Circuit-switched Communication Networks Research Articles

Nonstationary analysis of circuit-switched communication networks

Circuit-switched communication networks have been analyzed extensively in the stationary case, i.e. where the arrival and/or service rates are independent of time. In this paper, we study a circuit-switched network where the rates of external arrivals at the network are time-dependent functions. The circuit-switched network is modelled as a nonstationary queueing network with population constraints, which is analyzed approximately in order to obtain the blocking probability functions. Using this method we model two circuit-switched networks, namely, a traffic-groomed tandem optical network and a single-orbit LEO satellite network.

Application of optimization techniques to a nonlinear problem of communication network design with nonlinear constraints

Nonlinear optimization under nonlinear constraints is usually difficult. However, standard ad-hoc search techniques may work successfully in some cases. Here, we consider an augmented Lagrangian formulation, and we develop a "projection heuristic" that "guides" the iterative search toward the optimum. We demonstrate the effectiveness of this approach by applying it to the problem of maximizing a circuit-switched communication network's throughput under quality-of-service (QoS) constraints by means of choosing the input offered load. This problem is useful for "sizing" the network capacity. Performance results using several versions of the algorithm demonstrate its robustness, in terms of its accuracy and convergence properties.

Traffic management of a satellite communication network using stochastic optimization

The performance of nonhierarchical circuit switched networks at moderate load conditions is improved when alternate routes are made available. Alternate routes, however, introduce instability under heavy and overloaded conditions, and under these load conditions network performance is found to deteriorate. To alleviate this problem, a control mechanism is used where, a fraction of the capacity of each link is reserved for direct routed calls. In this work, a traffic management scheme is developed to enhance the performance of a mesh-connected, circuit-switched satellite communication network. The network load is measured and the network is continually adapted by reconfiguring the map to suit the current traffic conditions. The routing is performed dynamically. The reconfiguration of the network is done by properly allocating the capacity of each link and placing an optimal reservation on each link. The optimization is done by using two neural network-based optimization techniques: simulated annealing and mean field annealing. A comparative study is done between these two techniques. The results from the simulation study show that this method of traffic management performs better than the pure dynamic routing with a fixed configuration.

An algorithm to compute blocking probabilities in multi-rate multi-class multi-resource loss models

In this paper we consider a family of product-form loss models, including loss networks (or circuit-switched communication networks) and a class of resource-sharing models. There can be multiple classes of requests for multiple resources. Requests arrive according to independent Poisson processes. The requests can be for multiple units in each resource (the multi-rate case, e.g. several circuits on a trunk). There can be upper-limit and guaranteed-minimum sharing policies as well as the standard complete-sharing policy. If all the requirements of a request cannot be met upon arrival, then the request is blocked and lost. We develop an algorithm for computing the (exact) steady-state blocking probability of each class and other steady state descriptions in these loss models. The algorithm is based on numerically inverting generating functions of the normalization constants. In a previous paper we introduced this approach to product-form models and developed a full algorithm for a class of closed queueing networks. The inversion algorithm promises to be even more useful for loss models than for closed queueing networks because fewer alternative algorithms are available for loss models. Indeed, for many loss models with sharing policies other than traditional complete sharing, our algorithm is the first effective algorithm. Unlike some recursive algorithms, our algorithm has a low storage requirement. To treat the loss models here, we derive the generating functions of the normalization constants and develop a new scaling algorithm especially tailored to the loss models. In general, the computational complexity grows exponentially in the number of resources, but the computation can often be reduced dramatically by exploiting conditional decomposition based on special structure and by appropriately truncating large finite sums. We illustrate our numerical inversion algorithm by applying it to several examples. To validate our algorithm on small models, we also develop a direct algorithm. The direct algorithm itself is of interest, because it tends to be more efficient when the number of resources is large, but the number of request classes is small. Furthermore, it also allows a form of conditional decomposition based on special structure.

An algorithm to compute blocking probabilities in multi-rate multi-class multi-resource loss models

In this paper we consider a family of product-form loss models, including loss networks (or circuit-switched communication networks) and a class of resource-sharing models. There can be multiple classes of requests for multiple resources. Requests arrive according to independent Poisson processes. The requests can be for multiple units in each resource (the multi-rate case, e.g. several circuits on a trunk). There can be upper-limit and guaranteed-minimum sharing policies as well as the standard complete-sharing policy. If all the requirements of a request cannot be met upon arrival, then the request is blocked and lost. We develop an algorithm for computing the (exact) steady-state blocking probability of each class and other steady state descriptions in these loss models. The algorithm is based on numerically inverting generating functions of the normalization constants. In a previous paper we introduced this approach to product-form models and developed a full algorithm for a class of closed queueing networks. The inversion algorithm promises to be even more useful for loss models than for closed queueing networks because fewer alternative algorithms are available for loss models. Indeed, for many loss models with sharing policies other than traditional complete sharing, our algorithm is the first effective algorithm. Unlike some recursive algorithms, our algorithm has a low storage requirement. To treat the loss models here, we derive the generating functions of the normalization constants and develop a new scaling algorithm especially tailored to the loss models. In general, the computational complexity grows exponentially in the number of resources, but the computation can often be reduced dramatically by exploiting conditional decomposition based on special structure and by appropriately truncating large finite sums. We illustrate our numerical inversion algorithm by applying it to several examples. To validate our algorithm on small models, we also develop a direct algorithm. The direct algorithm itself is of interest, because it tends to be more efficient when the number of resources is large, but the number of request classes is small. Furthermore, it also allows a form of conditional decomposition based on special structure.

Network programming methods for loss networks

This paper describes how some of the insights available from the stochastic analysis of dynamic routing may be incorporated into the classical mathematical programming approach to the design of networks. In particular, we present the results of a number of numerical investigations into network architectures for circuit-switched communication networks. Our investigations use recent theoretical results integrating network flow optimization and Markov decision processes to provide performance bounds for dynamic routing strategies. Following a tutorial introduction of the above mentioned topics we develop a sequence of network examples. Our first examples are familiar ones, such as symmetric fully connected networks and networks with moderate amounts of asymmetry, and we describe how network programming methods complement earlier work on dynamic routing. We then consider a variety of example networks which have a more sparse collection of links. These examples indicate the potential applicability of the methods to a variety of areas, including studies of the design, performance and resilience of future communication networks. >

Synchronous relaxation for parallel simulations with applications to circuit-switched networks

Synchronous relaxation , a new, general-purpose, efficient method for parallel simulation, is proposed. The method is applied to obtain a new parallel algorithm for simulating large circuit-switched communication networks. To show that synchronous-relaxation method is efficient, we present the results of circuit-switched network simulation experiments, and analytic approximations derived from a mathematical model of the simulation method.

Loss circuit switched communication network-performance analysis and dynamic routing

We investigate a loss circuit switched communication network with state-dependent dynamic routing strategy, wherein the state of the network at the time of call arrival determines whether or not the call is accepted and, if accepted, its route. We develop an approximate approach to the network performance analysis. The approach enhances the Fixed Point Model by treating multiple solutions of the Fixed Point Equations. Assuming that the multiple solutions correspond to the long-living network modes, we develop the aggregated Markov chain that describes the network transitions among these modes. We also propose and discuss a new state-dependent dynamic routing strategy which we call Least-Expected-Blocking strategy (LEB). LEB accepts an incoming call only if this results in a decrease in the expected blocking probability and it chooses a route that yields the maximum decrease. The new strategy outperforms the previously known strategies by the criterion of network steady blocking probability.

Optimal routing in circuit switched communication networks

Consideration is given to the optimal circuit routing problem in an existing circuit-switched network. The objective is to find circuit routing which accommodates a given circuit demand while maximizing the residual capacity of the network. In addition, the cost of accommodating the circuit demand should not exceed a given amount. Practical considerations require that a solution be robust to the variations in circuit demand and cost. The objective function for the optimal circuit routing problem is not a smooth one. In order to overcome the difficulties of nonsmooth optimization, the objective function is approximated by smooth concave functions. The optimization algorithm for the circuit routing problem is obtained as a limiting case of the sequence of optimal routing strategies for the corresponding smooth convex optimization problems, and the proof of its convergence to the optimal solution is given. An approach to calculating the optimal multicommodity flow is presented. The optimization algorithm efficiently handles networks with a large number of commodities, satisfies the robustness requirements, and can be used to solve circuit routing problems for large networks. >

Routing in circuit-switched networks: optimization, shadow prices and decentralization

How should calls be routed or capacity allocated in a circuit-switched communication network so as to optimize the performance of the network? This paper considers the question, using a simplified analytical model of a circuit-switched network. We show that there exist implicit shadow prices associated with each route and with each link of the network, and that the equations defining these prices have a local or decentralized character. We illustrate how these results can be used as the basis for a decentralized adaptive routing scheme, responsive to changes in the demands placed on the network.

Routing in circuit-switched networks: optimization, shadow prices and decentralization

How should calls be routed or capacity allocated in a circuit-switched communication network so as to optimize the performance of the network? This paper considers the question, using a simplified analytical model of a circuit-switched network. We show that there exist implicit shadow prices associated with each route and with each link of the network, and that the equations defining these prices have a local or decentralized character. We illustrate how these results can be used as the basis for a decentralized adaptive routing scheme, responsive to changes in the demands placed on the network.

Quasi-stationary distributions and one-dimensional circuit-switched networks

We discuss the quasi-stationary distribution obtained when a simple birth and death process is conditioned on never exceedingK.An application of this model to one-dimensional circuit-switched communication networks is described, and some special cases examined.

Quasi-stationary distributions and one-dimensional circuit-switched networks

We discuss the quasi-stationary distribution obtained when a simple birth and death process is conditioned on never exceeding K. An application of this model to one-dimensional circuit-switched communication networks is described, and some special cases examined.

An Algorithm for Computing Average Loss Probability in a Circuit-Switched Communication Network

This paper describes an algorithm for estimating loss probability in a circuit-switched network. The estimate obtained by the algorithm is also compared with an estimate obtained through simulation.

Analytic Approximation of Blocking Probabilities in Circuit Switched Communication Networks

A method inspired from S. Katz's service evaluation algorithm [6] is presented. The new algorithm is recursive, rather than iterative, in nature, and especially suited for networks that do not contain cycles. It also introduces two new features which take existing theoretical results into account, and as such corresponds more closely to the current state of traffic theory.

Analysis of Circuit-Switched Networks Employing Originating-Office Control with Spill-Forward

This paper presents a single-moment method for determining the node-to-node grades of service of a circuit-switched communication network employing a routing strategy called originating-office control with spill-forward. An example of such a network is the European AUTOVON. The new method makes use of the concept of path-loss sequence and the techniques in system reliability analysis to determine the probability of each route being used to complete a call. Results from a digital computer implementation of the method and comparisons with other methods are discussed.

On Optimal Routing Through Communication Nets

This paper describes a procedure for a suboptimal routing of simultaneous multiterminal multicommodity flows in circuit switched communication networks. The procedure is based on a concept of topological importance of a branch in a capacitated net with a given structure and relative to a given pattern of communication requirements. Once these importance weights have been attached to the branches of the net, the problem reduces to finding in a weighted network the shortest path between two nodes. The chosen objective here is to optimize the grade of service (GS) by satisfying (on a long-range traffic policy basis) the changing "call" demands presented to the network, as fully as possible.