Low-Power Wide Area Network (LPWAN) technologies are characterized by
very low physical layer bit and message transmission rates. Moreover,
a response to a message sent by an LPWAN device may often only be
received after a significant delay. As a result, Round-Trip Time (RTT)
values in LPWAN are often (sometimes, significantly) greater than
typical default values of Retransmission TimeOut (RTO) algorithms.
Furthermore, buffering at network elements such as radio gateways may
interact negatively with LPWAN technology transmission mechanisms,
potentially exacerbating RTTs by up to several orders of magnitude.
This document provides guidance for RTO settings in LPWAN, and
describes an experimental dual RTO algorithm for LPWAN.

Low-power wide-area networks (LPWANs) are experiencing high momentum as an inexpensive solution for enabling the 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 the Internet protocols. Remarkably, many LPWAN scenarios exhibit a multimodal round-trip time (RTT) distribution, which deviates from the common Internet RTT characteristics. This leads to a significant mismatch between retransmission timeout (RTO), computed by the standard transmission control protocol (TCP) or alternative experimental RTO algorithms, and RTT. In this article, we present the Multimodal RTO algorithm, which is able to self-adapt to the current RTT mode and produce suitable RTO values. The 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.

background or methods

/pdf/multimodal-retransmission-timer-for-lpwan-1o52ihnxpg.pdf

RTO considerations in LPWAN

Multimodal Retransmission Timer for LPWAN

LPWANs are networks characterised by the scarcity of their radio resources and their limited payload size. LoRaWAN offers an open, easy-to-deploy and efficient solution to operate a long-range network. To efficiently communicate using IPv6, the LPWAN working group from the IETF developed a solution called Static Context Header Compression (SCHC). It uses context rules, which are linked to a given End Device, to compress the IPv6 and UDP header. Since there may be a huge variety of End Devices profile, it makes sense to store the rules remotely and use a system to retrieve the profiles dynamically. In this paper we propose a mechanism based on DNS to find the context rules associated with an End Device, allowing it to be downloaded from an HTTP Server. We evaluate the corresponding delay added to the communications using experimental measurements from a real testbed.

RTO considerations in LPWAN

Citations

Multimodal Retransmission Timer for LPWAN

DNS-based dynamic context resolution for SCHC

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