What protocol primarily operates in Layer 4 of the OSI model?

TCP, or Transmission Control Protocol, primarily operates at Layer 4 of the OSI model, which is the transport layer. This layer is responsible for providing reliable data transfer services to the upper layers, ensuring that data is delivered in the correct order and without errors. TCP accomplishes this through mechanisms such as connection establishment, data segmentation, flow control, and error recovery. This makes it a connection-oriented protocol, meaning that it requires a connection to be established between sender and receiver before data transmission begins.

In contrast, the other protocols mentioned in the options function at different layers of the OSI model. FTP (File Transfer Protocol) operates at Layer 7, the application layer, and is used for transferring files across a network. HTTP (Hypertext Transfer Protocol), also situated at Layer 7, is the foundation of data communication for the World Wide Web. Similarly, DNS (Domain Name System) also operates at Layer 7, handling the translation of domain names into IP addresses. Understanding the distinctions among these protocols and their respective layers helps clarify TCP's unique role in ensuring reliable communication between devices on a network.