Author: Marcin Bała, MSc Eng., Chief Technology Officer
Published: March 2026 | Updated: March 2026 | Reading time: 15 minutes
The backbone network was approaching the limits of its capacity. Classical scaling was becoming increasingly expensive. The operator decided on a thorough modernization toward an IP over DWDM architecture — no downtime, no new cable layer.
The Problem: Growing Traffic, Growing Costs, Shrinking Room to Maneuver
A Polish wholesale operator managing over 4,000 km of fiber-optic network carries traffic for other operators, data centers, 5G networks, and international connections. The rapid surge in bandwidth demand began hitting the limits of the existing architecture, and traditional scaling methods were no longer economically viable.
Adding more transponders was not the answer. A change of architecture was needed — not another layer of hardware.
Solution: IPoDWDM — the IP Layer Directly on Optics
Instead of classic transponders and separate DWDM systems, coherent modules were deployed directly in the routers. 18 transmissions at 400G and 12 at 100G were launched covering central and southern Poland — all on the existing DWDM infrastructure, without any downtime.
80%
reduction in operational costs across the entire network
vs. classic transponder-based solutions
10×
lower power consumption than classic transponders
coherent modules directly in routers
300G
stable transmission over ~1,000 km without external transponders
8QAM modulation, domestic-international route
Before and After — What Specifically Changed?
The modernization did not require building a new fiber layer. Coherent modules were slotted directly into router ports and connected to the existing DWDM infrastructure.
Before Modernization
✕Separate DWDM systems and transponders
✕High power consumption and heat output
✕Complex management of multiple layers
✕Scaling = buying more devices
✕Limited long-distance capabilities
After Modernization
✓Coherent modules directly in routers
✓10× lower power consumption per bit
✓Single layer — fewer devices, simpler management
✓Scaling without changes to the optical layer
✓300G over ~1,000 km without external transponders
Step-by-Step Modernization Process
The project was executed in phases, without downtime, without building new cable infrastructure.
01
Audit and IPoDWDM Architecture Design
Designing a network topology that optimizes both capital and operational costs — including power consumption and device maintenance costs.
Starting point
02
Deployment of 400G Routers with Coherent Modules
18 transmissions at 400G and 12 at 100G — central and southern Poland. Modules connected to the existing DWDM infrastructure without downtime and without new cabling.
Phase 1 — completed
03
Long-Distance Testing on ~1,000 km Routes
Verification of 400G modules in 8QAM mode on domestic and international routes. Result: 300G stable transmission without external transponders.
Confirmed
04
Expansion to Northern Poland
The next phase of modernization — creating a unified, high-throughput, energy-efficient backbone network as a platform for wholesale services and data centers.
Phase 2 — in progress
FAQ — IPoDWDM
In the classic architecture, the router does not see the optical layer — a separate transponder sits between them. IPoDWDM eliminates this intermediary. The coherent module slots directly into the router port and handles both the IP and optical layers simultaneously. The result: fewer devices, less rack space, less power, and simpler management.
No. Coherent modules connect into the existing DWDM infrastructure — without building a new fiber layer and without downtime. Modernization is carried out in phases on a live network.
Coherent modules consume up to ten times less energy than classic transponder solutions. Across the entire backbone network, this translates to an operational cost reduction of up to 80%. Lower power consumption also means less heat, which reduces cooling costs and supports ESG goals.
In 8QAM mode, 400G modules achieve stable 300G transmission over distances up to approximately 1,000 km without external transponders. On shorter routes up to 120 km, they operate at full 400G. The same hardware handles both short DCI links and international connections.
Modernization makes sense when network capacity is approaching the limits of the current architecture, maintenance and energy costs are growing faster than revenues, or you are planning expansion over the next 3–5 years. The earlier the modernization, the longer you benefit from lower operational costs.
Modernization is carried out in phases — region by region, without shutting down the live network. The actual deployment process does not require any production downtime.
Yes. The 400G ports and IPoDWDM architecture allow bandwidth scaling without costly changes to the optical layer. When 800G or 1600G modules become available, you simply swap the module in the existing router port — the cable and DWDM infrastructure remains unchanged.
Sources:
IPoDWDM project documentation
GBC Photonics 100G and 400G coherent module testing
