Layer 2 vs Wavelength vs Dark Fiber
Managed Ethernet vs Optical Transport vs Raw Infrastructure
Layer 2 Transport, Wavelength Services, and Dark Fiber represent three distinct approaches to enterprise fiber connectivity, each offering different levels of control, management, and scalability. Layer 2 Transport provides managed Ethernet services (VPLS, EVPN, E-Line) with carrier-provided equipment. Wavelength Services deliver dedicated optical channels (DWDM/CWDM lambdas) over shared fiber infrastructure. Dark Fiber provides unlit fiber strands with complete customer control over equipment and protocols.
The choice depends on bandwidth requirements, technical expertise, scalability needs, and preference for managed vs self-operated infrastructure. Large enterprises with in-house network teams often prefer dark fiber or wavelength services for maximum control and long-term cost efficiency. Organizations requiring turnkey solutions typically choose Layer 2 Transport for predictable monthly costs without capital expenditure.
All three options are available through our enterprise connectivity services across France with flexible deployment models.
Quick Summary
Raw fiber infrastructure for maximum control and performance with dedicated wavelengths.
Core Technology Differences
Understanding infrastructure models and operational characteristics
Management Model
Layer 2 Transport is fully managed by the carrier—equipment, monitoring, troubleshooting included. Wavelength Services provide managed optical transport but require customer equipment for Layer 2/3 protocols. Dark Fiber is completely unmanaged; customer owns and operates all active equipment, providing maximum flexibility but requiring in-house expertise.
Bandwidth Scalability
Layer 2 Transport scales via service upgrades (100M→1G→10G) with equipment swaps and lead times. Wavelength Services scale by adding lambdas or upgrading optics (10G→40G→100G→400G) on existing fiber. Dark Fiber scales unlimited—deploy any protocol, any speed, upgrade equipment independently without carrier involvement.
Equipment Ownership
Layer 2 Transport: carrier-owned CPE (demarcation device) at customer site. Wavelength Services: customer-owned transport equipment (DWDM/CWDM mux, optical amplifiers). Dark Fiber: customer owns entire optical layer (fiber patch panels, optics, switches, all active equipment).
Protocol Flexibility
Layer 2 Transport limited to Ethernet (802.1Q VLANs, MEF E-Line/E-LAN). Wavelength Services support any Layer 2/3 protocol customer equipment can handle. Dark Fiber supports absolutely any protocol—Ethernet, Fibre Channel, SONET/SDH, proprietary protocols, even analog signals.
Latency Characteristics
Layer 2 Transport adds switching latency (1-5ms) through carrier aggregation network. Wavelength Services provide near-wire-speed latency (<0.5ms) with minimal optical processing. Dark Fiber delivers absolute minimum latency—speed of light in fiber (~5μs per kilometer) with zero processing delay.
Cost Structure
Layer 2 Transport: monthly OpEx with no CapEx (carrier owns equipment). Wavelength Services: moderate CapEx (customer equipment) + monthly wavelength rental. Dark Fiber: high upfront CapEx (purchase all equipment) + low monthly fiber rental, best ROI for long-term high-bandwidth needs.
Detailed Comparison Matrix
Technical and operational characteristics side-by-side
| Feature | Layer 2 Transport | Wavelength Service | Dark Fiber |
|---|---|---|---|
| Infrastructure Type | Managed Ethernet service | Dedicated optical lambda | Unlit fiber strand(s) |
| Bandwidth Options | 100M, 1G, 10G, 100G (fixed) | 10G, 40G, 100G, 400G per lambda | Unlimited (customer equipment dependent) |
| Equipment Ownership | Carrier-owned CPE | Customer-owned DWDM/optics | Customer owns all active equipment |
| Network Management | Fully managed by carrier | Optical layer managed, customer manages L2/3 | 100% customer responsibility |
| Bandwidth Scalability | Service upgrade required (weeks) | Add lambdas or upgrade optics (days) | Instant (swap customer equipment) |
| Supported Protocols | Ethernet only (802.1Q) | Any L2/3 protocol | Any protocol (no restrictions) |
| Typical Latency | 2-5ms (includes switching) | <0.5ms (optical only) | ~5μs/km (wire speed) |
| Redundancy Options | Carrier-provided diverse paths | Multiple lambdas on diverse fiber | Multiple fiber pairs (customer managed) |
| Service Level Agreement | 99.9-99.99% with service credits | 99.9% optical availability | Physical fiber only (no service SLA) |
| Deployment Time | 4-8 weeks (service provisioning) | 6-12 weeks (wavelength allocation + equipment) | 8-16 weeks (fiber build + equipment procurement) |
| Required Expertise | Basic networking (Ethernet) | Advanced (DWDM/optical) | Expert (full stack optical + networking) |
Layer 2 Transport: Managed Ethernet Services
Turnkey connectivity with carrier-managed infrastructure
Layer 2 Transport services deliver Ethernet connectivity using carrier-owned and operated equipment. The carrier provides Customer Premises Equipment (CPE), manages the network, monitors performance, and handles troubleshooting. Customers receive a managed service with predictable monthly costs and guaranteed SLAs.
Common Layer 2 Technologies
E-Line (Point-to-Point)
MEF-certified point-to-point Ethernet service connecting two locations. Provides dedicated bandwidth with VLAN transparency. Typical use: datacenter interconnect, office-to-datacenter connectivity. Bandwidth: 100M-100G symmetric.
E-LAN (Multipoint)
Multipoint Ethernet LAN service connecting 3+ locations in full mesh or hub-and-spoke topology. VPLS or EVPN-based with MAC learning. Use: enterprise WAN, multi-site connectivity. Scales to 100+ sites.
EVPN (Ethernet VPN)
Modern L2VPN using BGP for MAC/IP advertisement. Provides active-active multihoming, fast convergence (<50ms), and integrated routing. Replaces traditional VPLS for large-scale deployments. Supports up to 16,000 sites per VPN instance.
VPLS (Virtual Private LAN Service)
Legacy but widely deployed L2VPN using MPLS for label switching. Full mesh of pseudowires between provider edge routers. Any-to-any connectivity with MAC learning. Typical latency: 2-5ms.
Use Cases
- Organizations without in-house network engineering teams
- Businesses requiring predictable monthly OpEx without CapEx
- Multi-site deployments where carrier manages complexity
- Compliance requirements for carrier-managed infrastructure
- Quick deployment needs (turnkey solution in 4-8 weeks)
- Bandwidth requirements under 10 Gbps per site
- Need for carrier SLA with service credits and support
Wavelength Services: Dedicated Optical Channels
High-capacity transport with customer-controlled Layer 2/3
Wavelength Services provide dedicated optical channels (lambdas) over the carrier's DWDM or CWDM infrastructure. Customer deploys their own Layer 2/3 equipment and controls protocols, while carrier manages the optical transport layer. Offers better price-per-bit than Layer 2 Transport at multi-gigabit speeds.
Wavelength Technologies
DWDM (Dense Wavelength Division Multiplexing)
Multiplexes 40-96+ wavelengths on single fiber pair using ITU-T grid (50 GHz or 100 GHz spacing). Each lambda carries 10G, 40G, 100G, or 400G. Enables massive capacity (40+ Tbps per fiber). Typical metro/long-haul deployment. Requires temperature-controlled lasers and optical amplifiers.
CWDM (Coarse Wavelength Division Multiplexing)
Multiplexes 8-18 wavelengths with wider spacing (20nm). Lower cost optics (no temperature control). Max distance ~80km without amplification. Ideal for metro applications. Each lambda typically 1G or 10G. Simpler, cheaper equipment vs DWDM.
OTN (Optical Transport Network)
ITU-T G.709 standard providing optical-layer framing, FEC, and OAM. Wraps client signals (Ethernet, Fibre Channel, etc.) for transport. Built-in error correction extends reach. Enables sub-wavelength multiplexing (ODUflex). Used in carrier-grade wavelength services.
Use Cases
- High-bandwidth needs (10G-400G per location)
- Organizations with network engineering expertise
- Protocol flexibility requirements (Ethernet, FC, custom)
- Multi-datacenter interconnect with low latency
- Scaling beyond Layer 2 Transport pricing sweet spot
- Long-term deployments justifying equipment CapEx
- Need for sub-millisecond latency (<0.5ms)
Dark Fiber: Unlit Infrastructure
Complete control and unlimited scalability
Dark Fiber provides unlit fiber strands leased from the carrier with no active equipment. Customer owns and operates all optical and networking gear, gaining complete protocol flexibility and unlimited bandwidth scalability. Highest upfront cost but best long-term economics for high-bandwidth, long-term deployments.
Dark Fiber Characteristics
Complete Infrastructure Control
Customer owns optical layer (lasers, amplifiers, DWDM/CWDM) and networking layer (routers, switches). Deploy any equipment, any protocol, any vendor. Upgrade independently—100G to 400G by swapping optics, no carrier dependency. Zero vendor lock-in.
Unlimited Bandwidth Scalability
Single dark fiber pair supports 40+ Tbps via DWDM (96 lambdas × 400G). Scale by adding wavelengths or upgrading optics without monthly cost increase. Future-proof: new technologies (800G, 1.6T) deployable on same fiber. Capacity limited only by customer equipment.
Long-Term Cost Efficiency
High upfront CapEx (€50k-500k equipment) offset by low monthly fiber rental (€200-1000/month). Break-even typically 2-4 years vs Layer 2 Transport. After break-even, 80-90% cost savings vs carrier services. Best ROI for 10G+ bandwidth over 5+ years.
Requires Expert Team
Demands in-house expertise: optical engineering (fiber loss budgets, dispersion), DWDM operations, network architecture, troubleshooting. Customer responsible for all monitoring, maintenance, and fault isolation. Not suitable for organizations without dedicated network team.
Use Cases
- Hyperscalers and cloud providers with massive bandwidth needs
- Financial institutions requiring ultra-low latency (<100μs)
- Enterprises with datacenter interconnect >10G sustained
- Organizations with in-house optical engineering teams
- Long-term deployments (5+ years) justifying CapEx
- Multi-protocol requirements (Ethernet + Fibre Channel + custom)
- Need for complete infrastructure control and zero vendor lock-in
Real-World Deployment Scenarios
How organizations choose connectivity approaches
Financial Trading Firm: Dark Fiber for Ultra-Low Latency
Profile: High-frequency trading firm requiring sub-100μs latency between trading datacenter and exchange colocation. Every microsecond of latency impacts profitability. Redundancy critical.
Solution: Dual dark fiber pairs (primary + backup) with customer-owned DWDM. Direct fiber route—no carrier aggregation. 100G Ethernet with precision time protocol (PTP). Total latency: 42μs over 8.4km.
Rationale: Layer 2 Transport adds 2-5ms switching latency—unacceptable for HFT. Wavelength Services still route through carrier aggregation (1-2ms). Dark fiber provides absolute minimum latency—speed of light only.
Result: 42μs latency (8.4km × 5μs/km fiber propagation). Competitive advantage worth €120k CapEx. Microsecond-level precision. Complete control over upgrades and monitoring.
Enterprise WAN: Layer 2 Transport for 50 Sites
Profile: Retail chain with headquarters and 50 stores requiring POS connectivity, inventory sync, and guest WiFi. IT team focused on applications, not network infrastructure.
Solution: E-LAN service (EVPN-based) connecting all 51 sites. Carrier-managed CPE at each location. 100 Mbps per store, 1 Gbps HQ. Carrier handles monitoring, troubleshooting, and expansion.
Rationale: No in-house optical expertise. Prefer predictable OpEx vs large CapEx. Need rapid store expansion (new sites in 4 weeks). Carrier SLA provides accountability and support.
Result: €75,000/month for 51-site network (€1,500/site average). Zero CapEx. Carrier-managed means IT focuses on business applications. Adding new stores: 4-week lead time with turnkey installation.
Cloud Provider: Wavelength Services for Multi-Datacenter
Profile: Regional cloud provider with 4 datacenters requiring high-bandwidth, low-latency interconnect. In-house network team with DWDM expertise. Scaling from 40G to 400G over 3 years.
Solution: Wavelength services: 4 lambdas (40G each) in ring topology. Customer-owned DWDM equipment with 400G-capable optics staged. Total capacity: 160G initial, expandable to 1.6T.
Rationale: Dark fiber CapEx too high for 4 routes (€500k+). Layer 2 Transport can't scale to required bandwidth economically. Wavelength provides balance: carrier manages fiber, customer controls Layer 2/3.
Result: €7,200/month OpEx (4 lambdas × €1,800). €160k CapEx (DWDM gear). Scaled 40G→100G by upgrading optics (€40k) without monthly cost increase. Sub-500μs latency between sites.
Hyperscaler: Dark Fiber for Massive Scale
Profile: Global cloud hyperscaler with 15 datacenters in France. Multi-Tbps interconnect requirements. Decades-long infrastructure timeline. Hundreds of network engineers on staff.
Solution: 96-strand dark fiber bundles on diverse routes between all datacenter pairs. Customer-owned 96-channel DWDM systems. 400G per lambda (38.4T per fiber pair). Redundant diverse paths.
Rationale: Layer 2 or Wavelength Services cannot scale to multi-Tbps per route. Complete control required for custom protocols, encryption, monitoring. Long-term (20+ year) deployment justifies massive CapEx.
Result: €5M CapEx (DWDM infrastructure across 15 sites). €180k/year OpEx (fiber rental). 38.4 Tbps per route. Upgrade path to 800G (76.8T) by swapping optics. Complete infrastructure ownership.
Decision Framework
Choosing the right connectivity approach
Bandwidth-Based Guidance
Under 1 Gbps: Layer 2 Transport (best economics, turnkey)
1-10 Gbps: Layer 2 Transport or Wavelength (compare 3-year TCO)
10-100 Gbps: Wavelength or Dark Fiber (depends on expertise and term)
100+ Gbps: Dark Fiber (only option with reasonable economics)
Expertise-Based Guidance
Basic Networking: Layer 2 Transport (carrier-managed, Ethernet only)
Advanced Networking: Wavelength Services (manage L2/3, carrier handles optical)
Optical Expertise: Dark Fiber (complete control, full responsibility)
Contract Term Guidance
1-2 Years: Layer 2 Transport (no CapEx commitment)
2-5 Years: Compare all options based on bandwidth and TCO
5+ Years: Wavelength or Dark Fiber (CapEx amortized, lower OpEx)
Control Requirements
Prefer Managed: Layer 2 Transport (carrier handles everything)
Hybrid Model: Wavelength (carrier optical, customer L2/3)
Maximum Control: Dark Fiber (customer owns infrastructure)
Frequently Asked Questions
Technical questions about connectivity options
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