Gerald Franzl

Path selection methods with multiple constraints in service-guaranteed WDM networks

We propose a new approach to constraint-based path selection for dynamic routing and wavelength allocation in optical networks based on WDM. Our approach considers service-specific path quality attributes, such as physical layer impairments, reliability, policy, and traffic conditions, and uses a flooding-based transfer of path information messages from source to destination to find multiple feasible paths. It is fully decentralized, as it uses local network state information. To better understand how multiple constraints impact the efficiency of wavelength routing, and consequently provision the service guarantees, we specifically focus on electronic regenerators that, while being widely considered as the basic building blocks for optical switching nodes, are likely to impose conflicting constraints on routing. For example, electronic regenerators extend the optical reach and could perform wavelength shifting, but also induce impairments, such as delays and operational costs. The question for constraint-based routing is how to account for these conflicting effects. To validate the network modeling, a wide range of networking scenarios are simulated, such as ring, mesh and interconnections of all-optical networks with electronic gateways. For all these scenarios, our approach is shown to efficiently accommodate multiple, conflicting routing metrics related to different services and network architectures.

Constraint-based path selection methods for on-demand provisioning in WDM networks

We propose a framework for decentralized path selection and on-demand wavelength channel provisioning in WDM networks with routing constraints. Within this framework, the path information of choice, such as transmission quality, reliability, policy and traffic conditions, is updated following a connection request, based on a local, autonomous and service-differentiated characterization of optical network elements. It is this local and autonomous network state information that makes our approach particularly suitable for distributed implementation, and applicable to optical network architectures and control protocols that support service level guarantees. To illustrate this, we study mesh networks consisting of transparent, short-reach networking segments interconnected by long-reach WDM links with electronically regenerative gateways, where different link types show different SNR degradation, reliability and delay. On the example of electronically regenerative gateways, we address a new class of constraint-based path selection problems, where a certain a type of network element can at the same time deteriorate and improve network performance; e.g. electronic regenerators improve optical path quality and can adapt to wavelengths, but induce delays or operational costs. The performance study has shown the capability of our methods to accommodate arbitrary number and type of optical path properties, related to different network architectures and services.

Quantum key distribution over optical access networks

It is well known that optical access networks are able to provide high data rates over long distances and to a reasonable number of users. Security and privacy are always a challenge for public accessible network infrastructures. Especially in time-division multiplexing passive optical networks (TDM-PONs), in which the downstream signal is broadcasted to all users connected via the same wavelength channel in a shared fiber link, privacy can be a critical concern. Although encryption at the application layer can provide a high level of security, this can be achieved only if the encryption key distribution is perfectly save. On the other hand, encryption on the physical layer such as quantum cryptography or, more precisely, quantum key distribution (QKD) is a very promising approach to achieve secure communication. However, there remain several issues that have to be solved before the quantum cryptography reaches the maturity level needed for a cost effective implementation in practical networks. In this paper, we address quantum key distribution (QKD) over passive optical access networks, which is an enabling technology required to cost efficiently deploy practical quantum encrypted data communication in the access area. We study different methods to integrate QKD systems in conventional optical access networks and quantitatively evaluate their suitability for a potential implementation.

QoS differentiation and Internet neutrality

Internet neutrality is a debate controversial to a tiered, application-aware Internet. Bandwidth and end-to-end delay of connections across the Internet may vary by several orders of magnitude, therefore unequal data handling per node is commonly applied to achieve differentiated QoS. This practice contradicts Internet neutrality if it is not restricted to pure application awareness. A strict separation of network operation from service provisioning would perfectly fit to achieve Internet neutrality. But this may lack economic business models for network operators, especially in a flat-rate world. This paper provides a review on differentiated quality requirements, discusses the different viewpoints of network and content providers, and closes with a discussion on potential differentiated charging intended to achieve a fair, autonomous, and cost-related revenue distribution among stakeholders.

QoS-based routing methods for multi-hop LEO satellite networks

We propose QoS-based routing methods for multi-hop LEO satellite networks aiming at minimising the number of link handovers per connection, while at the same time satisfying the QoS requirements. For the representation of the network topology as well as for the minimisation of connection re-routing attempts due to the connectivity changes, a graph-theoretical approach is used, where a new metric for inter-satellite links, called lifetime, is introduced. In addition to a QoS-based routing strategy where the best feasible path is found under multiple constraints, e.g. lifetime and delay, we also propose a distributed QoS-routing strategy, where a choice between a number of selected paths can be made based on particular QoS requirements.

Framework for evaluating energy efficiency of access networks

The ever-growing number of Internet users, the introduction of new bandwidth-hungry applications and services as well as the vision of the Internet of Things will set very high requirements on future access networks. Already today there are many different coexisting network technologies and protocols in the access area that have been developed and introduced to fulfill different needs of Internet users and heterogeneous applications. The growing complexity and increasing energy consumption of access networks raise a need for a comprehensive and effective modeling framework that enables a fast projection of energy efficiency of different access network infrastructures. This paper presents a comprehensive framework that joins technological parameters and various configuration options with socio-demographic characteristics and varying user behavior. The modeling framework can be used to evaluate different deployment and migration scenarios for both wireless and wired access networks by means of predicted energy efficiency. Taking into account possible further developments on technology, applications and traffic characteristics, the modeling framework enables predictions on the access related energy demands raised by forecast trends in conjunction with accompanying equipment change options. This modeling framework may serve operators of access networks to select network migration paths that are effective in the short term and efficient in the long term.

Long-term evolution of passive optical networks

With the recent increase of the number of Fiber-to-the-Home deployments worldwide, and the corresponding huge investment in infrastructure, there is a need to devise a migration path that assures the full future usability and enhanced performance of the installed fiber plant, possibly using emerging opto-electronic technologies. With this aim, within the IST ePhoton/One Network of Excellence, different technological solutions have been extensively analyzed and discussed. In this paper, a brief summary on access applications is presented.

Residual network and link capacity weighting for efficient traffic engineering in MPLS networks

This paper proposes a fast and promising on-line routing algorithm for dynamic routing of label switched paths (LSPs) with bandwidth guarantees in MPLS networks. The algorithm operates on-line by handling requests that arrive one at a time without exploiting a priori knowledge of the traffic pattern. We calculate the link weights as a function of residual network and link capacity, hence we call it Residual Network and Link Capacity (RNLC) routing algorithm. RNLC takes early precautions to avoid the usage of congested links when alternative lower loaded, paths are available. Simulation results prove that RNLC is effective in minimizing the traffic rejection probability, therefore increasing the achievable network throughput and shows better performance than some recently introduced on-line routing algorithms. Moreover, we highlight that RNLCs complexity is low, making it scalable for on-line routing in large networks.

A New Bandwidth Guaranteed Routing Approach for Online Calculation of LSPs for MPLS Traffic Engineering

This paper presents a fast on-line routing algorithm for dynamic routing of label switched paths (LSPs) with bandwidth guarantees in MPLS networks, which handles requests that arrive one at a time without exploiting a priori knowledge of the traffic characteristics. Trying to avoid exacting calculations for each on-demand LSP request (e.g., maximum flow computation), we introduce a new link weight function for path selection. The link weights are calculated as a function of residual network and link capacity, hence we call the approach Residual Network and Link Capacity (RNLC) routing algorithm.

Perspectives and limitations of QKD integration in metropolitan area networks.

Quantum key distribution (QKD) systems have already reached a reasonable level of maturity. However, a smooth integration and a wide adoption of commercial QKD systems in metropolitan area networks has still remained challenging because of technical and economical obstacles. Mainly the need for dedicated fibers and the strong dependence of the secret key rate on both loss budget and background noise in the quantum channel hinder a practical, flexible and robust implementation of QKD in current and next-generation optical metro networks. In this paper, we discuss these obstacles and present approaches to share existing fiber infrastructures among quantum and classical channels. Particularly, a proposal for a smooth integration of QKD in optical metro networks, which implies removing spurious background photons caused by optical transmitters, amplifiers and nonlinear effects in fibers, is presented and discussed. We determine and characterize impairments on quantum channels caused by many classical telecom channels at practically used power levels coexisting within the same fiber. Extensive experimental results are presented and indicate that a practical integration of QKD in conventional optical metro networks is possible.