Design and evaluation of virtual network migration mechanisms on shared substrate

The Internet faces well-known challenges in realizing modifications to the core architecture. To help overcome these limitations, the use of network virtualization has been proposed. Network virtualization enables the deployment of novel network architectures and services on existing Internet infrastructure. Virtual networks run over physical networks and use Internet paths and protocols as essentially a link layer in the virtual network. Virtual networks can also share the resources in the physical substrate. Effective use of the underlying substrate network requires intelligent placement of virtual networks so that underlying resources do not incur over-subscription. Because virtual networks can come and go over time, and underlying networks can experience their own dynamic changes, virtual networks need to be migrated---re-mapped to the physical network during active operation---to maintain good performance. While virtual network placement, and to a lesser extent migration, has been studied in the past, little attention has been devoted to designing, deploying, and evaluating migration mechanisms for virtual networks. In this dissertation, we design virtual network migration mechanisms for different substrate platforms and further design a system to mitigate the effects of virtual network migration. In particular this dissertation makes the following contributions: 1. With the goal of minimizing the disruption during a virtual network migration, we design three algorithms for scheduling the sequence of virtual router moves that takes a virtual network from its original placement to its new placement. 2. We design and implement a controller-based architecture for virtual network migration on PlanetLab. This work explores the challenges in implementing virtual network migration on real infrastructure. Recommendations are given for infrastructure that support virtual network migration. 3. We propose and implement a mechanism to mitigate the performance degradation resulting from virtual network migration through transport and application layer collaboration. We utilize a centralized controller to notify the end-systems or the gateways about the time of the virtual network migration such that we prevent packet loss to the application traffic of the end-systems.Ph.D

Metadata quality issues in learning repositories

Metadata lies at the heart of every digital repository project in the sense that it defines and drives the description of digital content stored in the repositories. Metadata allows content to be successfully stored, managed and retrieved but also preserved in the long-term. Despite the enormous importance of metadata in digital repositories, one that is widely recognized, studies indicate that what is defined as metadata quality, is relatively low in most cases of digital repositories. Metadata quality is loosely defined as "fitness for purpose" meaning that low quality of metadata means that metadata cannot fulfill its purpose which is to allow for the successful storage, management and retrieval of resources. In practice, low metadata quality leads to ineffective searches for content, ones that recall the wrong resources or even worse, no resources which makes them invisible to the intended user, that is the "client" of each digital repository. The present dissertation approaches this problem by proposing a comprehensive metadata quality assurance method, namely the Metadata Quality Assurance Certification Process (MQACP). The basic idea of this dissertation is to propose a set of methods that can be deployed throughout the lifecycle of a repository to ensure that metadata generated from content providers are of high quality. These methods have to be straightforward, simple to apply with measurable results. They also have to be adaptable with minimum effort so that they can be used in different contexts easily. This set of methods was described analytically, taking into account the actors needed to apply them, describing the tools needed and defining the anticipated outcomes. In order to test our proposal, we applied it on a Learning Federation of repositories, from day 1 of its existence until it reached its maturity and regular operation. We supported the metadata creation process throughout the different phases of the repositories involved by setting up specific experiments using the methods and tools of the MQACP. Throughout each phase, we measured the resulting metadata quality to certify that the anticipated improvement in metadata quality actually took place. Lastly, through these different phases, the cost of the MQACP application was measured to provide a comparison basis for future applications. Based on the success of this first application, we decided to validate the MQACP approach by applying it on another two cases of a Cultural and a Research Federation of repositories. This would allow us to prove the transferability of the approach to other cases the present some similarities with the initial one but mainly significant differences. The results showed that the MQACP was successfully adapted to the new contexts, with minimum adaptations needed, with similar results produced and also with comparable costs. In addition, looking closer at the common experiments carried out in each phase of each use case, we were able to identify interesting patterns in the behavior of content providers that can be further researched. The dissertation is completed with a set of future research directions that came out of the cases examined. These research directions can be explored in order to support the next version of the MQACP in terms of the methods deployed, the tools used to assess metadata quality as well as the cost analysis of the MQACP methods

Metadata quality issues in learning repositories

Metadata lies at the heart of every digital repository project in the sense that it defines and drives the description of digital content stored in the repositories. Metadata allows content to be successfully stored, managed and retrieved but also preserved in the long-term. Despite the enormous importance of metadata in digital repositories, one that is widely recognized, studies indicate that what is defined as metadata quality, is relatively low in most cases of digital repositories. Metadata quality is loosely defined as "fitness for purpose" meaning that low quality of metadata means that metadata cannot fulfill its purpose which is to allow for the successful storage, management and retrieval of resources. In practice, low metadata quality leads to ineffective searches for content, ones that recall the wrong resources or even worse, no resources which makes them invisible to the intended user, that is the "client" of each digital repository. The present dissertation approaches this problem by proposing a comprehensive metadata quality assurance method, namely the Metadata Quality Assurance Certification Process (MQACP). The basic idea of this dissertation is to propose a set of methods that can be deployed throughout the lifecycle of a repository to ensure that metadata generated from content providers are of high quality. These methods have to be straightforward, simple to apply with measurable results. They also have to be adaptable with minimum effort so that they can be used in different contexts easily. This set of methods was described analytically, taking into account the actors needed to apply them, describing the tools needed and defining the anticipated outcomes. In order to test our proposal, we applied it on a Learning Federation of repositories, from day 1 of its existence until it reached its maturity and regular operation. We supported the metadata creation process throughout the different phases of the repositories involved by setting up specific experiments using the methods and tools of the MQACP. Throughout each phase, we measured the resulting metadata quality to certify that the anticipated improvement in metadata quality actually took place. Lastly, through these different phases, the cost of the MQACP application was measured to provide a comparison basis for future applications. Based on the success of this first application, we decided to validate the MQACP approach by applying it on another two cases of a Cultural and a Research Federation of repositories. This would allow us to prove the transferability of the approach to other cases the present some similarities with the initial one but mainly significant differences. The results showed that the MQACP was successfully adapted to the new contexts, with minimum adaptations needed, with similar results produced and also with comparable costs. In addition, looking closer at the common experiments carried out in each phase of each use case, we were able to identify interesting patterns in the behavior of content providers that can be further researched. The dissertation is completed with a set of future research directions that came out of the cases examined. These research directions can be explored in order to support the next version of the MQACP in terms of the methods deployed, the tools used to assess metadata quality as well as the cost analysis of the MQACP methods

Packet switch architecture for efficient unicast and multicast traffic switching

У дисертацији је предложена једноставна архитектура свича као и алгоритми за ефикасно распоређивање и комутацију уникаст и мултикаст саобраћаја, што је од великог значаја за савремене телекомуникационе мреже у којима количина саобраћаја константно расте. Први дио доприноса ове дисертације чини приједлог рјешења свича за ефикасно управљање уникаст саобраћајем. Ово рјешење је развијено комбинујући најбоље особине постојећих рјешења, при том избјегавајући одређене њихове недостатке. Циљ је да се омогући што брже прослијеђивање пакета уз прихватљив ниво хардверске комплексности. Свич који је развијен у овој дисертацији представља комбинацију свичева са баферима на улазу и свичева који користе Биркхоф-фон Нојман принцип детерминистичког конфигурисања комутационог модула па се не захтијева прорачун конфигурација комутатора. При томе, за разлику од већине рјешења која користе Биркхоф-фон Нојман принцип конфигурисања, у предложеном рјешењу могуће је користити само један физички комутациони модул који би обављао функције оба логичка комутациона модула. Да би се гарантовало да није дошло до поремећаја редослиједа пакета, предложен је и једноставан алгоритам за одабир пакета за слање. Такође, дат је и приједлог унапријеђења подршке за фер сервис првобитно предложеног рјешења за комутацију уникаст саобраћаја. У другом дијелу дисертације, пажња је посвећена унапријеђењу предложеног рјешења за ефикасно управљање и мултикаст саобраћајем. Потреба за овим се јавила као посљедица развоја нових сервиса (нпр. IPTV, онлајн игре итд.) који генеришу такав тип саобраћаја. Како је удио мултикаст саобраћаја у мрежи постао незанемарљив, перформансе свичева који су развијени примарно за уникаст саобраћај значајно опадају. Рјешење које је предложено у првом дијелу дисертације је унапријеђено додавањем модула који служи за управљање мултикаст саобраћајем. Овдје је идеја да се оптерећење са улазног порта који прима мултикаст пакете распореди на више портова који треба да приме те пакете. Овако је на релативно једноставан начин омогућено ефикасно управљање мултикаст саобраћајем. У оквиру дисертације су урађене софтверске симулације које су показале да ова рјешења постижу врло добре перформансе у односу на постојећа. Такође, урађена је и хардверска имплементација предложеног основног уникаст рјешења која је показала релативно скромне захтјеве у погледу хардверских ресурса.The dissertation proposes a simple switch architecture as well as algorithms for efficient scheduling and switching of unicast and multicast traffic, which is of great importance for modern telecommunication networks because their traffic load is constantly and rapidly increasing. The first part of the dissertation’s contributions comprises a proposed switch which efficiently manages unicast traffic. The proposed switch is developed by using the best characteristics of the existing solutions while avoiding some of their drawbacks. The aim is to enable fast packet forwarding while achieving an acceptable level of hardware complexity. The proposed solution combines architecture with buffers at input ports and Birkhoff-von Neumann architecture based on deterministic switch module configurations. Hence, calculation of switch module configurations is not needed. Also, folded architecture is possible, which means that only one physical switching module is used for both switching stages of Birkhoff-von Neumann architecture. A simple algorithm for packet scheduling has been developed in order to avoid packet out-of-sequence problems. Finally, fair service support improvement is introduced for the originally proposed switch solution. The second part of the dissertation is devoted to the enhancement of the proposed unicast switch for efficient management of multicast traffic. The need for multicast support has emerged as a consequence of the development and introduction of new services (such as IPTV, online gaming, etc.) that generate multicast traffic. As the amount of multicast traffic is not negligible anymore, the performance of packet switches that were primarily developed for the unicast traffic is significantly degraded. The solution proposed in the first part of the diseration is enhanced with the module used for multicast traffic management. Here, the idea is that the multicast load at some input port is distributed over ports that are also destination for the multicast packets. This approach enables relatively simple but efficient management of multicast traffic. In this dissertation, software simulations were conducted, which confirmed that proposed solutions achieve very good performances compared to existing solutons. Furthermore, hardware implementation of the proposed basic unicast switch solution shows modest requirements in terms of needed hardware resources

Telecommunications Networks

This book guides readers through the basics of rapidly emerging networks to more advanced concepts and future expectations of Telecommunications Networks. It identifies and examines the most pressing research issues in Telecommunications and it contains chapters written by leading researchers, academics and industry professionals. Telecommunications Networks - Current Status and Future Trends covers surveys of recent publications that investigate key areas of interest such as: IMS, eTOM, 3G/4G, optimization problems, modeling, simulation, quality of service, etc. This book, that is suitable for both PhD and master students, is organized into six sections: New Generation Networks, Quality of Services, Sensor Networks, Telecommunications, Traffic Engineering and Routing