Luis F. Caro

All-Optical Unicast/Multicast Routing in WDM Networks

Optical transport networks (OTN) must be prepared in terms of better resource utilization, for accommodating unicast and multicast traffic together. Light-trees have been proposed for supporting multicast connections in OTN. Nevertheless when traffic grooming is applied in light-trees, resources can be underutilized as traffic can be routed to undesirable destinations in order to avoid optical-electrical-optical (OEO) conversions. In this paper, a novel architecture named S/G light- tree for supporting unicast/multicast connections is proposed. The architecture allows traffic dropping and aggregation in different wavelengths without performing OEO conversions. A heuristic that routes traffic demands using less wavelengths by taking advantage of the proposed architecture is designed as well. Simulation results show that the architecture can minimize the number of used wavelengths and OEO conversions when compared to light-trees.

S/G Light-tree: Multicast grooming architecture for improved resource allocation

Internet traffic demands are constantly increasing and a considerable amount of this increase is expected to be of multicast type. Optical transport networks (OTN)must be prepared in terms of better resource utilization for accommodating multicast traffic. For this purpose multicast traffic grooming has been considered. Light-trees have been proposed for supporting multicast connections in OTN. Nevertheless when light-trees are used with traffic grooming, resources can be overutilized as traffic can be routed to undesirable destinations in order to avoid optical-electrical-optical (OEO)conversions. In this paper a novel architecture named S/G light-tree for supporting multicast connections is proposed. The architecture allows to eliminate and aggregate traffic in different wavelengths without performing OEO conversions.The architecture uses labels supported by generalized multiprotocol label switching (GMPLS). A heuristic that routes traffic demands using less wavelengths by taking advantage of the proposed architecture is designed as well. Simulation results show that the architecture can minimize the number of used wavelengths and OEO conversions when compared to light-trees.

Improving Label Space Usage for Ethernet Label Switched Paths

Ethernet is becoming the dominant aggregation technology for carrier transport networks; however, as it is a LAN technology, native bridged ethernet does not fulfill all the carrier requirements. One of the schemes proposed by the research community to make ethernet fulfill carrier requirements is ethernet VLAN-label switching (ELS). ELS allows the creation of label switched data paths using a 12-bit label encoded in the VLAN TAG control information field. Previous label switching technologies such as MPLS use more bits for encoding the label. Hence, they do not suffer from label sparsity issues as ELS might. This paper studies the sparsity issues resulting from the reduced ELS VLAN-label space and proposes the use of the label merging technique to improve label space usage. Experimental results show that label merging considerably improves label space usage.

Ethernet label spaces dependency on network topology

Label space consumption has been studied in label-based forwarding architectures such as multi-protocol label switching (MPLS) to reduce forwarding table sizes and lookup complexity, to simplify network management, and to limit operational expenditures. On the other hand, nowadays label-based forwarding is also considered in the context of carrier class Ethernet architectures. Given that these architectures may use different label scopes (domain-wide vs. local) and size spaces (depending on their encoding), there is a need to analyse and compare the properties of their respective label spaces, particularly in terms of scalability. In this paper, the impact of topology characteristics on label space consumption is studied. The dependency on factors such as the number of nodes, the topology node degree and the network structure is determined (both analytically and via experimentation), allowing a detailed comparison between the properties of the evaluated label spaces. Proposed techniques that can be applied to improve label space usage for label-based Ethernet forwarding architectures are considered. The proposed methodology and results can serve as guidelines for the design of future label based forwarding architectures. Copyright

Impact of the number of SAB on architectures that support unicast/multicast traffic in WDM networks

Optical transport networks (OTN) should be prepared to jointly handle both multicast and unicast traffic. Both opaque and transparent architectures are available to handle these types of traffic. Light-trees have been proposed as a way to transport information in a transparent manner. The light-tree however, may route unwanted information through some links while performing grooming of unicast and multicast traffic. To solve this problem we propose S/G light-tree with the goal of optimising the resources from the point of view of the number of wavelengths and available capacity. S/G light-tree uses detection systems (DS) and splitter and amplifier banks (SABs) to determine when unicast traffic should not be routed jointly with a multicast one by eliminating it optically from the link. This article proposes an online heuristic with grooming policies which allows for the analysis of the effects of the number of SABs on the blocking probability in OTN with dynamic traffic.

Enhancing label space usage for Ethernet VLAN-label switching

Ethernet is positioning itself as an aggregation technology for carrier transport networks; however, as it was designed for local area networks, native bridged Ethernet does not fulfill all carrier requirements. Ethernet VLAN-label switching (ELS) has been designed to make Ethernet fulfill carrier requirements. ELS allows the creation of label switched data paths using a 12-bit label encoded in the VLAN TAG control information field. As previous label switching technologies use more bits to encode the label, they do not suffer from the label sparsity issues that ELS might. This paper studies the label sparsity issues resulting from the reduced ELS VLAN-label space. For this purpose the applicability of existing techniques for enhancing label space is studied and evaluated in the online routing scenario. Novel routing schemes are also proposed for taking advantage of the available techniques in order to further enhance the ELS VLAN-label space.

Carrier Ethernet "label" scalability

Ethernet is becoming one of the dominant aggregation technologies for carrier transport networks. Because it is a LAN technology, native bridged Ethernet does not fulfil all carrier requirements. Several schemes have been proposed to allow Ethernet to fulfil such requirements. Carrier Ethernet technologies rely on domain-wide or local label-based forwarding, although some of them use a smaller label size and different scope than existing label switching technologies (like Multi-Protocol Label Switching). Therefore, they can present label scalability issues, in the sense that a connection request can be blocked due to label unavailability. This article studies label scalability limitations of two of the existing carrier Ethernet solutions, Provider backbone bridges - Traffic Engineering (PBB-TE) and Ethernet VLAN-Label Switching (ELS). The applicability of existing techniques (like aggregation and label merging) that can overcome or reduce these limitations is evaluated. Additionally for PBB-TE a specific technique called VLAN-reutilization is formalized and the complexity of optimally applying it, is studied. The techniques are evaluated over an online routing scenario, results show that both solutions can present label scalability limitations when used without the studied techniques. These limitations can be greatly overcome by implementing the techniques.

Experimental analysis of optimization techniques on the road passenger transportation problem

Analyzing the state of the art in a given field in order to tackle a new problem is always a mandatory task. Literature provides surveys based on summaries of previous studies, which are often based on theoretical descriptions of the methods. An engineer, however, requires some evidence from experimental evaluations in order to make the appropriate decision when selecting a technique for a problem. This is what we have done in this paper: experimentally analyzed a set of representative state-of-the-art techniques in the problem we are dealing with, namely, the road passenger transportation problem. This is an optimization problem in which drivers should be assigned to transport services, fulfilling some constraints and minimizing some function cost. The experimental results have provided us with good knowledge of the properties of several methods, such as modeling expressiveness, anytime behavior, computational time, memory requirements, parameters, and free downloadable tools. Based on our experience, we are able to choose a technique to solve our problem. We hope that this analysis is also helpful for other engineers facing a similar problem.

Operational Cost Reduction in WDM Networks using Lighttours

Wavelength division multiplexing (WDM) networks have been adopted as a near-future solution for the broadband Internet. In previous work we proposed a new architecture, named enhanced grooming (G+), that extends the capabilities of traditional optical routes (lightpaths). In this paper, we compare the operational expenditures incurred by routing a set of demands using lightpaths with that of lighttours. The comparison is done by solving an integer linear programming (ILP) problem based on a path formulation. Results show that, under the assumption of single-hop routing, almost 15% of the operational cost can be reduced with our architecture. In multi-hop routing the operation cost is reduced in 7.1% and at the same time the ratio of operational cost to number of optical-electro-optical conversions is reduced for our architecture. This means that ISPs could provide the same satisfaction in terms of delay to the end-user with a lower investment in the network architecture.

Routing and Label Space Reduction in Label Switching Networks

This chapter is devoted to the analysis and modeling of some problems related to the optimal usage of the label space in label switching networks. Label space problems concerning three different technologies and architectures – namely Multi-protocol Label Switching (MPLS), Ethernet VLAN-Label Switching (ELS) and All-Optical Label Switching (AOLS) – are discussed in this chapter. Each of these cases yields to different constraints of the general label space reduction problem. We propose a generic optimization model and, then, we describe some adaptations aiming at modeling each particular case. Simulation results are briefly discussed at the end of this chapter.