In the previous six chapters, I have laid the groundwork for discussing the bottom four layers of the OSI model. Upon reading those, you should have a firm grasp on the operations and functions performed by the core protocols of the TCP/IP stack. These protocols, though, have almost no use without the existence of upper-layer protocols. The top three layers of the OSI model consist of protocols that support the very software that runs on PCs and servers. In this chapter, I am going to discuss those protocols that allow the software to take advantage of the network.
Introduction to Upper-Layer Protocols
Before moving into a discussion of the upper-layer protocols, I want to review the functions of the lower four layers.
- The physical layer handles the transformation of binary ones and zeros into actual signaling such as electrical or optical pulses. It uses specific types of media such as copper or fiber-optic cable. In some cases, water pressure, or even air pressure, could be used to transport signaling information.
- The data link layer handles access to the media. Protocols like Ethernet and Token Ring control how hosts actually put the ones and zeros on the local network.
- The network layer handles the end-to-end delivery of data. Since a large internetwork may consist of multiple types of Layer 2 networks, such as Ethernet, Frame Relay, or ATM, the network layer allows you to have a common data path over all types of media. Addressing between two ...