AWS paired its in-house AI chip Trainium (Trn) with a proprietary interconnect protocol called NeuronLink, positioned against NVLink. Why is its core still the generic PCIe standard?

Because AWS does not plan to develop its own switch chips for inter-die data forwarding. Custom interconnects typically need such chips, so it is unlikely to move away from PCIe.

Looking ahead, AWS may instead become a purchaser of UALink, the open interconnect standard formed by AMD and others. The latest NeuronLink is built on PCIe Gen6 and delivers 2,304 GB/s bidirectional bandwidth per card. Nvidia and AMD's new schemes reach 3.6 TB/s, about 1.6x AWS.

A scale-up interconnect must address three issues: line rate, error handling, and the set of cross-chip operations. The most critical is the first, the per-lane rate, which is determined by the SerDes.

Nvidia's in-house SerDes reaches 200G, and AMD, using Broadcom silicon, also reaches 200G. PCIe Gen6 is only 64G, roughly one-third of that. To make up bandwidth, either wait for PCIe to speed up in future gens or add more lanes.$Amazon(AMZN.US)

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