Abstract: In recent years, with the significant increase in communication technologies and network transmission capabilities, the requirements of applications have shown a diversified growth trend (such as video conferencing and online games with low latency, low delay jitter and software updates with high throughputs). In order to meet delay-insensitive data transmission and ensure efficient bottleneck bandwidth utilization, low priority congestion control (LPCC) algorithms such as LEDBAT(low extra delay background transport) have received increasing attention. These algorithms can occupy available bandwidth when the link is idle, and release the occupied bandwidth when the link load is high to ensure the transmission of delay-sensitive data. However, when AQM(active queue management) is deployed on the router, the reprioritization problem of LPCC occurs. When the link is under heavy load, the occupied bandwidth cannot be released by LPCC, which degenerates into an ordinary congestion control algorithm. To solve the problem, this paper proposes a heuristic dynamic threshold adjustment algorithm, called HDT which can dynamically search for the optimal dynamic delay threshold, ensuring it maintains low priority while coexisting with AQM without reducing link utilization. We establish different network scenarios in the network simulator NS2 to verify the effectiveness of the proposed algorithm. The results show that HDT can effectively solve the problem of reprioritization while ensuring the bandwidth utilization of the link.

Key words: congestion control algorithm, low extra delay background transport(LEDBAT) algorithm, active queue management(AQM), reprioritization, heuristic dynamic threshold