Less latency and better protection with AL-FEC sliding window codes: A robust multimedia CBR broadcast case study

Application-Level Forward Erasure Correction (AL-FEC) codes have become a key component of communication systems in order to recover from packet losses. This work analyzes the benefits of the AL-FEC codes based on a sliding encoding window (A.K.A. convolutional codes) for the reliable broadcast of real-time flows to a potentially large number of receivers over a constant bit rate channel. It first details the initialization of both sliding window codes and traditional block codes in order to keep the maximum AL-FEC decoding latency below a target latency budget. Then it presents detailed performance analyzes using official 3GPP mobility traces, representative of our use case which involves mobile receivers. This work highlights the major benefits of RLC codes, representative of sliding window codes, that outperform any block code, from Raptor codes (that are part of 3GPP MBMS standard) up to ideal MDS codes, both in terms of reduced added latency and improved robustness. It also demonstrates that our RLC codec features decoding speeds that are an order of magnitude higher than that of Raptor codes.