The motivation behind basing applications on peer-to-peer architectures derives to a large extent from their ability to function, scale and self-organize in the presence of a highly transient population of nodes, network and computer failures, without the need of a central server and the overhead of its administration. P2P networks are vulnerable to peers, who cheat, propagate malicious codes, or peers who do not cooperate. Traditional client-server security models are not sufficient to P2P networks because of their centralized nature. Absence of central authority in P2P poses unique challenges like identity management of the peers, secure reputation data management and Sybil attack for reputation management in the network. In this paper we present a cryptographic protocol for ensuring secure and timely availability of the reputation data of a peer extremely at low cost. The past behavior of the peer is encapsulated in its digital reputation and is subsequently used to predict the future actions. The cryptographic protocol is coupled with self-certification and cryptographic mechanisms for identity management and countering Sybil attacks. The latency associated with a file replication in a P2P system consists of two components: the query search time and the time required by the peers to transmit the file. In order to model the peer level latency, we develop a queuing model to evaluate the time required at each peerto serve its replication requests.
Any frequently used P2P protocol like BitTorrent or NapStar could be used for the purpose of simulation. The distribution is evaluated for 2 GB of a multimedia file downloaded from youtube.com. The proposed system is also evaluated with the other different size of the file which have different contents (other than multimedia). Understanding the security implementationof the proposed protocol, it has been seen that when the download request is originated from any client, the proposed framework will first attempt to evaluate the secure confidential identity of the peer nodes and once the authentication is positively accomplished, the cleaner chunk of the digital content requested by the authorized client starts downloading whereas the unauthorized clients will end-up either downloading a poisoned chunks of digital data which will render the unauthorized client to increase the download time to higher extent.
Since the ultimate goal of KM is allowing workers to learn and evolve within organizations, research in the areas of KM and collaborative learning could profit a lot from cross-fertilization. Nowadays, both collaborative learning [Erro! Argumento de opção desconhecido.,Erro! Argumento de opção desconhecido.] and KM [Erro! Argumento de opção desconhecido.,Erro! Argumento de opção desconhecido.] are converging for the use of the sense of community [Erro! Argumento de opção desconhecido.] to support learning. Collaborative learning communities can be seen as organizations that share both explicit and tacit knowledge. A common problem of these settings is the fact that the community’s resources are distributed among its members, thus it is not easy to find out who has the right piece of information, knowledge or advice. Targeting this problem, we propose Help&Learn (H&L), a peer-to-peersystem aimed at supporting the organization and sharing of distributed knowledge in collaborative learning communities. Peer-to-peer technology allows sharing of resources via direct exchange among individual systems in a digital network, naturally supporting KM by closely adopting the conventions of face-to-face communication [Erro! Argumento de opção desconhecido.]. In such networks, there are no central servers controlling the interactions among peers. This horizontal relationship between peers allows the creation of rich knowledge sharing environments, in which people look for each other based on common interests, social affinity and personal characteristics. This configuration can be quite interesting to support collaborative learning communities, reflecting the non-hierarchic relationship between teachers, students and other members.
The use of computer resources (work stations and servers) installed in research and teaching institutions located in Brasilia allowed us to construct in 2006 a network Peer-to-Peer, called p2pBIOFOCO that linked that institutions. This network is intended for processing Bioinformatics applications. In this system, two problems have been impacted enough the efficiency of the system: the location of hosts and the scheduling of tasks. To solve the first problem, we changed the system inclu- ding a new mechanism for searching peers. Thereby, it was implemented a network which uses the algorithm of a structure of distributed storage, DHT (Distributed Hash Table) , adopting the protocol Kademlia. This work seeks to solve the problem of scheduling of tasks in p2pBIOFOCO, implementing a strategy toin- corporate the p2pBIOFOCO the flexible use of schedulers. More specifically, we used the method WQR as scheduler. In addition, we have included a efficient data transfer mechanism using the method DP-RR, very useful for Bioinformatics appli- cations. The experiments showed that the p2pBIOFOCO had a better performance with the incorporation of the two methods, showing that it can be used to increase processing capacity both notation as comparative analyzes in sequencing projects of high performance.
(2) The emergence of “digital institutions”: As a growing fraction of human interaction and exchange is mediated by digital technologies, we have witnessed the emergence of a number of different kinds of “digital institutions”: digital technology-based platforms that facilitate economic exchangein the same way that economic institutions historically have done. For example, over the last 15 years, a digital ‘reputationsystem’ (which allows buyers and sellers to provide feedback about their transactions) has enabled semi-anonymous peers on the platform eBay to trade assets with each other without being physically collocated or having to relying on traditional business infrastructure. The digital rights management technologies of platforms like Apple’s iTunes and Amazon’s Kindle are, de facto, subsuming government-mediated intellectual property laws for digital music, video and books. Today, a wide variety of other digital identity verification, reputation and credit scoring systems (which often leverage the real-world social capital that mobile device usage, Facebook, LinkedIn and other social technologies bring online) facilitate trusted economic exchangein hundreds of different peer-to-peer marketplaces.
While the BitTorrent mechanism seems to be well designed to support file sharing applications its extension to a real-time distribution is still an open issue. This research aims to the design of a P2P real-time video distribution system using the BitTorrent protocol as its P2P basis. On a first analysis, BitTorrent seems not to be appropriate for being used as basis for a real-time video distribution system, due to the fact that it has been designed for the distribution of large static files and not being equipped with any kind of mechanism capable of the distribution of a continuously incremented bit stream, like those found in real time video distributions. Additionally functionalities like the rarest-first prioritization criteria used in the request for piece files, seem to make BitTorrent even more unappropritate, since their characteristics are not chronologically oriented as a video bit stream should be, originating an almost random receiving of the pieces on the downloading peer. Another challenging problem could be the considerable startup latencies verified by P2P systems in general. This well known issue has been targeted in several studies, like in , which similarly to this research, considers a P2P systemto deliver scalable video to peers.
DNS stands for Domain Name System and its purpose is to enable name address to Internet Protocol (IP) conversion. 1 This is what allows one to browse the Internet using a Fully Qualified Domain Name (FQDN) like www.di.ubi.pt, for example, instead of its less prac- tical IP address notation of 188.8.131.52. It was introduced in 1984 and its initial goal was to provide a better solution than what was used before. Instead of using a regularly updated single local stored hosts.txt text file, to hold all that information to match a FQDN to its corresponding IP address, DNS uses both characteristics of a hierarchical model and a P2P network. The features that provided its scalability, which allowed it to grow exponentially through the years, have been the starting point for much more recent P2P protocols. One of those features is that it allows hosts to act both as clients and servers, just like in nowadays P2P networks, due to the design of the protocol itself. DNS has to replicate and propagate requests across the Internet as new sites are added and changed frequently.
To enable a comparison with eCAN, we use a mechanism that builds LRC in a way that closely resembles the express- ways of eCAN. We must emphasize that this mechanism is an extremely simplified version of the complete eCAN solution, that only captures the fundamental impact of the expressway mechanism in routing, and does not attempt to reproduce other features of eCAN (such as the mechanisms that provide support for complex interaction schemes like pub- lish/subscribe). In spite of these simplifications, we believe that our implementationof expressways mimics the eCAN LRC mechanism with enough accuracy to allow a fair comparison. Hence, the idea is to make a first level division of the entire space in four big squares. Each node keeps LRC to two of these four squares: one to some node that is in the square above/below, the other to some node that is in the square at right/left. Then, the four big squares are further divided in other four smaller squares. This time, some of the squares in the middle may have a total number of four LRC (above, below, right and left). This process is repeated for as many levels as wanted. Figure 4d illustrates the eCAN-like LRC scheme. In our context we set the number of LRC to some predetermined level and stop creating new LRC as well as new subdivisions as soon as that number is reached. Since we select random points inside the squares we must proceed in a way similar to the small-world mechanism. Hence, the effective long range contact is the node responsible for the point that was randomly selected.
Esse modelo de negócio permitia que qualquer pessoa prestasse serviços ou vendesse/alugasse bens, que estavam subutilizados e, com isso, criar rendimento. O que mudou neste modelo de negócio foi a sua escala passando de uma escala muito reduzida para uma escala global podendo agora ser potenciado de modo a que mais pessoas possam beneficiar destes serviços. Com o aumento da escala das share economies criou-se um novo tipo de mercado, o mercado peer-to-peer. Este mercado funciona, na maioria dos casos, online e permite que pessoas possam encontrar serviços prestados por outras pessoas. Esses mercados têm como ponto principal a confiança, sendo fundamental que existam mecanismos de criação dessa confiança.
One research field in the sharing economy stems from consumer behaviour and investigates reasons for participating in the sharing economy and the behaviour of consumers inside these ventures. In the latter, particular attention is paid to predominant modes of consumption. Drawing from knowledge in consumer research from both the traditional economy and non-economic settings, the relevance of the predominant consumption modes market exchange, gift giving, and sharing is investigated in the context of the sharing economy. Belk (2010) describes marketplace exchange as transactions in an economic context which are high on egoism, stinginess, impersonality, and reciprocity. In particular, goods or services and money are exchanged simultaneously with both parties having balanced (tit-for-tat) or negative (each party is maximising its own output) reciprocal expectations (Belk, 2007). Putting these characteristics into the context of a prototype, Belk (2010) mentions the example of “buying bread in a store” (p. 718). In comparison, gift giving is less egoistic, stingy, and impersonal than marketplace exchange (Belk, 2007). Reciprocal expectations are prevalent, but tacit and do not occur simultaneously: After giving a gift, one party of the dyadic relationship is in debt of returning the favour every time (Belk, 2007). According to Giesler (2006), gift giving in a consumption context is prevalent in consumer gift systems – for example in the peer-to-peer music file sharing program Napster. As a prototype, Belk (2010) mentions the famous short story “The Gift of the Magi”, in which a man and a woman in love both sacrifice favourite belongings in order to make each other gifts. Sharing could be defined as "the act and process of distributing what is ours to others for their use as well as the act and process of receiving something from others for our use" (Belk, 2007, p. 127). Sharing is high on altruism, generosity, and personality, and does not involve any reciprocal expectations (Belk, 2007; Belk, 2010). A prototype are pooled resources in households (Belk, 2007): In families, income of parents is shared and reallocated among family members without direct reciprocity. Inside sharing, Belk (2010) classifies sharing practices either as sharing in or sharing out. This author defines sharing in as sharing executed by including others within the aggregate extended self, whereas sharing out implies sharing with clear boundaries between self and others. Simply put, sharing in is closer to sharing within the family or circle of friends for the expression of community, whereas sharing out is closer to gift giving and commodity exchange (Belk, 2010, p. 725).
The article will analyze the taxation of collaborative initiatives in the urban mobility sector, mainly the incidence of the Tax on Services, in view of the changes introduced by Complementary Law 157/2017 to Complementary Law 116/2003. Considering Law and Economics, the competence for the taxation is from the Municipality where the service provider is located and not the Municipality of the service taker.The justification of the study rests on the contemporaneity of the subject, lacking solid doctrinal analysis and jurisprudence, besides allowing an interdisciplinary view between law and economy, allied to the dialectical-juridical method and the national and foreign bibliographic.
In this paper, we propose a cluster based replication architecture for load-balancing inpeer-to-peer content distribution systems. In addition to an intelligent replica placement technique, it also consists of an effective load balancing technique. In the intelligent replica placement technique, peers are grouped into strong and weak clusters based on their weight vector which comprises available capacity, CPU speed, access latency and memory size. In order to achieve complete load balancing across the system, an intra- cluster and inter-cluster load balancing algorithms are proposed. We are able to show that our proposed architecture attains less latency and better throughput with reduced bandwidth usage, through the simulation results.
services to a potential edge node. Following this handshak- ing described in Section 3.1 is established. If this request is accepted by the edge node, then the edge manager initialises a container for the iPokeMon edge server. The cloud man- ager deploys the iPokeMon edge server and clones the data (to the edge database) of the users that will be connected to the edge node. User data rapidly changes when the game is played. For example, the GPS coordinates of the player and the Pok´emons. The local view on the edge server is updated by frequent update requests that are sent to the edge server. When the edge server has to be terminated, as considered in Section 3.1, then the edge database is merged with the global database located on the cloud. The user is redirected back to the cloud server for continuing the session. If a new edge node is available, then the above process is repeated.
The research on P2P computing, which has been fuelled by the need to find more robust and scalable solutions, has been classifying P2P systems according to two traversal dimensions: network structure and search mechanisms. Network structure refers to the existence of some sort of structure according to which, some peers have different responsibilities or are hierarchically organized within the network. In terms of network structure, P2P systems can either be pure (also referred to as unstructured), where all peers are equal in responsibilities and no hierarchy exists; or hybrid (also referred to as structured), where peers are organized in specific hierarchies or some peers – also referred to as super-peers or ultra-peers – have different responsibilities, or peers are connected according to a specific structure based on the resources that they manage. The search mechanism dimension classifies P2P systems according to the way peers search other peers or specific resources in the network. According to this classification, P2P systems can employ uninformed searches (also referred to as blind searches), where each peer searches the network by randomly querying other peers; or informed searches, where a peer uses additional information about other peers’ resources to select the peers that will be contacted during the search process . In the following sub-sections we provide an overview of the existing search mechanisms both in unstructured and structured networks.
Nesta seção, a arquitetura WS-DDM é comparada à arquitetura WSIM (Web Services Internet Management) [PUL 04], compatível com a arquitetura HLA, em termos de número de mensagens necessárias para a manutenção da consistência da simulação. Na arquitetura WSIM os federados são máquinas controladas remotamente por clientes que possuem um visualizador/controlador. Esses clientes podem controlar um ou mais federados de uma vez. Na WSIM, o serviço de gerenciamento de interesse é dividido em três funções: RBAC (Role Based Access Control) que especifica que tipo de informação um usuário particular pode acessar; AOIM (Area of Interest Management) que especifica o raio de visão do usuário; e a AGIM (Aggregation Interest Management) que gerencia como os dados agregados serão apresentados. Na WSIM, os federados são máquinas que podem ser controladas por usuários remotamente através de um visualizador/controlador, sendo que cada usuário pode controlar mais de uma máquina.
contém, além do endereço do rastreador, outros metadados necessários para o correto funcionamento do sistema P2P. A comunicação com o rastreador é feita via HTTP (ou HTTPS). O usuário envia uma requisição do tipo GET, com um conjunto de parâmetros que identificam o arquivo desejado e informam o rastreador sobre o estado atual do peer, e recebe, como resposta do rastreador, uma lista contendo um conjunto aleatório de outros peers que estão compartilhando o arquivo solicitado além de outras informações de controle. Os detalhes dos parâmetros da requisição e da resposta na comunicação com o rastreador são apresentados no Apêndice B. Com esta lista de peers, o usuário passa, então, a conversar diretamente com cada um destes para trocar informações sobre quais partes do arquivo cada um tem e obter os pedaços deste arquivo de maneira colaborativa. Após o término da obtenção de cada pedaço, o hash é calculado e verificado com o existente no torrent, para conferir se os dados recebidos dos outros peers são realmente válidos. Na Figura 3.18 a troca de mensagens entre o usuário e outro peer é apresentada para facilitar a compreensão do protocolo.
Nesta época a IBM proveu um IBM 704, uma série de atualizações de hardware e acesso para alguns de seus engenheiros de sistema para o MIT (Massachusetts Institute of Technology). Sobre as máquinas da IBM foi que o MIT desenvolveu o CTSS (Compatible Time Sharing System), onde o programa supervisor agora tratava I/O dos consoles, agendamento das tarefas, armazenamento temporário e recuperação de programas durante o swap, monitoramento de discos e etc. O supervisor tinha controle total sobre todas as interrupções das máquinas virtuais em execução. Durante essa época a IBM trabalhava na montagem da família de computadores 360. O MIT no final de 1963 desenvolveria o projeto MAC baseado nos avanços em time sharing do CTSS, que mais tarde originaria o Multics. Multics (Multiplexed Information and Computing Service), o qual era um conceito muito adiante do seu tempo, foi o primeiro sistema operacional de tempo compartilhado. A última instalação operacional do Multics foi desligada apenas em 31 de outubro do ano de 2000. Neste projeto o MIT foi apoiado pela General Electrics usando o GE645 ao invés das máquinas da IBM.
After this analysis, we are in a condition to state that the use P2P accommodation among respondents is driven by the social benefits, which is consistent with Böckmann (2013), Botsman (2013) and Owyang (2014) suggestion on the social drivers of sharing economy (see Figure 3). This means that Portuguese travelers want to get to know, interact, and connect with local communities in a more meaningful way, to experience tourism destinations as a local, and to contribute to residents. This component accounts for 14,45% of the variability in all seven motives. The second factor suggests that users want to get more convenience as possible, for them staying close to tourist attractions, transports, restaurants and shops are important. Interesting to find that Portuguese users worry about sustainability questions with this factor emerging in third place, also consistent with Botsman and Rogers (2010a) and Botsman (2013) suggesting that people want to make better use of resources. Enjoyment comes out in fourth. These four motives explain 49,16% of variance, remembering that all are intrinsic motivations. Trust comes out in fifth place, economic benefits in sixth place and amenities found in the accommodation comes out in the last place. These last three motives concern intrinsic motivations, explaining 25,78% of the variance. Together, both intrinsic and extrinsic motivation, explain as mentioned before 74,94% of the variance.