Preserving and using context information in interprocess communication

Reviewer: William W. Oblitey

This paper will be of interest to people concerned with protocol performance and analysis and to those looking for ways of enhancing distributed systems. The authors introduce a newly developed interprocess communication protocol called Psync (for pseudosynchronous). This low-level protocol supports the exchange of messages among a well-defined set of processes and, in the presence of processor or communication failure, it preserves the partial ordering of the messages that have been exchanged among the participants. The paper presents an algorithm for implementing this protocol in a distributed environment along with a discussion of its operational subtleties. These involve problems with host failures and memory management, including three flow-control limitations that inhibit the protocol. The authors also discuss how to accommodate processor failures during conversations and clearly explain the recovery schemes. The paper reports on two sets of experiments that compare Psync with other protocols. The experiments consist of a measure of the round trip delay for Psync and three other protocols (an unreliable datagram protocol, a remote procedure call protocol, and a virtual circuit protocol) and a measure of the performance of Psync with more than two participating hosts. The comparisons are presented in tabular form together with a discussion of the relative performance of Psync as revealed by the experimental results.