Two general optimization techniques for low-latency services

Low-latency services have become indispensable in people's work and daily life. Various low-latency services exist, including video conferences for online communication and cloud games for entertainment, which can meet different requirements of users. These services make it convenient for users to interact anywhere in real time, thereby overcoming the limitations of traditional applications. Therefore, these services have recently attracted numerous users, and their deployment scale has rapidly expanded. With the development of 5G technology, the coverage of low-latency services will spread further; these services have broad development prospects. Therefore, performance optimization of low-latency services is a hotspot in academia and industry. The most critical performance indicator for low-latency services is end-to-end latency. In addition to maintaining low latency, achieving high throughput and link usage to improve service quality and attract more users is also necessary. Therefore, performance optimization is key in the further development of low-latency services.

Various performance optimization schemes used at different positions of the transmission path were proposed by researchers. Among them, the two most widely used schemes were the low-latency congestion control algorithm (CCA) deployed on the server side and the active queue management algorithm (AQM) deployed in the network. Their design tried to avoid queuing as much as possible and to reduce end-to-end delay. The CCA and AQM constantly updated their design to solve the limitations of previous algorithms, improved their performance, and enhanced the practicality of the algorithms for large-scale deployment. Specifically, CCA improved the estimation strategy of congestion signals to make them more accurate, completed the logic of the adjustment of the sending rate and incorporated consideration for fairness into the design. AQM focused on queuing delay and minimized the amount of parameters, trying to implement a more lightweight algorithm. Although CCA and AQM shared similar goals, they were researched in parallel and independently. Being in the same control loop and both affecting the quality of low-latency services, the synergistic effect between CCA and AQM attracted considerable academic attention. Existing evaluations indicated a potential mismatch, resulting in poor performance when they were used together. To achieve superior collaboration between CCA and AQM, various optimization solutions were proposed. Among them, general CCA and AQM based on machine learning and cross-layer joint optimization were representative schemes. Although these solutions aimed to solve the mismatch problem and proposed general algorithms, they faced challenges in real-world deployment.

This paper summarizes the main design ideas and performance evaluation of important low-latency CCA and AQM, sorts the performance and theoretical analysis of the combined use of the two algorithm types, analyzes the potential coordination problems between them, and further elaborates on the research work on the collaborative optimization of CCA and AQM. Through the summary, we propose that future research on low-latency services performance optimization must emphasize versatility and practical deployment and believe that cross-layer joint optimization is a practical idea to solve the existing mismatch, make CCA and AQM work well together and further improve the performance of low-latency services, which can be the focus of future research.