nies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Premises Technologies Premises Technologies nity to use the shared medium; and all have some kind of software called a network operating system (NOS) that controls the environment. All LANs have the same basic components as shown in Figure 5-14.A collection of devices such as PCs, servers, and printers serve as the inter- face between the human user and the shared medium. Each of these machines hosts a device called a network interface card (NIC), which pro- vides the physical connectivity between the user device and the shared medium. The NIC is either installed inside the system or, less commonly, as an external device. In laptop machines, the NIC is either a PC card that plugs into a slot in the machine, shown in Figure 5-15, or, more com- monly today, built into the system. In many machines today Wi-Fi is also built in; it's basically a wireless version of Ethernet. Shared Medium Figure 5-14 Typical LAN components Figure 5-15 A PC card network interface card (NIC) Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Premises Technologies Chapter 5 The NIC device implements the access protocol that devices wishing to access the shared medium use on their particular LAN. These access schemes will be discussed shortly. The NIC also provides the connectiv- ity required to attach a user device to the shared network. Topologically, LANs differ greatly. The earliest LANs used a bus archi- tecture-shown in Figure 5-16-so-called because they were literally a long run of twisted-pair wire or coaxial cable to which stations were peri- odically attached. Attachment was easy; in fact, early coax systems relied on a device called a "vampire tap," which poked a hole in the insulation surrounding the center conductor in order to suck the digital blood from the shared m