Open Transport

Open Transport was the name given by Apple Inc. to their implementation of the Unix-originated System V STREAMS. Based on code licenced from Mentat's Portable Streams product, Open Transport was built to provide the Mac OS with a modern TCP/IP implementation, replacing MacTCP. Apple also added their own implementation of AppleTalk to the stack to support legacy networks.^[1]

History

Open Transport was introduced in May 1995 with the Power Mac 9500. It was included with System 7.5.2, a release for the new PCI based Power Macs, but became available for older hardware later. MacTCP was not supported on PCI-based Macs but older systems could switch between MacTCP and Open Transport using Network Software Selector. Unlike MacTCP, Open Transport allowed users to save and switch between configuration sets.

Developer opinion on Open Transport was divided. Some felt it offered enormous speed improvements over Apple's existing TCP/IP implementation, MacTCP^{[citation needed]}. Some developers also liked it because it was flexible in the way it allowed protocols to be "stacked" to apply filters and other such duties. Some felt that MacTCP was simpler to develop for, especially for code ported from Unix-like platforms. The original TCP/IP stack was fairly unstable, leading to the nickname 'BrokenTransport'^{[citation needed]}. Others didn't like the fact that the API was designed in C++, which made binary compatibility problematic. Originally, OpenTransport could only be utilized using the MPW C/C++ compiler^{[citation needed]}. Classic Mac OS networking proved to be a mixed bag to the very end. The flexibility of the OpenTransport architecture, into which one could plug any desired protocol, was felt by some to be thoroughly overcomplicated, especially as it became clear that TCP/IP would dominate networking in the future.

Indeed, the vaunted flexibility of the Open Transport architecture was undermined and ultimately made obsolete by the rapid rise of TCP/IP networking during the mid-90's. Open Transport was abandoned during the move to Mac OS X, which uses the far more common Berkeley sockets networking system

The Open Transport APIs are still present and usable in a limited form as a compatibility layer for older applications, but are deprecated in the Mac OS X 10.4 and later SDKs.

References

1. ^ Apple Tech Note 1117 - Open Transport STREAMS FAQ

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