We present two strategies to balance the load in a system with multiple virtual machines (VMs) through automated live migration. When the push strategy is used, overloaded hosts try to migrate workload to less loaded nodes. On the other hand, when the pull strategy is employed, the light-loaded hosts take the initiative to offload overloaded nodes.The performance of the proposed strategies was evaluated through simulations. We have discovered that the strategies complement each other, in the sense that each strategy comes out as "best" under different types of workload. For example, the pull strategy is able to quickly re-distribute the load of the system when the load is in the range low-to-medium, while the push strategy is faster when the load is medium-to-high.Our evaluation shows that when adding or removing a large number of virtual machines in the system, the "best" strategy can re-balance the system in 4-15 minutes.

Quantum computers are expected to have a dramatic impact on numerous fields due to their anticipated ability to solve classes of mathematical problems much more efficiently than their classical counterparts. This particularly applies to domains involving integer factorization and discrete logarithms, such as public key cryptography. In this paper, we consider the threats a quantum-capable adversary could impose on Bitcoin, which currently uses the Elliptic Curve Digital Signature Algorithm (ECDSA) to sign transactions. We then propose a simple but slow commit–delay–reveal protocol, which allows users to securely move their funds from old (non-quantum-resistant) outputs to those adhering to a quantum-resistant digital signature scheme. The transition protocol functions even if ECDSA has already been compromised. While our scheme requires modifications to the Bitcoin protocol, these can be implemented as a soft fork.

This paper reports on a measurement and modeling study of session and message characteristics of BitTorrent traffic. BitTorrent is a Peer-to-Peer (P2P) replication and distribution system developed as an alternative to the classical client-server model to reduce the load on content servers and networks. Results are reported on measurement, modeling and analysis of application and link layer traces collected at the Blekinge Institute of Technology (BTH) and a local ISP in Sweden. Link layer traces and application logs were collected, modeled and analyzed using a dedicated measurement infrastructure developed at BTH to collect P2P traffic. New results are reported on important session and message characteristics of BitTorrent, i.e., session interarrivals, sizes and durations, request rates and response times. Our results show that session interarrivals can be accurately modeled by a second-order hyper-exponential distribution while session durations and sizes can be reasonably well modeled by various mixtures of the Log-normal and Weibull distributions. Response times have been observed to be modeled by a dual Log-normal mixture, while request rates are modeled as dual Gaussian distributions.

The paper reports on recent developments and challenges in reliable multicast communication, with special focus on reliable multicast communication at the application layer. The foundation of reliable multicast communication is given by several components, which are multicast communication, congestion control and error control. Our paper is providing a survey of these mechanisms in multicast environments. I. INTRODUCTION Group communication has emerged as one of the most important developments in Internet. Video conferencing, multimedia distribution, online gaming and long-distance education are today some of the most popular Internet applications, which generate large amounts of traffic. To support these applications, reliable multicast communication is a prerequisite. The purpose is to provide efficient and reliable communication services among a number of users, who are members of a multicast group. Traditional multicast communication demands for the presence of a multicast group, together with associated facilities for reliable multicast communication, to which the users can subscribe and participate. Even though IP multicasting was introduced twenty years ago [14], it is still not widely available as an open Internet service. Problems related to per-group state maintaining, scalability, reliability, congestion control and security have been postponing the wide deployment of IP multicast. On the other hand, other solutions have been developed for multicast service, to compensate for the above-mentioned limitations, e.g., MBone [18]. MBone provides an overlay network, which connects IP multicast capable islands by using unicast tunnel connections. Furthermore, other developments related to, e.g., video distribution and long-distance education, has further pushed the research and development of new alternative solutions for multicast, which are implemented at the application layer. Our paper is a survey on current solutions for multicast communication as well as on solutions for the provision of reliable communication in this context. By reliable multicast communication we mean a type of multicast communication that has included facilities of error and congestion control. The rest of the paper is as follows. Section II provides a survey of multicast communication. Section III presents some This work has been done within the research project "Routing in Overlay Networks (ROVER)", granted in 2006 by the EuroNGI NoE.

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