The Australian CSIRONET network links a variety of host mainframes, user terminals, and other systems, via an Australia-wide packet-switching subnetwork comprising over 120 minicomputers. A layered network architecture has been used in integrating different host systems into the network. Portable software has been used extensively in implementing various layers in different systems. This paper discusses the use of portable software in supporting file transfers on CSIRONET. Two important benefits result from the systematic use of portable software. The first is the ease with which a new type of system can be integrated into the network. The second is the high degree of flexibility in changing layer functions and protocols, and propagating these changes to the network interfaces on different systems. The original layer protocols on CSIRONET were CSIRONET-specific. However, as the OSI standards emerge, these are being phased into use through the portable interface software. These portable software concepts have universal value in the present environment of evolving network standards.

The critical region construct can be usefully extended by adding region entry conditions and replacing the mutual exclusion restriction by a more general restriction. This paper discusses an extended construct of this nature, and presents an implementation approach based on Dijkstra's secretary process concept, with the code for the secretary process generated automatically during program compilation. This type of implementation can produce efficient solutions to many complex synchronization problems. It is also applicable in a wide range of hardware/software environments, including many existing systems. The use of the construct is demonstrated by a number of programming examples.

A proposal is presented for low level hardware features which would assist in the realisation of the abstraction of a computer system as a set of asynchronous communicating processes. A low level synchronisation and communication mechanism, called a mailbox, is described, together with details of a hardware structure for configuring a complete system around a set of these mailboxes. Programming for this architecture is then discussed. It is shown how the new features can be used for controlling input/output, and for handling general synchronisation.