Explicit-feedback TCP for congestion control in LEO satellite communications networks

In Low Earth Orbit (LEO) satellite networks, traditional transmission control protocol (TCP) variants suffer from severe performance degradation due to the unique combination of high propagation delays, frequent topology changes, and random packet loss which is often misinterpreted as congestion packet loss, leading to unnecessary throughput degradation. Furthermore, the long feedback loop in satellite links prevents timely window adjustments. To address these challenges, this paper proposes Explicit-Feedback TCP (EFTCP), a cross-layer congestion control framework inspired by the explicit signaling philosophy exemplified by explicit congestion notification (ECN). Instead of relying solely on implicit loss- or delay-based signals, EFTCP exposes richer internal network state information to the transport layer. The main contributions are threefold: (1) an explicit network-state feedback mechanism that conveys quantitative congestion-related information to TCP, enabling it to distinguish congestion from random losses; (2) a lightweight concurrent node density model that leverages deterministic orbital mechanics to anticipate traffic hotspots and proactively adjust the congestion window; and (3) a residual bandwidth-aware allocation strategy that dynamically balances throughput efficiency and fairness. Extensive simulations demonstrate that EFTCP significantly outperforms state-of-the-art TCP variants in terms of throughput stability and fairness, particularly in high-loss scenarios ((Formula presented) ) and highly dynamic LEO topologies.