Spectrum-X: It's Bigger Than Software

There's been a lot of confusion around Spectrum-X, some of which NVIDIA seems to have created intentionally. The company's branding is part of the issue, as it seems to conflate Spectrum-X with the Spectrum line of Ethernet switch chips. In fact, Spectrum-X is simply a software license that enables new features across a set of existing hardware products.

The reality that Spectrum-X is a set of software, however, devalues what NVIDIA has actually delivered. Working on top of the company's end-to-end Ethernet hardware, the software creates the first merchant congestion-managed Ethernet fabric. Minimizing tail latency is critical to AI-training workloads, as detailed in our recent white paper. We use the merchant qualifier because some hyperscalers have developed their own congestion-management schemes that work with standard Ethernet-switch hardware. One example is Amazon, which developed the scalable reliable datagram (SDP) protocol for use with its internally-developed Nitro smart-NIC along with merchant switch silicon.

Spectrum-X (Source: NVIDIA)

Spectrum-X comprises software for BlueField-3 DPUs, residing in servers, and Ethernet switches based on Spectrum-4. The Spectrum-X announcement included the news that the Spectrum-4 51.2Tbps switch chip is now in production and available in new SN5000 Series switch systems. That follows BlueField-3 production availability, which NVIDIA revealed at GTC in March. At its core, Spectrum-X implements ROCEv2 adaptive routing and congestion management to create a lossless Ethernet fabric with predictable and bounded latency. As is the case with Amazon's SDP, adaptive routing enables optimal path selection on a per-packet basis, also known as packet spraying. This can result in out-of-order packets at the destination, which the DPU in the endpoint must handle. On the transmit side, the DPU can also limit the packet-injection rate in response to congestion notifications. Spectrum-4 provides realtime telemetry data (branded NetQ), such as queue depths.

NVIDIA's full-stack solution provides an Ethernet-based alternative to InfiniBand for AI training. The company positions Spectrum-X for multitenant clouds where AI isn't the only workload, whereas InfiniBand provides ultimate scaling for "AI factories." In other words, you won't be using Spectrum-X to train the next ChatGPT, which is the domain of the DGX GH200. Spectrum-X is also NVIDIA's answer to Ethernet scheduled fabrics available from Broadcom and Cisco. In Cisco's parlance, Spectrum-X is a telemetry-assisted Ethernet solution, which also describes Amazon's implementation. Fully-scheduled fabrics instead handle congestion management in the fabric and present standard Ethernet ports at ingress/egress. This approach enables servers to use standard NICs, such as NVIDIA's ConnectX-7, rather than smart-NICs (or DPUs). Although the scheduled fabric is vendor-specific (or proprietary), it decouples the switch fabric from the NIC.

We might think Spectrum-X is simply a defensive response to Ethernet competitors, aimed at protecting NVIDIA's sizable InfiniBand business. But the company is building what it says will be Israel's most powerful supercomputer, dubbed Israel-1, around the Spectrum-X fabric. Hyperscalers including Amazon and Meta are already using Ethernet fabrics in AI systems, but Spectrum-X will serve the next tier of cloud providers. In the race to build AI infrastructure, there's no one-size-fits-all network architecture, meaning neither NVIDIA's InfiniBand nor Broadcom's Tomahawk will be the dominant solution.


Popular posts from this blog

NVIDIA Networks NVLink

NVIDIA Reveals DGX GH200 System Architecture

Ultra Ethernet Promises New RDMA Protocol