Retransmission Timeout Estimation for Low-Delay Applications Using Multipath RTP

Abstract

Delay-sensitive media applications typically prioritise timeliness over reliability, therefore preferring UDP over TCP. Retransmission is a method to compensate for packet loss and requires the receiver to provide timely feedback to the sender. Delaying the retransmission request too long may result in the retransmitted media arriving late. Alternatively, aggressive error estimation, where slightly delayed packets are seen as lost, results in unnecessary bandwidth usage and may contribute to further congestion of the network. We study receiver-based retransmission timeout (RTO) estimation in the context of real-time streaming over Multipath RTP and propose a solution in which we use statistical methods to provide accurate RTO prediction which allows for timely feedback. The proposed approach allows the receiver to accurately estimate the RTO when receiving media over multiple paths irrespective of the scheduling algorithm used at the sender. This enables a sender to take advantage of multiple paths for load balancing or bandwidth aggregation by scheduling media based on dynamic path characteristics.