11.1. Interprocess-Communication Model

There were several goals in the design of the interprocess-communication enhancements to UNIX. The most immediate need was to provide access to communication networks such as the DARPA Internet [Cerf, 1978]. Previous work in providing network access had focused on the implementation of the network protocols, exporting the transport facilities to applications via special-purpose—and often awkward—character-device interfaces [D. Cohen, 1977; Gurwitz, 1981]. As a result, each new network implementation resulted in a different application interface, requiring most existing programs to be altered significantly or rewritten completely. The 4.2BSD interprocess-communication facilities were intended to provide a sufficiently general interface to allow network-based applications to be constructed independently of the underlying communication facilities.

The second goal was to allow multiprocess programs, such as distributed databases, to be implemented. The UNIX pipe requires all communicating processes to be derived from a common parent process. The use of pipes forced systems such as the Ingres database system to be designed with a somewhat contorted structure [Kalash et al, 1986]. New communication facilities were needed to support communication between unrelated processes residing locally on a single host computer and residing remotely on multiple host machines.