| United States Worldwide |
|
| United States Worldwide |
|
Large Scale Distribution(formerly Vantage)Fiscal 1995 Project Portfolio Report
Jim Waldo
Overall ObjectiveThe Large Scale Distribution project is centered around issues involved in making an interconnected set of computers aid groups of users in the performance of their work. The group is structured as an inter-related set of projects, each of which addresses some problems of scaling, partial failure, and the presentation of a comprehensible user model.
Objective for FY95During the 1995 fiscal year, the Large Scale Distribution group investigated problems concerning
DescriptionThe availability of large numbers of computers connected via a network opens up the possibility of utilizing all of the computational resources of an enterprise as a single, distributed system. However, there is little experience with distributed systems on this scale. In particular, such systems will be large enough that at any given time some component of the system is almost certainly going to fail, requiring that designers of protocols used by computational entities within such a system must design with failure in mind. Additionally, such systems open up the possibility of completely new ways of using the computing resources of an enterprise, allowing new ways for the people within the network to interact. Finally, such a system is different in kind from the stand-alone systems that users have grown used to; the user model of the enterprise-wide distributed system is not a simple extension of the individuals desktop.The various projects undertaken as part of the Large Scale Distribution project all center around one or more of these problems. The protocols designed and implemented in the reliable distributed computing investigation all deal explicitly with the problems of failure in large systems. The effort to base object invocations on ATM transport centered on investigating the impact of new networking technologies on the development of distributed application infrastructures. Email-enabled services allow us to study how the computational infrastructure of an enterprise can be used to provide basic services and cope with work-flow applications. The distributed video application toolkit is an attempt to provide users with tools to build applications that will utilize the network in new and different ways. Finally, the multi-screen X server is a way of increasing the amount of screen real estate available to the user, enabling experimentation into new user interface styles that may help in reflecting the enterprise-wide distributed system.
AccomplishmentsReliable Distributed ComputingIn the area of reliable distributed computing, we concentrated on the design of protocols that would guard against the problems introduced in a distributed system by the lack of global knowledge and the possibility of partial failure. Assuming a distributed system made up of interacting objects specified by an Interface Definition Language, we specified interfaces for
ATM transport for object invocationsThe ATMObjects project built a datagram-based transport for the network objects system. We wound up implementing a fairly general purpose message protocol. The protocol was not specific to RPC, but could be used to support a general purpose reliable message passing protocol for a variety of distributed computing purposes. The protocol was derived from a protocol devised by Liskov et. al. that used loosely synchronized clocks for connection management. This protocol allows for efficient connection management without the direct exchange of connection establishment messages.The current implementation runs on top of UDP. We wound up not targeting the ATM network layer directly for a number of reasons. The first reason was the lack of stability of the local ATM network. A second reason was that the local ATM network became dedicated to testing and use by the Parallel Open Systems Group for an extended period of time. A final reason was the lack of documentation and local expertise on writing or using ATM drivers. The longer term goal of investigating fast RPC protocols was met. The protocol that was implemented required a minimal amount of overhead in order to do connection management.
Email-enabled servicesDuring the past year, one email-enabled service was designed, implemented, and deployed, while another was designed and implemented. The service that was deployed utilized secure hashing functions to allow authors to register a hash of their work with the service. The service would gather these hashes and, once a week, a secure digest of these hashes would be published in The Boston Globe. This allowed the minimal date of the production of the document to be proved in the future, making the system into an electronic notary service. The service was completely automated on the server side up to (but not including) the placing of the classified ad in the Globe.This lead to the design and implementation of a complete document registration and clearance system based on electronic mail as the transport mechanism. Meant to replace the current paper-based system used in SML, the system allows the registration, notarization, archiving, and clearance (both management and legal) of documents. All communication is driven by electronic mail, and after the initial entering of a document in the system all viewing is accomplished through the web browser of choice for the person doing the viewing. This system will be deployed in the east coast SML over the summer, and in all of SML sometime in Q2 of the coming year.
Video application toolsDuring the year, the Video application tools project has built up a set of video services that can be manipulated using the TCL scripting language to build small video-based applications. Using a code base imported from MIT, the project has teased out the video functionality into a set of components that can be recombined quickly in a number of ways, allowing the construction of simple video-based applications with a single page of TCL code. In the process of doing this, a number of interesting problems were encountered concerning introducing a multi-threaded model into the original code, which was single threaded.Documentation and deployment of the toolkit is planned for the coming year.
Multi-screen X serverThe multi-screen X server, Xvan, developed in this group two years ago, continued to be evolved and maintained during the year. The server, which allows up to nine physical screens to be treated by the X server as a single bitmap, was moved to the X11R6 code base. The code has been publicly available for over a year as contributed software to the X Consortium, and Sun customers have developed products based on Xvan. The server is in daily use by most members of the east coast division of SML and by a number of engineers on the west coast. Use of the server allows experimentation into user interfaces that require large amounts of screen real estate, which we believe will be necessary in large distributed systems.Recent customer requests have generated considerable interest in Xvan by the Sun consulting organization. We are now in the process of transferring Xvan to that organization, which will take over the maintenance of the server. SunSoft has also shown interest in moving Xvan-like functionality into the standard Sun distribution of the X server.
ReferencesPublications"Events in an RPC Based Distributed System," J. Waldo, A. Wollrath, G. Wyant, S. Kendall, Proceedings of the 1995 Winter USENIX Conference, January, 1995. "Simple Activation for Distributed Objects," A. Wollrath, G. Wyant, J. Waldo, Proceedings of the 1995 USENIX Conference on Object Oriented Programming and Systems, June, 1995.
Return to the Table of Contents
webmaster@sunlabs.eng.sun.com | ||||||||||||||||||||||||||||||||