KK Yap
KK is a software engineer at Google with a focus on networking. After spending a few brave years at Stanford building the world of software-defined networking (SDN), he joined Google to help people send traffic across the peering edge with Espresso. These days, he’s dreaming up the future of telemetry and clock synchronization, and figuring out how to make ML and other demanding workloads even better—and then scheming up ways to build it all.
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CSIG: Congestion Signaling for Datacenter Transports
Abhiram Ravi
Brad Karp
MJ Akhbari
Weida Huang
Konstantinos Prasopoulos
2026
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Optimizing burst-heavy datacenter workloads necessitates fine-grained network control and visibility. We introduce CSIG, a protocol that delivers precise, multi-bit bottleneck congestion signals via a fixed-length Ethernet header. The architecture captures 𝜇s-granularity switch metrics, such as available bandwidth, and signals them to end-hosts using in-band, line-rate operations. We propose Fast Ramp-Up, a congestion control primitive that leverages these bottleneck signals to reduce median RPC latency by 20% and unclaimed bandwidth by 60% in production. Beyond transport-level performance, CSIG enables flow-aware observability by embedding 𝜇s-scale metrics into every packet, allowing individual application transfers to pinpoint their bottleneck location, such as the topology tier limiting their performance. CSIG thus transforms network telemetry from post-hoc correlation into a real time, contextaware capability. We demonstrate CSIG’s broad deployability by validating it across five generations of commodity switch hardware (up to 102.4 Tbps), four NIC generations, and five transport stacks. Our design proves that a streamlined Layer 2 approach, focusing exclusively on the principal path bottleneck, provides transport-agnostic gains without requiring forklift hardware upgrades.
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Taking the Edge off with Espresso: Scale, Reliability and Programmability for Global Internet Peering
Matthew Holliman
Gary Baldus
Marcus Hines
TaeEun Kim
Ashok Narayanan
Victor Lin
Colin Rice
Brian Rogan
Bert Tanaka
Manish Verma
Puneet Sood
Mukarram Tariq
Dzevad Trumic
Vytautas Valancius
Calvin Ying
Mahesh Kallahalla
Sigcomm (2017)
Preview abstract
We present the design of Espresso, Google’s SDN-based Internet peering edge routing infrastructure. This architecture grew out of a need to exponentially scale the Internet edge cost-effectively and to
enable application-aware routing at Internet-peering scale. Espresso utilizes commodity switches and host-based routing/packet processing to implement a novel fine-grained traffic engineering capability.
Overall, Espresso provides Google a scalable peering edge that is programmable, reliable, and integrated with global traffic systems. Espresso also greatly accelerated deployment of new networking features at our peering edge. Espresso has been in production for two years and serves over 22% of Google’s total traffic to the Internet.
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