Tiziana Ferrari

A measurement-based analysis of expedited forwarding PHB mechanisms

The differentiated services (Diffserv) architecture defines a new framework for the support of quality of service (QoS) in IP-based networks. In this paper, we focus on the mechanisms used to implement the expedited forwarding (EF) per-hop behavior (PHB). We analyze these mechanisms with respect to two main QoS parameters: delay and delay variation. Within a Diffserv node we study the impact of buffering and we compare the effectiveness of several different scheduling algorithms for the treatment of EF traffic. Tests are carried out in different network configurations under a range of different parameters and traffic conditions for the analysis of classification, metering, packet marking, policing and scheduling (WFQ and priority queuing). Our study has as its goal to explore quantitatively and in detail the operation of several different router mechanisms used to implement the EF PHB in production-class routers.

On advance reservation of heterogeneous network paths

The availability of information about properties and status of resources is essential for Grid resource brokers. However, while abstractions of computing and storage resources already exist, the notion of Grid network resource is far from being understood today. As a result, the integration of advanced network services is still difficult when a Grid system spans large-scale heterogeneous network infrastructures. In this paper, we propose a single definition of a Grid network resource abstraction for multiple types of network connectivity. This abstraction was successfully implemented and tested in a network resource management prototype supporting a variety of network technologies.

Resources and Services of the EGEE Production Infrastructure

This paper presents the pan-European EGEE Grid focusing on aspects such as production infrastructure, the management tools and the operational services offered. Usage statistics and the provided Quality of Service are analysed to assess the maturity level, the current penetration of Grid technologies in Europe and the current expansion trends. Being EGEE a large distributed infrastructure, operations are a joint effort of different regional centres with central coordination. EGEE operations rely on a common and agreed set of procedures, policies and interfaces, which are the foundation of operational services such as middleware deployment, Grid oversight, accounting, operational security management and support. A transition is in place to lead EGEE to a more sustainable approach based on a set of integrated National Grid Initiatives. With the support of the EGI-InSPIRE project the EGEE e-infrastructure and its services will migrate into a new governance model for the future sustainability of Grids in Europe.

Network monitoring for GRID performance optimization

Given the fundamental relevance of network performance for the optimization of distributed systems transactions over the network, the concept of a novel service called the Network-based Optimization Service is introduced and its architecture, based on the use of internal cost functions is presented. We show how network metrics can be combined to form complex compound metrics like the Closeness and the Proximity function. The Optimization Service can be used in a variety of different use cases; in this paper we show how Resource Brokers and Data Management can make use of network status for a considerable improvement of their decision-taking functions.

Adding instruments and workflow support to existing grid architectures

Many Grid architectures have been developed in recent years. These range from the large community Grids such as LHG and EGEE to single site deployments such as Condor. However, these Grid architectures have tended to focus on the single or batch submission of executable jobs. Application scientists are now seeking to manage and use physical instrumentation on the Grid, integrating these with the computational tasks they already perform. This will require the functionality of current Grid systems to be extended to allow the submission of entire workflows. Thus allowing the scientists to perform increasingly larger parts of their experiments within the Grid environment. We propose here a set of high level services which may be used on-top of these existing Grid architectures such that the benefits of these architectures may be exploited along with the new functionality of workflows.

Priority Queueing Applied to Expedited Forwarding: A Measurement-Based Analysis

The priority queueing mechanism is analysed to verify its effectiveness when applied for the support of Expedited Forwarding-based services in the Differentiated Services environment. An experimental measurement-based methodology is adopted to outline its properties and end-to-end performance when supported in real transmission devices. A test layout has been set up over a metropolitan area for the estimation of one-way delay and instantaneous packet delay variation. The effect of relevant factors like the buffering architecture, the background traffic packet size distribution and the EF traffic profile are considered. In particular, the complementary one-way delay probability function is computed for a given packet size distribution and the Aggregation Degree parameter is defined to quantify the effect of traffic aggregation on end-to-end QoS.

Agreement signalling and network service provisioning for grids

Resource-sharing is one of the grid intrinsic properties enabling efficient usage of services by clients from many virtual organizations. This is particularly true for network infrastructures, which are typically designed to serve a large number of heterogeneous users. In such an environment, the support of network quality of service requires the establishment of service level agreements between users and network service providers, admission control as well as network control planes for automatic or semi-automatic service provisioning. The availability of guarantees allows flexible usage of the distributed infrastructure and enables application-controllable performance. Nevertheless, many network providers today only offer best-effort services and do not support service level agreement signalling. In this paper we analyze requirements and introduce two bandwidth-oriented services for enhanced grid data transfer: the guaranteed delivery file transfer and virtual leased line services. We propose a complete architecture - fully integrated with grid middleware - for network service level agreement management and inter-domain network service provisioning. This is based on the functional division into agreement and service provider layers proposed by the Grid Resource Allocation and Agreement Protocol working group of the Global Grid Forum

Grid-Enabled Instrument Representation and Reservation

The integration of instruments with the grid promotes scientific and business collaboration by allowing shared access to rare and expensive instrumentation, regardless of its physical location. Instruments on the grid are virtualized resources similar to storage and computing devices, and can be part of composite services or workflows concurrently invoked by multiple users in such service-oriented environments. The requirement for real-time, interactive control of instruments poses a need for exclusive or limited access by concurrent clients. Unfortunately, instrument modeling and standardization of instrument reservation and management are still in a very early stage. According to a number of use case requirements, which we review in this work, we propose a standards-compliant model for the representation of instruments on the grid, and we describe a set of primitives for their reservation. The definition of these constructs can be used for the normative description of such reservation capabilities and the future specification of a standardized protocol.

HLRmon, a Tool for Advanced Visualization of Resource Utilization

Monitoring resource exploitation in Grids is challenging due to the large scale and the distributed nature of the infrastructure. For this reason, the role played by the accounting service that collects information about resource usage, is crucial. Visualization tools are responsible for providing users – such as Grid managers, site administrators, VO managers and Grid end–users – with usage records aggregated into different views. In this paper we describe HLRmon, a web portal which provides a set of user-friendly views of accounting information gathered by the Distributed Grid Accounting Service (DGAS).