Recovery in multilayer optical networks

The integration of different network technologies into a multilayer network, as in Internet-based networks carried by optical transport networks (OTNs), creates new opportunities but also challenges with respect to network survivability. In different network layers, recovery mechanisms that are active can be exploited jointly to reach a more efficient or faster recovery from failures. This interworking is also indispensable in order to overcome the variety of failure scenarios that can occur in the multilayer-network environment. A well-considered coordination between the different layers and their recovery mechanisms is crucial in order to attain high performance recovery. This paper provides an overview of multilayer recovery issues and solutions in an Internet protocol (IP)-over-optical-network environment, which is illustrated by quantitative case studies.     

Fault tolerant network design inspired by Physarum polycephalum

Physarum polycephalum, a true slime mould, is a primitive, unicellular organism that creates networks to transport nutrients while foraging. The design of these natural networks proved to be advanced, e.g. the slime mould was able to find the shortest path through a maze. The underlying principles of this design have been mathematically modelled in literature. As in real life the slime mould can design fault tolerant networks, its principles can be applied to the design of man-made networks. In this paper, an existing model and algorithm are adapted and extended with stimulation and migration mechanisms which encourage formation of alternative paths, optimize edge positioning and allow for automated design. The extended model can then be used to better design fault tolerant networks. The extended algorithm is applied to several national and international network configurations. Results show that the extensions allow the model to capture the fault tolerance requirements more accurately. The resulting extended algorithm overcomes weaknesses in geometric graph design and can be used to design fault tolerant networks such as telecommunication networks with varying fault tolerance requirements.     

The Design of an Allo-Optical Packet Switching Network

Recent advances in the all-optical signal processing domain report high-speed and nontrivial functionality directly implemented in the optical layer. These developments mean that the all- optical processing of packet headers has a future. In this article we address various important control plane issues that must be resolved when designing networks based on all-optical packet-switched nodes.     

Influence of GMPLS on network providers' operational expenditures: a quantitative study

GMPLS is promoted as a major technology for the automation of network operations. It is often claimed to allow the reduction of operational expenses. However, detailed analysis and quantitative evaluation of the changes induced by such technologies is very rare. In this article we quantify the cost reduction potential of GMPLS. We present a detailed analysis and modeling of traditional operator processes. We also develop a model for the expected changed processes when using GMPLS and identify the differences quantitatively. A survey with major telecom operators has been done, and the process models have been verified and parameterized. This allowed quantitative evaluations of the OPEX changes with GMPLS. The results show that, depending on the network operator's processes, different impacts can be expected. As an overall result we could verify that a reduction on the order of 50 percent of OPEX can be expected for most operational models.     

Adoption and Pricing: The Underestimated Elements of a Realistic IPTV Business Case

The adoption of IPTV increases competition for telecom operators. Especially video on demand and the move to HDTV push the bandwidth requirements to the limits. It is very challenging for an operator to construct a successful and sustainable introduction of IPTV over the existing infrastructure. This article gives an overview of a typical business case followed by a detailed discussion of the adoption and evaluation of the outcome. The results of this article indicate the importance of a correct choice of adoption model and related parameters. It illustrates how different IPTV-specific effects on adoption (i.e., competition and analog switchoff) might have a considerable impact on the outcome. After adoption, the article shows how the outcome of the business case can be used within pricing decisions by setting sustainable and competitive boundaries on the tariff. Finally, as pricing will also have an important impact on adoption (e.g., a price reduction could lead to increased adoption), the possible impact of this feedback loop is indicated. In this sense the approach discussed in the article could easily be extended with a highly detailed cost model of the network architecture and technology, leading to a full business case for IPTV introduction by a telecom operator.     

Routing in an AWG-Based Optical Packet Switch

For the next generation of the optical internet, focus is now moving from circuit switched networks, which occupy a wavelength continuously regardless of the demand at that time, towards optical packet/burst switching. By only occupying a wavelength when data is to be transmitted, a more efficient utilization of bandwidth in optical fibers is strived for. As bandwidth in fibers keeps increasing, the bottleneck of the optical network is now moving towards the switching node, since evolution of electronic routers cannot follow the speed of bandwidth increase. Thus a key component in these novel networks is the optical node. Through this node we want to switch traffic very fast and reliably, preferably transparent. Lack of efficient and practically realizable optical buffer, however, makes migration from electronic routers to optical routers a non-straightforward transition. In most optical nodes payload traffic can be switched transparently, whilst control information (e.g., in a header, on a control channel) is still converted to the electronic domain in every node, since optical processing is far from mature. In this paper we present a possible architecture for such a node, array waveguide gratings and all-optical tuneable wavelength converters. The concept of this switch is explained and the node is evaluated in terms of loss rate. We will see that an inherent problem of this switch is its internal blocking. This drawback can be greatly overcome by using an intelligent and efficient wavelength assignment algorithm within the node. Simulation of slotted operation will give some numerical results.     

Scheduling Algorithms for a Slotted Packet Switch with either Fixed or Variable Length Packets

We address the problem of congestion resolution in optical packet switching (OPS). We consider a fairly generic all-optical packet switch architecture with a feedback optical buffer constituted of fiber delay lines (FDL). Two alternatives of switching granularity are addressed for a switch operating in a slotted transfer mode: switching at the slot level (i.e., fixed length packets of a single slot) or at the burst level (variable length packets that are integer multiples of the slot length). For both cases, we show that in spite of the limited queuing resources, acceptable performance in terms of packet loss can be achieved for reasonable hardware resources with an appropriate design of the time/wavelength scheduling algorithms. Depending on the switching units (slots or bursts), an adapted scheduling algorithm needs to be deployed to exploit the bandwidth and buffer resources most efficiently.     

From IP over WDM to all-optical packet switching: economical view

In this paper, a technoeconomical study of several (optical) packet-switching node architectures is described. Therefore, different architectures proposed in IST-WASPNET and IST-LASAGNE projects as well as a standard optical circuit switching approach are considered, and their economical impact is estimated by means of cost comparisons between the different technologies. The switching architectures all use optical fiber as a transport medium, but each of them uses a different technology to process switching. Their cost is evaluated as a function of most characteristic parameters for each technology. In the all-optical approaches, the main cost is that related to the fiber assembly, whereas for electronic processing, the most expensive cost is related to the optical-electronic-optical (OEO) conversions. The results show that the integration of optical components is crucial to make all-optical packet-switching nodes feasible.     

Municipalities as a Driver for Wireless Broadband Access

Municipalities can form a driving force behind the deployment of new telecom infrastructure. While a telecom operator focuses on direct (financial) profits, a municipality is mainly interested in the social benefits for its inhabitants. In this paper, we evaluate a wireless municipality network from both a technical and an economic point of view. WiFi and WiMAX are considered as the most suited technologies for this purpose. A detailed techno-economic study has been performed including forecasting of the user adoption, dimensioning of the wireless network and modelling the related costs and revenues. The trade-off between installing a high number of relatively cheap WiFi access points, and a smaller number of more expensive WiMAX base stations for delivering full coverage is investigated in several scenarios.

Long-Term Planning of WDM Networks: A Comparison between Single-Period and Multi-Period Techniques

This paper studies the long-term planning (e.g. a planning horizon of 2 to 5 years) of survivable WDM networks. The problem is formulated as a multi-period model that combines network topology and capacity expansion. The ability to determine network expansion schedules of this type becomes increasingly important to the telecommunications industry and to its customers. Two inherently different solution methods are presented: a sequential single-period approach, which designs the networks for every time period separately in chronological order, and an integrated multi-period approach, which considers all time periods at once. For each of these approaches, different network design cost models can be applied. Extensive simulations on a wide range of problem instances are carried out, to measure the influence of the applied network design cost model and to assess the cost savings that can be expected by opting for a multi-period planning approach instead of a sequential network design method.