We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Random graphs

技術解説 IEEE Computer

Cloud computing builds upon advances on virtualization and distributed computing to support cost-efficient usage of computing resources, emphasizing on resource scalability and on demand services. Moving away from traditional data-center oriented models, distributed clouds extend over a loosely coupled federated substrate, offering enhanced communication and computational services to target end-users with quality of service (QoS) requirements, as dictated by the future Internet vision. Toward facilitating the efficient realization of such networked computing environments, computing and networking resources need to be jointly treated and optimized. This requires delivery of user-driven sets of virtual resources, dynamically allocated to actual substrate resources within networked clouds, creating the need to revisit resource mapping algorithms and tailor them to a composite virtual resource mapping problem. In this paper, toward providing a unified resource allocation framework for networked clouds, we first formulate the optimal networked cloud mapping problem as a mixed integer programming (MIP) problem, indicating objectives related to cost efficiency of the resource mapping procedure, while abiding by user requests for QoS-aware virtual resources. We subsequently propose a method for the efficient mapping of resource requests onto a shared substrate interconnecting various islands of computing resources, and adopt a heuristic methodology to address the problem. The efficiency of the proposed approach is illustrated in a simulation/emulation environment, that allows for a flexible, structured, and comparative performance evaluation. We conclude by outlining a proof-of-concept realization of our proposed schema, mounted over the European future Internet test-bed FEDERICA, a resource virtualization platform augmented with network and computing facilities.

On the optimal allocation of virtual resources in cloud computing networks

Handbook of Approximation: Algorithms and Metaheuristics

Utilizing the dormant path diversity through multipath routing in the Internet to reach end users—thereby fulfilling their QoS requirements—is rather logical. While offering better resource utilization, better reliability, and often even much better quality of experience (QoE), multipath routing and provisioning was shown to help network and data center operators achieve traffic engineering in the form of load balancing. In this survey, we first highlight the benefits and basic Internet multipath routing components. We take a top-down approach and review various multipath protocols, from application to link and physical layers, operating at different parts of the Internet. We also describe the mathematical foundations of the multipath operation, as well as highlight the issues and challenges pertaining to reliable data delivery, buffering, and security in deploying multipath provisioning in the Internet. We compare the benefits and drawbacks of these protocols operating at different Internet layers and discuss open issues and challenges.

A Survey on Internet Multipath Routing and Provisioning

In this paper we propose the concept of an end-to-end (e2e) Self-Protecting Multi-Path (SPM) as a protection switching mechanism that may be implemented, eg, in Multiprotocol Label Switching (MPLS) networks In case of local outages, resilient networks redirect the traffic from a failed link over an e2e backup path to its destination In this case, Quality of Service (QoS) can only be provided if sufficient extra capacity is available If backup capacity can be shared among different backup paths, multi-path routing allows for considerable savings regarding this extra capacity The SPM consists of disjoint paths that carry the traffic both in normal operation mode and during local outages If a partial path is affected by a network failure, the traffic is just distributed to the remaining working paths This structure is easy to configure and the switching to failure mode operation is simple since no signalling is required Based on analytical results, we show that load balancing of the traffic across the disjoint paths can reduce the required backup capacity significantly The backup performance depends strongly on the network topology, and the SPM outperforms simple Open Shortest Path First (OSPF) rerouting by far

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Self-Protecting Multipaths — A Simple and Resource-Efficient Protection Switching Mechanism for MPLS Networks

In this work, we present several end-to-end protection switching mechanisms for application in multiprotocol label switching (MPLS). In case of local outages in the network, they deviate the traffic around the failed element over backup paths. They are easy to implement and reduce the additional capacity to maintain the quality of service (QoS) on the backup paths. We study the capacity savings of the presented methods for various protection schemes with different traffic matrices. We further test the influence of different resilience constraints such as the set of protected failure scenarios, bandwidth reuse restrictions due to optical communication, and traffic reduction due to failed border routers.

Sensitivity of backup capacity requirements to traffic distribution and resilience constraints

During past decades, Ethernet progressively became the most widely used Local Area Network LAN technology. Apart from LAN installations, Ethernet also became attractive for other application areas such as industrial control, automotive, and avionics. In traditional LAN design, the objective is to minimize the network deployment cost. However, in embedded networks, additional constraints and ambient conditions add to the complexity of the problem. In this paper, the authors propose a Simulated Annealing SA algorithm to optimize the physical topology of an embedded Ethernet network. The various constraints and ambient conditions are modeled by a cost map. For networks with small number of nodes and/or switches, the authors were able to find the optimal solutions using adapted algorithms. These solutions will serve as a lower bound for the solutions obtained via the SA algorithm. However, the adapted algorithms are time consuming and application specific. The paper shows that the SA algorithm can be applied in all cases and finds near-optimal solutions.

Cost-Based Topology Optimization of Embedded Ethernet Networks

The deployment of Internet Protocol television (IPTV)-like services or other content delivery solutions into constantly evolving telecommunication infrastructures requires significant efforts. Among many other facets, it involves developing an extensible architecture that is ready for future IPTV-like solutions and deploying an expensive dedicated service delivery infrastructure. To reduce the effort and cost of producing complete, dedicated solutions in an environment with ever shorter development and time-to-market cycles, we propose an infrastructure add-on to networks. The intelligent service–oriented network infrastructure (ISONI) separates service development from resource provisioning and deployment. It allows for testing and running several IPTV or other content delivery services of different sizes in parallel without affecting each other and introduces resource sharing capabilities into the deployed infrastructure. It follows the service-oriented architecture (SOA) approach as found within the Internet market. Service development is mostly detached from infrastructure management, glued together only via resource virtualization. ISONI can flexibly adapt to new service demands and can optimally utilize its existing resources. Service developers can realize new services more rapidly by concentrating on the service development process alone.

A service-oriented infrastructure for providing virtualized networks

Orthogonal frequency division multiple access (OFDMA) is the basis for several emerging wireless systems, such as 802.16e (WiMAX) or 3GPP long term evolution (LTE). In OFDMA, different users are multiplexed in time and frequency. In the 802.16e adaptive modulation and coding (AMC) downlink, the data bursts for a particular terminal have a rectangular shape and need to be placed in the two-dimensional time/frequency plane. The position and shape of the rectangles is arbitrary, and it is the task of the frame packer to pack the frame efficiently, wasting as little space as possible. In this paper, we treat the frame packing problem as a strip-packing problem. We solve this combinatorial optimization problem by developing a suitable representation for a genetic algorithm. This algorithm can reach within 5% of the theoretical lower bound for the packing efficiency.

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Andreas Reifert

Papers

Self-Protecting Multipaths — A Simple and Resource-Efficient Protection Switching Mechanism for MPLS Networks

Sensitivity of backup capacity requirements to traffic distribution and resilience constraints

Cost-Based Topology Optimization of Embedded Ethernet Networks

A service-oriented infrastructure for providing virtualized networks

Optimized Frame Packing for OFDMA Systems