Open Transport

Open Transport was the name given by Apple Inc. to its implementation of the Unix-originated System V STREAMS networking stack. Based on code licensed from Mentat's Portable Streams product, Open Transport was built to provide the classic Mac OS with a modern TCP/IP implementation, replacing MacTCP. Apple also added its own implementation of AppleTalk to the stack to support legacy networks.

Prior to the release of Open Transport, the classic Mac OS used a variety of stand-alone INITs to provide networking functionality. The only one that was widely used throughout the OS was the AppleTalk system. Among the other supported, MacTCP was becoming increasingly important as the Internet boom started to gain momentum. MacTCP emulated the Berkeley sockets system, widely used among Unix-like operating systems.

MacTCP and the previous generation AppleTalk library were slow on PowerPC-based Macintoshes because they were written for previous generation 680x0-based Macintoshes and therefore ran under emulation on PowerPC-based machines. MacTCP was also lacking in features, however, and a major upgrade was clearly needed if Apple was to keep its hand in the Internet market.

Through the late 1980s several major efforts to re-combine the many Unix derivatives into a single system were underway, and the most significant among these was the AT&T-led System V. System V included an entirely new networking stack, STREAMS, replacing the existing Berkeley sockets system. STREAMS had a number of advantages over sockets, including the ability to support multiple networking stacks at the same time, the ability to plug in modules into the middle of existing stacks to provide simple mechanisms for filtering and similar duties, while offering a single application programming interface to the user programs. At the time it appeared STREAMS would become the de facto standard.

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