The Experts below are selected from a list of 111 Experts worldwide ranked by ideXlab platform

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

  • Designing telecommunications networks for the reseller market
    Management Science, 1991
    Co-Authors: Jonathan F. Bard, Wassim A. Bejjani
    Abstract:

    This paper presents an algorithm for minimizing the monthly cost of telecommunications networks characterized by multichannel queues with forced balking and hierarchical routing plans. The problem is of major interest to resellers of long distance services and corporate network managers who lease their lines from AT&T and Other Common Carriers. The algorithm can be used to select the most economical combination of lines to meet a desired grade of service, set here to an average blockage rate of 1% during the busy hour. Because of the nonlinearities involved, the problem is Formulated as a dynamic program and solved with forward recursion. The Erlang Loss Formula is used to determine blockage in the case of Poisson arrivals, while Wilkinson's equivalent random theory is adopted when the input traffic is peaked. Model validation is achieved with a SLAM II simulation. The algorithm is applied to the network of National Telecommunications of Austin, which consists of 5 hierarchical levels and 52 candidate nodes, and carries about 2.3 million minutes of monthly traffic. Current services range from FX connections to Specialized WATS. The results indicate that cost reductions of over 18%, or $30,000 per month, can be achieved by periodically adjusting trunk group sizes to match the forecast demand.

  • Designing Telecommunications Networks for the Reseller Market
    1
    Co-Authors: Jonathan F. Bard, Wassim A. Bejjani
    Abstract:

    This paper presents an algorithm for minimizing the monthly cost of telecommunications networks characterized by multichannel queues with forced balking and hierarchical routing plans. The problem is of major interest to resellers of long distance services and corporate network managers who lease their lines from AT&T and Other Common Carriers. The algorithm can be used to select the most economical combination of lines to meet a desired grade of service, set here to an average blockage rate of 1% during the busy hour. Because of the nonlinearities involved, the problem is Formulated as a dynamic program and solved with forward recursion. The Erlang Loss Formula is used to determine blockage in the case of Poisson arrivals, while Wilkinson's equivalent random theory is adopted when the input traffic is peaked. Model validation is achieved with a SLAM II simulation. The algorithm is applied to the network of National Telecommunications of Austin, which consists of 5 hierarchical levels and 52 candidate nodes, and carries about 2.3 million minutes of monthly traffic. Current services range from FX connections to Specialized WATS. The results indicate that cost reductions of over 18%, or $30,000 per month, can be achieved by periodically adjusting trunk group sizes to match the forecast demand.telecommunications, resellers, dynamic programming, Lagrangian relaxation, hierarchical routing

Jonathan F. Bard - One of the best experts on this subject based on the ideXlab platform.

  • Designing telecommunications networks for the reseller market
    Management Science, 1991
    Co-Authors: Jonathan F. Bard, Wassim A. Bejjani
    Abstract:

    This paper presents an algorithm for minimizing the monthly cost of telecommunications networks characterized by multichannel queues with forced balking and hierarchical routing plans. The problem is of major interest to resellers of long distance services and corporate network managers who lease their lines from AT&T and Other Common Carriers. The algorithm can be used to select the most economical combination of lines to meet a desired grade of service, set here to an average blockage rate of 1% during the busy hour. Because of the nonlinearities involved, the problem is Formulated as a dynamic program and solved with forward recursion. The Erlang Loss Formula is used to determine blockage in the case of Poisson arrivals, while Wilkinson's equivalent random theory is adopted when the input traffic is peaked. Model validation is achieved with a SLAM II simulation. The algorithm is applied to the network of National Telecommunications of Austin, which consists of 5 hierarchical levels and 52 candidate nodes, and carries about 2.3 million minutes of monthly traffic. Current services range from FX connections to Specialized WATS. The results indicate that cost reductions of over 18%, or $30,000 per month, can be achieved by periodically adjusting trunk group sizes to match the forecast demand.

  • Designing Telecommunications Networks for the Reseller Market
    1
    Co-Authors: Jonathan F. Bard, Wassim A. Bejjani
    Abstract:

    This paper presents an algorithm for minimizing the monthly cost of telecommunications networks characterized by multichannel queues with forced balking and hierarchical routing plans. The problem is of major interest to resellers of long distance services and corporate network managers who lease their lines from AT&T and Other Common Carriers. The algorithm can be used to select the most economical combination of lines to meet a desired grade of service, set here to an average blockage rate of 1% during the busy hour. Because of the nonlinearities involved, the problem is Formulated as a dynamic program and solved with forward recursion. The Erlang Loss Formula is used to determine blockage in the case of Poisson arrivals, while Wilkinson's equivalent random theory is adopted when the input traffic is peaked. Model validation is achieved with a SLAM II simulation. The algorithm is applied to the network of National Telecommunications of Austin, which consists of 5 hierarchical levels and 52 candidate nodes, and carries about 2.3 million minutes of monthly traffic. Current services range from FX connections to Specialized WATS. The results indicate that cost reductions of over 18%, or $30,000 per month, can be achieved by periodically adjusting trunk group sizes to match the forecast demand.telecommunications, resellers, dynamic programming, Lagrangian relaxation, hierarchical routing

James Roberts - One of the best experts on this subject based on the ideXlab platform.

  • Design, Performance
    2015
    Co-Authors: Thomas Bonald, Telecom Paristech, James Roberts
    Abstract:

    We demonstrate that the Internet has a Formula linking de-mand, capacity and performance that in many ways is the analogue of the Erlang Loss Formula of telephony. Surpris-ingly, this Formula is none other than the Erlang delay for-mula. It provides an upper bound on the probability a flow of given peak rate suffers degradation when bandwidth shar-ing is max-min fair. Apart from the flow rate, the only rel-evant parameters are link capacity and overall demand. We explain why this result is valid under a very general and re-alistic traffic model and discuss its significance for network engineering. Categories and Subject Descriptors C.2.5 Local and wide-area networks –Internet, C.4 Perfor-mance of systems – modeling studie

  • Internet and the Erlang Formula
    Computer Communication Review, 2012
    Co-Authors: Thomas Bonald, James Roberts
    Abstract:

    We demonstrate that the Internet has a Formula linking de- mand, capacity and performance that in many ways is the analogue of the Erlang Loss Formula of telephony. Surprisingly, this Formula is none other than the Erlang delay Formula. It provides an upper bound on the probability a flow of given peak rate suffers degradation when bandwidth sharing is max-min fair. Apart from the flow rate, the only relevant parameters are link capacity and overall demand. We explain why this result is valid under a very general and realistic traffic model and discuss its significance for network engineering.

Mateo Restrepo - One of the best experts on this subject based on the ideXlab platform.

  • Erlang Loss models for the static deployment of ambulances
    Health Care Management Science, 2008
    Co-Authors: Mateo Restrepo, Shane G. Henderson, Huseyin Topaloglu
    Abstract:

    How should one allocate a fleet of ambulances to fixed bases with the goal of keeping response times to calls as small as possible? We present two new models for this problem, both of which are based on the Erlang Loss Formula. The first model is stylized, and shows that allocating ambulances in proportion to the offered load is not necessarily optimal and can often be substantially improved upon. The second model can be used to screen potential allocations to try to identify top candidates for further investigation. Computational experiments on the first model provide insights on how we should modify ambulance allocations in response to different levels of offered load. Computational experiments on the second model compare this model with the so-called A-hypercube model and show that the our model has comparable, and in many cases, better performance in terms of the accuracy of the estimates of performance measures. Thus, our models can be used as pre-screening tools to identify promising ambulance allocations and these promising ambulance allocations can subsequently be evaluated carefully through simulation.

  • Computational methods for static allocation and real-time redeployment of ambulances
    2008
    Co-Authors: Mateo Restrepo
    Abstract:

    We propose new approaches to tackle the problems of static and dynamic ambulance fleet allocation. Static ambulance fleet allocation refers to deciding on home bases for ambulances, to which they return after serving calls. The number and location of bases are given. The goal is to keep response times to calls as small as possible. The first part introduces two models for this problem. Both of them are based on the Erlang Loss Formula. The first model is stylized and serves to illustrate that allocating ambulances to bases in proportion to base offered load is often non-optimal. The second model is similar in spirit to queueing theoretical models developed in the past but uses the Erlang Loss function as a key ingredient. A careful computational comparison shows that the predictions obtained from our model are often more accurate than those produced by previous models, especially in low utilization regimes. This model can be used as a prescreening tool to find promising candidate allocations to be further evaluated through detailed simulation. Dynamic redeployment concerns the real-time relocation of idle ambulances so as to ensure better preparedness. The second part of this dissertation Formulates this problem as a dynamic program in a high-dimensional and uncountable state space, and then resort to approximate dynamic programing (ADP) techniques to obtain approximate solutions. To this end, a specially tailored approximation architecture for the problem is developed. The architecture depends on a small number of free parameters which are tuned using simulated cost trajectories of the system and linear regression. Computational experiments show that the relocation policies obtained from this approach offer significant performance improvements relative to benchmark static-relocation policies. In the third part we use the linear programming approach to ADP on the dynamic-redeployment problem, using the previously developed approximation architecture. We conclude that, although the policies obtained are comparable in quality to those obtained using regression, there are serious issues related to numerical stability. Furthermore, the amount of computation required makes this approach less practical than the regression-based one.

François Baccelli - One of the best experts on this subject based on the ideXlab platform.

  • A SPATIAL MARKOV QUEUEING PROCESS AND ITS APPLI- CATIONS TO WIRELESS Loss SYSTEMS
    2012
    Co-Authors: François Baccelli
    Abstract:

    We consider a pure-jump Markov generator which can be seen as a generalization of the spatial birth-and-death generator, which allows for mobility of particles. Conditions for the regularity of this generator and for its ergodicity are established. We also give the conditions under which its stationary distribution is a Gibbs measure. This extends previous work in [13] by allowing particle mobility. Such spatial birth-mobility-and-death processes can also be seen as generalizations of the spatial queueing systems considered in [15]. So our approach yields regularity conditions and alternative conditions for ergodicity of spatial open Whittle networks, complementing the results in [10]. Next we show how our results can be used to model wireless communication networks. In particular we study two spatial Loss models for which we establish an expression for the blocking probability that might be seen as a spatial version of the classical Erlang Loss Formula. Some specific applications to CDMA (Code Division Multiple Access) networks are also discussed

  • A spatial Markov Queueing Process and its Applications to Wireless Loss Systems
    2007
    Co-Authors: François Baccelli, Bartlomiej Blaszczyszyn, Mohamed Karray
    Abstract:

    We consider a pure-jump Markov generator that which can be seen as a generalization of the spatial birth-and-death generator, which allows for mobility of particles. Conditions for the regularity of this generator and for its ergodicity are established. We also give the conditions under which its stationary distribution is a Gibbs measure. This extends previous work in~\cite{Preston1977} by allowing particle mobility. Such spatial birth-mobility-and-death processes can also be seen as generalizations of the spatial queueing systems considered in~\cite{Serfozo1999}. So our approach yields regularity conditions and alternative conditions for ergodicity of spatial open Whittle networks, complementing the results in~\cite{SerfozoHuang1999}. Next we show how our results can be used to model wireless communication networks. In particular we study two spatial Loss models for which we establish an expression for the blocking probability that might be seen as a spatial version of the classical Erlang Loss Formula. Some specific applications to CDMA (Code Division Multiple Access) networks are also discussed.

  • Blocking Rates in Large CDMA Networks via a Spatial Erlang Formula
    2005
    Co-Authors: François Baccelli, Bartlomiej Blaszczyszyn, Mohamed Kadhem Karray
    Abstract:

    This paper builds upon the scalable admission control schemes for CDMA networks developed in 2005}. These schemes are based on an exact representation of the geometry of both the downlink and the uplink channels and ensure that the associated power allocation problems have solutions under constraints on the maximal power of each station/user. These schemes are decentralized in that they can be implemented in such a way that each base station only has to consider the load brought by its own users to decide on admission. By load we mean here some function of the configuration of the users and of their bit rates that is described in the paper. When implemented in each base station, such schemes ensure the global feasibility of the power allocation even in a very large (infinite number of cells) network. The estimation of the capacity of large CDMA networks controlled by such schemes was made in these references. In certain cases, for example for a Poisson pattern of mobiles in an hexagonal network of base stations, this approach gives explicit Formulas for the infeasibility probability, defined as the fraction of cells where the population of users cannot be entirely admitted by the base station. In the present paper we show that the notion of infeasibility probability is closely related to the notion of blocking probability, defined as the fraction of users that are rejected by the admission control policy in the long run, a notion of central practical importance within this setting. The relation between these two notions is not bound to our particular admission control schemes, but is of more general nature, and in a simplified scenario it can be identified with the well-known Erlang Loss Formula. We prove this relation using a general spatial birth-and-death process, where customer locations are represented by a spatial point process that evolves over time as users arrive or depart. This allows our model to include the exact representation of the geometry of inter-cell and intra-cell interferences, which play an essential role in the load indicators used in these cellular network admission control schemes.