Introduction to TCP/IP

Introduction

With the acceptance of TCP/IP as a standard platform-independent network protocol, and the explosive growth of the Internet, the Windows Sockets API (application program interface) has emerged as the standard for network programming in the Windows environment. This document will introduce the basic concepts behind Windows Sockets programming and get you started with your first application created with SocketWrench.

SocketWrench is part of a package developed by Catalyst called the SocketTools Visual Edition. In addition to the comprehensive, but fairly low-level, access that SocketWrench provides, SocketTools includes components and libraries for many of the popular Internet application protocols, such as FTP, POP3, SMTP and HTTP. For more information about the complete SocketTools package, visit the Catalyst website at www.catalyst.com. It is assumed that the reader is familiar with Visual Basic and has installed the SocketWrench control. If you're already familiar with sockets programming, feel free to skip this section.

The Windows Sockets specification was created by a group of companies, including Microsoft, in an effort to standardize the TCP/IP suite of protocols under Windows. Prior to Windows Sockets, each vendor developed their own proprietary libraries, and although they all had similar functionality, the differences were significant enough to cause problems for the software developers that used them. The biggest limitation was that, upon choosing to develop against a specific vendor's library, the developer was "locked" into that particular implementation. A program written against one vendor's product would not work with another's. Windows Sockets was offered as a solution, leaving developers and their end-users free to choose any vendor's implementation with the assurance that the product will continue to work.

There are two general approaches that you can take when creating a program that uses Windows Sockets. One is to code directly against the API. The other is to use a component which provides a higher-level interface to the library by setting properties and responding to events. This can provide a more "natural" programming interface, and it allows you to avoid much of the error-prone drudgery commonly associated with sockets programming. By including the control in a project, setting some properties and responding to events, you can quickly and easily write an Internet-enabled application. And because of the nature of custom controls in general, the learning curve is low and experimentation is easy. SocketWrench provides a comprehensive interface to the Windows Sockets library and will be used to build a simple client-server application in the next section of this document. Before we get started with the control, however, we'll cover the basic terminology and concepts behind sockets programming in general.

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