6.34 Network architectures and interconnection

The network structure—its architecture —typifies what are known as wide area networks (WANs). The nodes, and users for that matter, are spread geographically over longdistances. "Long" has no precise definition, and is intended to suggest that the communication links vary widely. The Internetis certainly the largest WAN, spanning the entire earth and beyond. Local area networks , LANs, employ a single communication link and special routing. Perhaps the best knownLAN is Ethernet . LANs connect to other LANs and to wide area networks through specialnodes known as gateways ( [link] ). In the Internet, a computer's address consists of a four bytesequence, which is known as its IP address (Internet Protocol address). An example address is 128.42.4.32 : each byte is separated by a period. The first two bytes specify the computer's domain (here Rice University). Computers are also addressed by a more human-readable form: a sequence ofalphabetic abbreviations representing institution, type of institution, and computer name. A given computer has both names( 128.42.4.32 is the same as soma.rice.edu ). Data transmission on the Internet requires the numerical form. So-called name servers translate between alphabetic and numerical forms, and the transmitting computer requests this translation beforethe message is sent to the network.