Costas K. Constantinou

Multicast routing algorithms for sparse splitting optical networks

This work proposes novel routing approaches for transparent optical networks where only a fraction of the network nodes are multicast capable (MC) and can split the optical power from a single input to multiple output ports. The remaining, multicast-incapable (MI) nodes, can have either Drop-or-Continue (DoC) or Drop-and-Continue (DaC) capabilities. For the case of DaCs, if a MI node is a destination of the multicast group, it can drop a fraction of the incoming signal locally and transmit the rest to the next node. The current paper presents an Integer Linear Programming (ILP) formulation as well as novel heuristic multicast routing algorithms under the sparse-splitting constraint, for networks with or without DaC nodes. Performance results show that the proposed algorithms achieve an important decrease of the average cost of the derived solutions, compared to existing relevant techniques, and attain results very close to the lower bound provided by the ILP.

Survivable multicast routing in mixed-graph mesh optical WDM networks

A new multicast protection algorithm for mixed-graph mesh optical WDM networks is presented. Simulations show that the proposed algorithm outperforms the existing ones for this category of networks, in terms of blocking probability and average cost.

Test System for Mapping Interdependencies of Critical Infrastructures for Intelligent Management in Smart Cities

The critical infrastructures such as power distribution networks (PDN), water networks, transportation and telecommunication networks that are settled within the area of a city produce a large amount of data from applications such as AMI, SCADA, Renewable Energy Management Systems, Asset Management Systems, and weather data. To convert these massive data into useful information, visualization is an effective solution. Visualizing this large amount of data in a holistic view of critical infrastructures mapping at a city level is a missing link. Visualization means here to convert the flow of continuous coming data into useful information. In this paper we propose a technique to visualize critical infrastructure data by using a system that consists of Geographic Information System (GIS) for buffer spatial analysis and Google Earth in sync with realistic planning and operation methodologies specific for each infrastructure modelled. The major goal of this work is to design, model and validate a benchmark system that is capable to visualize and map as well as to prepare the next inter-linking phase of modelling and analysis of interdependencies of several critical infrastructures. Furthermore, we aim to provide the grounds for a theoretical framework that can capture the interdependencies between critical infrastructures using techniques from graph theory, machine learning, econometric science and operation research. The proposed framework for modeling the interdependencies between several infrastructures within a city territory is based on hybrid system automata and it is among the first steps needed in developing fundamental mechanisms for resilient management of critical infrastructures and the safe operation of smart cities. An example on how this framework can be applied is also presented.

Heuristic algorithms for efficient allocation of multicast-capable nodes in sparse-splitting optical networks

Optical splitters are utilized in optical nodes for splitting the received signal into multiple copies, in order to efficiently provide multicast capabilities in optical networks. In practice, only a fraction of the network nodes are equipped with optical splitters. These nodes are called multicast-capable (MC) and the remaining nodes are called Multicast Incapable (MI). In some networks, if the MI nodes are destinations of the multicast request, they can drop a small fraction of the incoming signals power locally and transmit the rest to the next node. This ability is called Drop-and-Continue (DaC) and the relevant networks are called DaC networks. In the absence of the DaC capabilities, the network is called Drop-or-Continue (DoC). The current paper deals with both aforementioned categories of networks, and proposes three heuristic algorithms for the efficient allocation of a limited number of MC nodes in the network, so as to achieve a low average cost of the light-trees that are calculated for routing the multicast requests. It is shown through simulations that the proposed techniques significantly outperform the relevant conventional splitter placement techniques. This work also investigates the impact of networks having DaC rather than DoC capabilities, as well as the impact of the percentage of MC nodes on the network performance, providing guidance for the efficient design of optical networks with sparse multicasting capabilities.

Survivable multicast routing in mixed-graph sparse-splitting optical networks

This paper investigates the survivability of multicast requests in mixed-graph optical networks, where only a fraction of the nodes have optical splitting capabilities (sparse-splitting optical networks). Mixed-graph networks have both bidirectional and unidirectional connections between their nodes, and they result due to resource holding of the already established requests. A new multicast protection heuristic for this category of networks, is presented and evaluated in terms of the blocking ratio of the arriving multicast requests. Its performance results are compared with existing approaches, developed for undirected-graph sparse-splitting optical networks.

Shortest Path Routing in Transportation Networks with Time-Dependent Road Speeds.

The current paper deals with the subject of shortest path routing in transportation networks (in terms of travelling time), where the speed in several of the networks roads is a function of the time interval. The main contribution of the paper is a procedure that is faster compared to the conventional approaches, that derives the roads traversal time according to the time instant of departure, for the case where the roads speed has a constant value inside each time interval (in general, different value for each time interval). Furthermore, the case where the roads speed is a linear function of time inside each time interval (in general, different linear function for each time interval) is investigated. A procedure that derives the roads traversal time according to the time instant of departure is proposed for this case as well. The proposed procedures are combined with Dijkstras algorithm and the resulting algorithms, that are practically applicable and of low complexity, provide optimal shortest path routing in the networks under investigation.

A load balancing technique for efficient survivable multicasting in mesh optical networks

Abstract The current paper deals with the problem of survivable multicasting in mesh optical networks. A load balancing technique is presented that can be combined with any appropriate survivable multicast algorithm. Simulations on several test networks have shown that the proposed technique outperforms the conventional methods as it efficiently intersperses the network load, as well as keeps low the percentage of highly congested arcs at each network state, thus decreasing the blocking ratio for the newly arriving multicast requests.

A New Arc-Disjoint-Trees scheme for survivable multicasting in mixed-graph sparse-splitting optical networks.

This work addresses the problem of survivable multi-cast request provisioning in mixed-graph optical networks, where only a fraction of the nodes have optical splitting capabilities. An effective scheme for the calculation of a pair of disjoint trees, namely the New Arc-Disjoint Trees (NADT) protection scheme, is presented. The key idea of this technique is to gradually construct the primary tree, verifying that after the addition of each one of the destinations of the multicast session, a secondary (arc-disjoint) tree can still be obtained. The proposed protection technique is combined with two existing heuristics for multicast routing in mixed-graph sparse-splitting networks. Performance results demonstrate that the proposed NADT protection technique clearly outperforms the conventional approach in terms of blocking ratio, and presents a negligible increase of the average cost of the derived pair of arc-disjoint trees.

Survivable multicasting in sparse-splitting optical networks

In this work, the problem of provisioning survivable multicast connections in optical networks is investigated, under the assumption that not all network nodes are multicast capable (MC). A MC capable node is a node that can forward the incoming signal to multiple output ports. An integer linear programming (ILP) formulation is presented, as well as a heuristic algorithm to address the problem. Simulations show that the proposed heuristic gives an average cost of the derived multicasting subgraphs that is very close to the optimal one obtained by the ILP.

Calculation of arc-disjoint trees in mixed-graph arbitrary mesh optical networks

In the paper, a heuristic algorithm that deals with the problem of finding arc-disjoint trees in mixed-graph mesh optical networks is presented. A mixed graph is defined as one that has both unidirectional and bidirectional links between its nodes. The calculation of pairs of arc-disjoint trees is applied for provisioning survivable multicast requests. The development of algorithms that work efficiently for this kind of networks is important, since in practice the network is modeled as a mixed graph. Simulations show that for the case of mixed-graph networks, the proposed multicast protection algorithm is able to calculate arc-disjoint tree pairs with lower blocking ratio and average cost compared to the existing algorithms, especially for multicast sessions with destination sets that comprise of up to half of the network nodes.