Optimized active redundancy with just-in-time duplication for safety critical mobile video streaming

Abstract

In safety-critical applications reliable delivery and timely arrival of data are equally important properties and yet known to be conflicting in real-time multimedia streaming. Whenever real-time systems depend on unreliable communication infrastructure like for instance IP networks, multihoming the availability of redundant network paths can provide fault tolerance and significantly increase overall systems reliability. This thesis examines different transmission strategies for multihomed setups to improve the reliability while at the same time considering latency and link efficiency requirements. Duplicating the entire stream onto multiple paths is simple but adds a significant data overhead. Retransmitting packets merely upon a detected loss, as offered by TCP, lowers data overhead but causes non-deterministic latency characteristics. Thus, the author of this thesis proposes Deadline Based Preemptive Retransmission (DPR), a transmission scheduling strategy that delays multipath packet duplication to meet the latency requirement just-in-time. This allows for more efficient link utilization by avoiding unnecessary data duplication. DPR is implemented as an extension to Concurrent Multipath Transmission (CMT), which is itself an extension of the Stream Control Transmission Protocol (SCTP). This thesis assesses the constraints and requirements of real-time transmission as well as the consequences of late packet arrival. This thesis presents new metrics to assess and quantify the performance of transmission strategies to satisfy the requirement of timely delivery of data as well as the penalty of introduced data overhead. The proposed transmission scheduling DPR and other investigated scheduling approaches are validated embedded in a multimedia-streaming pipeline with a modified version of GStreamer and an emulated network environment. The conducted experiments investigate the characteristics, performance and drawbacks of different duplication strategies under various network characteristics. The empirical analysis demonstrates the conspicuous benefits of DPR.