Group and Session Management for Collaborative Applications

This thesis deals with the design and implementation of a group and session management system for collaborative applications. The need for such a system has been identified during work on group communication systems and collaborative applications. Currently, the support for collaborative applications provided by group communication systems is not very powerful (from the point of view of designers of collaborative applications). The goal of this thesis is to develop a system which provides designers of collaborative applications with group and session management functionality that can be used to easily build group communications. The architecture of the group and session management system (GMS) consists of a component which is integrated on the user side (typically, the direct user of the group and session management system is a group communication system), and a specialized directory service which is accessed by the user-side component. The two main aspects of the group and session management system are the data model and the functional model. The data model describes the object types which can be used for group and session management and the operations which can be used with these object types. The functional model describes how the operations are carried out inside GMS, ie how GMS works internally. The GMS data model consists of six object types and a number of relations which can be established between objects of these types. The user object type represents a person or entity using GMS. Each user has an identity (a name) and one or more methods of self-authentication. The group object type is used to define groups which can consist of users and/or groups. The flow object type represents one connection for data transport. The session data type is the main metaphor for group communication. Each session is used to logically group a number of flows and to create an abstraction for management, authorization, and admission control for flows. Two additional object types are certificates and flow templates, which are used for security purposes and for storing information related to the creation of flows. GMS is a distributed system which defines two protocols: an access protocol for communicating with the distributed system, and a system protocol for communications between the distributed entities of the system. The access protocol is based on a reliable, connection-oriented transport service. The system protocol uses two different transport services: a reliable, connection-oriented service and a reliable, FIFO ordered multicast service. A prototype of GMS has been implemented on a Unix platform and a number of performance tests and evaluations have been performed. The results showed that the GMS approach to group and session management is feasible and that the system can easily be used by designers of group communication systems. However, the prototype implementation has some performance drawbacks, for which possible solutions are also suggested.