Cost-efficient FEC Scheme for Time-sensitive Multi-hop Transmissions in Overlay Networks

In pursuit of low latency, real-time communication (RTC) service providers usually use multi-hop overlay links worldwide to bypass congested links, especially for medium- and long-distance transmissions. In such multi-hop long-distance transmission scenarios, utilizing retransmission to recover lost packets can result in increased end-to-end latency. Therefore, Forward Error Correction (FEC) is viewed as a promising way to solve the loss problem. However, for multi-hop overlay transmission, existing FEC schemes either introduce a non-negligible processing delay at each hop or reduce the processing delay at the cost of a high coefficient overhead. In this work, we propose a multi-hop FEC scheme, i.e., FEC-OEM, which considers both processing delay and coefficient overhead. FEC-OEM is designed based on two observations we obtained from measurements. First, coefficient overhead can only be reduced through an implicit transmission way. Therefore, we design a modulation-based recoding module that enables implicit coefficient transmission and hop-by-hop recoding at the same time. Second, using on-the-fly computation is a promising way to reduce processing delay. Accordingly, we design an elimination method to make the modulation-based recoding can be carried out on-the-fly. Real-world experiments demonstrate that FEC-OEM can reduce the processing delay by up to 88% without increasing the coefficient overhead compared to state-of-the-art schemes. We also use FEC-OEM to transmit packets for applications with different loss tolerances, and the results show that FEC-OEM can improve the QoE more effectively than state-of-the-art coding schemes.