CCC: Re-architecting Delay-based Congestion Control in Datacenter Networks#

Wanchun Jiang, et al. (Central South University), Danfeng Shan (Xi'an Jiaotong), Fengyuan Ren (Tsinghua), Jiawei Huang, Jianxin Wang (Central South)

• Why: TIMELY/SWIFT-style delay CC runs in production, but the paper's key insight — that even perfectly measured delay can yield incorrect congestion-information deduction under certain conditions — explains instability modes practitioners see and haven't had a framework for.
• What: A re-architecture of delay-based CC that makes rate adjustments depend not just on congestion state but on trustworthiness of the deduction from delay signals. The resulting CCC matches INT-based CCs (HPCC, PowerTCP) using only delay — no INT headers, no special switch support — and beats DCQCN, TIMELY, and SWIFT.
• How: Demarcates operating regions where delay-derived congestion info is untrustworthy (using congestion criteria plus system inertia), applies probing-style rate adjustment there, and applies analytical adjustment elsewhere to reach the target state while keeping the deduction trustworthy.
• Where applicable: Standard datacenter fabrics — the whole point is needing nothing beyond RTT signals. Validated with DPDK testbeds and large-scale simulation. General technique, no hardware prerequisites; a serious competitor to deployable delay-based schemes like SWIFT.