Optimizing IGP Link Costs for Improving IP-level Resilience

Recently, major vendors have introduced new router platforms to the market that support fast IP-level failure pro- tection out of the box. The implementations are based on the IP Fast ReRoute–Loop Free Alternates (LFA) standard. LFA is simple, unobtrusive, and easily deployable. This simplicity, however, comes at a severe price, in that LFA usually cannot protect all possible failure scenarios. In this paper, we give new graph theoretical tools for analyzing LFA failure case coverage and we seek ways for improvement. In particular, we investigate how to optimize IGP link costs to maximize the number of protected failure scenarios, we show that this problem is NP- complete even in a very restricted formulation, and we give exact and approximate algorithms to solve it. Our simulation studies show that a deliberate selection of IGP costs can bring many networks close to complete LFA-based protection

Optimization in Telecommunication Networks

Network design and network synthesis have been the classical optimization problems intelecommunication for a long time. In the recent past, there have been many technologicaldevelopments such as digitization of information, optical networks, internet, and wirelessnetworks. These developments have led to a series of new optimization problems. Thismanuscript gives an overview of the developments in solving both classical and moderntelecom optimization problems.We start with a short historical overview of the technological developments. Then,the classical (still actual) network design and synthesis problems are described with anemphasis on the latest developments on modelling and solving them. Classical results suchas Menger’s disjoint paths theorem, and Ford-Fulkerson’s max-flow-min-cut theorem, butalso Gomory-Hu trees and the Okamura-Seymour cut-condition, will be related to themodels described. Finally, we describe recent optimization problems such as routing andwavelength assignment, and grooming in optical networks.operations research and management science;

Optimal Algorithms for Near-Hitless Network Restoration via Diversity Coding

Diversity coding is a network restoration technique which offers near-hitless restoration, while other state-of-the art techniques are significantly slower. Furthermore, the extra spare capacity requirement of diversity coding is competitive with the others. Previously, we developed heuristic algorithms to employ diversity coding structures in networks with arbitrary topology. This paper presents two algorithms to solve the network design problems using diversity coding in an optimal manner. The first technique pre-provisions static traffic whereas the second technique carries out the dynamic provisioning of the traffic on-demand. In both cases, diversity coding results in smaller restoration time, simpler synchronization, and much reduced signaling complexity than the existing techniques in the literature. A Mixed Integer Programming (MIP) formulation and an algorithm based on Integer Linear Programming (ILP) are developed for pre-provisioning and dynamic provisioning, respectively. Simulation results indicate that diversity coding has significantly higher restoration speed than Shared Path Protection (SPP) and p-cycle techniques. It requires more extra capacity than the p-cycle technique and SPP. However, the increase in the total capacity is negligible compared to the increase in the restoration speed.Comment: An old version of this paper is submitted to IEEE Globecom 2012 conferenc

Protection and restoration algorithms for WDM optical networks

Currently, Wavelength Division Multiplexing (WDM) optical networks play a major role in supporting the outbreak in demand for high bandwidth networks driven by the Internet. It can be a catastrophe to millions of users if a single optical fiber is somehow cut off from the network, and there is no protection in the design of the logical topology for a restorative mechanism. Many protection and restoration algorithms are needed to prevent, reroute, and/or reconfigure the network from damages in such a situation. In the past few years, many works dealing with these issues have been reported. Those algorithms can be implemented in many ways with several different objective functions such as a minimization of protection path lengths, a minimization of restoration times, a maximization of restored bandwidths, etc. This thesis investigates, analyzes and compares the algorithms that are mainly aimed to guarantee or maximize the amount of remaining bandwidth still working over a damaged network. The parameters considered in this thesis are the routing computation and implementation mechanism, routing characteristics, recovering computation timing, network capacity assignment, and implementing layer. Performance analysis in terms of the restoration efficiency, the hop length, the percentage of bandwidth guaranteed, the network capacity utilization, and the blocking probability is conducted and evaluated

Topology overlays for dedicated protection Ethernet LAN services in advanced SONET/SDH networks

The explosion of information technology (IT) services coupled with much-increased personal and scientific computing capabilities has resulted in great demand for more scalable and reliable networking services. Along these lines, carriers have spent large sums to transition their legacy\u27 SONET/SDH voice-based networking infrastructures to better support client-side Ethernet data interfaces, i.e., next-generation SONET/SDH (NGS). In particular, a key addition here has been the new virtual concatenation (VCAT) feature which supports inverse multiplexing to \u27split\u27 larger connection requests in to a series of independently-routed \u27sub-connections\u27. As these improved infrastructures have been deployed, the design of new Ethernet over SONET/SDH (EoS) services has become a key focus area for carriers, i.e., including point-to-point and multi-point services. In light of the above, this thesis focuses on the study of improved multi-point EoS schemes in NGS networks, i.e., to provision robust \u27virtual LAN\u27 capabilities over metro and wide-area domains. Indeed, as services demands grow, survivability considerations are becoming a key concern. Along these lines, the proposed solution develops novel multi-tiered (partial) protection strategies. Specifically, graph-theoretic algorithms are first proposed to interconnect multi-point node groups using bus and minimum spanning tree (MST) overlays. Next, advanced multi-path routing schemes are used to provision and protect these individual overlay connections using the inverse-multiplexing capabilities of NGS. Finally, post-fault restoration features are also added to handle expanded failure conditions, e.g., multiple failures. The performances of the proposed multi-point EoS algorithms developed in this research are gauged using advanced software-based simulation in the OPNET ModelerTM environment. The findings indicate that both the bus and MST overlays give very good performance in terms of request blocking and carried load. However, the MST-based overlays slightly outperform the bus-based overlays as they allow more efficient topology designs. In addition, the incorporation of dynamic load state information in the selection of bus and/or MST overlays is also very beneficial as opposed to just using static hop count state. Furthermore, inverse-multiplexing is highly-effective, yielding notably higher carried loads when coupled with load-balancing sub-connection routing. Finally, results also show that post-fault restoration is also a very effective means of boosting EoS LAN throughputs for partially-protected demands, consistently matching the reliability of full-protection setups.\u2

Design of survivable WDM network based on pre-configured protection cycle

Wavelength Division Multiplexing (WDM) is an important technique which allows the trans- port of large quantities of data over optical networks. All optical WDM-based networks have been used to improve overall communication capacity and provide an excellent choice for the design of backbone networks. However, due to the high traffic load that each link can carry in a WDM network, survivability against failures becomes very important. Survivability in this context is the ability of the network to maintain continuity of service against failures, since a failure can lead to huge data losses. In recent years, many survivability mechanisms have been studied and their performance assessed through capacity efficiency, restoration time and restorability. Survivability mechanisms for ring and mesh topologies have received particular attention

Route recovery schemes for link and node failure and link congestion

Link/Node failure occurs frequently causing service disruption in computer networks. Hardware techniques have been developed to protect the network from Link/Node failure. These techniques work in physical layer, therefore their convergence time is very small. On the other hand, many schemes have been proposed to mitigate the failure influence on the network. These schemes work in upper layers such as the network layer. However, hardware solutions faster than other schemes, but they are expensive. Link/Node failure causes all flows which were using the failed link/node are temporarily interrupted till a new path reestablished. Three recovery algorithms have been proposed that mitigate the changes occur in the network. These changes are link/node failure and link congestion. The algorithms mainly pre-compute a backup next hop for each destination in the network. This path is feasible to accommodate re-routed traffic when a failure occurs without causing congestion or loops. Simulations have been conducted to show the performance of the proposed algorithms using ns2 network simulation tool. The results show fast recovery for all flows were using the link/node failure. Furthermore, the throughput per node also increases due to decrease interruption service time