TABLE OF CONTENTS OSI provides a standard organization and vocabulary to define compatibility issues. To understand how the structure works, we begin with a brief description of the various layers and the functions they encompass. By convention, we begin at the bottom layer and work our way up. See Figure 7-1.
Layer 1 describes the transmission of bits over a physical medium. In the simplest terms, Layer 1 is the bit pipe over which our digital information will be sent. Layer 1 addresses such issues as physical connectors and the signal encoding. Depending on the media to be used, that encoding might be electrical, optical, or radio. In a wired LAN, the primary physical medium for desktop access is the Category 5e or Category 6 unshielded twisted pair (UTP) cabling. For example, a Layer 1 protocol for wired LANs would be 10 Base-T or 100 Base-T, which define how we encode the 1 bits and 0 bits as electrical signals to be transported over the cable path. In a wireless LAN, the radio link protocols, 802.11a, b, g, or n define the Layer 1 options.
The link layer provides rules for the transmission of data between devices over a single transmission link or through a single network. The link layer describes how transmission elements called frames are formatted, addressed, and how they are introduced onto the transmission link. LAN protocols...
