CSIG: Congestion Signaling in the AI Era#

Speakers: Abhiram Ravi (Google), Jai Kumar (Broadcom)

• Why: Millisecond-duration AI bursts expose the limits of ECN-only congestion signals; this is the mechanism-level answer, and it's deployed, standardized, and multi-vendor — the trifecta for judging whether something is real.
• What: Congestion Signaling (CSIG) — line-rate, always-on telemetry in application context, plus fine-grained per-packet congestion feedback that captures both the state and the location of the bottleneck on a path. Includes Google production results showing improvements to congestion control and load balancing. (from abstract only)
• How: Sub-millisecond-granularity switch traffic measurements embedded in signaling, feeding both congestion control responsiveness and load-balancing quality; being standardized under UEC with multiple switch vendors supporting it.
• Where applicable: Deployed at Google production scale — Google-specific results, but the mechanism is being standardized at UEC and supported by multiple switch vendors, so it is broadly relevant to anyone designing AI fabric feedback loops.