ork deployment in multitenant office buildings and corporate facilities because of low cost, high utility, and ease of management. Contention-based LANs are the most commonly deployed LAN topolo- gies. Distributed-polling environments, however, do have their place. Distributed-Polling LANs In addition to the gladiatorial combat approach to sharing access to a transmission facility, there is a more civilized technique known as dis- tributed polling, or as it is more commonly known, token passing. IBM's Token-Passing Ring is perhaps the best known of these products, fol- lowed closely by FDDI, a 100 Mbps version occasionally seen in campus and metropolitan area networks (although the sun seems to be setting on FDDI). In token-passing LANs, stations take turns with the shared medium, passing the right to use it from station-to-station by handing off a "token" that gives the bearer the one-time right to transmit while all other sta- tions remain quiescent. Thus, the Harvard Approach. This is a much Figure 5-22 LAN switching 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 Premises Technologies fairer way to share access to the transmission medium than CSMA/CD, because while every station has to wait for its turn, it is absolutely guar- anteed that it will get that turn. These systems are therefore character- ized by bounded delay, because there is a maximum amount of time that any station will ever have to wait for the token. Token-passing rings work as shown in Figure 5-23. When a station wishes to transmit a file to another station on the LAN, it must first wait for the "token" a small and unique piece of code that must be "held" by a station to validate the frame of data that is created and transmitted. Let's assume for a moment that a station has secured the token because a prior station has released it. The station plac