Q&A BROADCOM LINEAR PLUGGABLE OPTICS
LINEAR PLUGGABLE OPTICS:
A REVOLUTION IN THE MAKING? Linear Pluggable Optics (LPO)s is revolutionising the way data centres, telecommunication networks, and enterprise IT infrastructures manage and transmit data. This cutting-edge technology leverages modular optical transceivers, which have a number of advantages including lower power consumption and greater reliability than those currently in use. Optical Connections editor Peter Dykes spoke with Laurent Hendrichs , senior product line manager of high-speed Ethernet adapters and Pete Del Vecchio , Data Centre Switch Product Line Manager at Broadcom, to find out more about this emerging technology.
What factors are driving the development of LPO?
What are the main technical differences between LPO and pluggables in common use today
What sort of throughput speeds can LPOs achieve currently and in the future? 800G and 400G LPO transceivers are available today. The current target of OIF and the LPO MSA is
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(e.g. ZR, ZR+ etc)?
It depends on who you ask. Hyperscalers view it as a way to improve AI compute density by
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The essential difference is the elimination of the DSP from the optical module made possible by
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reducing the power consumed in the network, thereby leaving more power available for GPUs. Network reliability is a second driver. Simpler modules with fewer active components are inherently more reliable than conventional designs. However, more importantly, the lower power of LPO transceivers enables them to run at lower temperatures, which considerably improves reliability. Broadcom estimates a 3x improvement in MTTF (Mean time to failure) for LPO vs conventional optics. Server vendors like LPOs for their low power consumption. This is especially important for network adapters deployed in hot-aisle configurations, where the optics are cooled by hot exhaust air coming from inside the server. In such configurations, it is particularly challenging to cool conventional optical transceivers. LPO transceivers, in contrast, require much less cooling airflow due to their lower power. Broadcom estimates that LPOs offer up to 40-60% power reduction over conventional equivalents. Finally, cost-sensitive users appreciate the lower cost of LPOs made possible by the elimination of the DSP inside the module.
100G serial links. Work is already in progress, however, for 200G serial.
the advanced capabilities of the SerDes in the latest generation of Ethernet NIC and switch ASICs. As an example, Broadcom has included in their recent SerDes design features that were previously only found in optical DSPs. With LPO transceivers, equalisation or reconditioning of the signal is therefore done inside the NIC or switch ASIC.
Where does LPO fit into the future marketplace for pluggables?
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We expect to see multiple technologies coexist in the market. There will be use cases
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for LPO, Linear Receive Optics (LRO), Co-packaged optics (CPO), and retimed optics. Adoption of a particular technology will result from a trade-off between performance and the imperative need to reduce connectivity power as SerDes speeds increase and AI servers pack ever more compute density. Module vendors such as Eoptolink are already offering commercially available LPO transceivers. A selection of LPO transceivers will feature on the module compatibility list of server vendors. Hyperscalers who typically prefer to use cables will likely adopt Active Optical Cables (AOC), in which one or both transceivers will use the LPO technology.
Is it possible to mix LPO and existing pluggables?
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Yes. Broadcom and multiple other equipment vendors have demonstrated the feasibility of
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deploying LPO transceivers on one side of the link and conventional transceivers on the other side. This is the focus of Optical Internetworking Forum (OIF). An OIF-compliant LPO module will be fully compatible with the existing optics ecosystem. By contrast, the LPO MSA focuses on LPO-to-LPO links, allowing for lower power, lower cost, and better end-to- end link performance by removing the constraint of compatibility with retimed optics.
Will DSPs still have a role in optical transmission if LPO becomes widely used?
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| ISSUE 38 | Q3 2024
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