MQTT-SN, CoAP, and RTP in wireless IoT real-time communications
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MQTT‑SN, CoAP, and RTP in wireless IoT real‑time communications Rolando Herrero1 Received: 23 December 2019 / Accepted: 5 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A great number of Internet of things (IoT) applications rely on real-time communication (RTC) mechanisms for transmission of media. Essentially, applications analyze and process media to make decisions that typically affect actuation and control of embedded devices. IoT networks, however, are subjected to constrains that limit the computational and resource complexity of all entities involved. This is particularly critical when considering the traditional RTC protocols like real-time protocol (RTP) that was not designed to perform well in the context of low-power lossy networks (LLNs). This paper focuses on alternatives to media transport in IoT networks. Specially, constrained application protocol (CoAP) and the message queuing telemetry transport sensor network protocol (MQTT-SN) are presented as valid technologies for media propagation in LLNs. The paper models and compares CoAP, RTP, and MQTT-SN to determine the most efficient scenario for audio, speech, and video transmission. Keywords IoT · LLN · CoAP · MQTT-SN · RTP
1 Introduction Different IoT applications have different quality-of-service (QoS) requirements. In particular, certain IoT applications that rely on real-time communication (RTC) are highly sensitive to network latency and packet loss that can seriously affect the performance of the solution. For example, in a scenario where unmanned aerial vehicles (UAVs) are used to capture and transmit hyperspectral images to a central processor known as the planner, any delay in decisionmaking becomes a liability as it can lead not only to failure but also to physical and personal damage. In the context of low-power lossy networks (LLNs) and as shown in Fig. 1, long battery life is the ultimate cause of high network packet loss and low transmission rates that, in turns, are responsible of excessive network latency. Specifically, when power consumption is lowered to preserve battery life, the signalto-noise ratio lowers, resulting in decreased Raleigh fading channel capacity [1] and higher bit error rate (BER). Limited
Communicated by R. Steinmetz. * Rolando Herrero [email protected] 1
Northeastern University, 360 Huntington Avenue, Boston, MA 02115‑5000, USA
channel capacity leads to low transmission rates, while high BER causes packets to be dropped by error detection mechanisms. Moreover, high network packet loss induces retransmissions than combined with low transmission rates which leads to increased network latency. Retransmissions, on the other hand, can be introduced at different layers depending on the protocol. For example, IEEE 802.15.4 supports, under certain circumstances, optional timeout-based retransmission at the media access control (MAC) layer, while CoAP supports a confirmable transmission mode that by means of retransmission provides session layer reliabilit
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