Adelbert Groebbens

Intelligent optical networking for multilayer survivability

In recent years, telecommunication networks have faced explosive (IP) traffic growth. As traffic keeps growing, network reliability gains more and more importance. This article investigates to which extent switched connections and fast connection provisioning, typical for intelligent optical networks (IONs), can be used to provide resilience in an IP-over-optical multilayer network scenario. This solution, based on transport network flexibility, is compared with more traditional static multilayer resilience schemes in terms of cost (capacity) requirements and operational (dis)advantages.

Benefits of GMPLS for multilayer recovery

IP-based backbone networks are gradually moving towards a network model consisting of high-speed routers that are flexibly interconnected by lightpaths set up by an optical transport network consisting of WDM links and optical cross-connects. Recovery mechanisms at both network layers are crucial to reach the high availability requirements of critical services. In such a model, the GMPLS protocol suite can provide a distributed control plane that can be used to deliver rapid and dynamic circuit provisioning of end-to-end optical lightpaths. This article explains that it can be very beneficial to exploit this functionality to enhance the cost effectiveness of multilayer recovery significantly. Several practical case studies illustrate this concept and highlight the opportunities and challenges to be faced.

Efficient Protection in MPλS Networks Using Backup Trees: Part One—Concepts and Heuristics

Multi-protocol lambda switching (MPλS) has recently been applied in the optical network control plane to provide fast lightpath provisioning. As an increasing amount of traffic is carried in optical transport networks (OTNs), single network failures can affect a vast amount of traffic, making lightpath protection crucial. Therefore, shared backup tree (BT) lightpath protection is a promising paradigm in MPλS networks due to its ability of fast recovery and its efficiency in consumed resources. A shared BT is used to protect a group of working lightpaths towards the same destination. From the working lightpaths in such a group, only one affected lightpath at a time can be recovered using the BT. The main problem is how to group and route the working paths (WPs) and how to route the BTs, in such a way that the capacity resources used by the WPs and the BTs are minimized. In Part One of this study (presented in this paper), we propose three approaches to cope with this problem. The first approach is a purely integer linear programming (ILP) based method. The second one is a combination of ILP and a heuristic technique. The last one is a purely heuristic approach. In this paper, these approaches are theoretically compared. In Part Two [1] of this study, several simulations are carried out in order to compare these approaches in terms of performance and computing effort. The experimental results are in line with the theoretical expectations.

Efficient Protection in MPλS Networks Using Backup Trees: Part Two—Simulations

In Part One of this study [1], we presented three approaches for organizing backup tree (BT) protection, where a BT was used to protect a group of working paths (WPs) against single failures. Shared BT protection uses less capacity compared to d edicated (path) protection (DP), while having the same fast recovery. Using shared BT protection is particularly suitable for multi-protocol lambda switching (MPλS) networks and can save about 15% capacity resources compared to DP. In this paper, we present a simulation study in which we apply the approaches presented in Part One for several network topologies with different demand scenarios. The effects of network and demand characteristics on the capacity gain obtained with these approaches are analyzed. In addition, the comparison between BTs and 1 : N protection is made.

Logical topology design for IP rerouting: ASONs versus static OTNs

IP-based backbone networks are gradually moving to a network model consisting of high-speed routers that are flexibly interconnected by a mesh of light paths set up by an optical transport network that consists of wavelength division multiplexing (WDM) links and optical cross-connects. In such a model, the generalized MPLS protocol suite could provide the IP centric control plane component that will be used to deliver rapid and dynamic circuit provisioning of end-to-end optical light paths between the routers. This is called an automatic switched optical (transport) network (ASON). An ASON enables reconfiguration of the logical IP topology by setting up and tearing down light paths. This allows to up- or downgrade link capacities during a router failure to the capacities needed by the new routing of the affected traffic. Such survivability against (single) IP router failures is cost-effective, as capacity to the IP layer can be provided flexibly when necessary. We present and investigate a logical topology optimization problem that minimizes the total amount or cost of the needed resources (interfaces, wavelengths, WDM line-systems, amplifiers, etc.) in both the IP and the optical layer. A novel optimization aspect in this problem is the possibility, as a result of the ASON, to reuse the physical resources (like interface cards and WDM line-systems) over the different network states (the failure-free and all the router failure scenarios). We devised a simple optimization strategy to investigate the cost of the ASON approach and compare it with other schemes that survive single router failures.

Dimensioning studies for transparent optical backbone networks

The ITEA TBONES (Transparent Optical Backbone Network Simulator) project aims at demonstrating the feasibility of a unified control plane using the innovative GMPLS-protocol suite and mechanisms. Within the scope of this project a dimensioning tool (DT) was implemented which calculates the dimensioning for a given topology of the network and a realistic traffic-trace over this network. With this DT, three research cases were investigated, considering the dimensioning of (multiple) logical layers over a physical layer, the techno-economical implications of grooming strategies and the design of an optimal logical topology when taking single failures into account. The DT can also be used for initializing the developed TBONES control plane emulator. This paper will give a general overview of the DT and the considered case studies, as well as some illustrative results obtained within the three separate research cases.

Logical topology optimisation for dynamic multilayer recovery schemes

This paper summary includes an overview description and first results of ongoing work on a logical topology optimisation problem. The problem is to find an optimal IP topology that routes a given IP demand matrix and makes it resilient against single router failures. The functionality of an underlying ASON is used to ensure survivability against single router failures, leading to what is called a dynamic multilayer resilience strategy. The routing in the IP layer is chosen to be OSPF in order to limit operational complexity. The recovery mechanisms in the optical layer make it survivable against cable cuts or optical node failures. The objective is to minimise the total cost of the needed resources, like IP router interfaces and WDM line system equipment. New in this optimisation problem is the possibility, as a result of the ASON, to reuse resources over the failure free and the failure scenarios.

Cost-efficient deployment of survivable next-generation IP-over-optical networks

As more and more traffic is transported over communication networks, network survivability becomes a key issue in network design and planning. In this paper first the need for deploying network recovery techniques at multiple layers is motivated. Then the efficient coordination of these network recovery techniques is studied. Not only static but also dynamic multi-layer survivability strategies are presented and studied in this paper: dynamic multi-layer survivability strategies benefit from the ability of the underlying transport network to provide switched connection services in order to allow reconfiguring the logical network at the time of a failure. As not only the traffic volume keeps growing, but also more and more services with distinct reliability requirements are deployed, the benefit of differentiating the multi-layer survivability strategy per traffic class is investigated in this paper. Whereas the case studies in this paper focus on the cost-efficiency of the presented strategies and techniques, also a broader theoretic discussion is given on these techniques.

Evaluation of the dimensioning and economical benefits of intelligent optical networks

In order to cope with the increasing capacity requirements in the optical backbone network, the introduction of optical cross connects (OXC) and intelligent optical networking (ION) capable components such as ASON (automatically switched optical networking) or GMPLS (generalized multi-protocol label switching) might become a necessity. In this paper we study the benefits of the introduction of such ION-capable components in the network, using a multi-purpose dimensioning tool (DT) developed within the scope of the ITEA TBONES (transparent optical backbone network simulator) project. The introduction of ION-capable components in the network allows to use the capacity in the network more efficiently, especially when considering a highly dynamic traffic. The enhanced flexibility of the ION-capable components also allows to optimize the capacity-usage in case of network-failures. Optimization of the logical topology could further reduce the capacity-requirements for incorporating a specific resilience scheme in the network. In the light of the ongoing traffic growth in the backbone network, these capacity savings could also result in network cost savings, depending on the moment and price for the introduction of a new OXC in each specific node. By optimizing this estimated cost of the network, an optimal schedule for the introduction of the OXCs can be proposed

Recovery strategies in multilayer networks

Due to a continuous stream of technological advances, enormous amounts of traffic are aggregated onto a single fiber. The main drive for this is the cost savings that are realized due to the economy of scale. However, a major drawback is the impact of a single failure (e.g., cable cut), which can become very and even unacceptably large. This paper aims at discussing the different techniques that can be applied to deal with such circumstances.