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7.4.2.1. Ethernet System Hierarchy
The figure below shows the flow of information from an embedded networking application to the Ethernet.
The structure presented in the figure shows a typical embedded networking system. In general, a user application performs a job that defines the goal of the embedded system, such as controlling the speed of a motor or providing the UI for an embedded kiosk. The networking stack provides the application with an application programming interface (API), usually the Sockets API, to send networking data to and from the embedded system.
The stack itself is a software library that converts data from the user application into networking packets, and sends the packets through the networking device. Networking stacks tend to be very complicated software state machines that must be able to send data using a wide variety of networking protocols, such as address resolution protocol (ARP), transmission control protocol (TCP), and user datagram protocol (UDP). These stacks generally require a significant amount of processing power.
The stack uses the Ethernet device to move data across the physical media. Most of a networking stack’s interaction with the networking device consists of shuttling Ethernet packets to and from the Ethernet device.
You must consider the link layer, or physical media over which the Ethernet datagrams travel, when constructing a network enabled system. Depending on the location of the embedded system, the Ethernet datagrams might traverse a wide variety of physical links, such as 10/100 Mb twisted pair and fiber optic. Additionally, the datagrams might experience latency if they traverse long distances or need to pass through many network switches in order to arrive at their destination.