Kris Struyve

Escalation between recovery schemes: beyond ATM backup recovery

This paper introduces the concept of escalation between recovery techniques and discusses its advantages and drawbacks. A generic modular recovery architecture is defined to discuss the different objects involved. The escalation concept is applied to a sample case study, i.e. a fast ATM backup recovery scheme is combined with a dynamic distributed path recovery algorithm to address spare resource contention as well as multiple network failure situations. Different escalation strategies are proposed and an alternative ATM backup recovery scheme is presented. The survivability performance is assessed using computer simulations. It is shown that escalation provides a considerable gain in the availability of the network.

Application, design, and evolution of WDM in GTS's pan-European transport network

A pan-European transport network must cope with enormous traffic inflation by introducing appropriate network solutions. WDM technology is the solution adopted by GTS, driven by capacity requirements, infrastructure availability, flexibility, and cost. The deployment of this new technology presents specific technical issues, but more important, it lays the foundation of future optical networking. We describe the motives underlying the deployment of WDM technology in the long-haul and short-haul areas of GTSs operational transport network. Next, after presenting the use of WDM as the multiservice platform for SDH and IP overlay networks as well as native WDM services, we focus on the design of SDH-over-WDM and IP-over-WDM networks. Finally, we discuss future WDM networking and management requirements to better serve the needs of a pan-European carrier such as GTS.

Design and Evaluation of Distributed Link and Path Restoration Algorithms for ATM Meshed Networks

Two distributed restoration algorithms are presented in this paper to restore disrupted traffic in meshed broadband networks due to link or node failures. Both algorithms are based on a multi-sender approach. The first algorithm uses link restoration, whereas the second algorithm uses path restoration. The performances of these algorithms are analyzed on two test networks. It is shown that they achieve fairly high restoration ratios within seconds. The algorithms are compared with other distributed restoration algorithms published in literature and with graph theoretical algorithms.

Design and evaluation of multi-layer survivability for SDH-based ATM networks

To realise end-to-end survivable networks several single-layer recovery mechanisms at different layers have to interwork. This paper proposes a classification of multi-layer survivability strategies, and presents a performance evaluation of a sequential bottom-up interworking approach for an SDH-based ATM test network. The SDH layer employs dynamic distributed flooding-based recovery, whereas the ATM layer utilises backup VP restoration. It is shown that multi-layer survivability provides a considerable availability gain even within the crucial 2 seconds time period. Moreover, it turns out that an SDH recovery ratio based technique to pass the responsibility between layers is to be preferred to a hold-off time based technique.

Common pool survivability for meshed SDH-based ATM networks

In order to improve the overall availability of SDH-based ATM transport networks in a cost-effective way, a survivability strategy coordinating the recovery schemes at both ATM and SDH layers has to be devised. This paper proposes a new survivability concept, common pool survivability, for multi- layer ATM over SDH transport networks. The basic idea is to share a common pool of spare resources amongst the ATM and SDH recovery schemes. This can be accomplished by supporting the ATM spare link capacity through unprotected preemptible connections in the SDH network. It is shown on a set of sample networks that common pool survivability yields considerable cost savings when compared to traditional multilayer survivability designs.

Design and evaluation of an accelerated ATM backup virtual path recovery protocol

This paper proposes a novel protocol, called ABACKRES, to recover disrupted VPs via so-called backup VPs in the event of failures in meshed ATM layer networks. A performance comparison with a representative protocol published in literature reveals that although ABACKRES is as simple, it is faster and achieves a substantial higher grade of network survivability. In addition, a centralised heuristic, called POSTRES, is presented to administer backup VPs during post-recovery phases and at repair events.

A novel interworking configuration to protect gateways in between survivable sub-networks

The paper first discusses the interworking between survivable sub-networks in transport networks. It then presents a novel generic interworking configuration to protect gateways between survivable sub-networks. A gateway comprises the network resources interconnecting neighbouring survivable sub-networks. The issue of gateway failures is relevant to both public as well as private networks where traffic may cross multiple sub-networks operated by different organisations. The proposed configuration is simple, achieves fast recovery of any single failure and requires only minimal coordination. The configuration has been simulated for a mesh-mesh and a ring-mesh structured survivable ATM layer network.

A novel generic gateway protection configuration applied to ATM networks

The main purpose of this paper is to present a novel generic configuration to protect traffic against gateway failures. A gateway comprises the network resources interconnecting neighbouring sub-networks. The issue of gateway failures is relevant to both public as well as private networks where traffic may cross multiple sub-networks operated by different organisations. The proposed configuration is simple and requires only minimal co-ordination. The configuration is applied to a mesh-mesh and a ring-mesh structured ATM layer network.

Time analysis of fault propagation in SDH-based ATM networks

This paper provides a detailed analysis of the fault propagation in an SDH-based ATM network from a network view. Both transient and steady state conditions are considered and their influence on the triggering of recovery mechanisms.