tailieunhanh - Internetworking with TCP/IP- P5

Internetworking with TCP/IP- P5: TCP/IP has accommodated change well. The basic technology has survived nearly two decades of exponential growth and the associated increases in traffic. The protocols have worked over new high-speed network technologies, and the design has handled applications that could not be imagined in the original design. Of course, the entire protocol suite has not remained static. New protocols have been deployed, and new techniques have been developed to adapt existing protocols to new network technologies | 8 Introduction And Overview Chap. 1 late 1987 it was estimated that the growth had reached 15 per month. By 2000 the global Internet reached over 50 million computers in 209 countries. Early adoption of TCP IP protocols and growth of the Internet has not been limited to government-funded projects. Major computer corporations connected to the Internet as did many other large corporations including oil companies the auto industry electronics firms pharmaceutical companies and telecommunications carriers. Medium and small companies began connecting in the 1990s. In addition many companies have used the TCP IP protocols on their internal corporate internets even though they choose not to be part of the global Internet. Rapid expansion introduced problems of scale unanticipated in the original design and motivated researchers to find techniques for managing large distributed resources. In the original design for example the names and addresses of all computers attached to the Internet were kept in a single file that was edited by hand and then distributed to every site on the Internet. By the mid 1980s it became apparent that a central database would not suffice. First because computers were being added to the Internet at an increasing rate requests to update the file would soon exceed the personnel available to process them. Second even if a correct central file existed network capacity was insufficient to allow either frequent distribution to every site or on-line access by each site. New protocols were developed and a naming system was put in place across the global Internet that allows any user to resolve the name of a remote machine automatically. Known as the Domain Name System DNS the mechanism relies on machines called name servers to answer queries about names. No single machine contains the entire domain name database. Instead data is distributed among a set of machines that use TCP IP protocols to communicate among themselves when answering a query. The .