WTH is a lossless network?

Thu, 12 Nov 2026 00:00:00 +0000

In this article I explore a few specific behaviors of modern AI networks, building on the work of two papers: Congestion Control for Large-Scale RDMA Deployments (Zhu et al., SIGCOMM 2015), which introduced DCQCN and described the victim-flow problem, and HPCC: High Precision Congestion Control (Li et al., SIGCOMM 2019), whose simulator we use.

1. Background

Recently, I was intrigued by incast storms and how they can cause micro-bursts of congestion. I thought this was normal TCP behavior and expected TCP fairness to do its magic. This led me to look at how ECN could improve this scenario, which I thought was the primary tool used in modern AI fabrics. But then I realized lots of these AI fabrics don’t even use TCP. That sent me to find out what all the fuss about RoCEv2 is.

Dcqcn on Flavio Castro

WTH is a lossless network?

1. Background