Computer and Communication Networks (paperback)

8.6. Summary

All end-to-end communications, such as packet segmentation, packet reassembly, and error checking are managed through the transport layer . The transport layer is responsible for connection signaling and file transfer. The two most important forms of transport are the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP).

TCP provides a reliable service. Reliability is provided using an automatic repeat request (ARQ) protocol. TCP also provides flow control using a sliding-window scheme, as well as congestion control. Additive increase, multiplicative decrease control performs a slow increase in the congestion window size when network congestion decreases and a fast drop in the window size when congestion increases . A better technique is the slow-start method , which increases the congestion window size nonlinearly. The fast retransmit of segments sometimes leads to a retransmission of the lost packet before the associated timeout periods. We looked at various congestion- avoidance mechanisms, including the TCP normalized mechanism.

UDP is another transport-layer protocol described in this chapter. UDP is placed on top of the network layer and is a connectionless protocol, as there is no handshaking between sending and receiving points before sending a segment.

The next chapter presents the application layer in the protocol stack. This layer is responsible for networking applications, e-mail and the World Wide Web (WWW). The chapter ends with a discussion of network management.