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Peer-to-peer (P2P) paradigm, for its scalability and low cost management, is widely used in today’s network. Based on the typical designs for request/response services, a lot of efforts have been made to support publish-subscribe services in P2P networks. Gossip-based publish-subscribe system, which is commonly used in unstructured P2P networks, can provide great flexibility in query language and does not require special efforts on maintaining topology. The purpose of our work is to investigate effective and efficient mechanisms to build gossip-based publish-subscribe systems in unstructured P2P networks. Specifically, the probabilistic bi-quorum system (PBQS), for its assurance in effectiveness, becomes the object of our study. Uniform sampling is a fundamental tool to construct PBQS. By adopting uniform sampling, PBQS provides a bound on the likelihood that data messages will find a copy of the subscription. A random walk of length O(log n) is commonly used to gain a uniform sample on an expander graph of size n. To obtain a multitude of uniform samples thus requires an equivalent number of random walks of length O(log n) each. A number of works have relied on the Chernoff bound to analytically reduce the overhead needed to obtain a multitude of uniform samples. Besides, researchers have also shown that it is not necessary to replicate both data and query on uniformly chosen nodes. Alternatively, BubbleStorm performs controlled flooding on a constructed overlay to build PBQS. BubbleStorm does not require nodes forming a bubble to be uniformly chosen at random, and the probabilistic bound computed by BubbleStorm is different from uniform sampling based PBQS. In this thesis, we first show that the Chernoff bound on the statistical properties of samples collected from a random walk does not help in selecting uniformly random nodes. We then re-examine the role of uniform sampling in PBQS, and found that when multiple data answer a single subscription, it is sufficient and necessary for each data to be distributed uniformly at random. Looking into BubbleStorm, we examine more closely the probabilistic bound provided by this system. We found that, unlike uniform sampling based PBQS, the bubble intersection in BubbleStorm is distance dependent. Given a specific pair of publisher-subscriber, the data may never find the subscription. We further investigate the topology construction and found that re-creating topology prior to each controlled flooding or keeping topology with high degree of churn can help alleviate the distance dependency problem. We arrive at the conclusion that BubbleStorm construction is equivalent to caching of random walks. We show that re-using this cache to obtain samples over time leads to degradation of uniformity of the samples. We evaluate topology re-wiring as a simple method to keep the cache fresh, thereby benefiting from the low latency of controlled flooding without degrading the uniformity of samples over time. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Push is an Internet technology, which allow people to subscribe to a content- or service provider that automatically update the subscriber?s computer or Personal Digital Assistant (PDA) with the latest information without having the subscriber to first request for new information. The Ericsson Mobile Positioning Center (MPC) is a gateway that provides geographical positions of mobile stations to various applications. This Master Thesis gives the reader an overview of these technologies and presents an alternative way in integrating a third part Push-solution with the MPC. The integration proposal is also evaluated against the current Push functionality that Ericsson has developed and integrated into the MPC. / Push är en Internetteknik som ger Internetanslutna användare möjlighet att abbonnera på automatisk nyhetsuppdatering från olika informationskällor direkt till deras dator utan att användaren behöver efterfråga densamma upprepade gånger. Ericsson Mobile Positioning Center (MPC) är en gateway vilken förser olika nyhetstjänster den geografiska positionen av en mobiltelefon. Denna Magisteruppsats ger en översikt inom båda dessa områden samt presenterar ett förslag på hur dessa tekniker kan integreras. Integrationsförslaget jämförs även med den lösning Ericsson själva har valt att implementera. / Stellan Boström Adress: Vendesgatan 1B Tel: 044-218793 / 0733-228105 E-mail: stellan_bostrom@hotmail.com

Currently, the development of embedded system requires a variety of software and tools. Moreover, most of this software and tools are standalone applications, thus they are unconnected and their data can be inconsistent and duplicated. This increase both heterogeneity and the complexity of the development environment. To address this situation, tool integration solutions based on Linked Data are used, as they provide scalable and sustainable integration across different engineering tools. Different systems can access and share data by following the Linked-Data-based Open Service for Lifecycle Collaboration (OSLC) specification. OSLC uses the Tracked Resource Set (TRS) protocol to enable a server to expose a resource set and to enable a client to discover a resource in the resource set. Currently, the TRS protocol uses a client pull for the client to update its data and to synchronize with the server. However, this method is inefficient and time consuming. Moreover, high-frequency pulling may introduce an extra burden on the network and server, while low-frequency pulling increases the system’s latency (as seen by the client). A push-based low-latency solution for the TRS protocol was implemented using Message Queue Telemetry Transport (MQTT) technology. The TRS server uses MQTT to push the update patch (called a ChangeEvent) to the TRS client, then the client updates its content according to this ChangeEvent. As a result, the TRS client synchronizes with the TRS server in real time. Furthermore, a TRS adaptor was developed for Atlassian’s JIRA, a widely-used project and issue management tool. This JIRA-TRS adaptor provides a TRS provider with the ability to share data via JIRA with other software or tools which utilize the TRS protocol. In addition, a simulator was developed to simulate the operations in JIRA for a period of time (specifically the create, modify, and delete actions regarding issues) and acts as a validator to check if the data in TRS client matches the data in JIRA. An evaluation of the push-based TRS system shows an average synchronization delay of around 30 milliseconds. This is a huge change compared with original TRS system that synchronized every 60 seconds. / Nuvarande inbyggda system kräver en mängd olika program och verktyg för att stödja dess utveckling. Dessutom är de flesta av dessa programvara och verktyg fristående applikationer. De är oanslutna och deras data kan vara inkonsistent och duplicerad. Detta medför ökad heterogenitet och ökar komplexiteten i utvecklingsmiljön. För att hantera denna situation används verktygsintegrationslösningar baserade på Länkad Data, eftersom de ger en skalbar och hållbar integrationslösning för olika tekniska verktyg. Olika system kan komma åt och dela data genom att följa den Länkad Data-baserade tjänsten Open Service for Lifecycle Collaboration (OSLC). OSLC använder TRS-protokollet (Tracked Resource Set) så att en server kan exponera en resursuppsättning och för att möjliggöra för en klient att upptäcka en resurs i resursuppsättningen. TRS-protokollet använder för tillfället pull-metoden så att klienten kan uppdatera sin data och synkronisera med servern. Denna metod är emellertid ineffektiv och tidskrävande. Vidare kan en högfrekvensdriven pull-metod införa en extra börda på nätverket och servern, medan lågfrekvensdriven ökar systemets latens (som ses av klienten). I det här examensprojektet implementerar vi en pushbaserad låg latenslösning för TRS-protokollet. Den teknik som används är Message Queue Telemetry Transport (MQTT). TRS-servern använder MQTT för att pusha uppdateringspatchen (som kallas ChangeEvent) till TRS-klienten. Därefter uppdaterar klienten dess innehåll enligt denna ChangeEvent. Vilket resulterar i att TRS-klienten synkroniseras med TRS-servern i realtid. Dessutom utvecklas en TRS-adapter för Atlassians JIRA som är ett välanvänt projekt och problemhanteringsverktyg. JIRA-TRS-adaptern tillhandahåller en TRS-leverantör med möjlighet att dela data via JIRA med annan programvara eller verktyg som använder TRS-protokollet. Dessutom utvecklade vi en simulator för att simulera verksamheten i JIRA under en tidsperiod (specifikt skapa, ändra och ta bort åtgärder rörande problem) och en validator för att kontrollera om data i TRS-klienten matchar data i JIRA. En utvärdering av det pushbaserade TRS-systemet visar en genomsnittlig synkroniseringsfördröjning på cirka 30 millisekunder. Detta är en stor förändring jämfört med det ursprungliga TRS-systemet som synkroniseras var 60:e sekund.