Antonio Alves

An Approach to Support Traffic Classes in IP Networks

Per-hop behaviours capable of supporting different traffic classes are essential for the provision of quality of service (QoS) on the Internet according to the Differentiated Services model. This paper presents an approach for supporting different traffic classes in IP networks, proposing a new per-hop behaviour called D3 - Dynamic Degradation Distribution. The approach allows for the dynamic distribution of network resources among classes, based on the measured quality of service and on the sensitivity of classes to performance degradation, without implying any substantial change to current IP technologies. A router prototype developed according to the proposed approach is presented, along with the results of experimental tests that were performed. The test results demonstrate the feasibility and the effectiveness of the underlying ideas.

An effective scheduler for IP routers

At the Communications and Telematics Laboratory of the University of Coimbra is being developed a router prototype with the aim to provide QoS to different traffic classes. One of the most important mechanisms of this router is the IP packet scheduler. It is well known that the common scheduling discipline of current routers (first come first serve) makes them useless when QoS is needed-a different type of scheduler must be used. Our first idea to overcome this problem was to use a simple, open, and available scheduler, easy to adapt to the system we wanted to implement. We thought of the WFQ discipline, and, as we are using a testbed of Intel machines running FreeBSD OS, we admitted that the WFQ/ALTQ implementation would be an interesting choice. Nevertheless, a broad set of tests carried out at our laboratory proved the contrary. Most important, these tests guided us to a deep knowledge of the problems, and causes, that can weaken the effectiveness of IP schedulers. Given the importance of that surplus information, we decided to implement our own scheduler. The idea was to take advantage of a pragmatic view of scheduling activities to construct a scheduler with the best possible characteristics (but also very simple) able to reach very good performance levels. This paper presents the scheduler that resulted from our attempts. The proposed scheduler was subject to a set of tests that proved its ability to effectively differentiate traffic classes. The results of these tests are also presented and analyzed.

The role of packet-dropping mechanisms in QoS differentiation

Many research teams are developing technologies to turn the Internet into a QoS-capable network, which is one of the biggest challenges that this communication system currently faces. Naturally, at the core of such a challenge are IP routers and the technology they use. It is a well known fact that the common packet scheduling discipline that is used in routers (first come first served) makes them useless when QoS is needed. Thus, a different type of packet scheduling must be used. One of the most referred solutions for QoS-capable systems is the weighted fair queuing (WFQ) discipline. For FreeBSD-based routers, the ALTQ implementation of the WFQ discipline is, of course, an eligible and natural choice. Given this, it is important to fully understand the characteristics and operational behaviour of such an implementation. This paper presents several tests that guide the reader to a detailed knowledge about the WFQ/ALTQ operation-its behaviour, weaknesses, and flaws-with the purpose of showing how relevant can the influence of the dropper mechanism be on the effectiveness of IP routers.

Corrections to the Gaussian overlap approximation

Abstract It is observed that the validity of the Gaussian overlap approximation does not imply the validity of the harmonic approximation. A simple procedure for converting the integral eigenvalue equation of the generator coordinate method into a differential eigenvalue equation is presented. The method proposed assumes the validity of the Gaussian overlap approximation, but may be applied to highly anharmonic situations. A test of the method has been made with the Lipkin model.

PROQOS--Dynamic SLA Management in DiffServ Space Links

Several base elements for the provision of quality of service guarantees have been developed in the recent past. Of these, the Differentiated Services (DiffServ) architecture stands out as the most promising. In spite of this, various issues remain, especially when multidomain DiffServ services are concerned. In this case, some forms of distributed management of Service Level Agreements that allow the specification, exchange, enforcement and monitoring of quality of service data must be in place. Although, again, some isolated solutions exist for each of these problems, considerable effort is necessary to make them work together. The project presented in this paper tried to assess the feasibility of providing differentiated quality of service in satellite IP networks, by developing a dynamic Service Level Agreement management solution for an IP over Digital Video Broadcast Satellite system. The functionality of the implemented system comprises system configuration, dynamic SLA negotiation, QoS monitoring and metering, SLA conformance checking, and QoS reporting to customers.

Approach to the dynamic forwarding of packets in a differentiated service-based router

In the LCT-UC we are currently working on a new service model for Internet based communications. The main goal of this model is to provide QoS without too much complexity. For this, we need to reinvent and develop new mechanisms for routers, which effectively can differentiate the way packets are treated. This paper presents our scheduling approach, the first version of the prototype under construction, and some tests that prove its ability to efficiently differentiate traffic classes.

QoStat: a tool for the evaluation of QoS capable routers

This paper presents QoStat a GUI based tool, which gives us the possibility to visualize in real time the most important values related to QoS provision. With it we can also change on the fly the most important operational parameters of the mechanisms associated with QoS provision. In this way, it is possible to understand with depth the behavior of those systems--for instance, to study cause-effect relations between the values of the referred parameters and the QoS in fact provided to the different IP traffic flows or classes.

A Queue Management System for Differentiated-Services IP Routers

Packet scheduling and queue management strategies are key issues of DiffServ per-hop behaviours. This paper proposes a queue management system that, in conjunction with scheduling mechanisms, is able to support class differentiation. The general principles and the architecture of the queue management system are presented. The proposal is supported by a prototype that was subject to several tests, in terms of packet drops and burst tolerance. The test results are presented and analysed, allowing an assessment of the usefulness and effectiveness of the underlying ideas.