Transmission Control Protocol/Internet Protocol
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Visual Basic Winsock
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The Internet Transfer Control (ITC) is a handy control for Internet programming, but there is another control that is even more robust and helps programmers to create more flexible applications. The Winsock control comes with Visual Basic 6.0 (VB6) and is used to create applications that access the low-level functions of the Transmission Control Protocol/Internet Protocol (TCP/IP).
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TCP/IP is a specification that defines a series of protocols used to standardize how computers exchange information with each other. TCP/IP provides communication across interconnected networks that use diverse hardware architectures and various operating systems. The protocols in TCP/IP are arranged in a series of layers known as a protocol stack. Each layer has its own functionality.
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Winsock is a standard that is maintained by Microsoft. This standard is basically a set of routines that describe communications to and from the TCP/IP stack. These routines reside in a dynamic link library (DLL) that runs under Windows. The Winsock DLL is interfaced with TCP/IP and from there through the Internet.
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Ports Let's talk about the ports before we proceed any further. A port is a special memory location that exists when two computers are in communication via TCP/IP. Applications use a port number as an identifier to other computers. Both the sending and receiving computers use this port to exchange data.
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To make the job of communication easier, some port numbers have been standardized. These standard port numbers have no inherent value other than that users have agreed to use them with certain applications. The table below lists a number of popular and publicly accepted port numbers and their corresponding applications. HTTP - port=80, FTP - port=20 and 21, SMTP - port=25, POP3 - port=110.
See for more details: http://www.15seconds.com/issue/010820.htm
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Visual Basic Winsock
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