The behavior of loss-based TCP congestion control algorithms like TCP CUBIC continues to be a challenge in modern cellular networks. Due to the large RLC layer buffers required to deal with short-term changes in channel capacity, the behavior of both the Slow Start and congestion avoidance phases may be heavily impacted by the lack of packet losses and the resulting bufferbloat. While existing congestion control algorithms like TCP BBR do tend to perform better even in the presence of large bottleneck buffers, they still tend to fill the buffer more than necessary and can have fairness issues when compared to loss-based algorithms. In this paper, we analyze the issues with the use of loss-based congestion control algorithms by analyzing TCP CUBIC, which is currently the most popular variant. To mitigate the issues experienced by TCP CUBIC in cellular networks, we introduce TCP ROCCET, a latency-based extension of TCP CUBIC that responds to network congestion based on round-trip time in addition to packet loss. Our findings show that TCP ROCCET can reduce latency and bufferbloat compared to the standard CUBIC implementation, without requiring a specific network architecture. Compared to TCP BBRv3, ROCCET offers similar throughput while maintaining lower overall latency. The evaluation was conducted in real 5G networks, including both stationary and mobile scenarios, confirming ROCCET's improved response to network congestion under varying conditions.

翻译：基于丢包的TCP拥塞控制算法（如TCP CUBIC）在现代蜂窝网络中的行为仍面临挑战。由于处理信道容量短期变化需要大型RLC层缓冲区，慢启动和拥塞避免阶段的行为可能因缺乏数据包丢失及由此产生的缓冲区膨胀而受到严重影响。虽然现有拥塞控制算法（如TCP BBR）即使在存在大型瓶颈缓冲区时往往表现更佳，但它们仍倾向于过度填充缓冲区，且与基于丢包的算法相比可能存在公平性问题。本文通过分析当前最流行的变体TCP CUBIC，剖析了基于丢包的拥塞控制算法在应用中的问题。为缓解TCP CUBIC在蜂窝网络中遇到的问题，我们提出了TCP ROCCET——一种基于延迟的TCP CUBIC扩展，其除了响应数据包丢失外，还能根据往返时间对网络拥塞作出反应。研究结果表明，与标准CUBIC实现相比，TCP ROCCET能够在不依赖特定网络架构的情况下降低延迟和缓冲区膨胀。相较于TCP BBRv3，ROCCET在保持相似吞吐量的同时实现了更低的整体延迟。评估在真实5G网络中进行，涵盖静态和移动场景，证实了ROCCET在不同条件下对网络拥塞的响应能力得到提升。