|  |  | Overview
Similar to a house needing to have a foundation before it can be built, so too must a network have a foundation on which it can be built. In the OSI reference model, this foundation is called Layer 1 or the physical layer. The terms used in this chapter to describe how network functions are linked to Layer 1 of the OSI reference model. The physical layer is the layer that defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. In this chapter, you will learn about the network functions that occur at the physical layer of the OSI model. You will learn about different types of networking media that are used at the physical layer, including shielded twisted-pair cable, unshielded twisted-pair cable, coaxial cable, and fiber-optic cable. In addition, you will learn how network devices, cable specifications, network topologies, collisions and collision domains can help determine such things as how much data can travel across the network and how fast.
Note: In this chapter, you may need to convert units of measurements. A small utility to help you make the conversions is available here. You can access it from anywhere in this chapter via the Index button below.