Chapter 8. Transport and End-to-End Protocols

So far, we have covered networking activities at the physical, link, and network layers of the Internet Protocol stack. This chapter focuses on foundations of layer 4, the transport layer. We study several techniques for Transmission Control Protocol (TCP) congestion control. These techniques use a form of end-to-end congestion control in a TCP session when a sender sends a packet and a receiver acknowledges receipt of the packet. This chapter covers the following topics:

• Transport layer

• Transmission Control Protocol (TCP)

• User Datagram Protocol (UDP)

• Mobile Transport Protocols

• TCP Congestion Control

We first take a close look at layer 4, the transport layer , and explain how a file is transferred. Layer 4 handles the details of data transmission and acts as an interface protocol between a communicating host and a server through a network. We explain reliable end-to-end connection establishment under the Transmission Control Protocol (TCP).

Next, we present the user datagram protocol (UDP), a connectionless transport-layer protocol that is placed on top of the network layer. We also discuss TCP congestion control. Normally, it would take a significant amount of engineering effort to design a network with low or no congestion. Congestion in communication networks represents a state in which the traffic flow exceeds the availability of network resources to service the flow. Generally, congestion occurs at a network because of a lack of resources at links and devices. We distinguish between these two categories of resource deficits and explore precautionary solutions: flow control and congestion control , respectively. We end the chapter with a discussion of TCP and UDP applications.