tailieunhanh - Internetworking with TCP/IP- P10

Internetworking with TCP/IP- P10: 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 | 58 Internetworking Concept And Architectural Model Chap. 3 The User s View Remember that TCP IP is designed to provide a universal interconnection among computers independent of the particular networks to which they attach. Thus we want a user to view an internet as a single virtual network to which all machines connect despite their physical connections. Figure shows how thinking of an internet instead of constituent networks simplifies the details and makes it easy for the user to conceptualize communication. In addition to routers that interconnect physical networks software is needed on each computer to allow application programs to use an internet as if it were a single physical network. The advantage of providing interconnection at the network level now becomes clear. Because application programs that communicate over the internet do not know the details of underlying connections they can be run without change on any computer. Because the details of each machine s physical network connections are hidden in the internet software only the internet software needs to change when new physical connections are added or existing connections are removed. In fact it is possible to optimize the internal structure of the internet by altering physical connections while application programs are executing. A second advantage of having communication at the network level is more subtle users do not have to understand remember or specify how networks connect or what traffic they carry. Application programs can be written that communicate independent of underlying physical connectivity. In fact network managers are free to change interior parts of the underlying internet architecture without changing application software in most of the computers attached to the internet of course network software must be reconfigured when a computer moves to a new network . As Figure shows routers do not provide direct connections among all pairs of networks. It may be necessary .