Dirk Trossen

CCS: CORBA-Based Conferencing Service

An efficient conferencing service facilitates the implementation and the run-time control of conference applications. Key features of a conferencing service are conference management, multicast communication support, application state synchronization and user data marshalling. The paper defines a conferencing service to fulfil the requirements of conferencing applications. An object model of the service is defined and implemented using the CORBA distributed platform. The conference control protocol, which is used for our conferencing service, is introduced together with architecture of our implementation.

Minimizing the average cost of paging on the air interface-an approach considering privacy

Location management of mobile users in a cellular network is considered from a performance and privacy point of view. Location management covers tracking functionality and paging (searching) functionality. After a risk analysis of location management w.r.t. privacy, we focus on the paging strategy. A sequential search strategy is proposed which reduces the signaling on the air interface and also considers the users privacy.

Improved resource management for the ITU T.122 standard

Conferencing applications facilitate communication and cooperation between distributed end-systems. Both the progress in communications and distributed algorithms and the increased performance of computers and networks make the employment of these applications possible. The ITU defined standards for conference applications are collected in the T.120 standards. The paper gives an overview of the resource management concept of the multipoint communication service (T.122). A main conceptual weak spot is identified. The standard uses a central database to manage the internal resources, which leads to high response time and unnecessary load. An improved resource management scheme is introduced. Simulation results are shown to evaluate the approach.

Scalable conferencing support for tightly-coupled environments: services, mechanisms, and implementation design

Distributed conferencing applications have become more and more popular. Progress in communication systems and increased functionality of these applications are the main pushing factors from a technical point of view. The increasing costs and distribution of institutions are the pulling factors from a users point of view. Key features of group communication applications are conference management, multipoint communication, distributed application synchronization, and user data marshaling. These features are mostly independent from specific scenarios. Thus, it is useful to provide a generic service to accelerate and simplify the development of such applications. For global usage in the Internet, scalability in terms of group size and distribution of the entities is a big issue in the design of such services. The paper defines requirements for a scalable conferencing service introducing the services as well as the protocol mechanisms. Finally, the implementation design of the service is presented.

SCCS: scalable conferencing control service

An efficient conference service facilitates the implementation and the run-time control of conference applications. Key features of a conference service are conference management, multicast communication support, application state synchronization, user data marshalling and scalability. The paper defines a conferencing service to fulfil these requirements of conferencing applications. The conference control protocol, which is used for our conferencing service, is described in its main parts like topology, reconfiguration and multipoint transfer. An object model of the service is proposed together with the resulting architecture. A multipoint platform is introduced as a case study.

Combining CORBA and ITU-T.120 to an Efficient Conferencing Service

An efficient conference service facilitates the implementation and the run-time control of conference applications. Key features of a conference service are conference management, multicast communication support, application state synchronization, and user data marshalling. The paper compares the features offered by the T.120 standards and the CORBA distribution platform. Since they complement each other, it is discussed how a conference service based on a combination of T. 120 standards and CORBA can be realized.

Framework for Automatic SDL to C++ Translation

Due to the increasing complexity of distributed systems the need for a formal description of these systems arises. Specification description languages like SDL enable the formal specification of distributed systems for verification purposes of the system. For simplification of the development process the need for an automatic translation from the specification language to a programming language like C or C++ arises. High performance and a good readability of the translated code are crucial for the usability of an automatic translation. This paper introduces a framework for the automatic translation of an SDL specification to C++ providing high performance together with good readability of the resulting code. For that we present an object model together with an efficient implementation of the finite state machine with constant costs only using polymorphism. Additionally we present mechanisms to reduce copy and memory allocation operations. A performance evaluation for these mechanisms is also presented.

Strategies for Minimizing the Average Cost of Paging on the Air Interface

Location Management of mobile users in a cellular network covers tracking and paging (searching) functionality. In this paper a sequential search strategy is proposed which reduces the signaling on the air interface and also considers the user’s privacy using implicit addresses. After introducing some related work on paging and reducing the costs of paging, the basic idea of the search strategy is described. The used paging methods are crucial for the effectiveness of this strategy. For that, three different paging methods are proposed using fixed and variable segment sizes. The methods are evaluated according to their costs in terms of delay, bandwidth and paging steps. For that the model is described we used for our simulations. Metrics are defined to evaluate the strategies before presenting our results using an event-driven simulation.

Conference protocol evaluation: a load model to develop conference control protocols

Conference applications facilitate communication and cooperation between users at different locations. Crucial for the acceptance of a conference application is the optimal mapping of well known social group behavior to widely spread distributed system within a network. Efficient standardized protocols become mandatory to enable the connectivity among systems of different vendors and to facilitate the implementation of conference applications by providing a generic group communication functionality. For the performance evaluation of group communication protocols in terms of scalability, load and latency, simulations may be used. For the evaluation of the protocol, the generated load within the simulation is crucial for the significance of the evaluation. Statements about usability are useless, if the given load is not realistic. For that, our work presents a model to generate loads, which are typical of different group communication scenarios. These scenarios are evaluated and defined in a formal load model which may be used in simulations. We also present simulation result for the comparison of the resource management of the T.120 group communication standard and an improved scheme, which was developed at our department. It is shown that using our load mode, a detailed evaluation and improvement of group communication protocols is feasible without implementing and testing in large environments.

ITU T.120 series of standards as a basis for conference applications

Conference applications facilitate communication and cooperation between users at different locations. Increased costs and the distribution of institutions and companies lead to a stronger need for coherence applications as an efficient utility for collaboration. The deployment of coherence applications was enabled by research progress in communications and distributed algorithms as well as by increased performance of computers and networks. Efficient standardized protocols become mandatory to enable the connectivity among systems of different vendors and to facilitate the implementation of coherence applications. The ITU defined a number of standards for conference applications in the T.120 series of standards. The paper describes and evaluates the features of the ITU T.120 series of standards. The concepts and algorithms are analyzed with regard to the application scenarios that can be covered efficiently. The analysis shows two main conceptual weaknesses. First, efficient multicast capabilities of networks are not directly used since multipoint connections are inefficiently mapped on reliable point-to-point connections. Second, the administration of the conference data base is defined in a way not suited for conferences with many participants. The theoretical analysis is backed by a number of measurements performed with our implementation of the T.120.