A membership service is of paramount importance in the successful operation of a GCS. It is the membership view, mentioned earlier, that allows for a process to know what other processes it is able to communicate with at a particular time. A membership service can either be partitionable or only allow for an active primary partition. All three of the GCSs we will look at are partitionable. Basic membership service requirements are outlined below, with the last four being more advanced requirements:Figure 2.3 Message Ordering QoS HierarchyFigure 2.8 The Horus System (layered approach example)3.2.1 Filterfresh Membership Service4.1 JSDT and GCS Requirements4.2 Comparison of JSDT to existing GCS4.2.1 JSDT vs. TransisTransis, being a transport level GCS operates at a lower level than the JSDT, which exists more at the application level. The JSDT is intended for integration with a Java application or applet to enable collaborative functionality in what may have been a single-user program. Transis on the other hand is layered below the application to provide its GCS capabilities. While the JSDT can be used on the several platforms that support the Java Virtual Machine, Transis is restricted to the Unix environment, thus limiting the final destination of a GCS application employing Transis. Written in the C programming language, Transis takes advantage of the underlying system and network interfaces [3]. Although not explicitly tested, it would be reasonable to suggest that Transis provides better communication performance than that of the JSDT. Not only does any program employing the JSDT for group communication have to contend with the JVM layer for communication, it is also restricted to the transport protocols with which the JSDT tools can interface. As of version 1.4 of the JSDT, these are restricted to sockets (TCP/IP sockets), LRMP (light weight reliable multicast package), or RMI (remote method invocation). Version 1.5, which is not in full production at the time of this writing, provides an additional HTTP (Hyper-Text Transfer Protocol) option [11]. The JSDT is designed to keep the particular implementation interface invisible to the user and, as mentioned previously, provides the means to interface with arbitrary proprietary protocols as well as those based on standard networking interfaces [2]. Most of these differences are due to the fact that the primary focus of Transis is to provide a partitionable membership service, providing more fault-tolerance, while the main focus of the JSDT is to provide a flexible, collaborative computing environment.4.2.3 JSDT vs. HorusHorus is probably the most extensible of the early GCS systems that are mentioned. Like Transis and Totem, Horus is also limited to the Unix environment and other environments that can support the Horus APIs. It is also programmed using the C and ML programming languages, where the JSDT is programmed completely in Java. Thus, Horus provides a lesser degree of platform independence than the JSDT. This is not a very important factor when considering fault tolerant approaches to GCS. However, when considering the practicality of use of a distributed GCS system, it would be desirable to overlook the specifics of the potential platforms where each node will reside.4.2.4 JSDT vs. JGroup and FilterfreshAs the JGroup and Filterfresh tools are also 100% pure Java, a better mapping to the JSDT might be expected. However, both of these are also developed based on fault-tolerant approaches to GCS, leaving a direct comparison difficult. The fact that all of these tools are developed using Java suggests that more fault-tolerant approaches to GCS can be realized using the JSDT.4.4 JSDT and GCS Concluding RemarksThe crcProjectAccessToken protects the crcProjectAccessList. Any client, via the listener callback, has read access to the crcProject. When a Client wants to request edit access to a given card, it takes the following steps:5.6 The JSDT and Partitioning5.7 Collaborative CRCTool ConclusionGroup CommunicationJoshua A. Boggis, Richard C. Gronback, Harry L. Sauers, Adam P. UccelloUniversity of ConnecticutComputer Science and EngineeringCSE 298/300 – Distributed Object ComputingMay 04, 1999AbstractThe task of efficiently managing a group of inherently autonomous individualsworking on a common project is difficult at best; impossible at worst.Coordinating their efforts, allowing for the absence and addition of groupmembers, and ensuring all of them are reading from the same page of the"script" is a management task that originates with civilization itself. Theanalogous problem in achieving reliable, distributed interprocesscommunications among a number of computers, each with its own operator,seems even more difficult. In trying to solve this "problem within a problem,"many forms of Group Communication Services (GCS) have been developed andin some cases deployed in the recent past. They all deal, to one extent oranother, with phrases like virtual synchrony, partitionability, and fault-tolerance. In this paper, we will look at these phrases and compile a short listof what these services do and do not provide. Next, as the computing world isablaze with Java, we will determine what role Java has or will play in GCSs.Following that, we will take an in-depth look at one Java-based collaborativedevelopment API, the Java Shared Data Toolkit (JSDT), and determine itscapabilities with respect to the fundamentals of GCSs. Finally, we intend toprovide a high level specification of a JSDT-based application, detailing how toincorporate the basics of a truly collaborative development environment intoan existing stand-alone program.Page 2 of 76 05/04/991. IntroductionThe definition of group communication is as dynamic as most newly emergingtechnologies within the computing community. Depending on what oneconsiders a group, and what is meant by communication, it is possible for eachperson's expectation of what a Group Communication Service (GCS) shouldprovide to be unique. This paper will begin with an attempt to provide a generaldefinition of group communication and identify what services are necessary tofulfill its most basic aspects. As the concept grows in scope and popularity, sodoes the definition and therefore a set of extended services will be identifiedwhich address them as well.
View Full Document
Unlocking...