The Visual Basic has a WinSock control which allows the connection of hosts in a network and it does support TCP. The Windows Sockets specification defines two interfaces: API used by application developers, and the API guarantees that a conforming application will function correctly with a conformance protocol implementation from any network software vendor and SPI which provides a means for network software developers to add new protocol modules to the system. Each interface represents a contract. The SPI contract guarantees that a conformance protocol module may be added to Windows and will thereby be usable by an API-conformance application.