Introducing the Transport Layer

Transport layer protocols to provide the following:

• An interface for network applications— that is, a way for applications to access the network. The designers wanted to be able to target data not just to a destination computer, but to a particular application running on the destination computer.

• A mechanism for multiplexing/demultiplexing. Multiplexing, in this case, means accepting data from different applications and computers and directing that data to the intended recipient application on the receiving computer. In other words, the Transport layer must be capable of simultaneously supporting several network applications and managing the flow of data to the Internet layer. On the receiving end, the Transport layer must accept the data from the Internet layer and direct it to multiple applications. This feature, known as demultiplexing, allows one computer to simultaneously support multiple network applications, such as a Web browser, an email client, and a file-sharing application. Another aspect of multiplexing/demultiplexing is that a single application can simultaneously maintain connections with more than one computer.

• Error checking, flow control, and verification. The protocol system needs an overall scheme that ensures delivery of data between the sending and receiving machines.