Dynamic distributed systems

This paper introduces a new methodology for building flexible and programmable multiprocessor systems. It is based on a distributed implementation of monitors which is supported by a system-wide address relocation mechanism. This provides the dynamic reallocation of processes and monitors within the system. Methods of implementing the communications subsystem based on a number of common network architectures are presented. An algorithm which effects dynamic resource allocation is presented. Its effect is that groups of processes which are interacting through a monitor will tend to accumulate at various sites in the system in a manner reflecting the dynamic interaction patterns of the program. This is accomplished without there being any centralized control, or even knowledge of the overall program interactions. The feasibility of the system has been investigated using a model system running on a loosely connected dual processor system.     

Dynamic end-to-end QoS management middleware for distributed multimedia systems

In this paper, we present a separable, reusable middleware solution that provides coordinated, end-to-end QoS management over any type of service component, and can use existing (legacy) QoS management solutions (by using wrappers) in a distributed multimedia system. Our middleware solution incorporates strategic and tactical QoS managers, and supports protocols and messages between tactical managers and managed application components, and between QoS managers in the management hierarchy. Strategic QoS managers take a global view of QoS provided by a set of application components within the manager's policy domain. Tactical QoS managers provide local control over application components. We introduce the concept of QoS policy domains to scope the authority of a strategic QoS manager. We describe how the management hierarchy is dynamically configured and reconfigured based on runtime needs of the application.     

A reliable power management scheme for consistent hashing based distributed key value storage systems

Distributed key value storage systems are among the most important types of distributed storage systems currently deployed in data centers. Nowadays, enterprise data centers are facing growing pressure in reducing their power consumption. In this paper, we propose GreenCHT, a reliable power management scheme for consistent hashing based distributed key value storage systems. It consists of a multi-tier replication scheme, a reliable distributed log store, and a predictive power mode scheduler (PMS). Instead of randomly placing replicas of each object on a number of nodes in the consistent hash ring, we arrange the replicas of objects on nonoverlapping tiers of nodes in the ring. This allows the system to fall in various power modes by powering down subsets of servers while not violating data availability. The predictive PMS predicts workloads and adapts to load fluctuation. It cooperates with the multi-tier replication strategy to provide power proportionality for the system. To ensure that the reliability of the system is maintained when replicas are powered down, we distribute the writes to standby replicas to active servers, which ensures failure tolerance of the system. GreenCHT is implemented based on Sheepdog, a distributed key value storage system that uses consistent hashing as an underlying distributed hash table. By replaying 12 typical real workload traces collected from Microsoft, the evaluation results show that GreenCHT can provide significant power savings while maintaining a desired performance. We observe that GreenCHT can reduce power consumption by up to 35%–61%.     

Dynamic delegation framework for role based access control in distributed data management systems

This paper proposes a logic based framework that extends role based access control systems with dynamic delegation in a decentralised environment. It allows delegation of administrative privileges for both roles and access rights between roles. We have introduced the notion of trust in delegation and have shown how extended logic programs can be used to express and reason about roles and their delegations with trust degrees, roles’ privileges and their propagations, delegation depth as well as conflict resolution. Furthermore, our framework is able to enforce various role constraints such as separation of duties, role composition and cardinality constraints. The implementation of the framework is also discussed. The proposed framework is flexible and provides a sound basis for specifying and evaluating sophisticated role based access control policies in decentralised environments.     

Transaction management in distributed heterogeneous database management systems

Current distributed, heterogeneous database management systems (DBMSs) address the issue of distributed transaction management (DTM) in two different ways: some systems rely solely on unmodified local transaction managers (LTMs), thereby helping preserve local DBMS autonomy, but limit functionality (e.g. allow only unsynchronized retrievals, preclude distributed updates, etc.); others maintain full functionality but require the (re)design of the LTMs to enforce homogeneous DTM across all heterogeneous DBMSs, thereby giving up most of the local DBMS autonomy.

The goal of the work presented here is to establish the minimum set of modifications to LTMs that allow synchronized retrievals and distributed updates (whenever semantic conflicts can be resolved), and will continue to maintain a high degree of local DBMS autonomy. The problems of: (1) distribution of responsibility between DTM and LTMs, (2) concatenation of functionally-equivalent LTM mechanisms, and (3) providing compensation mechanisms for functionally-limited LTMs are introduced. Solutions to the above problems are shown to exist. However, the interconnection of autonomous, heterogeneous DBMSs is significantly more difficult than anticipated, despite communication standardization and current optimism.     

Conflicts in policy-based distributed systems management

Modern distributed systems contain a large number of objects and must be capable of evolving, without shutting down the complete system, to cater for changing requirements. There is a need for distributed, automated management agents whose behavior also has to dynamically change to reflect the evolution of the system being managed. Policies are a means of specifying and influencing management behavior within a distributed system, without coding the behavior into the manager agents. Our approach is aimed at specifying implementable policies, although policies may be initially specified at the organizational level and then refined to implementable actions. We are concerned with two types of policies. Authorization policies specify what activities a manager is permitted or forbidden to do to a set of target objects and are similar to security access-control policies. Obligation policies specify what activities a manager must or must not do to a set of target objects and essentially define the duties of a manager. Conflicts can arise in the set of policies. Conflicts may also arise during the refinement process between the high level goals and the implementable policies. The system may have to cater for conflicts such as exceptions to normal authorization policies. The paper reviews policy conflicts, focusing on the problems of conflict detection and resolution. We discuss the various precedence relationships that can be established between policies in order to allow inconsistent policies to coexist within the system and present a conflict analysis tool which forms part of a role based management framework. Software development and medical environments are used as example scenarios     

Dynamic transaction routing in distributed database systems

The authors investigate dynamic transaction routing strategies for locally distributed database systems in which the database is partitioned and distributed among multiple transaction-processing systems, and the incoming transactions are routed by a common front-end processor. If a transaction issues a database request referencing a nonlocal database partition, the request has to be shipped to the system owing the referenced partition for processing. Various dynamic strategies are studied. Their performance is compared with that of the optimal static strategy. A class of dynamic transaction routing strategies which take into account routing history and minimize the estimated response time of incoming transactions is proposed; they are found to provide a substantial improvement over the optimal static strategy. The robustness of the strategies is further studied through sensitivity analysis over various transaction loads, communication overheads, and database reference distributions     

Relationships between broadcast and shared memory in reliable anonymous distributed systems

We study the power of reliable anonymous distributed systems, where processes do not fail, do not have identifiers, and run identical programmes. We are interested specifically in the relative powers of systems with different communication mechanisms: anonymous broadcast, read-write registers, or read-write registers plus additional shared-memory objects. We show that a system with anonymous broadcast can simulate a system of shared-memory objects if and only if the objects satisfy a property we call idemdicence this result holds regardless of whether either system is synchronous or asynchronous. Conversely, the key to simulating anonymous broadcast in anonymous shared memory is the ability to count: broadcast can be simulated by an asynchronous shared-memory system that uses only counters, but read-write registers by themselves are not enough. We further examine the relative power of different types and sizes of bounded counters and conclude with a non-robustness result. James Aspnes is a Professor of Computer Science at Yale University. He received his Ph.D. from Carnegie-Mellon University in 1992. Faith Ellen Fich is a Professor of Computer Science at the University of Toronto. She received her Ph.D. from the University of California, Berkeley in 1982. Eric Ruppert was educated at the University of Toronto, where he completed his doctorate in 1999. He spent a year as a postdoctoral fellow at Brown University and is an Associate Professor at York University.     

Efficient and reliable service selection for heterogeneous distributed software systems

The service-oriented paradigm is emerging as a new approach to heterogeneous distributed software systems composed of services accessed locally or remotely by middleware technology. How to select the optimal composited service from a set of functionally equivalent services with different quality of service (QoS) attributes has become an active focus of research in the service community. However, existing middleware solutions or approaches are inefficient as they search all solution spaces. More importantly, they inherently neglect QoS uncertainty owing to the dynamic network environment. In this paper, based on a service composition middleware framework, we propose an efficient and reliable service selection approach that attempts to select the best reliable composited service by filtering low-reliability services through the computation of QoS uncertainty. The approach first employs information theory and probability theory to abandon high-QoS-uncertainty services and downsize the solution space. A reliability fitness function is then designed to select the best reliable service for composited services. We experimented with real-world and synthetic datasets and compared our approach with other approaches. Our results show that our approach is not only fast, but also finds more reliable composited services.     

Dynamic energy-aware sensor configuration in multi-application monitoring systems

A typical pervasive monitoring system like a smart building depends on an infrastructure composed of hundreds of heterogeneous wireless sensor devices. Managing the energy consumption of these devices poses a challenging problem that affects the overall efficiency and usability. Existing approaches for sensor energy consumption typically assume a single monitoring application to consume sensor data and a static configuration for sensor devices. In this paper, we focus on a multi-application context with dynamic requirements and multi-modal sensor devices. We present 3SoSM, an approach to optimize interactions between application requirements and wireless sensor environment in real-time. It relies on an energy-aware dynamic configuration of sensor devices to lower energy consumption while fulfilling application requirements. To bind together sensor configuration and dynamic management of data streams, we design a sustainable multi-application monitoring system architecture for pervasive environments that collects application requirements for sensor data streams and optimizes them into sensor configurations. To demonstrate the effectiveness of our approach, a set of experiments are designed in the context of smart buildings. We comparatively evaluate our approach to show how dynamic sensor configuration for multiple monitoring applications indeed outperforms the mainstream duty-cycling method.     

Dynamic structuring of distributed manufacturing systems

The paper addresses the problem of dynamic structuring of manufacturing systems. The approach presented in this paper is based on the decomposition of manufacturing objectives and the allocation of tasks to autonomous building blocks, i.e. work systems, in a dynamic environment. The allocation is based on a market mechanism that enables the self-structuring and optimization of a manufacturing system by evaluation and selection among competing work systems. The mechanism presented is based on logic relations and constraints. It enables the building of task-oriented manufacturing structures of work systems acting in series and/or in parallel. The approach is discussed in an example in the part fabrication domain.     

Microcomputers and distributed database management systems

The role of a DDBMS is to provide overall system integrity, appropriate data access, and recovery over the whole network. Many of the supermicros with powerful 16 and 32 bit architectures will soon be running advanced DBMS and DDBMS software, thus, playing an important role as a distributed database on a network. The article discusses this and future trends.     

Policy driven management for distributed systems

Separating management policy from the automated managers which interpret the policy facilitates the dynamic change of behavior of a distributed management system. This permits it to adapt to evolutionary changes in the system being managed and to new application requirements. Changing the behavior of automated managers can be achieved by changing the policy without having to reimplement them—this permits the reuse of the managers in different environments. It is also useful to have a clear specification of the policy applying to human managers in an enterprise. This paper describes the work on policy which has come out of two related ESPRIT funded projects, SysMan and IDSM. Two classes of policy are elaborated—authorization policies define what a manager is permitted to do and obligation policies define what a manager must do. Policies are specified as objects which define a relationship between subjects (managers) and targets (managed objects). Domains are used to group the objects to which a policy applies. Policy objects also have attributes specifying the action to be performed and constraints limiting the applicability of the policy. We show how a number of example policies can be modeled using these objects and briefly mention issues relating to policy hierarchy and conflicts between overlapping policies.     

Data access in distributed data base management systems

A software organization which provides for data definition and manipulation in a distributed data base system is presented by describing the functions and interrelations of the component processes; with its methodology for access, the physical location of the data is transparent to the user program. The concepts of distributed data bases are discussed and current research is summarized as a means of establishing a method for the data placement and location mechanism. Procedures for the movement of data in a distributed data base system are presented, along with the data manipulation procedures, in terms of their performance and integrity effects. Enhancements to the mechanisms are suggested.     

Key management for role hierarchy in distributed systems

As distributed computing systems grow in size, complexity and variety of applications, the protection of sensitive data against unauthorized disclosure and tampering becomes increasingly important. In this paper, a cryptographic Role-Based kEy Management (RBEM) is developed for the access control in distributed systems. This paper presents features of the RBEM that includes simple rules for key generation, key managements for dynamic hierarchy, algorithms for key generation/modification, and procedures of object assignments. The RBEM is extended from its prime design for one local domain to the design for multiple local domains. The RBEM is decentralized such that each local domain is managed by its local domain security administrator and modifications in any local domain do not affect the keys of roles or objects in other local domains. This paper presents a platform for the comprehensive assessment of the RBEM for the role-based access control. Compared with typical key-management methods, the RBEM updates much less number of keys for the roles and objects when new roles are added to the role hierarchy. This paper presents three typical case studies for illustrating the efficiency of the RBEM.     

Multilevel security issues in distributed database management systems

This paper describes the security needs in a distributed processing environment common to many enterprises and discusses the applicability of multilevel secure database management systems in such an environment.     

A reliable multicast protocol for distributed mobile systems:design and evaluation

Reliable multicast is a powerful communication primitive for structuring distributed programs in which multiple processes must closely cooperate together. We propose a protocol for supporting reliable multicast in a distributed system that includes mobile hosts and evaluate the performance of our proposal through simulation We consider a scenario in which mobile hosts communicate with a wired infrastructure by means of wireless technology. Our proposal provides several novel features. The sender of each multicast may select among three increasingly strong delivery ordering guarantees: FIFO, causal, total. Movements do not trigger the transmission of any message in the wired network as no notion of hand-off is used. The set of senders and receivers (group) may be dynamic. The size of data structures at mobile hosts, the size of message headers, and the number of messages in the wired network for each multicast are all independent of the number of group members. The wireless network is assumed to provide only incomplete spatial coverage and message losses could occur even within cells. Movements are not negotiated and a mobile host that leaves a cell may enter any other cell, perhaps after a potentially long disconnection. The simulation results show that the proposed protocol has good performance and good scalability properties     

A workbench for distributed production management systems

An end-user oriented workbench approach in the design of distributed production management systems (DPMS) is presented. We shall also deal with models and design of DPMS. Changes anticipated in design processes, roles and professionality required are discussed. In fact, complete structural rearrangements in the design of production management systems (PMS) are expected towards the end of this decade. The ideas presented are based on an on-going research project at Helsinki University of Technology (the so-called HUTDPMS project).