Table of Contents
Poutievski et al, 2022. Jupiter Evolving: Transforming Google’s Datacenter Network via Optical Circuit Switches and Software-Defined Networking, in: Proceedings of ACM SIGCOMM 2022. Presented at the SIGCOMM’22, Amsterdam, Netherlands. https://doi.org/10.1145/3544216.3544265
- This is a technical paper which describes the evolution of Google’s internal networking architecture, known as Jupiter. It’s mostly focused on the design and operation of the network, but has some interesting lessons relating to power consumption.
- The main energy-relevant innovation1 is the move from a Clos network
design to a direct-connect
topology among the machine aggregation blocks. This removes the aggregation
spine, which means the associated switches and optical networking components
are no longer needed.
- The other changes included switching to optical circuit switches and a centralized SDN control plane.
- The removal of the spine sections is responsible for the majority of reduced
power consumption, resulting in 5x higher speed and capacity, 30% reduction in
capex2 and 41% reduction in power.
- There is also the associated embodied energy in the equipment that no longer needs to be deployed. This isn’t a lifecycle analysis paper, so that isn’t considered other than in capex.
- In the past, power consumption had fallen even as capacity increased, allowing for improved network energy efficiency. However, those gains were slowing.
- The expected diminishing returns might have led some to predict that we’d see an energy efficiency plateau even as demand continues to increase. Instead, we have a major shift in approach which means power consumption is not following those expectations.
- This is important because many predictions of high power consumption by data centers, networks, and IT in general, extrapolate from past trends. A point made in the recent Joule paper I co-authored discussed how technology trends are the source of considerable uncertainty.
We can’t rely on these types of technology improvements precisely because they are so unpredictable, but this is a good example of the right incentives pushing innovation in the right direction. The challenge is how to model them – making predictions more than a few years (or even just 6-12 months!) into the future is generally a bad idea.