Flow Control in the Context of the Multiplexed Transport Protocol QUIC

QUIC is a novel transport protocol developed to solve some of the well-known problems in Internet data transfer. QUIC can separately manage data of multiple distinct flows (streams) within a QUIC connection. In contrast to other protocols, like e.g. SCTP, it also uses data Flow Control (FC) on the stream as well as the connection level. The QUIC FC uses a credit-based scheme on both levels. In order to evaluate the QUIC performance in detail, we implemented a QUIC simulation model featuring Congestion Control (CC) and FC according to the current standard [11]. During our evaluation, we observed suboptimal behavior of the credit-based FC algorithm, resulting in a significant degradation of the throughput of the entire connection and the goodput of each stream in the QUIC data transfer. In this paper, we propose some modifications to the credit-based FC scheme and show by means of simulation that these modifications completely mitigate the issues and enable achieving the optimum performance in FC-limited scenarios. We further show that the improved FC correctly cooperates with Congestion Control and Retransmission mechanisms and has no negative impact on the protocol performance in cases where the latter mechanisms dominate the protocol behavior.