Professional Visual Basic® 2008

Chapter 31. Network Programming

Just as it is difficult to live your life without talking with people, your applications also need to communicate, perhaps with other programs or perhaps with hardware devices. As you have seen throughout this book, you can use a variety of techniques to have your program communicate, including .NET Remoting, Web Services, and Enterprise Services. This chapter looks at yet another way to communicate: using the basic protocols on which the Internet and many networks have been built. You will learn how the classes in System.Net can provide a variety of techniques for communicating with existing applications such as web or FTP servers, or how you can use them to create your own network applications.

Before getting started on writing applications using these classes, however, it would be good to get some background on how networks are bolted together, and how machines and applications are identified.

Protocols, Addresses, and Ports

No discussion of a network is complete without a huge number of acronyms, seemingly random numbers, and the idea of a protocol. For example, the World Wide Web runs using a protocol called HTTP or Hypertext Transfer Protocol. Similarly, there are File Transfer Protocol (FTP), Network News Transfer Protocol (NNTP), and Gopher, also a protocol. Each application you run on a network communicates with another program using a defined protocol. The protocol is simply the expected messages each program will send the other, in the order ...