RETN shifts half its backbone to 400G ZR+ pluggables

RETN’s backbone now carries half its IP/MPLS traffic over 400G coherent ZR and ZR+ pluggable optics, a milestone that signals the technology’s transition from selective optimization to standard infrastructure. The operator completed the rollout in 2025, upgrading segments spanning 300 to 950 kilometers, and has since designated IP-over-DWDM as the default design for all new backbone routes. This decision reflects broader industry pressure to reduce power consumption and equipment complexity amid rising traffic volumes and budget constraints in long-haul networks across Europe and Asia.

What changed

The migration replaces traditional transport layers with coherent pluggables inserted directly into routing platforms. This consolidation eliminates intermediate boxes, reducing hardware footprints and energy use per transported bit. However, it also collapses operational boundaries: optical performance engineering now sits closer to IP teams, and troubleshooting workflows must adapt to fewer isolation points. RETN’s production-scale deployment suggests the architecture is viable beyond lab environments, though adoption remains uneven due to variables like fiber quality, distance, and operational maturity.

Why the shift matters

The move aligns with a broader industry trend toward denser, lower-power backbone designs as AI, cloud, and content traffic continue to grow. By treating 400G coherent optics as a planning assumption rather than a special case, RETN is reworking backbone economics around power density and fiber utilization. For competitors, this sets a benchmark: pluggable-based IP-over-DWDM is no longer experimental but a baseline for future upgrades.

Yet challenges persist. Vendor interoperability, internal skill gaps, and optical margins can limit deployment in demanding long-haul environments. Operators must also monitor whether the architecture weakens transport-layer resilience or complicates fault isolation. RETN’s experience indicates that while the model reduces equipment and power costs, it demands stricter operational discipline to maintain service levels.

What to watch

The next phase will test whether 400G pluggables deliver sustained cost savings without increasing operational overhead. Observers should track how other carriers adapt their procurement strategies, particularly in regions with lower fiber quality or longer distances. If RETN’s model proves scalable, it could accelerate the adoption of coherent pluggables as standard infrastructure, reshaping backbone design assumptions across the industry.