Reflections on VM/Pass-Through: A facility for interactive networking

VM/Pass-Through, an interactive networking facility, has gained widespread acceptance within IBM and with IBM customers. Pass-Through allows a single terminal access to many different computers, including those at distant locations. In building Pass-Through, and in observing its growing use, we have had an opportunity to study the practical implications of this facility and of our approach to its design. This paper is divided into two parts. The first, an introduction to Pass-Through networking, describes features of the system, supported configurations, and use of Pass-Through within the IBM Corporation. A brief history of Pass-Through's development is also provided. In the second part of the paper, Pass-Through is used to motivate a technical discussion of interactive network technology and virtual machine subsystems. Topics covered include appropriate use of the virtual machine environment, choice of routing strategy, and performance considerations. Although the introductory portions of the paper presume no prior knowledge of computer network or operating system technology, the subsequent technical discussions do depend on a basic understanding of these areas.