Architectures and technologies for quality of service provisioning in next generation networksud

摘要

A NGN is a telecommunication network that differs from classical dedicated networks because of its capability to provide voice, video, data and cellular services onudthe same infrastructure (Quadruple-Play). The ITU-T standardization body has defined the NGN architecture in three different and well-defined strata: the transport stratum which takes care of maintaining end-to-end connectivity, the service stratum that is responsible for enabling the creation and the delivery of services, and finally the application stratum where applications can be created and executed. The most important separation in this architecture is relative to transport and service stratum. The aim is to enable the flexibility to add, maintain and remove services without any impact on the transport layer; to enable the flexibility to add, maintain and remove transport technologies without any impact on the access to service, application, content and information; and finally the efficient cohesistence of multiple terminals, accessudtechnologies and core transport technologies. The Service Oriented Architecture (SOA) is a paradigm often used in systems deployment and integration for organizing and utilizing distributed capabilities under the control of different ownership domains. In this thesis, the SOA technologies in network architetures are surveyed following the NGN functional architecture as defined by the ITU-T. Within each stratum, the main logical functions thatudhave been the subject of investigation according to a service-oriented approach have been highlighted. Moreover, a new definition of the NGN transport stratum functionalities according to the SOA paradigm is proposed; an implementation of the relevant services interfaces to analyze this approach with experimental results shows some insight on the potentialities of the proposed strategy.udWithin NGN architectures research topic, especially in IP-based network architectures, Traffic Engineering (TE) is referred to as a set of policies and algorithmsudaimed at balancing network traffic load so as to improve network resource utilization and guarantee the service specific end-to-end QoS. DS-TE technology extends TEudfunctionalities to a per-class basis implementation by introducing a higher level of traffic classification which associates to each class type (CT) a constraint on bandwidthudutilization. These constraints are set by defining and configuring a bandwidth constraint (BC) model whih drives resource utilization aiming to higher load balancing, higher QoS performance and lower call blocking rate. Default TE implementations relies on a centralized approach to bandwidth and routing management, that require externaludmanagement entities which periodically collect network status information and provide management actions. However, due to increasing network complexity, it is desiderableudthat nodes automatically discover their environment, self-configure and update to adapt to changes. In this thesis the bandwidth management problem is approached adopting an autonomic and distributed approach. Each node has a self-management module, which monitors the unreserved bandwidth in adjacent nodes and adjusts the local bandwidthudconstraints so as to reduce the differences in the unreserved bandwidth of neighbor nodes. With this distributed and autonomic algorithm, BC are dinamically modified to drive routing decision toward the traffic balancing respecting the QoS constraints for eachudclass-type traffic requests. Finally, Video on Demand (VoD) is a service that provides a video whenever theudcustomer requests it. Realizing a VoD system by means of the Internet network requires architectures tailored to video features such as guaranteed bandwidths and constrainedudtransmission delays: these are hard to be provided in the traditional Internet architecture that is not designed to provide an adequate quality of service (QoS) and quality ofudexperience (QoE) to the final user. Typical VoD solutions can be grouped in four categories: centralized, proxy-based, Content Delivery Network(CDN) and Hybridudarchitectures. Hybrid architectures combine the employment of a centralized server with that of a Peer-to-peer (P2P) network. This approach can effectively reduce the server load and avoid network congestions close to the server site because the peers support the delivery of the video to other peers using a cache-and-relay strategy making use of their upload bandwidth. Anyway, in a peer-to-peer network each peer is free to join and leave the network without notice, bringing to the phenomena of peer churns. These dynamics are dangerous for VoD architectures, affecting the integrity and retainability of the service. In this thesis, a study aimed to evaluate the impact of the peer churn on the system performance is proposed. Starting from important relationships between system parameters such as playback buffer length, peer request rate, peer average lifetime andudserver upload rate, four different analytic models are proposed.ud ud