400G OpenZR+ in a live network: 300G over 1000 km directly from the router, no transponder required
A datasheet tells you what a module should do on an ideal path. A field trial tells you what it actually does on your specific route. In a national carrier's production IP/MPLS backbone, we plugged a GBC Photonics QSFP-DD 400G OpenZR+ module directly into a router and achieved a stable 300G at 8QAM over a nearly 1,000 km route from Poznań to Frankfurt. No transponders, no muxponders, just the existing DWDM system.
Results at a glance
All figures below are based on measurements from a production network, not a datasheet, lab, or simulation. The most demanding scenario was the route from Poznań to Frankfurt, nearly 1,000 km, within an active IP/MPLS backbone.
To our knowledge—as we have found no public description of a comparable deployment—this is one of the first publicly documented 300G 8QAM OpenZR+ links over approximately 1,000 km in the CEE region within a production IP/MPLS backbone, without the use of transponders.
A catalog tells you what a module should do. A field trial tells you what it actually does on your route.
Why this test is different from the catalog
The 400G module market is defined by datasheet ranges: 120 km, 480 km with an asterisk, or up to 600 km in 8QAM. These are nominal values based on lab conditions or ideal path budgets. We measured a real international route of approximately 1,000 km, including intermediate nodes and amplifiers, in an active carrier network, and achieved a stable 300G directly from the router. A datasheet shows what a module can do under ideal conditions. Our measurement shows what it actually does on a route of this class.
Context and configuration
We conducted the test with a national IP/MPLS infrastructure carrier as part of a backbone upgrade to IPoDWDM. We deployed 18 400G transmissions and 12 100G transmissions across central and southern Poland.
We plugged GBC Photonics QSFP-DD 400G OpenZR+ modules directly into routers at both ends, without transponders, muxponders, or intermediate devices, connecting them to the carrier's existing DWDM system. We set up the channel from the module level in about 10 seconds and configured compatibility with active equipment via SRD (Smart Recode Device)—a level of programmability not offered by vendor-locked modules.
Result: stable 300G over 1,000 km
The 100G and 300G transmissions integrated flawlessly. The 400G modules in 8QAM mode provided a stable 300G on the route from Poznań to Frankfurt, directly from the router, without external transponders. We were close to the full 400G capacity, which is why work is underway on newer 400G/8QAM versions for more challenging paths.
Why were we able to exceed 600 km? It was due to favorable path conditions: modern fiber, few intermediate nodes, high transmitter OSNR, and O-FEC margin. However, this does not mean 1,000 km is achievable on every route.
A stable 300G over approximately 1,000 km in a live network is a result at the very edge of what the current generation of pluggables can do.
Why 300G instead of 400G: it's physics, not module quality
16QAM provides 4 bits per symbol, offering the highest throughput, but the symbols are packed closely together, requiring a higher OSNR and limiting the range to a few hundred kilometers. 8QAM provides 3 bits per symbol; the constellations are less densely packed, which lowers the required OSNR and increases the margin.
For a 1,000 km route with multiple nodes, the OSNR budget is tight. Even with a transmitter OSNR of 43 dB, 16QAM is at the limit of its generation on this path. For an operator, this means a simple rule: 300G for the longest routes, 400G where the path quality is better. Modulation mode is an operational parameter, not a design one, so you can run 300G/8QAM today and upgrade later without replacing hardware.
The difference between 300G and 400G is determined by the physics of the path, not the quality of the module.
Hidden differentiator: 0 dBm output power
Standard coherent pluggables transmit at -10 dBm, while DWDM systems typically expect between -3 and 0 dBm at the multiplexer input. A -10 dBm module therefore requires an EDFA before the mux, adding another device, cost, and point of failure. The GBC Photonics module transmits at 0 dBm thanks to built-in amplifiers, allowing it to be plugged into existing DWDM systems without an EDFA and without downtime.
| Parameter | Typical 400ZR / ZR+ pluggable | GBC Photonics 400G OpenZR+ |
|---|---|---|
| Output power | −10 dBm | 0 dBm |
| EDFA before the mux | Usually required | Usually unnecessary |
| Entry into an existing DWDM | With path modification | No modification |
To be fair: higher output power is an advantage on matched paths. In a densely populated spectrum, you must verify non-linearities and compatibility with the line system, and the "no EDFA" claim applies to systems operating in the -3 to 0 dBm window, not every network.
Operational effects in IPoDWDM architecture
Moving the coherent layer from a separate transponder shelf directly into the router changes the operational balance of the entire node.
| Parameter | Classic transponder | Coherent pluggable (IPoDWDM) |
|---|---|---|
| Rack space | A separate shelf | A slot in the router |
| Power consumption | High | Up to 10× lower |
| Number of devices and points of failure | More | Fewer |
| Channel provisioning | A separate layer | From the module, ~10 s |
| Proof of operation | None | Field trial 300G / 1000 km |
On a network scale, this reduces OPEX by up to 80% compared to a classic transponder, muxponder, and ROADM stack. The exact value depends on the base architecture and investment horizon, which is why we calculate TCO for each case individually. Lower power consumption also supports ESG strategies.
Four takeaways for network planning
First, 300G without transponders over 1,000 km is available today, in production, on existing DWDM, and is sufficient for most backbones in Poland and the CEE region. Second, the limit for pluggables is further than many operators assume, as this is a real international route, not a short DCI link. Third, the modulation mode is an operational parameter: start at 300G/8QAM and migrate higher without replacing hardware. Fourth, modernization is possible without replacing the optical layer, provided the 0 dBm output power is compatible with your system.
Scope and conditions
The 300G result over approximately 1,000 km applies to this specific route, so do not extrapolate it to every link. Reach depends on the number of nodes, fiber quality, splices, amplifiers, and channel width. 400G OpenZR+ operates at approximately 60 Gbaud and requires a channel width of at least 75 GHz, which means a maximum of 200G per channel on a 50 GHz grid. Therefore, we measure distance and OSNR and verify channel widths before deployment.
For full verifiability, our publication includes: fiber type (e.g., G.652D), the number and type of nodes, amplifiers and ROADMs, spectrum occupancy, OSNR and receiver margin (rather than just transmitter specifications), uptime under production traffic, and FEC statistics.
This test demonstrates the technology's potential, not a guarantee for every route, and this transparency is what distinguishes a field trial from a catalog specification with an asterisk.
Check it out for your own routes!
FAQ:
Frequently asked questions
400G OpenZR+, a 300G field trial over roughly 1000 km, IPoDWDM architecture
Does 400G OpenZR+ achieve 300G over 1000 km?
Yes. In a field trial on a production IP/MPLS backbone, the GBC Photonics QSFP-DD 400G OpenZR+ module in 8QAM mode achieved a stable 300G on the route from Poznań to Frankfurt, close to 1000 km, straight from the router and without external transponders. The result applies to this specific route and depends on the path conditions.
How does a field trial differ from datasheet reach?
A datasheet quotes nominal values from a lab or from a budget on an ideal path, for example "up to 600 km in 8QAM". A field trial is a measurement on a real international route, with intermediate nodes and amplifiers, in a live carrier network. It shows what the module actually does on a route of this class, not what it can do under ideal conditions.
Why did the module reach 300G and not 400G?
It is the physics of the path, not the quality of the module. 16QAM (400G) packs 4 bits per symbol and requires the highest OSNR, which drops the reach to a few hundred km. 8QAM (300G) is 3 bits per symbol, with lower required OSNR and a larger margin. Over roughly 1000 km with nodes, the OSNR budget is too tight for 16QAM, despite a transmitter OSNR of 43 dB.
What does 0 dBm output power give in a coherent module?
Typical coherent pluggables transmit at around −10 dBm and require an EDFA before the multiplexer, because DWDM systems expect −3 to 0 dBm at the input. The GBC Photonics module transmits at 0 dBm thanks to built-in amplifiers, which lets it be plugged into an existing DWDM without an extra EDFA and without downtime. The result is less hardware, lower cost and fewer points of failure.
Can the 300G over 1000 km result be transferred to any route?
No. Reach depends on the number of nodes, fibre quality, splices, amplifiers and channel width. 400G OpenZR+ runs at around 60 Gbaud and requires a channel at least 75 GHz wide, so on a 50 GHz grid the maximum is 200G per channel. Before deployment we measure distance and OSNR and verify channel widths.
What is IPoDWDM architecture?
IPoDWDM integrates the IP layer directly with the optical DWDM layer: a coherent pluggable module is installed straight into the router, without separate transponders and muxponders. The result is lower power consumption, up to 10 times lower, fewer devices in the rack and an OPEX reduction of up to 80% compared with the classic transponder, muxponder and ROADM stack.
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