The high scalability and low CPU power requirements of IIoT field devices have encouraged the adoption of messaging protocols such as MQTT and CoAP for resource-constrained devices. These transports run on top of TCP or UDP and use TLS/DTLS for security. In this section, a brief description of the transports and their security assessment is presented.
TCP is an open standard maintained by IETF (IETF-TCP) and integral to the internet or TCP/IP protocol stack. TCP provides connection-oriented transport and has been widely used in HTTP-based applications such as e-commerce. In TCP, messages are delivered in order, and it supports retransmission of messages lost in transit, and as such requires considerable time and resources. As a result, message latencies may vary greatly when using TCP.
