ABSTRACT

This chapter discusses the basic Internet communication software and examines the second major communication protocol, Transmission Control Protocol (TCP). Because a router will discard datagrams when the router becomes overrun, the researchers who built the Internet knew that additional communication software would be needed. To handle the problem, they invented the TCP. TCP handles the problems of congestion and datagram loss. TCP is designed to work between any two hosts anywhere on the Internet. The magic of TCP lies in a sophisticated algorithm that automatically chooses how long to wait. TCP did not invent retransmission — before TCP was invented other computer communication protocols used the scheme of starting a timer and resending data if an acknowledgment failed to arrive before the timer expired. As it sends datagrams to a given destination, TCP measures how long it takes for each acknowledgment to arrive. In addition to retransmitting datagrams that have been discarded, TCP handles congestion.