Open and Disaggregated Optical, and IPoDWDM

The traditional optical network is a vendor-locked vertical stack: the transponder, the line system, and the management software all come from a single vendor and only interoperate among themselves. Two converging movements have broken that stack open. Open optical standardises the data models (OpenROADM, OpenConfig) and the optical interface specs (OIF 400ZR / OpenZR+) so terminals from one vendor can plug into a line system from another. IPoDWDM (“IP over DWDM”) goes further still: the coherent transponder shrinks to a QSFP-DD or OSFP pluggable that lives in a router faceplate, eliminating the dedicated transponder shelf and collapsing two equipment layers into one. This chapter covers the technology — data models, pluggable specs, form-factor envelopes, router-host integration — without naming vendors and without commenting on procurement economics.

Concept	What it says
OpenROADM and OpenConfig	The two dominant data models for open optical. OpenROADM is a multi-source-agreement YANG data model targeting line-system equipment (ROADMs, amplifiers, transponders) and defining standardised inter-vendor optical specs. OpenConfig is a vendor-neutral YANG project covering routers, transponders, and terminal devices through the `terminal-device` model.
400ZR / OpenZR+ / 800ZR	The coherent-pluggable interoperability specifications. 400ZR (OIF) defines a 400G interoperable interface for ~120 km amplified DWDM. OpenZR+ extends 400ZR with longer reach, additional rates, and stronger FEC. 800ZR / 800ZR+ double the symbol rate to ~96 Gbaud for 800G applications.
QSFP-DD / OSFP Form Factors	The two pluggable form factors that host coherent optics. QSFP-DD (Quad Small Form-factor Pluggable, Double Density) is the dominant 400G pluggable, ~14-20 W envelope. OSFP (Octal Small Form-factor Pluggable) has a slightly larger thermal envelope and is positioned for 800G+ applications.
IPoDWDM Operating Model	The architectural shift where the coherent transponder lives in the router’s QSFP-DD/OSFP cage instead of a dedicated transponder chassis. The router becomes its own optical terminal, and the demarc between IP and optical layers moves from a fibre patch panel to the pluggable’s electrical-optical interface inside the router.

Traditional Vendor-Locked Optical Architecture

In the traditional model, three layers stack vertically with proprietary boundaries between them:

flowchart TB
    ROUTER1["Router A<br/>(grey-optic SR4 / SR8 / DR4)"] -->|"Short-reach<br/>grey link"| XPDR1["Vendor-X<br/>transponder<br/>(coherent line side)"]
    XPDR1 -->|"DWDM<br/>colour"| OLS["Vendor-X line system<br/>(amplifiers + ROADMs)<br/>vendor-X NMS"]
    OLS -->|"DWDM<br/>colour"| XPDR2["Vendor-X<br/>transponder"]
    XPDR2 -->|"Grey link"| ROUTER2["Router B"]
    style ROUTER1 fill:#378ADD,stroke:#185FA5,color:#fff
    style ROUTER2 fill:#378ADD,stroke:#185FA5,color:#fff
    style XPDR1 fill:#1D9E75,stroke:#0F6E56,color:#fff
    style XPDR2 fill:#1D9E75,stroke:#0F6E56,color:#fff
    style OLS fill:#7F77DD,stroke:#534AB7,color:#fff

Properties of this model:

The transponder, the line system, and the optical management software all come from the same vendor.
The router connects to the transponder via short-reach grey optics — a separate optical link that costs power, port count, and a fibre patch.
Faults at the optical layer are visible only in the optical NMS; the router has no insight into the optical underlay.
The CapEx breakdown includes a dedicated transponder shelf for every router port that needs DWDM transport.

Open Line System (OLS) — The First Decoupling

An Open Line System standardises the optical interface between the line system and any conforming transponder. The line system is a black box that carries any wavelength meeting the published OSNR/CD/PMD/launch-power spec; the transponder can come from any vendor whose terminal meets the same spec.

flowchart TB
    ROUTER1["Router A"] -->|"Grey link"| XPDR1["Open transponder<br/>(any vendor)"]
    XPDR1 -->|"DWDM<br/>(per published<br/>OSNR/CD/PMD spec)"| OLS["Open Line System<br/>(any vendor)<br/>+ open management"]
    OLS -->|"DWDM<br/>spec-compliant"| XPDR2["Open transponder<br/>(any vendor)"]
    XPDR2 -->|"Grey link"| ROUTER2["Router B"]
    style ROUTER1 fill:#378ADD,stroke:#185FA5,color:#fff
    style ROUTER2 fill:#378ADD,stroke:#185FA5,color:#fff
    style XPDR1 fill:#D85A30,stroke:#993C1D,color:#fff
    style XPDR2 fill:#D85A30,stroke:#993C1D,color:#fff
    style OLS fill:#7F77DD,stroke:#534AB7,color:#fff

The OLS model alone delivers most of the operational decoupling: the line system can be replaced or upgraded independently of the transponders, and transponders can be sourced competitively. IPoDWDM is the further step that eliminates the dedicated transponder altogether.

Data Models — OpenROADM and OpenConfig

OpenROADM

The OpenROADM Multi-Source Agreement defines a YANG data model and a set of optical interoperability specifications targeting ROADM line systems. Two parts:

Device YANG — models for transponders, ROADMs, amplifiers, OSC, fibre, with leaf nodes for power, OSNR, channel state, and operational alarms.
Optical specifications — published per-channel OSNR floors, dispersion / PDL / PMD tolerance, frequency-grid, launch-power envelopes for each generation (W-class, MSA-100GHz, 200G/400G open coherent variants).

The aim is “any-to-any” interoperability: any conformant transponder must be able to interoperate with any conformant line system at the published spec.

OpenConfig

OpenConfig is a vendor-neutral YANG project — broader than just optical — covering routers, switches, transponders, and platforms. The openconfig-terminal-device model captures coherent-transponder operational state at the abstraction level of “logical channels” feeding “optical channels”: modulation format, symbol rate, FEC, central frequency, transmit power, OSNR, BER, pre-FEC error rate, and so on. This is the model most modern routers use to expose their embedded coherent optics to NMS automation.

Model	Scope	Maintainer	Adoption pattern
OpenROADM	Line systems + transponders, with optical interop spec	OpenROADM MSA	Carrier line-system deployments
OpenConfig terminal-device	Transponders + router-resident coherent optics	OpenConfig (vendor-neutral)	Cloud-scale and IP-led networks
ITU-T G.7711 / IETF CCAMP	Generic transport YANG	ITU-T / IETF	Crosslinks both above

Key Insight

OpenROADM and OpenConfig are not competing — they target overlapping but distinct slices. OpenROADM defines optical interop specs (the physical-layer compatibility); OpenConfig defines a vendor-neutral management surface (how an SDN controller talks to a coherent optic). Modern open networks use both layers.

TIP Phoenix

The Telecom Infra Project (TIP) Phoenix project, under TIP’s Open Optical & Packet Transport (OOPT) working group, defines an open, vendor-agnostic terminal-device specification and reference implementations. Phoenix targets a fully open coherent transponder — software, hardware specifications, and certification — usable in any conformant OLS.

Coherent Pluggable Evolution — 400ZR, OpenZR+, 800ZR

The coherent transponder used to be a half-rack chassis. A decade of integration has shrunk it to a 14-30 W pluggable that fits a router faceplate. The relevant specifications, in order of evolution:

Spec	Defining body	Line rate	Symbol rate	Modulation	FEC	Reach (typical)	Form factor target	Power envelope
400ZR	OIF	400 Gbit/s	59.84 Gbaud [1]	DP-16QAM	C-FEC (concatenated)	~120 km amplified DWDM, 75 GHz slot [1]	QSFP-DD, OSFP	~14-15 W
400ZR+ / OpenZR+	OpenZR+ MSA	100 / 200 / 300 / 400 Gbit/s	~60 Gbaud	DP-QPSK / 8QAM / 16QAM	Open FEC (stronger)	400-2500 km depending on rate	QSFP-DD, OSFP	~16-22 W
800ZR (draft)	OIF	800 Gbit/s	~118-130 Gbaud [2]	DP-16QAM	C-FEC class	~80-120 km amplified DWDM	QSFP-DD800, OSFP800	~18-25 W
800ZR+ (draft)	OpenZR+ MSA / OIF	800 Gbit/s	~118-130 Gbaud	PCS-shaped	Stronger FEC + PCS	Multi-hundred km	QSFP-DD800, OSFP800	~20-25 W

Note

400ZR is published (OIF-400ZR-01.0) [1]. 800ZR is in active development at OIF [2]; draft symbol rates and reach figures are provisional and may shift before ratification.

Rule of Thumb

400ZR is the metro-amplified-DWDM workhorse (~120 km). 400ZR+ / OpenZR+ extends to long-haul reach by trading rate for OSNR margin. 800ZR mirrors 400ZR’s metro positioning at double the rate; 800ZR+ extends to longer reaches when symbol rate and PCS allow.

Why the Reach Differs Across the Family

Reach is set by the OSNR budget (and nonlinear margin):

400ZR uses a relatively standard FEC; the design point is a ~120 km amplified link with ~25-26 dB launch OSNR.
400ZR+ uses a more powerful open FEC, gaining ~3-4 dB of OSNR margin and unlocking long-haul reach.
800ZR doubles symbol rate, which costs +3 dB of required OSNR — and matches the 400ZR metro reach because the FEC and link engineering are tuned identically.
800ZR+ layers PCS on top to recover the doubled-symbol-rate OSNR penalty plus add reach margin.

QSFP-DD and OSFP Form Factors

Pluggable coherent optics live in two form factors:

flowchart LR
    subgraph QSFP_DD ["QSFP-DD"]
        QHEAT["Heat dissipation:<br/>via host cage<br/>fins on top"]
        QPWR["Power envelope:<br/>14-20 W typical<br/>(class 8 = 14 W,<br/>some hosts qualify higher)"]
        QLANES["Electrical:<br/>8 lanes x 50 Gbaud<br/>(QSFP-DD800: 8 x 100 Gbaud PAM4)"]
    end
    subgraph OSFP_FF ["OSFP"]
        OHEAT["Heat dissipation:<br/>integrated heat sink<br/>on module body"]
        OPWR["Power envelope:<br/>up to ~25-30 W<br/>(thermal headroom)"]
        OLANES["Electrical:<br/>8 lanes x 50 Gbaud<br/>(OSFP800: 8 x 100 Gbaud PAM4)"]
    end
    style QPWR fill:#1D9E75,stroke:#0F6E56,color:#fff
    style OPWR fill:#1D9E75,stroke:#0F6E56,color:#fff
    style QHEAT fill:#7F77DD,stroke:#534AB7,color:#fff
    style OHEAT fill:#7F77DD,stroke:#534AB7,color:#fff
    style QLANES fill:#BA7517,stroke:#854F0B,color:#fff
    style OLANES fill:#BA7517,stroke:#854F0B,color:#fff

Property	QSFP-DD	OSFP
Module dimensions	Compact (familiar QSFP footprint)	Slightly larger
Heat sink	Host cage fins	Integrated on module body
Typical thermal envelope	14-20 W	18-30 W (more headroom)
Electrical lanes	8 × 50 Gbaud (DD), 8 × 100 Gbaud PAM4 (DD800)	Same lane structure
Backwards compatibility	Accepts QSFP+ / QSFP28 in same cage	OSFP-only
Coherent pluggable density	High (router faceplate full of 400ZR)	Slightly lower density, more thermal margin
Typical positioning	Mainstream router pluggable	High-power, premium coherent

Warning

Pluggable thermal envelopes are not advisory — exceeding the host’s qualified envelope causes the optic to throttle, errors to climb, and in worst cases the module to mark itself failed. Qualifying high-power coherent pluggables (>14 W) requires the host router to publish thermal-class support; not every router model qualifies every wattage.

IPoDWDM — Coherent Optics in the Router Faceplate

In IPoDWDM, a 400ZR / OpenZR+ / 800ZR pluggable lives in the router’s QSFP-DD or OSFP cage. The router faceplate becomes the optical terminal; there is no separate transponder.

flowchart TB
    subgraph TRAD ["Traditional terminal"]
        T_RA["Router A<br/>grey port"] --> T_X1["Transponder A<br/>(separate chassis)"]
        T_X1 --> T_OLS["Open Line System"]
        T_OLS --> T_X2["Transponder B<br/>(separate chassis)"]
        T_X2 --> T_RB["Router B<br/>grey port"]
    end
    subgraph IPO ["IPoDWDM"]
        I_RA["Router A<br/>+ 400ZR pluggable<br/>in QSFP-DD cage"] --> I_OLS["Open Line System"]
        I_OLS --> I_RB["Router B<br/>+ 400ZR pluggable"]
    end
    style T_RA fill:#378ADD,stroke:#185FA5,color:#fff
    style T_RB fill:#378ADD,stroke:#185FA5,color:#fff
    style T_X1 fill:#D85A30,stroke:#993C1D,color:#fff
    style T_X2 fill:#D85A30,stroke:#993C1D,color:#fff
    style T_OLS fill:#7F77DD,stroke:#534AB7,color:#fff
    style I_RA fill:#1D9E75,stroke:#0F6E56,color:#fff
    style I_RB fill:#1D9E75,stroke:#0F6E56,color:#fff
    style I_OLS fill:#7F77DD,stroke:#534AB7,color:#fff

Aspect	Traditional terminal	IPoDWDM
Equipment count	Router + dedicated transponder shelf	Router only
Power per terminal	Router port + transponder card (~150-300 W per coherent line side)	Router port + pluggable (~14-25 W)
CapEx	Two boxes per terminal	One box per terminal
OpEx	Two NMS surfaces, two install/maintenance teams	One NMS surface
Per-port performance ceiling	High (chassis-class transponder, premium optics, high-tap DSP)	Lower (pluggable thermal envelope caps DSP / FEC / launch power)
Reach	Up to thousands of km (long-haul)	Pluggable-class reach (typically metro to extended-metro for 400ZR; longer for 400ZR+)
Fault isolation	Optical NMS visibility independent of IP layer	Faults bridge IP and optical alarms — needs correlation
Control plane	Separate optical control plane	Router OS owns the coherent optic via OpenConfig
Thermal coupling	Router and transponder cooled independently	Router and pluggable share faceplate thermals

Key Insight

IPoDWDM is not strictly better than the traditional terminal — it is a different operating point. For metro DCI, where reach demands are modest and CapEx/OpEx pressure is intense, IPoDWDM is increasingly the default. For long-haul backbone, where the highest per-channel performance matters more than CapEx, dedicated transponders still win on raw performance.

Router-Host Integration — Telemetry and Alarm Correlation

Putting a coherent optic inside a router fundamentally changes how the optical layer is observed. The router OS becomes responsible for:

Telemetry surfaces. Per-channel OSNR, pre-FEC BER, post-FEC BER, CD readout, PMD/DGD, transmit power, receive power, frequency offset — all exposed via the OpenConfig terminal-device model and streamed to the NMS via gNMI/gRPC.
Alarm correlation. A router-port LOS event might be an IP-layer cable cut or an optical-layer wavelength failure. The router OS must correlate the pluggable’s alarms (loss-of-light, FEC threshold-crossed, frequency-out-of-range) with its own IP-layer state and present a single coherent fault picture.
Provisioning surface. The pluggable’s transmit frequency, modulation format, FEC mode, and transmit power are set by the router OS via the OpenConfig model — historically these were optical-NMS-only parameters.
Optical-layer visibility for the IP planner. Path computation must consider OSNR margin, ROADM cascade depth, and CD/PMD budget — concerns that used to be hidden in the optical layer’s planning tool.

The convergence forces tighter cooperation between IP and optical engineering teams: routers are now optical terminals, optical paths are now visible to BGP and IS-IS, and a multilayer SDN controller is increasingly the single source of truth.

Summary

The optical-network stack is opening on two axes simultaneously. Open data models (OpenROADM, OpenConfig terminal-device) and open optical interop specs (OIF 400ZR, OpenZR+, 800ZR) decouple the line system from the transponders so they can come from different vendors. IPoDWDM collapses the transponder layer entirely into the router’s pluggable cage, eliminating a hardware tier at the cost of pluggable-class per-port performance and forcing the router OS to absorb optical telemetry, alarms, and provisioning. The two trends together are reshaping how service providers and hyperscale operators source, deploy, and operate the optical underlay — even though raw long-haul performance still tilts toward dedicated transponders.

References

Standards and specifications (ITU-T / IETF / OIF / MSA)

OIF 400ZR Implementation Agreement (OIF-400ZR-01.0). https://www.oiforum.com/documents/
OIF 800ZR / 800LR Implementation Agreement (OIF, ongoing). https://www.oiforum.com/documents/
OpenZR+ MSA specification. https://www.openzrplus.org/
OpenROADM Multi-Source Agreement — device YANG and optical specifications. https://www.openroadm.org/
OpenConfig — vendor-neutral YANG project, including openconfig-terminal-device. https://www.openconfig.net/
OIF Common Management Interface Specification (CMIS). https://www.oiforum.com/documents/
ITU-T G.709/Y.1331 — Interfaces for the Optical Transport Network (06/2020). https://www.itu.int/rec/T-REC-G.709
ITU-T G.872 — Architecture of optical transport networks (10/2017). https://www.itu.int/rec/T-REC-G.872
IETF RFC 9093 — YANG Data Model for Layer 0 Types. https://www.rfc-editor.org/rfc/rfc9093
Telecom Infra Project (TIP) — Open Optical & Packet Transport (OOPT) Phoenix project. https://telecominfraproject.com/oopt/

Form-factor MSAs

QSFP-DD MSA specification. https://www.qsfp-dd.com/
OSFP MSA specification. https://osfpmsa.org/

Books

R. Ramaswami, K. N. Sivarajan, G. H. Sasaki, Optical Networks: A Practical Perspective, 3rd ed., Morgan Kaufmann, 2009.

Transport Network Guide

Explorer

Ch 08 — Open and Disaggregated Optical, and IPoDWDM

Open and Disaggregated Optical, and IPoDWDM

Traditional Vendor-Locked Optical Architecture

Open Line System (OLS) — The First Decoupling

Data Models — OpenROADM and OpenConfig

OpenROADM

OpenConfig

TIP Phoenix

Coherent Pluggable Evolution — 400ZR, OpenZR+, 800ZR

Why the Reach Differs Across the Family

QSFP-DD and OSFP Form Factors

IPoDWDM — Coherent Optics in the Router Faceplate

Router-Host Integration — Telemetry and Alarm Correlation

Summary

See Also

References

Standards and specifications (ITU-T / IETF / OIF / MSA)

Form-factor MSAs

Books

Graph View

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