--- title: "LPO or Retimed Optics? Qualify the Host Before Swapping the Module" description: "Leviathan Systems — Technical content Published 2026-10-20; updated 2026-10-20." canonical: "https://www.leviathansystems.co/articles/gpu-network-lpo-versus-retimed-optics" last-updated: "2026-10-20" --- # LPO or Retimed Optics? Qualify the Host Before Swapping the Module Leviathan Systems — Technical content Published 2026-10-20; updated 2026-10-20. LPO removes the pluggable optical module's DSP/retimer function and relies on a suitable host and linear signal path. A matching cage, advertised rate and fiber connector therefore cannot establish equivalence to a retimed module. Compare the supplier-supported host, module and complete link profile before accepting the substitution; an unchanged fiber assembly can remain a candidate while that decision is unresolved. ## Locate the signal conditioning before comparing the parts In a DSP-based retimed pluggable, the module performs digital signal processing in both transmit and receive paths. It introduces a processing stage between the host electrical interface and the optical path. Retiming does not eliminate the need for a supported host or suitable fiber channel. An LPO module omits that DSP/retimer stage. Signal correction instead depends on the host's SerDes, the circuitry that transmits and receives the high-speed electrical signals. Equalization compensates for signal degradation along the path. Arista's July 9, 2025 deployment guide describes this division of work in its LPO Technology Primer: correction is handled by the NIC and/or remote switch SerDes. Removing the module DSP does not remove the need for signal processing from the system. Optical conversion remains in the pluggable module. Linear does not mean a passive fiber assembly or a linear active copper cable. CPO makes a different packaging change by integrating optics with the switch package; the related CPO article covers that separate buying decision. References: [M1](https://www.lpo-msa.org/home/faqs.html), [A1](https://www.arista.com/assets/data/pdf/Arista-Broadcom-AI-Networking-Deployment-Guide.pdf), [B1](https://www.broadcom.com/info/optics/cpo) ## Qualify the actual host path, not just its ASIC family The electrical path from the ASIC to the pluggable module still matters with LPO. Broadcom's architecture discussion explicitly retains interconnect losses in its LPO comparison. A capable chip alone does not describe the complete host implementation. The purchasing consequence is to ask the equipment supplier which exact host model, hardware revision and port population support the proposed module and profile. Carry the applicable software or firmware release reference where support depends on it. Request the supplier's qualification evidence for that combination, including the host electrical channel; a chip-family name or an empty compatible cage is an incomplete answer. This evidence should describe a supplied, supported implementation. The buyer does not need to invent equalizer settings or derive an electrical loss allowance to complete the quote comparison. If supporting a proposed LPO module requires a different host implementation, that host change belongs in the offered package and its price. References: [B1](https://www.broadcom.com/info/optics/cpo), [M1](https://www.lpo-msa.org/home/faqs.html) ## Name the released optical profile The LPO MSA's March 25, 2025 announcement identifies the released 100G-DR-LPO specification as operating at 100 Gb/s per lane and covering 100 Gb/s, 200 Gb/s, 400 Gb/s and 800 Gb/s Ethernet parallel single-mode links. Its scope includes electrical and optical requirements. This is a named profile for discussing an 800G DR-LPO offer, rather than a definition of every LPO product. The MSA separately announced 400G-FR4-LPO on September 25, 2025, using four wavelength-division-multiplexed lanes. The published portfolio therefore includes a separate FR4 profile as well as DR. The two releases do not establish interchangeable optical interfaces. Ask each offer to identify its exact profile and revision alongside the module parts and endpoint modes. Specification release establishes a technical reference; it does not identify the qualified host or orderable package for a project. References: [M2](https://www.lpo-msa.org/news/lpo-msa-announces-release-of-specification-for-linear-pluggable-optica), [M3](https://www.lpo-msa.org/news/lpo-msa-announces-release-of-400g-fr4-lpo-specification-for-linear-plu) ## Qualify a mixed LPO/retimed link separately The MSA FAQ says LPO optical specifications differ from those of fully retimed modules. It describes interoperation with a retimed module as possible through an engineered link outside the scope of its specifications, while also discussing mixed architectures on its roadmap. Consequently, neither a shared DR label nor a roadmap statement establishes a supported mixed endpoint pair. Ask for evidence covering the actual combination. The same evidence rule avoids rejecting every mixed proposal as impossible: a supplier-supported engineered combination and an unspecified pairing are different offers. References: [M1](https://www.lpo-msa.org/home/faqs.html) ## Compare two 800G DR offers with the same declared interfaces Consider a fictional purchase comparison for one intended 800 Gb/s Ethernet connection. Both offers declare the same host cage form factor and the same parallel single-mode fiber interface, connector, polish and mapping. Both allocate one external fiber assembly, F01, to that connection. These are stipulated quote fields, not specifications inferred from an 800G label. Offer A names DSP-based retimed modules at both ends. For this example, the supplier has identified support for those parts on the stated hosts and channel. Offer B proposes LPO modules for the same connection but leaves the actual host electrical channels and their support evidence unspecified. No real product SKU or qualification result is represented by either offer. At this point B is an architecture proposal with a missing host qualification, rather than a defined module substitution. Preserve F01 as a candidate assembly: its declared fiber-facing fields still agree with the request. Do not mark it approved for B, because the complete offered endpoint and channel requirements have not been established. Equally, the missing host evidence alone does not establish that F01 must be replaced. The immediate comparison result is precise: the planned connection remains one connection, the external assembly remains one candidate item, and B's host/module/link package is unresolved. There is no supported basis yet for treating B as an equivalent substitution or declaring a performance winner. ## Turn the alternative into a defined package To complete B, the supplier must return the exact supported hosts and relevant ports, module parts at both ends, applicable operating and release references, optical profile, and the channel requirements against which F01 is assessed. If one end remains retimed, the return must cover that particular mixed combination. The equipment and network owners then have a defined alternative to review. Three purchasing outcomes follow. If B is supported on the originally stated hosts, compare it as a module alternative with the confirmed external channel. If B needs different hosts, compare the revised host-and-module package, including any physical scope changes. If the supplier cannot substantiate B, retain the stipulated supported A package or seek another defined offer. An unspecified LPO option cannot supply the missing qualification by being cheaper on the module line. Removing a DSP identifies an architectural difference; it does not supply a measured whole-system energy or cost saving. Compare any claimed benefit using evidence for the actual alternatives, including a required host change. No numerical power, latency or total-cost ranking is established here. ## Scope the external cabling work after the architecture decision Leviathan's structured cabling service covers agreed physical routing, dressing, connections, labeling, checks and handoff records using customer-furnished or separately sourced materials. The equipment and network owners retain acceptance of the host/module combination and optical channel. This article explains a buying decision; it supplies no equalization procedure or approval to exchange modules on equipment. For a physical project inquiry, share the selected host and module identities, supplier-supported endpoint profile, F01 or the revised assembly schedule, site location, approved routes and requested installation window. Identify the appointed materials supplier and the physical records and checks required. Instrument testing needs separately confirmed methods, instruments, personnel and criteria. The structured cabling service and project inquiry links below lead to discussion of that defined physical scope. References: [L1](https://www.leviathansystems.co/services/structured-cabling) ## Primary sources - [M1 — LPO MSA: Frequently Asked Questions](https://www.lpo-msa.org/home/faqs.html). Checked 2026-10-19. Official indexed FAQ body read; direct opens timed out. Architecture and mixed-link scope only; roadmap language is not current hardware support. - [A1 — Arista and Broadcom: High-Performance Ethernet Networking for Artificial Intelligence Systems](https://www.arista.com/assets/data/pdf/Arista-Broadcom-AI-Networking-Deployment-Guide.pdf). Checked 2026-10-19. July 9, 2025, 07-0018-01: page 24 LPO Technology Primer and page 25 issue date read. Used for host SerDes signal-correction responsibility, not its numerical savings, reliability rankings, product qualification or configuration instructions. - [B1 — Broadcom: Co-Packaged Optics architecture comparison](https://www.broadcom.com/info/optics/cpo). Checked 2026-10-19. Official indexed body read; ordinary open returned no substantive text. Used only for ASIC-to-module interconnect losses and the packaging distinction. Marketing superiority claims and LRO terminology are not adopted. - [M2 — LPO MSA: Release of the 100G-DR-LPO specification](https://www.lpo-msa.org/news/lpo-msa-announces-release-of-specification-for-linear-pluggable-optica). Checked 2026-10-19. Official indexed March 25, 2025 announcement body read; direct opens timed out. Preserves 100 Gb/s per lane and the listed Ethernet parallel-SMF rates. No product availability, future-lane completion or project qualification inferred. - [M3 — LPO MSA: Release of the 400G-FR4-LPO specification](https://www.lpo-msa.org/news/lpo-msa-announces-release-of-400g-fr4-lpo-specification-for-linear-plu). Checked 2026-10-19. Official indexed September 25, 2025 announcement body read; direct opens timed out. Establishes a separately released four-WDM-lane FR4 profile; its reach is not reproduced or applied to DR. - [L1 — Leviathan structured cabling: current service implementation](https://www.leviathansystems.co/services/structured-cabling). Checked 2026-10-19. Read the local public-page implementation at app/services/structured-cabling/page.tsx and the existing CTA route. Production was not accessed. Supports conditional physical scope only. ## Related Leviathan resources - [Structured cabling: agree the physical installation and handoff](/services/structured-cabling) - [Discuss the external cabling scope for your selected optics package](/contact?service=structured-cabling&from=/articles/gpu-network-lpo-versus-retimed-optics) - [400G, 800G and 1.6T: read the complete interface specification](/articles/400g-800g-1600g-optics-selection) - [CPO or pluggable optics: compare the packaging boundary](/articles/co-packaged-optics-cabling-deployment-boundary) - [DAC, AOC and AEC: compare the actual cable assembly](/articles/dac-vs-aoc-vs-aec-cabling) ## Define the physical scope for the selected optical package Share the supported endpoints, module and assembly list, site location, routes and required handoff. We can discuss the physical tasks, supply responsibilities and availability. [Discuss the scope](/contact?service=structured-cabling&from=/articles/gpu-network-lpo-versus-retimed-optics)