The high-availability seamless redundancy (HSR) protocol is a representative protocol that fulfills the reliability requirements of the IEC61850-based substation automation system (SAS). However, it has the drawback of creating unnecessary traffic in a network. To solve this problem, a dual virtual path (DVP) algorithm based on HSR was recently presented. Although this algorithm dramatically reduces network traffic, it does not consider the substation timing requirements of messages in an SAS. To reduce unnecessary network traffic in an HSR ring network, we introduced a novel packet transmission (NPT) algorithm in a previous work that considers IEC61850 message types. To further reduce unnecessary network traffic, we propose an extended dual virtual paths (EDVP) algorithm in this paper that considers the timing requirements of IEC61850 message types. We also include sending delay (SD), delay queue (DQ), and traffic flow latency (TFL) features in our proposal. The source node sends data frames without SDs on the primary paths, and it transmits the duplicate data frames with SDs on the secondary paths. Since the EDVP algorithm discards all of the delayed data frames in DQs when there is no link or node failure, unnecessary network traffic can be reduced. We demonstrate the principle of the EDVP algorithm and its performance in terms of network traffic compared to the standard HSR, NPT, and DVP algorithm using the OPNET network simulator. Throughout the simulation results, the EDVP algorithm shows better traffic performance than the other algorithms, while guaranteeing the timing requirements of IEC61850 message types. Most importantly, when the source node transmits heavy data traffic, the EDVP algorithm shows greater than 80% and 40% network traffic reduction compared to the HSR and DVP approaches, respectively.

In finding the optimal solution of virtual-path bandwidth allocation for large-scale networks, existing searching algorithms frequently call the process which calculate the bandwidth for given call blocking probability (CBP) and traffic loads. This is an inverse process of calculating CBP for given traffic loads and bandwidth. Because there is no analytic expression of calculating CBP, the process of calculating bandwidth with given CBP and traffic adopts an iteration algorithm. It leads to a tedious computation process. In this letter, a fast bandwidth evaluation algorithm is proposed and applied to the field of virtual path bandwidth allocation that aims at minimizing the worst call blocking probabilities in the network. The algorithm is proved to be accurate and fast. Finally, we provide comparison curves for the exact optimal CBPs obtained in the case of using OPBM against that of DCLPBM aided by the fast bandwidth evaluation algorithm.

In ATM networks, call processing on switches can be greatly simplified by using the concept of virtual path (VP); and good resource management strategies ensure that virtual channel connections (VCC) can be rapidly and efficiently established. In order to have good system performance, several methods of constructing virtual paths and strategies of allocating and managing resources should be considered. In this paper, several multicast strategies with dynamic routing are used and applied to the metropolitan LATA network. For the VP-based network, dynamic routing is also applied, and those strategies are discussed and investigated to show the versatility of the approach. Some results using dynamic multicast routing, such as call blocking rate, VP utilization, and VP adjustment rate, are obtained for the different strategies by simulation experiments.

This paper has a dual purpose. First, it proposes a virtual path management model for ATM networks. The model unifies VPC overlay network configuration, VCC routing, and capacity allocation in a single framework. It accommodates multiple end-to-end offered traffics of various QoS requirements and traffic types. Especially, it also supports point-to-multipoint as well as point-to-point connections in a resource-efficient manner. The objective is to minimize the overall network resource cost. To do so, it pursues an optimal trade-off among the gains offered by ATM technology. The application of the proposed model is naturally extended to the multiprotocol label switching framework. Second, it proposes an efficient algorithm to solve the model. The mathematical formulation of such a unifying model typically involves a very large-scale intractable optimization which, treated by a straightforward method, requires excessive computational efforts. In this paper, we show how the computational structure of formulation can be exploited to tailor a solution method providing good solutions in dramatically reduced computational efforts.

In order to make the ATM network fault-tolerant and the network service flexible, a method for the setting up of backup virtual paths (VP's for short) using multiagents is effective with respect to adaptability to change of network resource and user requirements, examples of which are failure of nodes and links and addition of VP's, respectively. In this method, under the assumption that candidates of backup VP's between different pairs of source and destination nodes are given, the optimum backup VP's are obtained by exchanging information among agents autonomously. First, this paper proposes measures for determining backup VP's between different pairs of source and destination nodes. Next, this paper presents simulation results to evaluate the adaptability of the method. The results show that the method efficiently obtains the optimum backup VP's even when the number of backup VP's increases and that different idle time at each destination node enables to shorten the total processing time while keeping complete detection of shared links.

In this paper, we present a new network design problem that is applicable for designing virtual paths (VP's) in an asynchronous transfer mode (ATM) network to efficiently support multicast applications, especially real-time multimedia applications. We first address several alternatives for the solution and compare their properties. Then we focus on a new solution which sets up a semi-permanent VP layout (VPL) and constructs VC trees for different multicast traffic demand patterns based on the constructed VPL. A three-phase heuristic solution is proposed for designing a good virtual-path layout for a given set of multicast traffic demand patterns. By varying the design parameters, we can obtain different VPLs which possess different tradeoffs among some important criteria, namely, the network overhead for a connection setup, routing table resources and control and management cost. Simulations are performed on randomly generated networks to demonstrate the performance and scalability of our solution. To the best of our knowledge, there is no prior known work which takes the multicast connection traffic into account for the VP layout design.

The Virtual Path (VP) concept in ATM networks simplifies network structure, traffic control and resource management. For VP formulation, a VP can carry traffic of the same type (the separate scheme) or of different types (the unified scheme). For VP adjustment, a certain amount of bandwidth can be dynamically assigned (reserved) to VPs, where the amount (the bandwidth incremental/decremental size) is a predetermined system parameter. In this paper, we study Least Loaded Path-based dynamic routing schemes with various residual bandwidth definitions under different bandwidth allocation (VP formulation and adjustment) schemes. In particular, we evaluate the call blocking probability and VP set-up processing load with varying (bandwidth) incremental sizes. Also, We investigate numerically how the use of VP trades the blocking probability with the processing load. It is found that the unified scheme could outperform the separate scheme in certain incremental sizes. Moreover, we propose two ways to reduce the processing load without increasing the blocking probability. Using these methods, the separate scheme always outperforms the unified scheme.

The ATM Virtual Path(VP)-based transport network is a candidate for the future multi-reliability and broadband integrated service infrastructure. This paper compares the performance attributes of the VP transport network with those of the conventional SDH network and future optical path-based transport network. This paper shows that the VP-based network is superior in terms of path-grooming efficiency and connection capability, and will still play an important role when WDM technologies are introduced to carrier networks. This paper also describes the recently fabricated VP Cross Connect(VP-XC) system configuration and the VP Automatic Protection Switching(APS) performance of the XC.

A new traffic engineering and operation of ATM networks is described, which features adaptive virtual path (VP) bandwidth control and VP network reconfiguration capabilities. We call this operation system resilient self-sizing operation. By making full use of self-sizing network (SSN) capabilities, we can operate an ATM network efficiently and keep high robustness against traffic demand fluctuation and network failures, while reducing operating costs. In a multimedia environment, the multimedia services and unpredictability of traffic demand make network traffic management a very challenging problem. SSNs, which are defined as ATM networks with self-sizing traffic engineering and operation capability are expected to overcome these difficulties. This paper proposes VP network operation methods of self-sizing networks for high flexibility and survivability. The VP network operation is composed of adaptive VP bandwidth control to absorb changes in traffic demand, VP rerouting control to recover from failures, and VP network reconfiguration control to optimize the network. The combination of these controls can achieve good performance in flexibility and survivability.

In the future asynchronous transfer mode (ATM) networks, an efficient virtual path (VP) control strategy must be applied to guarantee the network has high throughput with tolerable node processing load. The multistage VP control may be the best candidate since the tasks in this method are shared by the central node and local nodes, and it allows us to track the traffic changes while maintain a good state of the VP topology by reconfiguring it at regular or need based intervals. In this paper, we focus on the VP topology optimization problem in the multistage VP control. We first present the problem formulation in which the tradeoff between the network throughput and processing costs is considered, and then employ an algorithm based on a route-neuron Hopfield neural network (HNN) model to solve this problem. The numerical results demonstrate the HNN can converge to optimal solutions with high probability and stability while in other cases to near optimal solutions if the values of the system parameters in the route-neuron model are chosen according to some empirical formulas provided in this paper.

By reserving transmission capacity on a series of links from one node to another, making a virtual path connection (VPC) between these nodes, several benefits are obtained. VPCs will simplify routing at transit nodes, connection admission control, and QoS management by traffic segregation. As telecommunications traffics experience variations in the number of calls per time unit due to office hours, inaccurate forecasting, quick changes in traffic loads, and changes in the types of traffic (as in introduction of new services), there is a need to cope for this by adaptive capacity reallocation between different VPCs. We have developed a type of local VPC capacity management policy that uses an allocation function to determine the needed capacity for the coming updating interval, based on the current number of active connections. We suggest an allocation function that is independent of the actual traffic, and determine its optimal parameters and the optimal updating interval for different overhead costs. The local approach is shown to be able to combine benefits from both VP and VC routing by fast capacity reallocations. The method of signaling is easy to implement and evaluations indicate that the method is robust.

In B-ISDN, network reliability is a very significant theme. This paper proposes the Failure-Resistant Virtual Path (FRVP) scheme that prevents any information loss even with network failure, to realize a high-end reliability service in B-ISDN. The FRVP scheme is based on simple parallel transmission established using the superior characteristics of ATM. In the FRVP scheme, the transmitter duplicates user cells and transmits them across several VPs simultaneously. The receiver chooses the perfect cells and sends them to the user. As a result, the cell stream output by the receiver is not affected by VP failure if at least one VP remains active. I develop a prototype FRVP system and conduct field trials using NTT's nationwide ATM testbed network. The FRVP scheme is shown to achieve extremely-reliable ATM networks and services.

In this paper, we propose a new multicast routing algorithm for constructing the delay-constrained minimal spanning tree in the VP-based ATM networks, in which we consider the efficiency even in the case where the destination dynamically joins/departs the multicast connection. For constructing the delay-constrained spanning tree, we first generate a reduced network consisting of only VCX nodes from a given ATM network, originally consisting of VPX/VCX nodes. Then, we obtain the delay-constrained spanning tree with a minimal tree cost on the reduced network by using our proposed heuristic algorithm. Through numerical examples, we show that our dynamic multicast routing algorithm can provide an efficient usage of network resources when the membership nodes frequently changes during the lifetime of a multicast connection, while the existing multicast routing algorithm may be useful for constructing the multicast tree with a static nature of destination nodes. We also demonstrate that more cost-saving can be expected in dense networks when applying our proposed algorithm.

The Virtual Path (VP) concept is one of the versatile features of ATM/B-ISDN. Using the VP concept, a bundle of virtual circuits can be grouped together between any two switching nodes in the network. Further, the VP bandwidth and routing can be dynamic. Building on this idea, a dynamically reconfigurable, dynamic call routing wide area (backbone) broadband network concept is proposed. Specifically, this provides dynamism at two levels: at the VP level and at the connection level. For an incoming connection request, at most two logical virtual path connections (VPCs) are allowed between the origin and the destination; these logical VPCs are defined by setting virtual paths links (VPLs) which are, in turn, physically mapped to the transmission network. Based on the traffic pattern during the day, the bandwidth of such VPCs and their routing, as well as call routing, changes so that the maximum number of connection requests can be granted while maintaining acceptable quality of service (QoS) for various services. Within this framework, we present a mathematical model for network design (dimensioning) taking into account the variation of traffic during the day in a heterogeneous multi-service environment. We present computational results for various cost parameter values to show the effectiveness of such networks compared to static-VP based networks in terms of network cost.

This paper discusses the problems in designing virtual-path (VP) networks and underlying transmission-path (TP) networks using the "self-sizing" capability. Self-sizing implies an autonomous adjustment mechanism for VP bandwidths based on traffic conditions observed in real time. The notion of "bandwidth demand" has been introduced to overcome some of the problems with VP bandwidth sizing, e.g., complex traffic statistics and diverse quality of service requirements. Using the bandwidth demand concept, a VP-bandwidth-sizing procedure is proposed in which real-time estimates of VP bandwidth demand and successive VP bandwidth allocation are jointly utilized. Next, TP bandwidth demand, including extra capacity to cover single-link failures, is defined and used to measure the congestion level of the TP. Finally, a TP provisioning method is proposed that uses TP "lifetime" analysis.

In this paper, we propose a new design method to construct the highly reliable ATM network based on the virtual path (VP) concept. Through our method, we can guarantee a network survivability, by which we mean that connectivity between every pair of two end nodes is assured even after the failure, and that quality of service (QoS) requirements of each VC connection are still satisfied. For achieving a reliable network, every VP connection between two end nodes is equipped with a secondary VP connection such that routes of primary and secondary VPs are established on completely disjoint physical paths. Our primary objective of the current paper is that the construction cost of the VP-based network with such a survivability is minimized while the QoS requirement of traffic sources in fulfilled. For this purpose, after all the routes of VPs are temporarily established by means of the shortest paths, we try to minimize the network cost through (1) the alternation of VP route and (2) the separation of a single VP into several VPs, and optionally through (3) the introduction of VCX nodes. Through numerical examples, we show how the increased cost for the reliable network can be sustained by using our design method.

In order to pave the way to B-ISDN, one of the most important issues for network providers is to identify the most efficient B-ISDN introduction strategy. This paper focuses on the costs of introducing ATM transmission systems into backbone transport networks which must provide highly reliable broad band transmission capability. In this context, the main rival to ATM is Synchronous Transfer Mode (STM); recent Synchronous Digital Hierarchy (SDH) equipment supports the establishment of advanced STM-based high speed transport networks. This paper offers a cost comparison of ATM and STM based backbone transport networks. A digital path network in STM has a hierarchical structure determined by the hierarchical multiplexing scheme employed. The minimum cost STM path network can only be determined by developing a path design method that considers all hierarchical path levels and yields the optimum balance of link cost and node cost. Virtual paths have desirable features such as non-deterministic path bandwidth and non-hierarchical and direct multiplexing capability into high speed optical transmission links. These features make it possible to implement a non-hierarchical VP network with ATM cross connect systems which can handle any bandwidth VP with a universal cell switching function. This paper shows that the non-hierarchical VP routing, which strongly minimizes link cost, can be implemented without significantly increasing node cost. Network design simulations show that the virtual path scheme, possible only in an ATM network, yields the most cost effective path network configuration.

An ATM network design algorithm is treated as a resource allocation problem. As an effective way to facilitate a coexistence of traffic with its diverse characteristics and different quality of service (QOS) requirements in ATM networks, a virtual path (VP) concept has been proposed. In attempting to design the VP (Virtual Path)-based ATM network, it requires to consider a network topology and traffic pattern generated from users for minimizing a network construction cost while satisfying QOS requirements such as cell / call loss probabilities and cell delay times. In this paper, we propose a new heuristic design algorithm for the VP-based ATM network under QOS constraints. A minimum bandwidth required to transfer a given amount of traffic is first obtained by utilizing an equivalent bandwidth method. After all the routes of VPs are temporarily established by means of the shortest paths, we try to minimize the network cost through the alternation of VP route, the separation of a single VP into several VPs, and the introduction of VCX nodes. To evaluate our design algorithm, we consider two kinds of traffic; voice traffic as low speed service and still picture traffic as high speed service. Through numerical examples, we demonstrate that our design method can achieve an efficient use of network resources, which results in the cost-effective VP-based ATM network.

This paper presents a newly developed analytical method which evaluates the virtual path bandwidth control effects for a general topology ATM (Asynchronous Transfer Mode) transport network. The virtual path concept can enhance the controllability of path bandwidth. Required link capacity to attain a specified call blocking probability can be reduced by applying virtual path bandwidth control. This paper proposes an analytical method to evaluate the call blocking probability of a general topology ATM network, which includes many virtual paths, that is using virtual path bandwidth control. A method for the designing link capacities of the network is also proposed. These methods make it possible to design an optimum transport network with path bandwidth control. Finally, a newly developed approximation technique is used to develop some analytical results on the effects of dynamic path bandwidth control are provided to demonstrate its effectiveness.

The new algorithm for VP bandwidth control described and analyzed in this paper is a revised version of the Successive Modification Method. Its operation is based only on call-level performance (call blocking probabilities) measured in real time, without explicitly taking the cell-level performance into account. This algorithm does not need to predict future traffic demand and to perform network-wide optimization according to the predicted traffic. These features are well suited for a B-ISDN environment, with the variety of ATM bearer services and the uncertainty of their traffic demand and other characteristics. This paper describes the relationship between the proposed control and other traffic controls in ATM networks, such as CAC and VP shaping/policing. It also offers a solution to the problem of the competition that arises when several VPs in the same transmission path need increased bandwidth. Evaluation of the transient behavior of the VP bandwidth occupied by VCs shows that there is a lower limit in the control cycle and that this limit can be estimated as the longest average holding time of VCs among all services. Numerical results obtained using a call-by-call simulator show that proposed control is effective in preventing the performance degradation caused by a large traffic imbalance in communications networks. Comparison of the proposed control with a dynamical alternate routing for VC reveals that the VP bandwidth control is effective in relieving only the areas showing serious performance degradation, but that it is not so effective in improving the overall network performance.