Copa-D: Delay Consistent Copa for Dynamic Cellular Networks

The lack of consideration for application delay requirements in standard loss-based congestion control algorithms (CCAs) has motivated the proposal of several alternative CCAs. Among these new CCAs, Copa is one of the promising few CCAs that have attracted attention from both academia and industry. The delay performance of Copa is governed by a mostly static latency-throughput tradeoff parameter, $\delta$. However, a static $\delta$ parameter makes it difficult for Copa to achieve consistent delay and throughput over a range of bottleneck bandwidths. In particular, the coexistence of 4G and 5G networks and the wide range of bandwidths experienced in NG-RANs can result in inconsistent CCA performance. To this end, we propose Copa-D, a modification to Copa that dynamically tunes $\delta$ to achieve a consistent delay performance. We evaluate the modification over fixed, 4G, and 5G emulated bottlenecks. Our results show that Copa-D achieves consistent delay with minimal impact on throughput in fixed capacity bottlenecks. Copa-D also allows a more intuitive way of specifying the latency-throughput tradeoff and achieves more accurate and predictable delay in variable cellular bottlenecks.