Thomas K. Stidsen

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.

Multi-Objective Design Space Exploration of Embedded System Platforms

In this paper we present a multi-objective genetic algorithm to solve the problem of mapping a set of task graphs onto a heterogeneous multiprocessor platform. The objective is to meet all real-time deadlines subject to minimizing system cost and power consumption, while staying within bounds on local memory sizes and interface buffer sizes. Our approach allows for mapping onto a fixed platform or onto a flexible platform where architectural changes are explored during the mapping.

Hierarchical Ring Network Design Using Branch-and-Price

We consider the problem of designing hierarchical two layer ring networks. The top layer consists of a federal-ring which establishes connection between a number of node disjoint metro-rings in a bottom layer. The objective is to minimize the costs of links in the network, taking both the fixed link establishment costs and the link capacity costs into account.Hierarchical ring network design problems combines the following optimization problems: Clustering, hub selection, metro ring design, federal ring design and routing problems. In this paper a branch-and-price algorithm is presented for jointly solving the clustering problem, the metro ring design problem and the routing problem. Computational results are given for networks with up to 36 nodes.

The generalized fixed-charge network design problem

Abstract In this paper we present the generalized fixed-charge network design (GFCND) problem. The GFCND problem is an instance of the so-called generalized network design problems. In such problems, clusters instead of nodes have to be interconnected by a network. The network interconnecting the clusters is a fixed-charge network, and thus the GFCND problem generalizes the fixed-charge network design problem. The GFCND problem is related to the more general problem of designing hierarchical telecommunication networks. A mixed integer programming model is described and a branch-cut-and-price algorithm is implemented. Violated constraints and variables with negative reduced costs are found using enumeration. The algorithm is capable of obtaining optimal solutions for problems with up to 30 clusters and up to 300 nodes. This is possible, since the linear programming relaxation bound is very tight and there are few non-zero variables and few binding constraints.

Complete rerouting protection

Feature Issue on AvailabilityProtection of communication against network failures is becoming increasingly important, and here we present what we believe to be the most capacity-efficient protection method possible, the complete rerouting protection method, when we require that all communication should be restored in the case of a single link network failure. We present a linear programming model of the protection method and a column-generation algorithm. For six real-world networks, the minimal restoration overbuild network capacity is between 13% and 78%. We further study the importance of the density of the network, derive analytical bounds, and study methods to speed up the column-generation algorithm. We expect that the suggested protection method will be used for calculating lower bounds required for protection, but not as a functioning protection method.