Design of self-healing algorithm for ATM networks

This paper discusses how a backup virtual path (VP) between each pair of a source node and a destination node is set up such that when some nodes and links in primary VP's fail, primary VP's are changed to backup VP's rapidly. Then, this paper proposes a multiagent-based method for such rapid restoration from primary VP's to backup VP's. The proposed method consists of the following three steps. The first step enumerates candidates of backup VP between each pair of a source node and a destination node. In the second step, capacities of shared links in backup VP candidates between different pairs of a source node and a destination node are obtained. The last step determines a backup VP with the minimum capacities of shared links between each pair of a source node and a destination node. The proposed method has potentially good adaptability for change of both network resource such as topology and link capacity and resource requirements such as capacities of primary VP and backup VP.

Recently, many self-healing algorithms have been proposed to achieve survivability requirements when a failure occurs in the network. The so-called, pre-assigned backup VP (virtual path) restoration algorithm has been proved to have a fast restoration from failure, but its success greatly depends on how the traffic is distributed and how the spare capacity is dimensioned over the network. In this paper, we address the problem of spare capacity resource control, in order to guarantee complete restoration, improving the survivability performance of the self-healing algorithm. Centralized and distributed controls are used as methods for backup VP assignment. The performance of each method and the management of spare resources are investigated by simulation. The results show that the centralized method has higher efficiency, in resource utilization, than the distributed one. Furthermore, the spare resource control can achieve good fairness performance in resource utilization.

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.

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.

An improved scheme for self-healing in ATM networks

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).

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.

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.

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.

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.

This paper proposes a new self-healing concept for ATM networks: multi-reliability self-healing. First, we show the necessity of multi-reliability self-healing in the future B-ISDN era, and propose a multi-reliability virtual path (VP) network concept achieved through multi-reliability self-healing. Next, we propose a new self-healing scheme based on the multi-reliability VP network by extending the existing self-healing scheme. Finally, evaluations confirm the effectiveness of the proposed scheme and the feasibility of multi-reliability VP networks.

To create a highly reliable ATM transport network, one of the most important issues for network providers is to identify the most efficient restoration technique against network failure. This paper determines which virtual path route alteration techniques can restore virtual paths against single‐link failure in a nationwide ATM transport network within a few seconds.First, centralized restoration techniques are classified and the relative benefits of the techniques are clarified. Then the evaluate restoration time, necessary spare capacity, size of data storage and necessary time for data distribution from the control center to cross connect systems for restoration are evaluated. This study shows that virtual path grouping and predetermined route alteration scenarios are extremely effective in restoring damaged virtual paths rapidly. High‐speed data distribution links or predistributed route alteration data also are important for rapid restoration from failure.

The transmission of ATM cells through a virtual path (VP) which comprises one or more virtual channel (VCs) multiplexed through a VP is examined. Constant bit rate (CBR) sources are used. During the process, there are ATM cell loss, cell delay, and the performance degradation. This paper proposes the techniques of CDMA, OOCs code and 2/sup n/ prime code for improve the performance and to compare two codes when using an ATM network. The results show that when using the same code length a 2/sup n/ prime sequence code has a greater performance than OOCs code.

To make the operation, administration, and maintenance (OAM) functions of virtual path (VP) in the ATM transport network efficient, the authors present a trace method which collects VP route configuration information automatically. This method enables rapid search of VP routes which are managed dynamically. Therefore, it becomes easy to operate and manage the accurate network configuration in ops.In this paper, the requirements for the VP trace method are clarified and mechanisms for the VP trace method realization are presented. Then, the VP trace OAM cell format, the VP trace processing algorithms in each ATM network system, and the implementation of the required functions are discussed. Finally, the VP performance is evaluated.