Virtual path self-healing scheme based on multi-reliability ATM network concept

Terminal-pair reliability (TR) in an asynchronous transfer mode (ATM) virtual path (VP) network corresponds to probabilistic quantization of robustness between two VP terminators, given a VP layout and failure probabilities of physical links. Existing TR algorithms are not viable for ATM VP networks owing to either high complexity or failure dependency among the VPs. The paper proposes two efficient algorithms for TR computation between two VP terminators by means of variants of path-based and cut-based partition methods which have been effectively used for TR computation in traditional networks. The first variant, called the path-based virtual path reliability (PVPR) algorithm, partitions the search space based on a physical path embedding the shortest route of VPs from the source to the destination terminator. The second variant, called the cut-based virtual path reliability (CVPR) algorithm, in lieu, performs the partition on the basis of a physical cutset separating the source from the remaining terminators. In both algorithms, each subproblem is recursively processed by means of partition until the source and destination terminators are contracted or disconnected. Experimental results reveal that, CVPR outperforms PVPR with respect to computation time. Moreover, compared to one of the most promising TR algorithms, both CVPR and PVPR exhibit superior performance. The two algorithms and their promising results consequently facilitate the real-time computation of the reliability or robustness of ATM VP networks.

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.

Virtual paths (VPs) facilitate rapid movement of end-to-end traffic streams in ATM networks by keeping processing at intermediate nodes at a minimum. For low volumes of traffic, however, VPs may suffer from poor statistical multiplexing gain, and thus result in low utilisation of transmission resources. Balancing between processing and utilisation, we study a procedure whereby lightly loaded VPs are decomposed into at most two segments, which require only one intermediate switching for an end-to-end traffic stream. The resulting segments are then aggregated with other segments or existing VPs. The resulting VPs can thus achieve higher multiplexing efficiency for marginally increased processing. For our test networks, experimental results show that about 95% of the lightly loaded VPs will be decomposed and aggregated by our procedure. When applied to networks where the VPs are adjusted over time to meet traffic variations, the procedure results in an increase in carried traffic and reduced overall overhead by providing a more stable VP network configuration with fewer modifications.

An algorithm is presented for designing the logical topology of the virtual path (VP) network, an important task in ATM network design. We prove that the algorithm provides a VP network topology that is asymptotically optimal with respect to both connectivity and the diameter of the network. These optimality properties are combined with algorithmic simplicity and polynomial running time, thus overcoming the notorious "optimality vs. scalability" dilemma. This result is made possible by applying the theory of random graphs to this type of networks. This theory has the methodological advantage of increased accuracy with growing network size, thus turning the "curse of dimensionality" into a blessing. Therefore, the paper exemplifies that the theory of random graphs, beyond supporting analysis purposes, may serve as a useful tool in the design of algorithms that overcome the "scalability bottleneck", a problem that prevents current approaches from finding near-optimal solutions as today's networks grow in size and complexity.

Automatic and rapid network service restoration (self-healing) when failures occur is of increasing importance for network operations and management as network speed and bandwidth increase. In this paper, we study the self-healing problem of an ATM network at the virtual path (VP) configuration level. We analyze the design issues of self-healing algorithms, and develop a state transition and bandwidth division model of individual VPs and links. On top of the model, we design a restoration algorithm that searches and activates alternate VPs for the failed VPs by combining a preplan method and a double search method. The preplan method activates preassigned backup VPs dynamically, while the double search method searches for alternate VPs from both the source and destination nodes of failed VPs. The double search method is also applied to reconstruction of the backup VP plan. Simulations demonstrate that our new algorithms outperform existing preplanned and dynamic self-healing algorithms in both restoration time and restoration ratio.

Deterministic algorithm for VP assignment in ATM networks

In an ATM network, a virtual path (VP) is a labeled path which can be used to transport a bundle of virtual connections (VCs) and to manage the resources used by these connections. The ATM multimedia leased line service is provided across user-to-user VPs. The customers can increase/decrease the VP bandwidth according to their demand. This paper proposes a method to derive the least required bandwidth on a VP which is the minimum amount of bandwidth estimated to satisfy the QoS requirement of the VCs. The least required bandwidth can be a warranty of the VP resource reallocation.

We study virtual path layouts in ATM networks. Packets are routed along virtual paths in the network by maintaining a routing field whose subfields determine intermediate destinations of the packet, i.e., the endpoints of virtual paths on its way to the final destination. Most of the research on virtual path layouts has focused on tradeoffs between load (i.e., the maximum number of virtual paths passing through a link) and the hop number of the layout (i.e., the maximum number of virtual paths needed to travel between any two nodes). There is however another important limitation on construction of layouts, resulting from technological properties of switches situated at nodes. This bound is the degree of the layout (i.e., the maximum number of virtual paths with a common endpoint). In this paper we study relations between these three parameters of virtual path layouts, for the all-to-all problem. For any integer h, we show tradeoffs between load and degree of h-hop layouts in the ring and in the mesh by establishing upper and lower bounds on these parameters. Our bounds on the degree of an h-hop layout of given load are asymptotically tight and the bounds on the load of an h-hop layout of given degree are asymptotically tight for constant h.

Since routers in IP network are connected with ATM virtual path (VP) permanent virtual connection (PVC) and each VP contains bundles of VCs, a VP layer network can serve as a server layer and each IP layer network can be a client layer. Therefore the effective Internet service provisioning completely depends on the reliability of VP server layer network from the perspective of the optimality and the network survivability. This paper proposes the distributed ATM VP PVC restoration framework with the dynamic rerouting schemes in hierarchical transport network. The rerouting algorithm aims to provide rapid ATM VP PVC restoration in the case of fault or performance degradation in terms of maximization of network resource utilization and satisfaction of the end user's QoS requirement. It guarantees the IP network survivability in spite of ATM network faults or performance degradations. In addition, this paper evaluates the rerouting performance for a real network, the High Speed Information Network (HSIN).

Real-time communication with performance guarantees is expected to become an important feature of future computer networks. Given an ATM network topology, its virtual path (VP) layout, and its traffic demands, we consider in this paper the problem of selecting for each virtual circuit (VC) with timing requirements a route (i.e., a sequence of VPs) along which sufficient resources are available to meet the user-specified end-to-end delay requirements. Our objective is to (i) provide the timing guarantee for the VC, while not jeopardizing the QoS guarantees to other existing VCs. We adopt the real-time channel model to characterize the traffic characteristics and the timing requirements of a VC. We then propose a distributed VC routing scheme based on the distributed Bellman-Ford algorithm to identify an "appropriate" route through the network. By "appropriate", we mean that the route traverses a minimum number of VPs among all possible routes that have sufficient resources over to fulfill the end-to-end timing requirement of the VC. To ensure that there are sufficient bandwidths over all the VPs along the selected route, we incorporate in our proposed scheme a priority assignment method to calculate the minimum worst-case traversal time which messages of a VC will experience on a VP along which the VC is routed. We also comment on the performance of, and the message overhead incurred in the proposed scheme.

In our previous work, we elaborated the multistage virtual path (VP) control strategy and the VP topology optimization problem in which we assume a set of alternative routes exist between each source-destination (SD) pair. In the first part of this paper, a supplementary algorithm, which can yield all possible routes between two nodes and can be used for general routing problems, is provided. Based this algorithm, a dynamic VC routing policy is studied. The proposed policy distinguishes from other strategies in that it is considered in a generic networking environment. In the last part of this paper, we present a dynamic VP routing algorithm which is an important component of the dynamic VC routing policy. Detailed analyses and experimental results demonstrate these algorithms are correct, practical and useful.

An improved scheme for self-healing in ATM networks

BFRA: bounded flooding routing algorithm for provisioning the globally optimal route in a hierarchical ATM network

Techniques for network reliability enhancement using the virtual path strategy are described. The digital path scheme in synchronous transfer mode (STM) networks and the virtual path scheme in asynchronous transfer mode (ATM) networks are compared in terms of path management. It is shown how the dynamic network reconfiguration capability is effectively provided with the virtual path scheme. Some virtual path applications for network reliability enhancement are proposed. >

Routing and planning of working capacity and spare capacity in WDM networks were investigated. Joint optimization technique has been used and the problem has been formulated to restore the general failure scenarios. The difference between the cost for the restoration of one node failure and the cost for the restoration of one link failure is decreased as more wavelengths per fiber are used. The difference between the cost of virtual wavelength path (VWP) network and the cost of wavelength path (WP) network is increased as more wavelengths per fiber are used.