The correct answer is: A. TCP
TCP (Transmission Control Protocol) is a connection-oriented protocol that provides reliable, ordered, and error-checked delivery of data between applications running on hosts communicating by an IP network. It is one of the core protocols of the Internet protocol suite.
TCP is a transport layer protocol, which means that it sits above the Internet Protocol (IP) layer and below the application layer. It provides a reliable connection between two applications by using a three-way handshake to establish the connection, and then sending data in segments that are acknowledged by the receiver. If a segment is lost or corrupted, TCP will retransmit it.
TCP is used by a wide variety of applications, including web browsing, email, and file transfer. It is also used by many IoT devices, such as smart thermostats and security cameras.
The other options are incorrect because they are not transport layer protocols. IP (Internet Protocol) is a network layer protocol, which means that it is responsible for routing data packets between hosts on an IP network. API (Application Programming Interface) is a software interface that allows two applications to communicate with each other. UDP (User Datagram Protocol) is a connectionless protocol that does not provide reliable delivery of data.
In conclusion, most IoT problems are addressed at the TCP layer. TCP is a transport layer protocol that provides reliable, ordered, and error-checked delivery of data between applications running on hosts communicating by an IP network. It is one of the core protocols of the Internet protocol suite.