The aim of this thesis is to investigate an ultrasound transducer testing system calledProbeHunter and determine the limits of the device. This device requires custom configuratedfiles to adapt to and be applicable for new ultrasound probes. The task was to investigate theimprovement possibilities for the file creation and thus broaden the use of the system.The study shows that file creation is theoretically possible for certain models of probes. Ingeneral, there is a lack of files in Västmanland and that needs to improve to keep up with thelarge amounts of probes. Multiplexed array probes are, however, not possible to create files forat the state the system is in currently. / Introduktion: Sjukvården söker ständigt utveckling i sitt dagliga arbete för patientsäkerhet. Föratt uppnå detta behövs ett samarbete med externa företag som utvecklar system för att utföradessa kvalitetssäkringar. Medicinsk teknik i region Västmanland har under en längre tid varit påjakt efter en bra utrustning för test av ultraljudsprober och har använt sig av ett flertalundersökningsmetoder. ProbeHunter var en kandidat till flertal alternativ och kom att utnyttjasför att förbättra sjukvården. Syfte: Syftet med arbetet är att undersöka så många prob modeller med ProbeHunter sommöjligt. Identifiera vart gränserna med ProbeHunter går och därmed bredda på användningen avsystemet. Detta innebär inte nödvändigtvis att alla prober måste gå att testa men att man har gjorten rimlig procentökning. Metod: En mindre del av rapporten består av litteraturstudie tillsammans med mest praktisktarbete. Större del av rapportens källor för det primära arbetet består av intervjuer ochProbeHunters egna manualer. Som utgångspunkt hade det praktiska arbetet mycket fokus på atttesta så många prober som möjligt med systemet för att uppfylla de krav som var satta på arbetet. Resultat: Detta projekt gav möjligheten till en ökning av antal prober som kan testas på 11% avde 240 prober som finns i Västmanland sjukhus. Där 11% (= 27 prober) motsvarar de tester somhar blivit godkända. Medan de totalt skapade och editerade probespecifika filerna motsvara testav 27% (=65 prober av 240). Dessa filer inkluderar både fungerande och icke fungerande filer. Slutsats: ProbeHunter behöver förbättras ytterligare i några aspekter. Det är inte på något sättdet perfekta instrumentet men lyckas ändå ge bra resultat om rätt material är närvarande vidtestning. Aktiv utveckling krävs för att eliminera vissa nackdelar med systemet. ProbeHunter ärfortfarande en bra konkurrent till andra liknande system och kan komma att bli ännu bättre.

Peer to Peer (P2P) models are based on user altruism, wherein a user shares its content with other users in the pool and it also has an interest in the content of the other nodes. Most P2P systems in their current form are not fair in terms of the content served by a peer and the service obtained from swarm. Most systems suffer from free rider's problem where many high uplink capacity peers contribute much more than they should while many others get a free ride for downloading the content. This leaves high capacity nodes with very little or no motivation to contribute. Many times such resourceful nodes exit the swarm or don't even participate. The whole scenario is unfavorable and disappointing for P2P networks in general, where participation is a must and a very important feature. As the number of users increases in the swarm, the swarm becomes robust and scalable. Other important issues in the present day P2P system are below optimal Quality of Service (QoS) in terms of download time, end-to-end latency and jitter rate, uplink utilization, excessive cross ISP traffic, security and cheating threats etc. These current day problems in P2P networks serve as a motivation for present work. To this end, we present an efficient data distribution framework in Peer-to-Peer (P2P) networks for media streaming and file sharing domain. The experiments with our model, an alliance based peering scheme for media streaming, show that such a scheme distributes data to the swarm members in a near-optimal way. Alliances are small groups of nodes that share data and other vital information for symbiotic association. We show that alliance formation is a loosely coupled and an effective way to organize the peers and our model maps to a small world network, which form efficient overlay structures and are robust to network perturbations such as churn. We present a comparative simulation based study of our model with CoolStreaming/DONet (a popular model) and present a quantitative performance evaluation. Simulation results show that our model scales well under varying workloads and conditions, delivers near optimal levels of QoS, reduces cross ISP traffic considerably and for most cases, performs at par or even better than Cool-Streaming/DONet. In the next phase of our work, we focussed on BitTorrent P2P model as it the most widely used file sharing protocol. Many studies in academia and industry have shown that though BitTorrent scales very well but is far from optimal in terms of fairness to end users, download time and uplink utilization. Furthermore, random peering and data distribution in such model lead to suboptimal performance. Lately, new breed of BitTorrent clients like BitTyrant have shown successful strategic attacks against BitTorrent. Strategic peers configure the BitTorrent client software such that for very less or no contribution, they can obtain good download speeds. Such strategic nodes exploit the altruism in the swarm and consume resources at the expense of other honest nodes and create an unfair swarm. More unfairness is generated in the swarm with the presence of heterogeneous bandwidth nodes. We investigate and propose a new token-based anti-strategic policy that could be used in BitTorrent to minimize the free-riding by strategic clients. We also proposed other policies against strategic attacks that include using a smart tracker that denies the request of strategic clients for peer listmultiple times, and black listing the non-behaving nodes that do not follow the protocol policies. These policies help to stop the strategic behavior of peers to a large extent and improve overall system performance. We also quantify and validate the benefits of using bandwidth peer matching policy. Our simulations results show that with the above proposed changes, uplink utilization and mean download time in BitTorrent network improves considerably. It leaves strategic clients with little or no incentive to behave greedily. This reduces free riding and creates fairer swarm with very little computational overhead. Finally, we show that our model is self healing model where user behavior changes from selfish to altruistic in the presence of the aforementioned policies.

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