Multimodal retransmission timer for LPWAN
Gómez Montenegro, Carlos; Crowcroft, Jon
Low Power Wide Area Networks (LPWANs) are experiencing high momentum as an inexpensive solution for enabling Internet of Things (IoT) applications. Recent Internet connectivity support developments are expected to further fuel the adoption of LPWAN. However, the latter present challenges to Internet protocols. Remarkably, many LPWAN scenarios exhibit a multimodal Round Trip Time (RTT) distribution, which deviates from common Internet RTT characteristics. This leads to a significant mismatch between Retransmission TimeOut (RTO), computed by the standard TCP or alternative experimental RTO algorithms, and RTT. In this paper, we present the Multimodal RTO algorithm, which is able to selfadapt to the current RTT mode and produce suitable RTO values. Evaluation results show that the Multimodal RTO reduces the RTO versus RTT misalignment of the TCP RTO algorithm by an average factor of up to 5, and reduces latency in the presence of losses by up to 2 orders of magnitude, while operating safely. The Multimodal RTO is currently being considered by the IETF as a candidate mechanism for standardization
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