In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer.^[1] This layer may be implemented by a PHY chip.

The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying packets across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet.

The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly referred to as TCP/IP.

In computer networking, the User Datagram Protocol (UDP) is one of the core members of the Internet protocol suite. The protocol was designed by David P. Reed in 1980 and formally defined in RFC 768. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol (IP) network.

The 7-Layer BRM for OSI

The BRM for OSI consists of 7 layers of protocols, i.e., of 7 different areas in which the protocols operate. In principle, the areas are distinct and of increasing generality; in practice, the boundaries between the layers are not always sharp. The model draws a clear distinction between a service, something that an application program or a higher-level protocol uses, and the protocols themselves, which are sets of rules for providing services.

Here are the seven layers in the Basic Reference Model for Open Systems Interconnection: