型を重視した通信ネットワークトポロジー設計手法の研究

通信ネットワークの設計において，ネットワークトポロジー設計は，通信コストや通信性能を確保するという観点から重要な項目である．その設計手法には大きく分けて，従来からの人手による経験的なアプローチと，コンピュータによる自動設計があるが，特に実世界での物理的な通信ネットワークトポロジー設計においては，多くの場合に人手による伝統的な設計手法が用いられて来た．特に，現実世界でのWAN等の物理トポロジー設計は，Star，Bus，Ring 等の典型的なトポロジー型を積極的に利用したものとなっている.コンピュータによる自動設計については，Kleinroch 以降，通信ネットワークトポロジー設計を最適化問題とし定式化するアプローチとして，計算機ネットワークの応用分野の拡大により様々な展開が見られる．しかし，その多くは実世界で多用されるStar，Bus，Ring などのトポロジー型を考慮しない．このため，論理ネットワーク設計には有効であるが，広域物理ネットワークのトポロジー設計で重視されるトポロジーの型への指向性が弱い．これもあり，実世界での物理的な通信ネットワークのトポロジー設計においては，多くの場合に人手による伝統的な設計手法が用いられて来た．伝統的設計法では，まず通信フロー行列をもとに，典型的なトポロジー型もしくはその組み合わせによる有望な構成案を探しだし, それを通信速度，冗長性，コストなどの現実世界の要求を満たすように加工・変形することにより，様々な環境に適応させるという方法をとっている. 現代の通信ネットワークにおいても構造的な型ベースのトポロジー設計は重要である．そこで本研究では，この伝統的手法の自動化を目標とし，性能（平均遅延時間）を充足する多様な型を階層化したトポロジー（型階層トポロジー）を自動生成する方法を提案する．ネットワーク設計者には生成された型階層トポロジーがその属性（費用，平均遅延，ノード次数，平均リンク容量，平均リンク長）と共に提示され，ネットワーク設計者は適切な案を選択できる．具体的には，まず，型階層生成の母体となる局所星状木型のネットワークトポロジー生成手法を提案する．局所星状木とは局所的なStar クラスタが連結された全域木であり，物理ネットワーク設計に適したトポロジーである．ここでは，Kleinrochが定式化した最適化問題を型が木という制約条件下で解き，与えられたノード間距離行列と通信フロー行列のもとで，目標遅延時間を満足するコストが小さい木型ネットワークを生成する．本手法の特色は解候補集合の生成方法にあり，ノード間の完全グラフのリンクに，リンク距離とフロー強度を反映した重み付きリンクコストを与え，重み付けパラメータを変えてKruskal 法で最小全域木を求めることにより，リンク容量最小のStar から総リンク長最小のMST までの多様な局所星状木をパラメトリックに生成する．論文ではこの性質の数学的基礎の解明もおこなった．最終目的である多様な型階層トポロジーの生成は，まず，上記手法をボトムアップに繰り返しこのStar 型階層トポロジーを得る．その後，特定階層のStar を他の型（Bus, Ring）に書き換えることで多様な型階層トポロジーを生成する．さらに，目標平均遅延時間を実現するリンク容量を求めたのち，人による最終案の選択を支援するための属性を計算して提示する．現実世界では業種や業態に合わせて通信特性とリンク費用関数特性の組み合わせで分類される異なるトポロジーのタイプが見られる．例えば，平均遅延時間制約が強い金融系などの場合はStar 型を中心としたトポロジーが重用され，性能に比してリンク費用がより重視される場合にはBus やRing 型が重用される．そこで，提案したトポロジー生成方式の入力である通信行列特性とリンク費用関数特性を変更させたものを組み合わせて通信ネットワーク構築の際の環境条件を模擬し，トポロジー生成を試みた．得られたトポロジーの型は，現実世界で環境に応じて重用される型と整合しており，提案方式の有用性を示す結果であると考える．電気通信大学201

Topology Reduction for Approximate Symbolic Analysis

The paper deals with a procedure for approximate symbolic analysis of linear circuits based on simplifying the circuit model. The procedure consists of two main steps. First, network elements whose influence on the circuit function is negligible are completely removed, i.e. their parameters are removed from the resulting symbolic formula. The second step consists in modifying the voltage and current graphs in order to decrease the number of common spanning trees. The influence of each modification of the circuit model is ranked numerically. A fast method based on the use of cofactors is presented. It allows evaluating all the prospective simplifications using at most two matrix inversions per one frequency point

An extensive English language bibliography on graph theory and its applications, supplement 1

Graph theory and its applications - bibliography, supplement

Learning mutational graphs of individual tumour evolution from single-cell and multi-region sequencing data

Background. A large number of algorithms is being developed to reconstruct evolutionary models of individual tumours from genome sequencing data. Most methods can analyze multiple samples collected either through bulk multi-region sequencing experiments or the sequencing of individual cancer cells. However, rarely the same method can support both data types. Results. We introduce TRaIT, a computational framework to infer mutational graphs that model the accumulation of multiple types of somatic alterations driving tumour evolution. Compared to other tools, TRaIT supports multi-region and single-cell sequencing data within the same statistical framework, and delivers expressive models that capture many complex evolutionary phenomena. TRaIT improves accuracy, robustness to data-specific errors and computational complexity compared to competing methods. Conclusions. We show that the application of TRaIT to single-cell and multi-region cancer datasets can produce accurate and reliable models of single-tumour evolution, quantify the extent of intra-tumour heterogeneity and generate new testable experimental hypotheses

Using the PALS Architecture to Verify a Distributed Topology Control Protocol for Wireless Multi-Hop Networks in the Presence of Node Failures

The PALS architecture reduces distributed, real-time asynchronous system design to the design of a synchronous system under reasonable requirements. Assuming logical synchrony leads to fewer system behaviors and provides a conceptually simpler paradigm for engineering purposes. One of the current limitations of the framework is that from a set of independent "synchronous machines", one must compose the entire synchronous system by hand, which is tedious and error-prone. We use Maude's meta-level to automatically generate a synchronous composition from user-provided component machines and a description of how the machines communicate with each other. We then use the new capabilities to verify the correctness of a distributed topology control protocol for wireless networks in the presence of nodes that may fail.Comment: In Proceedings RTRTS 2010, arXiv:1009.398

Optimisation of piping network design for district cooling system

A district cooling system (DeS) is a.scheme for centralised cooling energy distribution which takes advantage of economies of scale and load diversity. . A cooling medium (chilled water) is generated at a central refrigeration plant and then supplied to a district area, comprising multiple buildings, through a closed-loop piping circuit. Because of the substantial capital investment involved, an optimal design of the distribution piping . configuration is one of the crucial factors for successful implementation of a district 1'. cooling scheme. Since there. exists an enormous number of different combinations of the piping configuration, it is not feasible to evaluate each individual case using an exhaustive approach. This thesis exammes the problem of determining an optimal distribution piping configuration using a genetic algorithm (GA). In order to estimate the spatial and temporal distribution of cooling loads; the climatic conditions of Hong Kong were investigated and a weather database in the form of a typical meteorological year (TMY) was developed. Detailed thermal modelling of a number of prototypical buildings was carried out to determine benchmark cooling loads. A novel Local Search/Looped Local Search algorithm was developed for finding optimal/near-optimal distribution piping configurations. By means of computational . experiments, it was demonstrated that there is a promising improvement to GA performance by including the Local Search/Looped Local Search algorithm, in terms of both solution quality and computational efficiency. The effects on the search performance of a number of parameters were systematically investigated to establish the most effective settings. In order to illustrate the effectiveness of the Local Search/Looped Local Search algorithm, a benchmark problem - the optimal communication,spanning tree (OCST) was used for comparison. The results showed that the Looped Local Search method developed in this work was an effective tool for optimal network design of the distribution piping system in DCS, as well as for optimising the OCST problem.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Outlier Detection Techniques For Wireless Sensor Networks: A Survey

In the field of wireless sensor networks, measurements that significantly deviate from the normal pattern of sensed data are considered as outliers. The potential sources of outliers include noise and errors, events, and malicious attacks on the network. Traditional outlier detection techniques are not directly applicable to wireless sensor networks due to the multivariate nature of sensor data and specific requirements and limitations of the wireless sensor networks. This survey provides a comprehensive overview of existing outlier detection techniques specifically developed for the wireless sensor networks. Additionally, it presents a technique-based taxonomy and a decision tree to be used as a guideline to select a technique suitable for the application at hand based on characteristics such as data type, outlier type, outlier degree

Outlier detection techniques for wireless sensor networks: A survey

In the field of wireless sensor networks, those measurements that significantly deviate from the normal pattern of sensed data are considered as outliers. The potential sources of outliers include noise and errors, events, and malicious attacks on the network. Traditional outlier detection techniques are not directly applicable to wireless sensor networks due to the nature of sensor data and specific requirements and limitations of the wireless sensor networks. This survey provides a comprehensive overview of existing outlier detection techniques specifically developed for the wireless sensor networks. Additionally, it presents a technique-based taxonomy and a comparative table to be used as a guideline to select a technique suitable for the application at hand based on characteristics such as data type, outlier type, outlier identity, and outlier degree