The Transport layer

While the application layer is the layer of the OSI model that the vast majority of .NET developers work with in their daily lives, it would be useless without sound, reliable protocol implementations on the transport layer. It's on this layer that the connections are made and the data is streamed. It's the lowest layer in the stack that an individual host is directly responsible for, and in the transport layer, TCP and UDP reign supreme. Each provide their own mechanisms for delivering streams of data to their destination, and each present their own trade-offs, to be considered when choosing a transport protocol for your network services. As with all of these protocols, we'll take a closer look at them later in this book, but for now let's learn what they are and why they came to be.

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