tailieunhanh - Internetworking with TCP/IP- P25

Internetworking with TCP/IP- P25: 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 | 13 Reliable Stream Transport Service TCP Introduction Previous chapters explore the unreliable connectionless packet delivery service that forms the basis for all internet communication and the IP protocol that defines it. This chapter introduces the second most important and well-known network-level service reliable stream delivery and the Transmission Control Protocol TCP that defines it. We will see that TCP adds substantial functionality to the protocols already discussed but that its implementation is also substantially more complex. Although TCP is presented here as part of the TCP IP Internet protocol suite it is an independent general purpose protocol that can be adapted for use with other delivery systems. For example because TCP makes very few assumptions about the underlying network it is possible to use it over a single network like an Ethernet as well as over a complex internet. In fact TCP has been so popular that one of the International Organization for Standardization s open systems protocols TP-4 has been derived from it. The Need For Stream Delivery At the lowest level computer communication networks provide unreliable packet delivery. Packets can be lost or destroyed when transmission errors interfere with data when network hardware fails or when networks become too heavily loaded to accommodate the load presented. Networks that route packets dynamically can deliver them out of order deliver them after a substantial delay or deliver duplicates. Furthermore 209 210 Reliable Stream Transport Service TCP Chap. 13 underlying network technologies may dictate an optimal packet size or pose other constraints needed to achieve efficient transfer rates. At the highest level application programs often need to send large volumes of data from one computer to another. Using an unreliable connectionless delivery system for large volume transfers becomes tedious and annoying and it requires programmers to build error detection and recovery into each