separate these components, allowing operators to source SLTE from different vendors than the wet plant provider, creating competition and enabling technology refresh without cable replacement.
1.1 Business Benefits of Open Cables
Operators can select best-in-breed wet plant vendors based purely on performance metrics and cost, independent of SLTE technology preferences.
SLTE can be selected closer to Ready for Service (RFS) date, leveraging latest coherent modem technology with 18-24 month innovation cycles.
Per-fiber pair ownership enables multiple system owners to operate independently with different SLTE vendors and upgrade schedules.
Operators can leverage high-volume terrestrial SLTE purchases for both submarine and terrestrial networks, reducing costs through economies of scale.
Unified network management across submarine and terrestrial segments when using same SLTE vendor simplifies operations and reduces training requirements.
Elimination of vendor lock-in creates broader, more secure supply chain with improved competition and reduced single-vendor dependency risks.
1.2 Evolution Drivers
The transition to open cable architectures was enabled by three key technological advances:
Optical Amplifiers (1990s): Introduction of Erbium-Doped Fiber Amplifiers (EDFAs) created the first separation between wet plant and transmission bit rate. Systems deployed as 2.5G could be upgraded to 10G by replacing only terminal equipment.
Coherent Modems (2010s): Digital Signal Processing (DSP) enabled chromatic dispersion management in the electronic domain, eliminating complex dispersion-compensated fiber maps. This simplified wet plant design to single fiber type systems.
SDM and Advanced Modulation (2020s): Space Division Multiplexing and flexible modulation formats (QPSK, 16-QAM, 64-QAM) enable capacity scaling within existing fiber infrastructure through software upgrades.
2. Historical Evolution of Submarine Cable Systems
The submarine cable industry has undergone four major technology transitions, each enabling higher capacity and greater operational flexibility. The current open cable era represents the culmination of these advances, providing unprecedented operator choice while maintaining system reliability and performance.
3. Wet Plant and Dry Plant Architecture
The fundamental architecture of open submarine cable systems is based on the clear separation between wet plant (submarine infrastructure) and dry plant (land-based equipment). This separation enables the open cable model and provides operators with unprecedented flexibility.
3.1 Wet Plant Components
Wet plant comprises all submerged equipment designed to operate for 25 years at depths up to 8,000 meters under extreme environmental conditions including hydrostatic pressure, temperature variations, and potential mechanical stress from marine activities.
3.2 Dry Plant Components
Dry plant equipment resides in cable landing stations and provides the interface between submarine cable infrastructure and terrestrial networks. In open cable systems, dry plant can be sourced from vendors different than the wet plant supplier.
Function: Submarine Line Terminal Equipment performs optical-electrical-optical conversion, wavelength multiplexing/demultiplexing, and signal conditioning.
Key Features:
- Coherent modems (QPSK, 16-QAM, 64-QAM)
- WDM multiplexing (80-120 channels)
- Pre-emphasis control
- FEC encoding/decoding
- Supervisory signal insertion
Function: PFE provides stabilized DC current (up to 1.5A typical) at voltages up to 15kV to power all submarine repeaters and active components.
Key Features:
- Constant current regulation
- Voltage monitoring
- Earth fault protection
- Remote monitoring
Function: CTB provides the physical interface between submarine cable and land-based equipment, separating optical fibers and power conductor.
Key Features:
- Fiber breakout and protection
- Power conductor isolation
- Environmental sealing
- Testing access points
Function: NMS provides centralized monitoring, control, and provisioning of both wet plant and dry plant components through standardized APIs.
Key Features:
- REST/JSON APIs
- Alarm management
- Performance monitoring
- Configuration management
4. Signal Quality Metrics: OSNR, GSNR, and SNR
Open submarine cable systems require well-defined signal quality metrics for acceptance testing and capacity planning. Unlike traditional turnkey systems that used Q-factor measurements with installed SLTE, open cables must be characterized using wet-plant-only metrics, primarily OSNR and GSNR.
4.1 OSNR (Optical Signal-to-Noise Ratio)
OSNR is defined as the ratio of signal power to noise power in a reference optical bandwidth (typically 12.5 GHz or 0.1 nm at 1550 nm). For submarine systems, OSNR primarily captures Amplified Spontaneous Emission (ASE) noise from optical amplifiers.
OSNR Formula: OSNR = P_signal / P_noise[B₀]
Where B₀ is the reference optical bandwidth (12.5 GHz standard)
For identical repeatered spans:
OSNR (dB) ≈ P_in - 10×log₁₀(N_repeaters) - NF + 58 dB
Where P_in is repeater input power per channel, N_repeaters is number of amplifiers, and NF is noise figure.
4.2 GSNR (Generalized Signal-to-Noise Ratio)
GSNR extends OSNR by including nonlinear noise contributions from fiber Kerr effects and GAWBS. This metric more accurately predicts transmission performance in modern high-capacity systems where nonlinear impairments are significant.
GSNR Components:
1. Linear SNR (SNR_ASE): Amplifier noise dominates in low-power regimes. Approximately 60% of total impairment budget in modern systems.
2. Nonlinear SNR (SNR_NLI): Includes self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM). Becomes dominant at high launch powers. Approximately 30% of impairment budget.
3. GAWBS SNR (SNR_GAWBS): Acoustic wave scattering in fiber. Typically <10% of total impairment, distance and power dependent.
Generalized Droop Model:
When combining multiple noise sources under constant total power constraint:
1 + 1/GSNR = (1 + 1/SNR_ASE) × (1 + 1/SNR_NLI) × (1 + 1/SNR_GAWBS)
This product rule accounts for signal depletion and mutual noise droop interactions.
4.3 Acceptance Criteria for Open Cables
Open cable acceptance cannot use Q-factor since no SLTE is installed initially. Instead, acceptance is based on measured GSNR meeting contractual specifications:
Requires coherent test equipment that can separate signal from all noise contributions including nonlinear effects. Measurements must:
- Remove transponder distortion
- Account for fiber nonlinearity
- Be SLTE-vendor agnostic
- Use standardized modulation (QPSK/16-QAM)
Typical specifications:
- Average GSNR: 12-16 dB
- Slope of tilt: ±0.5 dB/THz
- Gain deviation: ±2 dB max
- OSNR floor: >18 dB typical
From measured GSNR, operators can predict achievable capacity with different SLTE vendors using Shannon capacity formula:
C = 2 × B_e × log₂(1 + eSNR)
Where eSNR accounts for modem implementation penalties.
5. Network Management and Integration
Successful open cable deployments require comprehensive network management integration across wet plant, dry plant, and terrestrial network segments. Modern systems use RESTful APIs and SDN principles for unified operations.
5.1 API Integration Requirements
Modern open cable systems require well-defined API interfaces between components:
Standard Interface Protocol:
- HTTP/1.1 for request/response
- JSON or XML data formats
- WebSockets for event notification
- OAuth 2.0 authentication
- Rate limiting and quota management
OSS/BSS Integration:
- Service order management
- Inventory synchronization
- Alarm forwarding and correlation
- PM data export for analytics
- Configuration backup/restore
Element Management:
- SLTE control (vendor-specific)
- Wet plant supervisory commands
- PFE voltage/current regulation
- Test equipment integration
- Real-time telemetry collection
6. Current Trends and Future Developments (2024-2025)
The submarine cable industry continues to evolve rapidly, driven by exponential traffic growth, hyperscaler investment, and emerging applications. Recent developments highlight several key trends shaping the future of open cable systems.
6.1 Market Growth and Investment
The global submarine cable systems market is experiencing unprecedented growth. Market size for wet-plant products alone reached USD 10.1 billion in 2025 and is projected to reach USD 16.8 billion by 2030, representing a compound annual growth rate (CAGR) of 10.8%.
Key drivers include:
- Hyperscaler Self-Funding: Content providers (Google, Meta, Microsoft, Amazon) now dominate subsea investment, owning 59 international submarine cables in 2024, up from 20 in 2017. These companies increasingly pursue single-owner builds to accelerate decision cycles and enable bespoke designs with >32 fiber pairs for Space Division Multiplexing (SDM).
- AI Workload Requirements: Artificial intelligence applications and real-time cloud services drive capacity requirements beyond traditional internet traffic patterns. Google's Pacific Connect program (Proa and Taihei cables) exemplifies this shift with multi-terabit links across the Pacific.
- Route Diversity and Resilience: Following major cable disruptions in the Red Sea (February 2024) and Baltic Sea (November 2024), operators prioritize route diversity and redundancy. The EU's 2025 Joint Communication on Cable Security reflects growing governmental recognition of submarine infrastructure criticality.
6.2 Technology Advances
Systems with ≥25 fiber pairs show fastest growth at 19.4% CAGR through 2030. SDM-ready optical amplifiers and multi-fiber joint technologies enable massive capacity scaling within existing cable physical envelope.
Science Monitoring And Reliable Telecommunications (SMART) cables integrate seafloor sensors (seismometers, accelerometers, temperature, pressure) within repeater housings, supporting climate monitoring and earthquake early warning systems. ITU-T and UNESCO-IOC formally adopted SMART Cables as emerging GOOS network in 2024.
Flexible modulation formats beyond 64-QAM enable capacity optimization based on reach requirements. Probabilistic constellation shaping and geometric shaping techniques maximize spectral efficiency at given GSNR operating points.
Reconfigurable Optical Add-Drop Multiplexer branching units with wavelength-selective switching enable dynamic bandwidth allocation, spectrum sharing, and service protection without wet plant intervention.
6.3 Regulatory and Security Developments
Governmental attention to submarine cable infrastructure has intensified globally:
European Union: The 2025 Action Plan on Submarine Cable Security addresses resilience, redundancy, and protection of critical infrastructure. BEREC's draft report on submarine cables (June 2025) analyzes economic regulation across 27 countries with direct cable access.
Asia-Pacific: ASEAN Digital Ministers' Meetings (ADGMIN) in February 2024 and January 2025 committed to building secure, diverse, and resilient submarine cable networks. The 2019 ASEAN Guidelines for Strengthening Resilience seek to simplify permitting processes across jurisdictions.
International Standards: The International Advisory Body for Submarine Cable Resilience, established by ITU in 2024, works with ICPC (founded 1958) to identify resilience improvement methods. ITU-T Recommendation G.977.1 on open cable standards continues development with industry participation.
6.4 Challenges and Solutions
Cable Security: Approximately 200 cable faults occur annually, primarily from natural causes (fishing, anchors) rather than deliberate acts. However, geopolitical tensions in strategic waterways (Baltic Sea, Red Sea, South China Sea) have elevated security concerns. Solutions include improved cable burial depth, route monitoring systems, and faster repair response capabilities.
Repair Fleet Availability: Waiting times for cable ship availability can be substantial due to logistics and vessel distance to fault locations. Building dedicated regional repair fleets reduces repair time from months to weeks.
Permitting Delays: Cumbersome permit processes, especially in contested waters, significantly extend repair timeframes. Vietnam's 2024 cable outages took nearly 8 months to fully restore due to permit challenges. International cooperation frameworks aim to streamline emergency repair authorizations.
7. Practical Implementation Guidance
7.1 Open Cable Procurement Checklist
Organizations procuring open submarine cable systems should address the following considerations:
Required Parameters:
- Average GSNR (with methodology)
- Slope of tilt specification
- Gain deviation limits
- Span loss budget details
- Repeater TOP and NF values
- Fiber specifications (Aeff, dispersion, PMD)
- Repair allocation assumptions
- BOL to EOL aging margins
Key Requirements:
- SLTE-independent operation
- Open REST API interfaces
- Repeater/BU monitoring and control
- Works with partial spectrum loading
- Non-conditional warranty terms
- Full commissioning data provision
- SDN integration capability
Future-Proofing:
- Open coupling ports for expansion
- WSS-based integration options
- Adequate margin for coupling loss
- Power management coordination
- ASE idler generation control
- Spectrum assignment flexibility
Validation Methods:
- GSNR measurement procedures
- OSNR validation across spectrum
- Repeater scan baseline establishment
- BU passband characterization
- Full system SLD documentation
- Power feed current verification
7.2 SLTE Selection Criteria
When selecting SLTE vendors for open cable deployment, operators should evaluate:
Technical Capability:
- Coherent modem performance at target GSNR
- Flexible modulation format support (QPSK through 64-QAM+)
- FEC coding gain and latency
- DSP capability for nonlinear compensation
- Wavelength count and channel spacing flexibility
- Supervisory channel compatibility
Operational Integration:
- NMS compatibility with existing infrastructure
- REST API availability for automation
- SDN controller integration capability
- OTDR and monitoring tool support
- Vendor support and field presence
Economic Factors:
- Capex competitiveness
- Power consumption (opex impact)
- Maintenance and sparing requirements
- Upgrade path economics
- Volume purchase discounts (terrestrial alignment)
8. Conclusion and Key Takeaways
Open submarine cable systems represent the culmination of technological evolution in undersea telecommunications, enabling operational flexibility and vendor choice while maintaining the exceptional reliability required for critical global infrastructure.
The separation of wet plant and dry plant, enabled by coherent transmission and DSP-based dispersion management, creates truly vendor-agnostic submarine systems. GSNR-based acceptance criteria provide objective, measurable specifications independent of SLTE selection.
Open cables eliminate vendor lock-in, align technology refresh with terrestrial innovation cycles, enable multi-owner models, and create healthy competition in both wet plant and dry plant markets. These benefits translate to reduced costs and improved service agility.
With hyperscaler dominance, standardization efforts (ITU-T G.977.1), and proven deployments worldwide, open cables have transitioned from experimental to mainstream deployment model. Market growth projections and vendor ecosystem development confirm this trajectory.
Open architecture naturally accommodates emerging technologies including SDM, advanced modulation formats, AI-driven network optimization, and SMART cable sensor integration. The model scales to meet exponential traffic growth while preserving operator flexibility.
Ten Essential Points
- Wet-Dry Separation: Open cables separate submarine infrastructure from terminal equipment, enabling multi-vendor solutions.
- GSNR Acceptance: Generalized SNR provides objective, SLTE-independent acceptance criteria for open systems.
- Technology Alignment: SLTE selection near RFS date leverages latest coherent modem advances with 18-24 month innovation cycles.
- Coherent Enablement: DSP-based dispersion management simplified wet plant to single fiber type, eliminating complex dispersion maps.
- Multi-Owner Support: Per-fiber pair ownership models enable independent operations and upgrade schedules.
- API Integration: RESTful interfaces and SDN principles enable unified management across terrestrial and submarine segments.
- Performance Metrics: Linear SNR (ASE), nonlinear SNR (Kerr), and GAWBS combine to determine total system GSNR.
- Market Leadership: Hyperscalers drive innovation with single-owner builds featuring advanced SDM and capacity optimization.
- Standards Evolution: ITU-T, SubOptic, and industry bodies actively develop interoperability standards and best practices.
- Future Technologies: SDM, SMART sensors, probabilistic shaping, and AI-driven optimization extend cable value and capability.
For educational purposes in optical networking and DWDM systems
Note: This guide is based on industry standards, best practices, and real-world implementation experiences. Specific implementations may vary based on equipment vendors, network topology, and regulatory requirements. Always consult with qualified network engineers and follow vendor documentation for actual deployments.
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