The TCP/IP Model

While the OSI model is an excellent theoretical guide, the TCP/IP model (also known as the Internet Protocol Suite) is the set of communication protocols used on the internet and most commercial networks today. It's a more practical and streamlined model. The TCP/IP model is typically described as having four layers, though sometimes a fifth is included to better align with the OSI model. The lowest layer is the Link Layer (or Network Access/Interface Layer), which combines the functions of the OSI's Physical and Data Link layers. It deals with the physical hardware, such as Ethernet or Wi-Fi, and protocols for transmitting data on the physical network. Above this is the Internet Layer, which is equivalent to the OSI's Network Layer. Its primary function is to move packets from a source to a destination across one or more networks. The Internet Protocol (IP) is the core protocol here, responsible for logical addressing (IP addresses) and routing. The next layer is the Transport Layer, which mirrors the OSI Transport Layer. It provides end-to-end communication services for applications. The two most important protocols here are the Transmission Control Protocol (TCP), which provides a reliable, connection-oriented service, and the User Datagram Protocol (UDP), which offers a faster, connectionless service. The top layer is the Application Layer, which combines the functions of the OSI's Session, Presentation, and Application layers. This layer contains the high-level protocols that users interact with, such as HTTP for web browsing, FTP for file transfer, SMTP for email, and DNS for name resolution.