Experience with connected and disconnected operation of portable notebook computers in distributed systems

DOC (Disconnected Operation Cache) is a two-level client caching system designed and implemented to support connected and disconnected operation of small form-factor, battery-powered portable computers. This paper describes some design features of DOC, and our experiences with running it in the software engineering environment of AST Research. The uniqueness of the DOC project stems from the fact that it has been designed to completely support client caching and disconnected operation of currently existing portable notebook computers. The AST's local area network, consisting of several Novell servers and top-of-the-line notebooks running MS-DOS 6.2 as clients communicating via an Ethernet connection, is used to support the system and perform experiments. DOC supports "connected", "partially disconnected", and "disconnected" modes of operation. The "partially disconnected" mode has been designed to permit DOC to respond, without server involvement, to requests on certain files that are not modified frequently. Results of our experiments indicate not only considerable performance gains for "connected" and "partially disconnected" systems, but also successful operation in the disconnected mode.