Shipping Basics: Controlling Shipments Using Shipping Labels

Shipping Basics: Controlling Shipments Using Shipping Labels

When you decide to ship a package using any well-known shipping company, you fill out a shipping label, attach it to the package, and leave the package where the shipper will find it when he stops by that day. In short, you tell the shipper where to send the package and then choose among several options for delivery. Magically, the package appears at the correct destination.

Although you might think that shipping labels are rather boring, there are a couple of key facts about them that are practically identical to TCP. For instance, shipping labels

• Include the shipper's address on the form

• Include the recipient's address on the form

• Specify other options, such as speed of delivery, insurance, and phone numbers in case there is a problem

• Put each bit of information in the same place, every time

• Ensure that everyone who touches the package at various points in its trip knows exactly what to do with the package

Okay, back to networking. The term "encapsulation" refers to the same general idea for networking as does the shipping label for shipping packages. For example, Figure 9-2 illustrates a more detailed example of a simple HTTP GET request for a home page, with TCP encapsulation shown. Keith's browser requests the home page. However, the browser does not actually send the request over the network; it simply asks the TCP software on Keith's computer to send the data for it. (In this chapter, I am ignoring other network detailssuch as the physical transmissionbut that does happen as well.)