Monilinjaus fylogeniapuun ohjaamana

Suoraviivainen monilinjauksen toteutus vie eksponentiaalisesti aikaa ja muistia. Siksi on kehitetty monia heuristisia menetelmiä. Tässä paperissa keskityn yhteen heurististen monilinjausmenetelmien luokkaan, progressiiviseen fylogeniapuun mukaan etenevään monilinjaukseen. Menetelmä on kehitetty globaaliin linjaukseen, lokaalin linjaamisen puolelta löytyy joitain samansuuntaisia menetelmiä. Olen soveltanut progressiivisen fylogeniapuun ohjaaman monilinjauksen lokaalisti geenien säätelyalueita etsivään EELohjelmaan. Koska selkeästi hyvää tapaa yleistää EELohjelman käyttämä linjauksen pisteytys ei ole, olen toteuttanut progressiiviseen monilinjaukseeni kolme erilaista pisteytystä: parien summa, parilinjauksen pisteytyksestä yleistetty pisteytys sekä edustavia sekvenssejä käyttävä, puun mukainen pisteytys. Monilinjauksen mahdollistama useamman sekvenssin käyttäminen tarkentaa parilinjauksella löydettyjä säätelyalueita ja vahvistaa säilyvien alueiden merkitystä.

An XML Messaging Service for Mobile Devices

In recent years, XML has been accepted as the format of messages for several applications. Prominent examples include SOAP for Web services, XMPP for instant messaging, and RSS and Atom for content syndication. This XML usage is understandable, as the format itself is a well-accepted standard for structured data, and it has excellent support for many popular programming languages, so inventing an application-specific format no longer seems worth the effort. Simultaneously with this XML's rise to prominence there has been an upsurge in the number and capabilities of various mobile devices. These devices are connected through various wireless technologies to larger networks, and a goal of current research is to integrate them seamlessly into these networks. These two developments seem to be at odds with each other. XML as a fully text-based format takes up more processing power and network bandwidth than binary formats would, whereas the battery-powered nature of mobile devices dictates that energy, both in processing and transmitting, be utilized efficiently. This thesis presents the work we have performed to reconcile these two worlds. We present a message transfer service that we have developed to address what we have identified as the three key issues: XML processing at the application level, a more efficient XML serialization format, and the protocol used to transfer messages. Our presentation includes both a high-level architectural view of the whole message transfer service, as well as detailed descriptions of the three new components. These components consist of an API, and an associated data model, for XML processing designed for messaging applications, a binary serialization format for the data model of the API, and a message transfer protocol providing two-way messaging capability with support for client mobility. We also present relevant performance measurements for the service and its components. As a result of this work, we do not consider XML to be inherently incompatible with mobile devices. As the fixed networking world moves toward XML for interoperable data representation, so should the wireless world also do to provide a better-integrated networking infrastructure. However, the problems that XML adoption has touch all of the higher layers of application programming, so instead of concentrating simply on the serialization format we conclude that improvements need to be made in an integrated fashion in all of these layers.

TCP Performance with Vertical Handoff

With the proliferation of wireless and mobile devices equipped with multiple radio interfaces to connect to the Internet, vertical handoff involving different wireless access technologies will enable users to get the best of connectivity and service quality during the lifetime of a TCP connection. A vertical handoff may introduce an abrupt, significant change in the access link characteristics and as a result the end-to-end path characteristics such as the bandwidth and the round-trip time (RTT) of a TCP connection may change considerably. TCP may take several RTTs to adapt to these changes in path characteristics and during this interval there may be packet losses and / or inefficient utilization of the available bandwidth. In this thesis we study the behaviour and performance of TCP in the presence of a vertical handoff. We identify the different handoff scenarios that adversely affect TCP performance. We propose several enhancements to the TCP sender algorithm that are specific to the different handoff scenarios to adapt TCP better to a vertical handoff. Our algorithms are conservative in nature and make use of cross-layer information obtained from the lower layers regarding the characteristics of the access links involved in a handoff. We evaluate the proposed algorithms by extensive simulation of the various handoff scenarios involving access links with a wide range of bandwidth and delay. We show that the proposed algorithms are effective in improving the TCP behaviour in various handoff scenarios and do not adversely affect the performance of TCP in the absence of cross-layer information.