Both the Transport Control Protocol (TCP) and the User Datagram Protocol (UDP) have a place in an IoT system. REST, for example, is TCP-based, and MQTT was designed to work with TCP. However, the need to support temporal and bandwidth constrained networks and devices has resulted in a move away from TCP and toward the use of the UDP. For example, MQTT-SN is a tailored version of MQTT that works with UDP. Other protocols such as CoAP are also designed to work well with UDP. Given the significant reliance on UDP at this layer, protocols such as Datagram Transport Layer Security (DTLS) exist as an alternative to Transport Layer Security (TLS), used for securing TCP communications.
Transport protocols
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