a network, SO the connection between, the invention of telegraphy in the nineteenth century. for example, a desktop computer and an external However, the use of data networks has expanded tre- modem (if there are any readers who remember such mendously with the proliferation of computers and other an impractical arrangement) is a data link rather than digital devices. Today, networks extend everywhere, and a data network. However, more sophisticated cabling the Internet-the network of networks-allows com- systems such as the small computer system interface, puters almost anywhere in the world to communicate which allow sharing of a single continuous cable bus with each other using these networks. between multiple stations, may be regarded as Data networks can be organized in a hierarchy based networks. More recently, wireless PANs (WPANs) on physical extent. The physical reach of the network is have become available, with the ambition to replace a useful figure of merit both for technical and practical the tangle of cabling that moves data between reasons. Information cannot move faster than the speed devices today. Wired PANs were purely dedicated of light, SO as the distance covered by a network grows, its to moving data, though some WPAN technologies latency-the minimum time needed to send a bit be- (such as Bluetooth, discussed in section 5.1.5.1) tween stations-grows too. Latency has important con- also support voice traffic. sequences on how networks are designed and operated: if Local area networks (LANs): LANs were invented to the transmitter has to wait a long time for a reply to connect computers within a single facility, originally a message, it makes sense to send large chunks (packets) defined as a room or small building and later of information at once, because otherwise the medium extended to larger facilities and multisite campuses. will simply be idle while awaiting confirmation. Long LANs extend a few hundred meters to a few Communications Engineering Desk Reference; ISBN: 9780123746481 Copyrigh