Figure 9-3. TCP Treats All the Data as Data
TCP just needs to worry about the TCP header and doing what it says. In this case, as long as TCP gets the first chunk of data to the server and the second chunk back from the server to the browser, its job is finished.
TCP calls the TCP header and the data behind it a TCP segment. Later in this chapter, in the section titled "Big Box, Small TruckWhat Do You Do?," it will be clear why the people who made up TCP chose to call it a segment.
One of the largest benefits of a layered networking model relates to how TCP behaves in Figure 9-3. The fact that TCP doesn't have to think about what HTTP is trying to do means that the TCP software does not need to know anything about how HTTP works. So, the person who writes the TCP software can keep it simple. The person who writes HTTP software and any other application protocol that intends to use TCP can keep it simple as well, relying on TCP to deliver the data.
If you're feeling a little uncomfortable about TCP at this point, it's okay. So far, this chapter has described some mechanisms that TCP uses, but it hasn't explained much about why TCP is useful to applications. In the next section, you'll learn about error recoveryone of the most important features of TCP.