VP formulation and dynamic routing in ATM networks

Deterministic algorithm for VP assignment in ATM networks

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.

Quality control methods for an asynchronous transfer model (ATM) network to which the virtual path (VP) concept is applied are discussed. The factors which affect the quality of service (QOS) of virtual circuits (VCs) given a layered multiplexing structure are clarified, and the evaluation methods of each VC's QOS using these factors are presented. The necessity for each VP to perform traffic shaping in order to control each VC's QOS based on the above evaluation is discussed. A two-level bandwidth allocation control method which assures each VC's QOS is also presented. Two approaches for realizing a range of QOS requirements of VCs through VPs are investigated and compared from the viewpoint of transmission-path utilization efficiency. >

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.

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.

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.

The configuration of virtual path (VP) connection services is expected to play an important role in the operation of large-scale asynchronous transfer mode (ATM) networks. A major research challenge is to understand the fundamental tradeoff between the network call throughput and the processing load on the signaling system and to provide an algorithm for VP capacity allocation that achieves an optimal network operating point while guaranteeing quality of service (QoS) at the call level and satisfies a priori bounds on the processing load of the call processors. We present a taxonomy of previous approaches to the problem and identify their strengths and weaknesses. Based on these observations, we provide an algorithm for the VP capacity allocation problem that satisfies nodal constraints on the call processing load and blocking constraints for each source-destination (SD) pair. The algorithm maximizes the network revenue under the above set of constraints and is parameterized by the number of traffic classes in the network, the method of presentation of networking resources, the admission control policy used in every link and VP, and the network routing scheme. Finally, we apply the algorithm to three sample networks and study several of its performance characteristics. In one case, we applied the calculated VP distribution to the Xunet ATM testbed and verified experimentally the predicted performance.

In an ATM network, bandwidth is allocated at different levels and in different stages. At the physical level, the ATM topology can be dynamically reconfigured by adding/removing truns between ATM switches. This allocation of bandwidth is made possible by the SONET Synchronous Transfer Mode (STM) infrastructure equipped with Digital Cross Connect Systems (DCSs). We will refer to this allocation asSTM allocation. At the ATM level, we can allocate bandwidth to individual Virtual Circuits (ATM-VC allocation) as well as to Virtual Paths (ATM-VP allocation). For example, in order to implement the Connectionless Network Access layer functions we find it convenient to organize the Virtual Paths in a Connectionless Overlay Network. This introduces another type of bandwidth allocation (CLS allocation). In this paper, we address and formulate the above bandwidth allocation problems, and propose efficient techniques for their solution. We illustrate these techniques with examples based on STM and CLS allocation, respectively.

The advantages of applying the virtual path (VP) concept to asynchronous transfer mode (ATM) networks are summarized. The implementation techniques of VPs with ATM cross-connect systems and some VP applications are presented. It is demonstrated that network capability can be effectively increased by applying VP techniques. >

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).

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.

An improved scheme for self-healing in ATM networks

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.

In the paper we describe a framework for resource management and traffic control which is based on the virtual network concept. In this context the virtual networks are used as a toot for customization of networks management functions and for virtual separation of network resources. We identify three main categories of virtual network applications (service, user and management oriented virtual networks). We discuss generic and application oriented problems, which have to be solved to take full advantage of the proposed framework. We also study the relation between the virtual network concept and the virtual path concept in the context of bandwidth management. The study indicates that using virtual paths for bandwidth management involves some inherent contradictions.