The Congestion Signaling (CSIG) protocol enables fine-grained network control and visibility for burst-heavy datacenter workloads. CSIG collects precise, multi-bit bottleneck congestion signals in a space-efficient Ethernet header and reflects them to senders in a transport header. It is usable by all transports that run over Ethernet, including the Falcon transport.
The Ultra Ethernet Consortium (UEC) is standardizing CSIG. Once the UEC specification of CSIG has been released, the persistent URL https://purl.org/csig/spec, which currently redirects to this page, will redirect to the UEC CSIG specification.
In the interim, for reference, the following publicly available materials describe CSIG:
- IETF Internet-Draft Congestion Signaling (CSIG)
- AIDC-IETF118 Slides Congestion Signaling (CSIG)
- OCP 2023 Presentation Simple and Effective In-band Signals for Efficient Traffic Management in HPC and AI/ML Networks
- OCP 2025 Presentation CSIG Congestion Signaling in the AI Era
- SIGCOMM 2025 AI Networking Tutorial Slides CSIG: Fine-Grained Congestion Signals for ML Workloads