Publications

2026

1. IEEE ToN

   Flowcut Switching: High-Performance Adaptive Routing with In-Order Delivery Guarantees

   Tommaso Bonato, Daniele De Sensi, Salvatore Di Girolamo, and 4 more authors

   IEEE/ACM Transactions on Networking, Jan 2026

   DOI arXiv
2. EuroSys’26

   REPS: Recycled Entropy Packet Spraying for Adaptive Load Balancing and Failure Mitigation

   Tommaso Bonato, Abdul Kabbani, Ahmad Ghalayini, and 7 more authors

   In Proceedings of the European Conference on Computer Systems (EuroSys’26), Apr 2026

   DOI arXiv

2025

1. arXiv

   SMaRTT: Sender-based Marked Rapidly-adapting Trimmed & Timed Transport

   Tommaso Bonato, Abdul Kabbani, Daniele De Sensi, and 11 more authors

   Apr 2025

   Preprint

   arXiv
2. HOTI’25

   Demystifying NCCL: An In-depth Analysis of GPU Communication Protocols and Algorithms

   Zhiyi Hu, Siyuan Shen, Tommaso Bonato, and 6 more authors

   , Virtual Event, Aug 2025

   Abs DOI arXiv Slides

   The NVIDIA Collective Communication Library (NCCL) is a critical software layer enabling high-performance collectives on large-scale GPU clusters. Despite being open source with a documented API, its internal design remains largely opaque. The orchestration of communication channels, selection of protocols, and handling of memory movement across devices and nodes are not well understood, making it difficult to analyze performance or identify bottlenecks. This paper presents a comprehensive analysis of NCCL, focusing on its communication protocol variants (Simple, LL, and LL128), mechanisms governing intra-node and inter-node data movement, and ring- and tree-based collective communication algorithms. The insights obtained from this study serve as the foundation for ATLAHS, an application-trace-driven network simulation toolchain capable of accurately reproducing NCCL communication patterns in large-scale AI training workloads. By demystifying NCCL’s internal architecture, this work provides guidance for system researchers and performance engineers working to optimize or simulate collective communication at scale.

3. SC’25

   Bine Trees: Enhancing Collective Operations by Optimizing Communication Locality

   Daniele De Sensi, Saverio Pasqualoni, Lorenzo Piarulli, and 5 more authors

   In Proceedings of the International Conference for High Performance Computing, Networking, Storage and Analysis (SC’25), St. Louis, MO, USA, Nov 2025

   Abs DOI arXiv

   Communication locality plays a key role in the performance of collective operations on large HPC systems, especially on oversubscribed networks where groups of nodes are fully connected internally but sparsely linked through global connections. We present Bine (binomial negabinary) trees, a family of collective algorithms that improve communication locality. Bine trees maintain the generality of binomial trees and butterflies while cutting global-link traffic by up to 33%. We implement eight Bine-based collectives and evaluate them on four large-scale supercomputers with Dragonfly, Dragonfly+, oversubscribed fat-tree, and torus topologies, achieving up to 5x speedups and consistent reductions in global-link traffic across different vector sizes and node counts.

4. SC’25

   ATLAHS: An Application-centric Network Simulator Toolchain for AI, HPC, and Distributed Storage

   Siyuan Shen^*, Tommaso Bonato^*, Zhiyi Hu, and 3 more authors

   In Proceedings of the International Conference for High Performance Computing, Networking, Storage and Analysis (SC’25), Nov 2025

   Best Student Paper Finalist

   DOI arXiv
5. SC’25

   Uno: A One-Stop Solution for Inter- and Intra-Datacenter Congestion Control and Reliable Connectivity

   Tommaso Bonato^*, Sepehr Abdous^*, Abdul Kabbani, and 11 more authors

   In Proceedings of the International Conference for High Performance Computing, Networking, Storage and Analysis (SC’25), Nov 2025

   DOI arXiv

2024

1. NSDI’24

   Swing: Short-cutting Rings for Higher Bandwidth Allreduce

   Daniele De Sensi, Tommaso Bonato, David Saam, and 1 more author

   In 21st USENIX Symposium on Networked Systems Design and Implementation (NSDI ’24), Apr 2024

   DOI arXiv Slides

2022

1. SC’22

   HammingMesh: A Network Topology for Large-Scale Deep Learning

   Torsten Hoefler, Tommaso Bonato, Daniele De Sensi, and 7 more authors

   In Proceedings of the International Conference for High Performance Computing, Networking, Storage and Analysis (SC’22), Nov 2022

   SC22 Reproducibility Advancement Award and invited as CACM Research Highlight

   DOI arXiv