isr.co.ro : glossary MacTCP an extension to the Macintosh operating system that provides the code needed to connect to networks using TCP/IP (Transmission Control Protocol/Internet Protocol). It's used to connect to both intranets (internal networks) and the Internet. You need a copy of MacTCP or an equivalent for either a direct connection to the Net or for connection through a remote protocol link such as PPP (Point-to-Point Protocol) or SLIP (Serial Line Interface Protocol). But if you're connecting to the Net through a "shell" account, your computer is acting only as a terminal for your service provider's system, and you only need standard serial communications software.