This thesis describes the architecture of a portable, network-transparent communication system (NTCS), which supports the message passing requirements of a large class of distributed systems. These are large-grain, loosely-coupled systems, distributed at the process level. The NTCS provides interprocess communication, while isolating the application from issues such as physical location, underlying communication details, and internetting. It also allows for dynamic reconfiguration; processes can be transparently distributed across different machines while running. By developing applications around the NTCS, the design process is simplified and enhanced, the resultant architecture can apply to a broader `class' of systems, and the implementation will be less tightly bound to a single machine or set of machines. For these reasons, this approach works well in testbed environments.

Full implementations of this NTCS have been used extensively during its development over the past two years, as the foundation of a distributed information retrieval system testbed: the Utah Retrieval System Architecture (URSA) project. The NTCS is built on top of the existing interprocess communication system on each machine, following a cleanly layered design. Except for a small, nonportable conversion layer, it is entirely portable. Additional upper layers provide internet support, dynamic reconfiguration, and a naming service. It was implemented in the C programming language.