This chapter explains the related content of the Real Time-Thread (RT-Thread) network framework. The first to third layers belong to the lower three layers of the Open System Interconnect (OSI) reference model and are responsible for creating links for network communication connections; the fourth to seventh layers are the upper four layers of the OSI reference model and are responsible for end-to-end data communication. The capabilities of each layer are further detailed in this framework to achieve interconnectivity, interoperability, and application portability in an open system environment. The Transmission Control Protocol/Internet Protocol reference model was first implemented in a computer system. It has a stable implementation on UNIX and Windows platforms and provides a simple and convenient programming interface on which a wide range of applications are developed. User Datagram Protocol is a connectionless protocol. Each datagram is a piece of separate information, including the complete source address and destination address.