Jose L. Marzo

User Modeling, Adaption and Personalization

This book constitutes the proceedings of the third annual conference under the UMAP title, adaptation, which resulted from the merger in 2009 of the successful biannual User Modeling (UM) and Adaptive Hypermedia (AH) conference series, held on Girona, Spain, in July 2011. The 27 long papers and 6 short papers presented together with15 doctoral consortium papers, 2 invited talks, and 3 industry panel papers were carefully reviewed and selected from 164 submissions. The tutorials and workshops were organized in topical sections on designing adaptive social applications, semantic adaptive social Web, and designing and evaluating new generation user modeling.

On optimal computation of MPLS label binding for multipoint-to-point connections

Most network operators have considered reducing Label Switched Routers (LSR) label spaces (i.e. the number of labels that can be used) as a means of simplifying management of underlaying Virtual Private Networks (VPNs) and, hence, reducing operational expenditure (OPEX). This letter discusses the problem of reducing the label spaces in Multiprotocol Label Switched (MPLS) networks using label merging - better known as MultiPoint-to-Point (MP2P) connections. Because of its origins in IP, MP2P connections have been considered to have tree- shapes with Label Switched Paths (LSP) as branches. Due to this fact, previous works by many authors affirm that the problem of minimizing the label space using MP2P in MPLS - the Merging Problem - cannot be solved optimally with a polynomial algorithm (NP-complete), since it involves a hard- decision problem. However, in this letter, the Merging Problem is analyzed, from the perspective of MPLS, and it is deduced that tree-shapes in MP2P connections are irrelevant. By overriding this tree-shape consideration, it is possible to perform label merging in polynomial time. Based on how MPLS signaling works, this letter proposes an algorithm to compute the minimum number of labels using label merging: the Full Label Merging algorithm. As conclusion, we reclassify the Merging Problem as Polynomial-solvable, instead of NP-complete. In addition, simulation experiments confirm that without the tree-branch selection problem, more labels can be reduced.

Full label space reduction in MPLS networks: asymmetric merged tunneling

Traffic Engineering objective is to optimize network resource utilization. Although several works have been published about minimizing network resource utilization in MPLS networks, few of them have been focused in LSR label space reduction. This letter studies Asymmetric Merged Tunneling (AMT) as a new method for reducing the label space in MPLS network. The proposed method may be regarded as a combination of label merging (proposed in the MPLS architecture) and asymmetric tunneling (proposed recently in our previous works). Finally, simulation results are performed by comparing AMT with both ancestors. They show a great improvement in the label space reduction factor.

Label space reduction in MPLS networks: how much can a single stacked label do?

Most network operators have considered reducing LSR label spaces (number of labels used) as a way of simplifying management of underlaying Virtual Private Networks (VPNs) and therefore reducing operational expenditure (OPEX). The IETF outlined the label merging feature in MPLS-allowing the configuration of MultiPoint-to-Point connections (MP2P)-as a means of reducing label space in LSRs. We found two main drawbacks in this label space reduction scheme: a it should be separately applied to a set of LSPs with the same egress LSR--which decreases the options for better reductions, and b LSRs close to the edge of the network experience a greater label space reduction than those close to the core. The later implies that MP2P connections reduce the number of labels asymmetrically. In this article we propose a solution to these drawbacks achieved by stacking an additional label onto the packet header. We call this type of reduction Asymmetric Merged Tunnels (AMT). A fast framework for computing the optimal reduction using AMTs is proposed. Our simulations show that the label space can be reduced by up to 20% more than when label merging is used.

Topology-focused availability analysis of basic protection schemes in optical transport networks

We present a novel study of the availability in optical networks based on network topology. Connection availability is studied under two basic path protection schemes. Different topologies are selected in order to have heterogeneity in geographic coverage, network diameter, link lengths, and average node degree. Connection availability is also computed considering the reliability data of physical components and a well-known network availability model. Results report some useful information to select the suitable protection algorithms according to the network topology features and the required levels of availability.

Partial disjoint path for multi-layer protection in GMPLS networks

In this paper, different recovery methods applied at different network layers and time scales are used in order to enhance the network reliability. Each layer deploys its own fault management methods. However, current recovery methods are applied to only a specific layer. New protection schemes, based on the proposed partial disjoint path algorithm, are defined in order to avoid protection duplications in a multi-layer scenario. The new protection schemes also encompass shared segment backup computation and shared risk link group identification. A complete set of experiments proves the efficiency of the proposed methods in relation with previous ones, in terms of resources used to protect the network, the failure recovery time and the request rejection ratio.

Reliable services with fast protection in IP/MPLS over optical networks

Feature Issue on High Availability in Optical NetworksWe define new quality-of-service (QoS) routing schemes with protection in Internet Protocol (IP)/Multiprotocol Label Switching (MPLS) over optical networks. The novelty of the proposed routing schemes is the use of the knowledge of the logical links already protected by the optical layer. The logical topology defined by the optical layer is given and fixed, and we assume that it is partially protected. Thereby, at the IP/MPLS layer, spare capacity is reserved to protect only those links that are unprotected. Moreover, we also characterize the traffic services based on their level of reliability and QoS requirements. In order to guarantee fast protection, segment protection and shared backups are combined, resulting in suitable fault recovery time and resource consumption. A complete set of experiments proves that the proposed schemes are more efficient than the previous ones in terms of resources used to protect the network, failure impact, and blocking probability.

Multiobjective optimization model and heuristic algorithm for dynamic multicast routing

We propose a multiobjective traffic engineering scheme using different distribution trees to dynamic multicast groups (i.e., in which egress nodes can change during the connections lifetime). If a multicast tree is recomputed from scratch, it may consume a considerable amount of CPU time and all communication using the multicast tree will be temporarily interrupted. To alleviate these drawbacks we propose an optimization model (dynamic model MHDB-D) that makes use of a previously computed multicast tree (static model MHDB-S) in order to add new egress nodes. Using these two models, our aim is to combine into a single aggregated metric, the following weighting objectives: maximum link utilization, hop count, total bandwidth consumption and total end-to-end delay. Moreover, our proposal solves the traffic split ratio for multiple trees. The problem is NP-hard, therefore, a novel multicast multiobjective dynamic routing algorithm is proposed for optimizing the different objectives. We compare the dynamic multicast routing model with the algorithm proposed. The proposed approach can be applied in MPLS networks by allowing explicit routes to be established in multicast events. The main contributions of this paper are the optimization model for dynamic multicast routing; and the heuristic algorithm proposed with polynomial complexity.

Performance evaluation of minimum interference routing in network scenarios with protection requirements

Minimum interference routing schemes are good options for achieving fewer working-path request rejections. They improve the vast majority of the current QoS routing proposals. However, when backup paths are added there is no guarantee of achieving a similar performance. In this paper, we analyze the suitability of these routing schemes in protected network scenarios. The main objective was to define the network scenarios in which the required performance can be achieved using only minimum interference. Some simulation results are presented to consider different network topologies and different routing schemes and to show the main drawbacks and advantages of using minimum interference schemes in protected network scenarios.

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