Hierarchical spanning tree network design with Nash genetic algorithm

This paper presents a multi-criteria decision model and multi-criteria genetic algorithm (MCGA) approach to improve backbone topology by leveraging the virtual link (VL) system in an hierarchical link-state (LS) routing domain. Given that the sound backbone topology structure has a great impact on the overall routing performance in an hierarchical LS domain, the importance of this research is evident. The proposed decision model is to find an optimal configuration of VLs that properly meets two-pronged engineering goals in installing and maintaining VLs: i.e., operational costs and network reliability. The experiment results clearly indicates that it is essential to the effective operations of hierarchical LS routing domain to consider not only engineering aspects but also specific benefits from systematical layout of VLs, thereby presenting the validity of the decision model and MCGA

We formulate and investigate the Multi-Weighted Steiner Problem (MWS), a generalization of the Steiner problem in graphs, involving more than one weight function. As a special case, it contains the hierarchical network design problem. With the notion of "bottleneck length/distance", a min-max measure, we analyze the interaction between differently weighted edges in a solution. Combining the results with known methods for the Steiner problem in graphs and the hierarchical network design problem, two heuristics for the MWS are developed, one based on weight modifications and the other on exchanging edges. Both are of time complexityO(kv2), withv the number of nodes andk the number of special nodes in the graph. The first is also suited for thedirected MWS; the second is expected to perform better on the undirected version. Before actually solving the Steiner problem in graphs and the hierarchical network design problem, preprocessing techniques exploiting tests to reduce the problem graphs have proven to be valuable. We adapt three prominent tests for use in the MWS.

This paper studies a multi-facility network synthesis problem, called the Two-level Network Design (TLND) problem, that arises in the topological design of hierarchical communication, transportation, and electric power distribution networks. We are given an undirected network containing two types of nodes—primary and secondary—and fixed costs for installing either a primary or a secondary facility on each edge. Primary nodes require higher grade interconnections than secondary nodes, using the more expensive primary facilities. The TLND problem seeks a minimum cost connected design that spans all the nodes, and connects primary nodes via edges containing primary facilities; the design can use either primary or secondary edges to connect the secondary nodes. The TLND problem generalizes the well-known Steiner network problem and the hierarchical network design problem. In this paper, we study the relationship between alternative model formulations for this problem (e.g., directed and undirected models), and analyze the worst-case performance for a composite TLND heuristic based upon solving embedded subproblems (e.g., minimum spanning tree and either Steiner tree or shortest path subproblems). When the ratio of primary to secondary costs is the same for all edges and when we solve the embedded subproblems optimally, the worst-case performance ratio of the composite TLND heuristic is 4/3. This result applies to the hierarchical network design problem with constant primary-to-secondary cost ratio since its subproblems are shortest path and minimum spanning tree problems. For more general situations, we express the TLND heuristic worst-case ratio in terms of the performance of any heuristic used to solve the embedded Steiner tree subproblem. A companion paper develops and tests a dual ascent procedure that generates tight upper and lower bounds on the optimal value of a multi-level extension of this problem.

A branch and cut algorithm for the hierarchical network design problem

Inter-domain routing protocol routes network reachability information between autonomous systems (ASs) in the network. Network reachability information contains the details about the neighbors of the ASs and it contains messages used to maintain the connection between ASs. On one hand, given the size and the rapid growth of the Internet, any inter-domain routing protocol should satisfy basic desirable algorithmic properties, such as scalability, robustness and rapid convergence by Griffin, T., and Wilford, G. 1999. On the other hand, for economic reasons inter-domain routing should support policy routing, where Internet service providers (ISPs) have the flexibility to implement a wide variety of private routing policies that ISPs choose not to reveal. Moreover, the routing protocol should provide sufficient information to enable ISPs to make informed policy decisions. Border gateway protocol (BGP) by Goodell, G. et al. (2003) is the inter-domain routing protocol that is currently being used. BGP has a number of problems which includes scalability and large convergence time by Labovitz, C et al. (2000). This paper explains in detail the alternative to BGP which is the hybrid optimized link-state path-vector routing protocol (HLP) [1] and gives a comparison based on the simulation of these protocols. The comparison shows us that HLP overcomes some of the important problems faced in BGP.

Traditionally, Internet Service Providers (ISPs) make profit by providing Internet connectivity, while content providers (CPs) play the more lucrative role of delivering content to users. As network connectivity is increasingly a commodity, ISPs have a strong incentive to offer content to their subscribers by deploying their own content distribution infrastructure. Providing content services in an ISP network presents new opportunities for coordination between traffic engineering (to select efficient routes for the traffic) and server selection (to match servers with subscribers). In this work, we develop a mathematical framework that considers three models with an increasing amount of cooperation between the ISP and the CP. We show that separating server selection and traffic engineering leads to sub-optimal equilibria, even when the CP is given accurate and timely information about the ISP's network in a partial cooperation. More surprisingly, extra visibility may result in a less efficient outcome and such performance degradation can be unbounded. Leveraging ideas from cooperative game theory, we propose an architecture based on the concept of Nash bargaining solution. Simulations on realistic backbone topologies are performed to quantify the performance differences among the three models. Our results apply both when a network provider attempts to provide content, and when separate ISP and CP entities wish to cooperate. This study is a step toward a systematic understanding of the interactions between those who provide and operate networks and those who generate and distribute content.

In 1999, the Internet development varies considerably by geographic region. The network of networks is the most transforming invention and is developing at a far greater speed than any other technology of the 20th century. The Internet affects the way people do business, learn, play and work and TCP/IP is the protocol which defines the Internet. The levels of change are very different : social and cultural changes through increased networking, re-location of companies and new forms of businesses and organisations, restructuring of supply and demand chains and new working methods as well as reshaping of processes in retail and wholesale business. These changes influence the spatial structure due to the kind and geographic spread of access and connectivity to networks beside the location pattern of the Internet industry itself. The growth potentials of the Internet are mainly influenced by the availability and performance of physical network infrastructure. Since Internet Service Providers (ISPs) partially use the public-switched network, access to backbone network resources via leased lines, local access via unbundled local loops, co-location and interconnection are important to the growth of the information society. The key drivers for the development of telecommunications infrastructure for access to the Internet and global connectivity are to ensure competition and appropriate regulation of dominance to maximise the roll-out to rural geographic areas, to new subscribers and to ensure a reasonable quality of service while at the same time encouraging carriers to compete for those markets. This paper provides insight behind the Internet cloud and the regulatory environment which has a significant impact on the development and connectivity of places and thus spatial structures within regions and countries. It considers the broad infrastructural issues, the structure of the market and the role played by tele¬ communications operators and discusses the market dynamics of access and Internet interconnection. In order to understand market dynamics of the Internet industry and the spatial implications, issues of traffic flows and communication structures, recent backbone market changes and interconnection on the backbone as well as local level regarding peering and transit systems need to be observed. Pricing of leased lines and Internet access pricing as well as special access products offered by Incumbents to ISPs to connect their customers are important elements which define the different developments of the Internet throughout geographic regions. Considering costs of connectivity and access, localisation of traffic nodes and geography of investments in new IP infrastructure, space and distance remain important for the evolution of the Internet

Link state-routing protocols such as OSPF and IS- IS are used in most if not all Internet Service Provider and enterprise networks. They both rely on flooding to distribute the network topology to all routers. Upon topology changes, all routers update their forwarding tables asynchronously which leads to transient events such as micro-loops and packet losses. We propose two improvements to OSPF in an extension called oFIQUIC. First, we use QUIC to exchange routing information between neighboring routers. Second, we revisit the OSPF flood- ing process. Instead of relying entirely on flooding to distribute topology changes, we establish secure remote QUIC sessions with distant OSPF routers to inform them of topology changes. This enables oFIQUIC to prevent transient loops by ordering the updates of the forwarding tables of all routers after a topology change. We add oFIQUIC to the BIRD implementation of OSPF. Our evaluation demonstrates that oFIQUIC prevents loops and converges quickly in different topologies.

The internet is playing an increasingly crucial role in both personal and business activities. In addition, with the emergence of real-time, delay sensitive and mission-critical applications, stringent network availability requirement is put forward for internet service providers (ISPs). However, commonly deployed intradomain link-state routing protocols react to link failures by globally exchanging link state advertisements and recalculating routing table, inevitably causing significant forwarding discontinuity after a failure. Therefore, the loop-free criterion (LFC) approach has been widely deployed by many ISPs for coping with the single network component failure scenario in large internet backbones. The success of LFC lies in its inherent simplicity, but this comes at the expense of letting certain failure scenarios go unprotected. To achieve full failure coverage with LFC without incurring significant extra overhead, we propose a novel link protection scheme, hybrid link protection (HLP), to achieve failure resilient routing. Compared to previous schemes, HLP ensures high network availability in a more efficient way. HLP is implemented in two stages. Stage one provides an efficient LFC based method (MNP-e). The complexity of the algorithm is less than that of Dijkstra's algorithm and can provide the similar network availability with LFC. Stage two provides backup path protection (BPP) based on MNP-e, where only a minimum number of links need to be protected, using special paths and packet headers, to meet the network availability requirement. We evaluate these algorithms in a wide spread of relevant topologies, both real and synthetic, and the results reveal that HLP can achieve high network availability without introducing conspicuous overhead. HLP not only needs around 10% time of that of full protection, but also provides full protection capabilities that full protection provide.

As a hierarchical layout design method that can handle hierarchical designs of large‐scale integrated circuits, the BSG method, one of the general structural layout methods, is hierarchical and has evolved as a layout method including interconnections. It is the objective of this paper to construct a design system that will provide feedback as a guideline for circuit design modification in which the layers in the circuit design are faithfully represented and are evaluated from the point of view of layout, and the placement is reconstructed for optimization. Hierarchical BSG is realized by combining smaller BSGs (elemental BSGs) with root trees. The size, number, and hierarchical trees of BSGs can be specified by the designer. An experiment to demonstrate the hierarchical effect is carried out by artificially setting a hierarchical design environment with a combination of several thousands of cells. Performance competitive with that without a hierarchical approach is obtained in the resultant areas and interconnect lengths. As a layout algorithm, the number of rectangles to be treated is increased by one order of magnitude so that several tens of thousands of rectangles can be placed with high quality. © 2001 Scripta Technica, Electron Comm Jpn Pt 3, 85(3): 12–21, 2002

A new routing protocol for ad hoc networks, called zone-based hierarchical link state routing, is proposed. In this protocol, the network is divided into non-overlapping zones. Each node only knows the node connectivity within its zone and the zone connectivity of the whole network. The link state routing is performed on two levels: local node and global zone levels. Unlike other hierarchical protocols, there is no cluster head in this protocol. The zone level topological information is distributed to all nodes. This peer-to-peer manner mitigates the traffic bottleneck, avoids single point of failure and simplifies mobility management. Since only zone ID and node ID of a destination are needed for routing, the route from a source to a destination is adaptable to changing topology. The zone ID of the destination is found by sending one location request to every zone. Simulation results show that our location search scheme generates less overhead than other schemes based on flooding. The results also confirm that the communication overhead for creating and maintaining the topology in our protocol is smaller than that in flat link state routing. This new routing protocol provides a flexible, efficient and effective approach to accommodate changing topology in wireless networks.

This paper presents a novel unsupervised image sequence segmentation method using hierarchical wavelet domain hidden Markov tree model(WDHMT). The key idea is that with a priori information introduced into the segmentation framework, we can capture both local and global statistical information using WDHMT model. Firstly, each frame extracted from the image sequence is transformed through discrete wavelet transform(DWT) to obtain a compressive representation of the original one. Then we capture the context information of wavelet coefficients at each level through tree-structured probabilistic graph. After the model parameters are learned through up-down iterated expectation maximization(EM) algorithm, we deduced the maximum likelihood(ML) segmentation at the finest level. The boundary information is then fused with the a priori region information. Finally, we quantitatively evaluated the performance of this algorithm by using a sequence of tobacco leaf images polluted by Gaussian white noise. The simulation results show that the proposed algorithm can achieve high classification accuracy, preferable specificity and sensitivity properties.

Link state routing protocols, like OSPF, are used in IP backbones to correctly define the routes. During failure situations, the OSPF process needs a due time to react and find new routes. During this time, the routes can present instability with high packet loss rate, which affects backbone reliability. This study proposes a proactive approach named E-CER in order to reduce the OSPF packet loss rate during the reaction time. This approach is evaluated in representations of synthetic and real backbone topologies, and also in a network simulator to analyze the reduction of packet loss rate, which has rendered rather satisfactory outcomes.

Co-evolutionary algorithms to solve hierarchized Steiner tree problems in telecommunication networks

Security is an important concern in today's information age and particularly so in satellite systems, where eavesdropping can be easily performed. This paper addresses efficient key management for encrypted multicast traffic transmitted via satellite. We consider the topic of encrypting traffic in large multicast groups, where the group size and dynamics have a significant impact on the network load. We consider life cycle key management costs of a multicast connection, and show for a logical key hierarchy (LKH) how member preregistration and periodic admission reduces the initialization cost, and how the optimum outdegree of a hierarchical tree varies with the expected member volatility and rekey factor. This improves network utilization, but encryption at the network layer can pose problems on satellite links. We, therefore, propose and analyze an interworking solution between multilayer Internet protocol security (IPSEC) and LKH that also reduces key management traffic while enabling interworking with performance enhancing modules used on satellite links.