Flexible public transport in low density areas

Publicado em "Recent Advances in Engineering Mechanics, Structures and Urban Planning" (ISBN : 978-1-61804-165-4) ; Mathematics and Computers in Science and Engineering Series, 8 (ISSN : 2227-4588)A public transport system is of crucial importance to ensure an equitable and more sustainable mobility to all citizens of a region, since it allows the possibility to travel long distances instead of the use of private cars. However, conventional public transport systems have a rigid framework with routes where specific locations are predefined in order to have a regular service that serves as much population as possible. Well designed regular bus services are usually economically viable, but in low density areas the demand is not sufficient to ensure viability and the same service ofcentral urban areas. Thus, it is necessary to introduce some flexibility in public transport service, to allow coverage of the entire population, without destroying the viability of the bus operator of low density areas. This approach isnow being applied in a case study in low density areas of the municipality of Braga, where the bus service is poor and inadequate to ensure the mobility needs of its population. In this study, the implementation of a flexible public transport is preliminarily analysed, as a possible solution to this problem

Admission control in multiservice IP networks : architectural issues and trends

The trend toward the integration of current and emerging applications and services in the Internet has launched new challenges regarding service deployment and management. Within service management, admission control (AC) has been recognized as a convenient mechanism to keep services under controlled load and assure the required QoS levels, bringing consistency to the services offered. In this context, this article discusses the role of AC in multiservice IP networks and surveys current and representative AC approaches. We address and compare the architectural principles of these AC approaches and their main features, virtues and limitations that impact on the quality control of network services. We identify important design aspects that contribute to the successful deployment of flexible and scalable AC solutions in multiservice networks

Scheduling time-sensitive IP traffic

This article presents an hybrid priority queuing model based scheduler for real-time traffic differentiation. The proposed scheduler is designed as a mechanism to provide queuing delay differentiation among real-time traffic classes. The novel characteristic of the presented scheduler is the capability to simultaneously try to achieve an upper time limit for queuing delays and, under heavy load conditions, deny class starvation by providing an expectable differentiation schema for excess queuing delays. The attractiveness of the proposed scheduler is its hybrid differentiation capabilities based on a simple queue selection procedure. Additionally, the enhanced differentiation behavior of the scheduler is also highlighted as three distinct configuration modes are possible

Distributed admission control for QoS and SLS management

This article proposes a distributed admission control (AC) model based on on-line monitoring to manage the quality of Internet services and Service Level Specifications (SLSs) in class-based networks. The AC strategy covers intra- and interdomain operation, without adding significant complexity to the network control plane and involving only edge nodes. While ingress nodes perform implicit or explicit AC resorting to service-oriented rules for SLS and QoS parameters control, egress nodes collect service metrics providing them as inputs for AC. The end-to-end operation is viewed as a cumulative and repetitive process of AC and available service computation.We discuss crucial key points of the model implementation and evaluate its two main components: themonitoring process and the AC criteria. The results show that, using proper AC rules and safety margins, service commitments can be efficiently satisfied, and the simplicity and flexibility of the model can be explored to manage successfully QoS requirements of multiple Internet services.(undefined

Handling concurrent admission control in multiservice IP networks

Comunicação apresentada na "Consumer Communications & Networkin Conference 2006", Las Vegas, Nevada, USA, 8-10 Janeiro 2006.This paper debates the problem of handling concurrent admission control decisions in multiservice networks, putting forward solutions to mitigate the negative impact that distributed admission of flows might have on the service level guarantees provided to network customers. Keeping in mind that simplicity is a key factor for deployable solutions, we suggest and discuss the use of (i) a service-dependent concurrency index; (ii) a token-based system and (iii) a rate-based credit system, as alternative or complementary proposals to minimize or solve QoS degradation resulting from AC false acceptance

Improving the quality and reliability of traffic differentiation in IP networks

This article presents a modular scheduling architecture for multi-QoS metric differentiation in class-based IP networks. The rationale of the supported differentiation modules is presented, highlighting the distinct differentiation semantics that might be used to control the delay, loss and rate metrics associated with the traffic classes. The devised modules resort to several relative and hybrid differentiation models to bound QoS metrics on high priority classes. In the proposed scheduling architecture, the differentiation modules may act jointly in order to control simultaneously multiple QoS metrics. The results show that using simple and intuitive configuration procedures the proposed architecture is able to provide enhanced QoS differentiation behavior in IP networks according to the users and applications needs

Ensuring IP services consistency through lightweight monitoring-based admission control

This paper evaluates the performance of a distributed and lightweight AC model based on per-class edge-to-edge monitoring feedback for ensuring the quality of multiple services in class-based IP networks. The model resorts to service-dependent AC rules for controlling QoS parameters and SLSs utilization, both intradomain and end-to-end. To provide a proof-of-concept of the proposed AC solution, a prototype of the AC model has been developed and tested using a simulation platform. The devised test scenarios aim at exploring the AC criteria's ability in satisfying each service class QoS levels and existing SLSs commitments. Generically, the results show that the proposed AC model, using a two-rule AC criterion defined on a service class basis, is able to control service levels and achieve high network utilization, without adding significant complexity to the network elements. The use of systematic edge-to-edge on-line monitoring and of a controlled degree of overprovisioning proved to be essential design aspects contributing for reaching a good compromise between simplicity and performance.Fundação para a Ciência e Tecnologia FC