The Experts below are selected from a list of 165 Experts worldwide ranked by ideXlab platform

L. Georgiadis - One of the best experts on this subject based on the ideXlab platform.

  • Replicated Server Placement with QoS Constraints
    IEEE Transactions on Parallel and Distributed Systems, 2006
    Co-Authors: G. Rodolakis, S. Siachalou, L. Georgiadis
    Abstract:

    The network planning problem of placing Replicated Servers with QoS constraints is considered. Each Server site may consist of multiple Server types with varying capacities and each site can be placed in any location among those belonging to a given set. Each client can be served by more than one location as long as the round-trip delay of data requests satisfies predetermined upper bounds. Our main focus is to minimize the cost of using the Servers and utilizing the link bandwidth, while serving requests according to their delay constraint. This is an NP-hard problem. A pseudopolynomial and a polynomial algorithm that provide guaranteed approximation factors with respect to the optimal for the problem at hand are presented

  • Replicated Server placement with qos constraints
    International Workshop on Quality of Service, 2005
    Co-Authors: G. Rodolakis, S. Siachalou, L. Georgiadis
    Abstract:

    The problem of placing Replicated Servers with QoS constraints is considered. Each Server site may consist of multiple Server types with varying capacities and each site can be placed in any location among those belonging to a given set. Each client can de served by more than one locations as long as the request round-trip delay satisfies predetermined upper bounds. Our main focus is to minimize the cost of using the Servers and utilizing the link bandwidth, while serving requests according to their delay constraint. This is an NP-hard problem. A pseudopolynomial and a polynomial algorithm that provide guaranteed approximation factors with respect to the optimal for the problem at hand are presented.

A. Schiper - One of the best experts on this subject based on the ideXlab platform.

  • SRDS - Preventing orphan requests in the context of Replicated invocation
    22nd International Symposium on Reliable Distributed Systems 2003. Proceedings., 2003
    Co-Authors: S. Pleisch, A. Kupsys, A. Schiper
    Abstract:

    In today's systems, applications are composed from various components that may be located on different machines. The components (acting as Servers) may have to collaborate in order to service a client request. More specifically, a client request to one component may trigger a request to another component. To ensure fault-tolerance, components are generally Replicated. Replicated components lead to the problem of a Replicated Server invoking another Replicated Server. We call this the problem of Replicated invocation. Replicated invocation has been considered in the context of deterministic Servers. However, the problem is more difficult to address when Servers are non-deterministic. In this context, work has been done to enforce deterministic execution. In this paper, we consider a different approach: instead of preventing non-deterministic execution of Servers we discuss how to handle it. We present the problem of non-deterministic Replicated invocation. Our solution then consists of sharing sufficient undo information among the replicas of the Server invoking another Server.

  • Preventing orphan requests in the context of Replicated invocation
    22nd International Symposium on Reliable Distributed Systems 2003. Proceedings., 2003
    Co-Authors: S. Pleisch, A. Kupsys, A. Schiper
    Abstract:

    In today's systems, applications are composed from various components that may be located on different machines. The components (acting as Servers) may have to collaborate in order to service a client request. More specifically, a client request to one component may trigger a request to another component. To ensure fault-tolerance, components are generally Replicated. Replicated components lead to the problem of a Replicated Server invoking another Replicated Server. We call this the problem of Replicated invocation. Replicated invocation has been considered in the context of deterministic Servers. However, the problem is more difficult to address when Servers are non-deterministic. In this context, work has been done to enforce deterministic execution. In this paper, we consider a different approach: instead of preventing non-deterministic execution of Servers we discuss how to handle it. We present the problem of non-deterministic Replicated invocation. Our solution then consists of sharing sufficient undo information among the replicas of the Server invoking another Server.

  • SRDS - Chasing the FLP impossibility result in a LAN: or, How robust can a fault tolerant Server be?
    Proceedings 20th IEEE Symposium on Reliable Distributed Systems, 2001
    Co-Authors: P. Urban, X. Defago, A. Schiper
    Abstract:

    Fault tolerance can be achieved in distributed systems by replication. However Fischer, Lynch and Paterson (1985) have proven an impossibility result about consensus in the asynchronous system model, and similar impossibility results exist for atomic broadcast and group membership. We investigate, with the aid of an experiment conducted in a LAN, whether these impossibility results set limits to the robustness of a Replicated Server exposed to extremely high loads. The experiment consists of client processes that send requests to a Replicated Server (three replicas) using an atomic broadcast primitive. It has parameters that allow us to control the load on the hosts and the network, as well as the timeout value used by our heartbeat failure detection mechanism. Our main observation is that the atomic broadcast algorithm never stops delivering messages, not even under arbitrarily high load and very small timeout values (1 ms). So, by trying to illustrate the practical impact of impossibility results, we discovered that we had implemented a very robust Replicated service.

  • Chasing the FLP impossibility result in a LAN: or, How robust can a fault tolerant Server be?
    Proceedings 20th IEEE Symposium on Reliable Distributed Systems, 2001
    Co-Authors: P. Urban, X. Defago, A. Schiper
    Abstract:

    Fault tolerance can be achieved in distributed systems by replication. However Fischer, Lynch and Paterson (1985) have proven an impossibility result about consensus in the asynchronous system model, and similar impossibility results exist for atomic broadcast and group membership. We investigate, with the aid of an experiment conducted in a LAN, whether these impossibility results set limits to the robustness of a Replicated Server exposed to extremely high loads. The experiment consists of client processes that send requests to a Replicated Server (three replicas) using an atomic broadcast primitive. It has parameters that allow us to control the load on the hosts and the network, as well as the timeout value used by our heartbeat failure detection mechanism. Our main observation is that the atomic broadcast algorithm never stops delivering messages, not even under arbitrarily high load and very small timeout values (1 ms). So, by trying to illustrate the practical impact of impossibility results, we discovered that we had implemented a very robust Replicated service.

G. Rodolakis - One of the best experts on this subject based on the ideXlab platform.

  • Replicated Server Placement with QoS Constraints
    IEEE Transactions on Parallel and Distributed Systems, 2006
    Co-Authors: G. Rodolakis, S. Siachalou, L. Georgiadis
    Abstract:

    The network planning problem of placing Replicated Servers with QoS constraints is considered. Each Server site may consist of multiple Server types with varying capacities and each site can be placed in any location among those belonging to a given set. Each client can be served by more than one location as long as the round-trip delay of data requests satisfies predetermined upper bounds. Our main focus is to minimize the cost of using the Servers and utilizing the link bandwidth, while serving requests according to their delay constraint. This is an NP-hard problem. A pseudopolynomial and a polynomial algorithm that provide guaranteed approximation factors with respect to the optimal for the problem at hand are presented

  • Replicated Server placement with qos constraints
    International Workshop on Quality of Service, 2005
    Co-Authors: G. Rodolakis, S. Siachalou, L. Georgiadis
    Abstract:

    The problem of placing Replicated Servers with QoS constraints is considered. Each Server site may consist of multiple Server types with varying capacities and each site can be placed in any location among those belonging to a given set. Each client can de served by more than one locations as long as the request round-trip delay satisfies predetermined upper bounds. Our main focus is to minimize the cost of using the Servers and utilizing the link bandwidth, while serving requests according to their delay constraint. This is an NP-hard problem. A pseudopolynomial and a polynomial algorithm that provide guaranteed approximation factors with respect to the optimal for the problem at hand are presented.

Maarten Van Steen - One of the best experts on this subject based on the ideXlab platform.

  • globule a platform for self replicating web documents
    Lecture Notes in Computer Science, 2001
    Co-Authors: Guillaume Pierre, Maarten Van Steen
    Abstract:

    Replicating Web documents at a worldwide scale can help reduce user-perceived latency and wide-area network traffic. This paper presents the design of Globule, a platform that automates all aspects of such replication: Server-to-Server peering negotiation, creation and destruction of replicas, selection of the most appropriate replication strategies on a per-document basis, consistency management and transparent redirection of clients to replicas. Globule is initially directed to support standard Web documents. However, it can also be applied to stream-oriented documents. To facilitate the transition from a non-Replicated Server to a Replicated one, we designed Globule as a module for the Apache Web Server. Therefore, converting Web documents should require no more than compiling a new module into Apache and editing a configuration file.

  • PROMS - Globule: A Platform for Self-Replicating Web Documents
    Lecture Notes in Computer Science, 2001
    Co-Authors: Guillaume Pierre, Maarten Van Steen
    Abstract:

    Replicating Web documents at a worldwide scale can help reduce user-perceived latency and wide-area network traffic. This paper presents the design of Globule, a platform that automates all aspects of such replication: Server-to-Server peering negotiation, creation and destruction of replicas, selection of the most appropriate replication strategies on a per-document basis, consistency management and transparent redirection of clients to replicas. Globule is initially directed to support standard Web documents. However, it can also be applied to stream-oriented documents. To facilitate the transition from a non-Replicated Server to a Replicated one, we designed Globule as a module for the Apache Web Server. Therefore, converting Web documents should require no more than compiling a new module into Apache and editing a configuration file.

Dipak Ghosal - One of the best experts on this subject based on the ideXlab platform.

  • design and analysis of a Replicated Server architecture for supporting ip host mobility
    Mobile Computing and Communications Review, 1998
    Co-Authors: Dipak Ghosal
    Abstract:

    Mobility support in IP networks requires Servers to forward packets to mobile hosts and to maintain information pertaining to a mobile host's location in the network. In the mobile Internet Protocol (mobile-IP), location and packet forwarding functions are provided by Servers referred to as home agents. These home agents may become the bottleneck when there are a large number of mobile hosts in the network. In this paper, we consider the design and analysis of a Replicated Server architecture in which multiple home agents are used to provide mobility support. In order to minimize the delay across the home agents, one of the key aspects is the design of load balancing schemes in which a home agent may transfer the control of a mobile host to another home agent in the same network. The methods for triggering the transfer and the policy for selecting the next home agent define various load balancing schemes which have different performance characteristics. In this paper, we design a protocol that forms the building block for implementing such load balancing schemes, and we then study the performance characteristics of random, round-robin, and join the shortest queue (JSQ) selection policies, and timer-, counter- and threshold-based transfer policies.

  • Design and analysis of a Replicated Server architecture for supporting IP–host mobility
    Cluster Computing, 1998
    Co-Authors: Dipak Ghosal
    Abstract:

    Mobility support in IP networks requires Servers to forward packets to mobile hosts and to maintain information pertaining to a mobile host's location in the network. In the mobile Internet Protocol (mobile-IP), location and packet forwarding functions are provided by Servers referred to as home agents. These home agents may become the bottleneck when there are a large number of mobile hosts in the network. In this paper, we consider the design and analysis of a Replicated Server architecture in which multiple home agents are used to provide mobility support. In order to minimize the delay across the home agents, one of the key aspects is the design of load balancing schemes in which a home agent may transfer the control of a mobile host to another home agent in the same network. The methods for triggering the transfer and the policy for selecting the next home agent define various load balancing schemes which have different performance characteristics. In this paper, we design a protocol that forms the building block for implementing such load balancing schemes, and we then study the performance characteristics of three selection schemes, namely, random, round-robin, and join the shortest queue (JSQ), and three transfers policies, namely, timer-, counter- and threshold-based. The key results of this study are as follows: (1) The results show that both random and round-robin selection policies can yield modest load balancing gains, and that these gains increase when the traffic is more bursty (burstiness is defined as the ratio of the peak arrival rate to the mean arrival rate) as well as when there are more home agents. (2) The threshold-based transfer policy performs better than timer-based and counter-based policies, since in threshold-based policies transfers are made only when the queue is overloaded, unlike counter- and timer-based policies in which transfers can be made from an unloaded home agent to an overloaded home agent.