A Quick Look at TCP/IP Networking

The practice of describing protocol systems in terms of their layers is widespread and nearly universal. The layering system does provide insights into the protocol system, and it's impossible to describe TCP/IP without first introducing its layered architecture. However, focusing solely on protocol layers also creates some imitations.

First, talking about protocol layers rather than protocols introduces additional abstraction to a subject that is already excruciatingly abstract. Second, itemizing the various protocols as subheads within the greater topic of a protocol layer can give the false impression that all protocols are of equal importance. In fact, though every protocol has a role to play, most of the functionality of the TCP/IP suite can be described in terms of only a few of its most important protocols. It is sometimes useful to view these important protocols in the foreground, against the backdrop of the layering system described earlier in this hour.

Figure 2.4 describes the basic TCP/IP protocol networking system. Of course, there are additional protocols and services in the complete package, but Figure 2.4 shows most of what is going on.

The basic scenario is as follows:

Of course, there are endless details describing how each protocol goes about fulfilling its assigned tasks. For instance, how does TCP provide flow control, how do ARP and RARP map physical addresses to IP addresses, and how does IP know where to send a datagram addressed to a different subnet? These questions are explored later in this book. You'll also learn more about the TCP/IP protocols and about the processes described in this section in later hours.