atically different network require- ments. With standard text-based exchanges (i.e., the downloading of largely text- based pages), Web surfing is not a highly challenging application. But as mentioned in the Introduction and emphasized throughout Part III, "The New Generation of Networks," the introduction of applications that include images, animation, real- time voice, real-time video, streaming media, and interactivity creates the need for greater capabilities in the network. This includes the need for more bandwidth support the demanding interactive audio/video realm and mechanisms that address quality of service (QoS), which enables the control of priorities, latencies (delays), and packet losses. As discussed in Part III and Part IV, "Wireless Com- munications," optical and wireless broadband technologies are delivering more and more bandwidth, and QoS techniques are increasingly finding their way into networks. Today, it's possible to append an entire family vacation photo album to an e-mail message, and such a massive file requires a lot of bandwidth. But e-mail in its generic text-based form is a low-bandwidth application that is delay insensi- tive. If an e-mail message gets trapped somewhere in the Net for several seconds, its understandability will not be affected because by the time you view it, it will have all been put on the server where your e-mail resides, waiting for you to pick it up. Another important issue with e-mail is error control. Networks today rarely perform error control because it slows down the traffic too much, so error control and recovery need to be handled at the endpoints. Instead, internetworking proto- cols deployed at the end node, such as TCP, detect errors and request retransmis- sions to fix them. The Evolution of Data Communications Another prevalent data networking application is transaction processing. Examples of transaction processing include a store getting approval for a credit card purchase and a police officer checking a database for your driver's license numbe