Lawrence Berkeley National Laboratory

Distributed computing systems require accurate network simulation tools to optimize data transfer and resource allocation across geographically distributed facilities. We extend DISTRI, a discrete-event simulator for multi-facility distributed computing, with a comprehensive Transmission Control Protocol (TCP) stack supporting multiple congestion control algorithms (CCAs) and network topologies. This unified TCP implementation enables realistic simulation of both inter-facility wide-area and intra-facility local network communications. We validate DISTRI’s TCP stack accuracy by comparing inter-facility scenarios against real-world experiments on the FABRIC testbed. Using a dumbbell topology with competing data transfers, we analyze TCP Reno’s behavior through congestion window (CWND) evolution, round-trip time (RTT), throughput, and packet loss patterns. Results demonstrate that DISTRI accurately captures essential TCP dynamics, with behavioral trends closely matching real-world observations. This validation establishes DISTRI as a reliable, cost-effective tool for developing and testing network optimization algorithms in distributed computing environments. Beyond qualitative validation, we outline directions for incorporating more detailed quantitative error analysis between simulated and measured TCP traces as part of future work.