Irene Katzela

Schemes for fault identification in communication networks

A single fault in a large communication network may result in a large number of fault indications (alarms) making the isolation of the primary source of failure a difficult task. The problem becomes worse in cases of multiple faults. In this paper we present an approach for modelling the problem of fault diagnosis. We propose a graph based network model that takes into account the dependencies among the different objects in the telecommunication environment and a novel approach to estimate the domain of an alarm. Based on that model, we design an algorithm for fault diagnosis and analyze its performance with respect to the accuracy of the fault hypotheses it provides. We also propose and analyze a fault diagnosis algorithm suitable for systems for which an independent failure assumption is valid. Finally, we examine the importance of the information of dependency between objects for the fault diagnosis process.

Centralized vs. distributed fault localization

In this paper we compare the performance of fault localization schemes for communication networks. Our model assumes a number of management centers, each responsible for a logically autonomous part of the whole telecommunication network. We briefly present three different fault localization schemes: namely, “Centralized”, “Decentralized” and “Distributed” fault localization, and, we compare their performance with respect to the computational effort each requires and the accuracy of the solution that each provides.

Distributed fault identification in telecommunication networks

Telecommunications networks are often managed by a large number of management centers, each responsible for a logically autonomous part of the network. This could be a small subnetwork such as an Ethernet, a Token Ring or an FDDI ring, or a large subnetwork comprising many smaller networks. In response to a single fault in a telecommunications network, many network elements may raise alarms, which are typically reported only to the subarea management center that contains the network element raising the alarm. As a result, a particular management center has a partial view of the status of the network. Management Centers must therefore cooperate in order to correctly infer the real cause of the failure. The algorithms proposed in this paper outline the way these management centers could collaborate in correlating alarms and identifying faults.

Routing in an ATM-based mobile network

This paper presents a new routing algorithm for a wireless ATM LAN. The LAN combines positive aspects of connection-oriented and datagram communications schemes in its usage of the ATM VP/VC concept. In this scheme, a set of VPI trees, rooted at each node in the LAN, are preestablished. This has the effect of emulating “connectionless” networking which simplifies handoffs and other mobility management tasks. Given that the VPI sink trees are preestablished, there is a need for a procedure to compute and update the routes of these VPI trees with changing conditions in the LAN. Since traffic conditions are likely to change rapidly in mobile networks, we develop the Virtual Trees Routing Protocol (VTRP) to dynamically update the routing of VPI trees to handle congestion and/or topological changes in the network.

MRMA: A Multicast Resource Management Architecture for IP Platforms

Multicast with QoS guarantees is a bandwidth-efficient transmission scheme for the delivery of multi-user multimedia applications. Unlike most other related work, which focuses primarily on the algorithmic or protocol aspects of the multicast problem, our work focuses on the architecture and implementation aspects. In this paper, we present MRMA, a multicast resource management architecture designed to provision multicast with QoS guarantees over the IP platform. MRMA offers a flexible framework for integrating the necessary components for implementing the key multicast functions that are needed for creating, maintaining and terminating multicast sessions: QoS-sensitive route selection and tree construction, address allocation, and session advertisement. Taking into account network operations that are unique to multicast-with-QoS, MRMA implements a hierarchical architecture that features centralized monitoring of network state and semi-distributed persession multicast management. The architecture also implements the idea of moving the heavy computational load of administering multicast operations outside the network and onto the hosts.