to do your work and print anytime you wanted-except, of course, for the dis- ruption caused by all of those people standing behind you with floppy disks in their hands promising you that "It's only one just take a second." Thus was born the term "Sneakernet;" in order to print something, you had to put the document on a diskette (probably a 51/4- inch floppy, back when floppies really were floppy), walk over to the machine with the directly attached printer, and beg and wheedle for per- mission to print the file-not the most efficient technique for sharing a printer. Something else was needed. That something was the local area network (LAN). LAN Basics A LAN is exactly what the name implies: A physically small network, typically characterized by high-speed transport, low error rate, and pri- vate ownership, which serves the data transport needs of a geographi- cally small community of users. Most LANs provide connectivity, resource sharing, and transport services within a single building, although they can operate within the confines of multiple buildings on a campus. When LANs were first created, the idea was to design a network option that would provide a low-cost solution for transport. Up until their arrival, the only transport option available was dedicated private line from the telephone company or X.25 packet switching. Both were expen- sive, and X.25 was less reliable than was desired. Furthermore, the devices being connected together were relatively low-cost devices; it sim- ply didn't make sense to interconnect them with expensive network resources. That would defeat the purpose of the LAN concept. All LANs, regardless of the access mechanism, share certain charac- teristics. They all rely on some form of transmission medium that is shared among all the users on the LAN; all use some kind of interrupt and contention protocol to ensure that all devices get an equal opportu- Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Compa