Klaus Wehrle

Evaluation of differentiated services using an implementation under Linux

Current efforts to provide distinct levels of quality-of-service in the Internet are concentrated on the differentiated services (DS) approach. In order to investigate the gain for users of those differentiated services, early experiences with implementations with respect to real applications are needed. Simulation models are often not sufficient if a judgement of the behavior under realistic traffic scenarios is desired. Because implementing new functionality into dedicated router hardware is difficult and time-consuming, we focused on a software implementation for standard PC hardware. In this paper we present an implementation of differentiated services functions for a PC-based router running under the Linux operating system. Two per-hop forwarding behaviors for assured service and premium service were realized. Components for traffic conditioning such as traffic meter, token bucket, leaky bucket and traffic shaper were implemented as well as an efficient traffic classificator and queueing disciplines. We describe the design and implementation issues of these components, which were validated in detail by measurements. Evaluation of these measurements shows that the proposed forwarding behaviors work well for boundary and interior routers. But, it also becomes apparent that standard applications using short-lived TCP connections cannot always exploit the requested service completely whereas rate-controlled sending applications are able to take full advantage of it. Furthermore, it is planned to release the implementation to the public for research purposes.

Group communication in differentiated services networks

The Differentiated Services (DiffServ) approach will also bring benefits for multicast applications which need quality of service support. For instance, a highly reliable multicast service can be provided based on the proposed expedited forwarding behavior. Such a service may also be used advantageously in a global computing cluster infrastructure, e.g., for distribution of synchronization messages. However, DiffServ multicast services have not been addressed in a very detailed manner yet. This paper illustrates some of the problems which will arise when IP Multicast is used in DiffServ networks without taking special precautions into account for providing it. Those problems mainly lead to situations in which other service users are affected adversely. In order to retain the benefits of the DiffServ approach, a quite simple and scalable solution for those problems is needed, not resulting in additional complexity or costs in a DiffServ domain. The proposed architecture in this paper requires only an additional entry for the DiffServ Codepoint in multicast routing tables and some support by management mechanisms. The discussion of the related problems and presentation of the solution is illustrated and confirmed by some measurements performed with a Linux implementation of DiffServ, and an adapted Linux multicast router.

An Open Architecture for Evaluating Arbitrary Quality of Service Mechanisms in Software Routers

This paper presents an open framework for building and evaluating new Quality of Service elements in a Linux based software router. Conventional QoS behavior, like bucket metering models or scheduling algorithms, have been split up to their elementary components to make the reuse and the variation of them easier. Therefore five kinds of QoS behavior types will be introduced. Based on this pool of the so called Behavior Elements, QoS behavior can be built by combining these basic elements. In the most cases, new QoS behaviors, i.e. new PHBs for the Differentiated Services architecture can be created from existing elementary QoS models. Furthermore, the concept of Hooks is introduced, which are strategic points within network protocols to extended them with QoS behavior. E.g. within the Internet Protocol five Hooks can be identified to access a certain set of packets.

DiffServ in the Web: Different Approaches for Enabling Better Services in the Worl Wide Web

The paper discusses several approaches to use the Differentiated Services Architecture for providing better services to the users of the World Wide Web. In the future Internet a user wants to have the possibility to select between different service levels to get specific web-contents. The sender orientation of the Differentiated Services Architecture imposes some difficulties in providing the user with a means for determining the service he wants to get out of a web-server. In this paper three approaches for providing better services to the users of the World Wide Web based on the Differentiated Services Architecture are presented. Additionally, an overview over implementation issues using Linux is presented.

Improving the Performance of TCP on guaranteed bandwidth connections

This paper discusses the performance of the Transmission Control Protocol under two aspects: First, the future Internet will provide some kind of service differentiation and bandwidth guarantees. Nevertheless, TCP connections often cannot fully exploit the reserved bandwidth over time. The congestion control mechanisms like slow start and congestion avoidance have to be revised in the context of guaranteed services, where no congestions occur for special flows.

BPP: a protocol for exchanging pricing information between autonomous systems

We focus on the distribution of pricing information between autonomous systems in the Internet. Therefore we propose the border pricing protocol (BPP) as a protocol for exchanging pricing information in analogy to the border gateway protocol, the current Internet standard for inter-autonomous system routing protocols. The open pricing framework is sketched as well as its relation to the differentiated services architecture. The mechanisms of the BPP are presented and the content of the pricing and charging information base is discussed.

Elements of an Open Framework for Pricing in the Future Internet

As soon as a networkoffers different service levels, pricing is needed to give incentives for not always using the highest quality of service (QoS). An open issue is how to derive a price for a certain service based on the transfer costs for data within this service. This paper shows that there is a need for a frameworkfor end-to-end pricing between providers and for inter-domain interchange of price information. The presented frameworklea ves the freedom of choosing a certain pricing model within domains in order to foster competition among different providers. It uses a hierarchical, domain centered approach which can be easily deployed within Differentiated Services networks because it may use already available components for pricing purposes.

Advanced mechanisms for available rate usage in ATM and differentiated services networks

The available bit rate (ABR) service category was defined for ATM networks in order to provide a minimal guaranteed rate while letting a user exploit additional unused capacity from other service categories. In this paper, experiences with an implementation of a driver enabling ABR support and the steps needed to integrate it in an end system are described. Furthermore, the deployment of ABR in an xDSL environment is discussed. Additionally, an approach is presented that transfers the idea of using the available rate from ATM to IP networks based on differentiated services. A new forwarding behavior is proposed and evaluated by simulations.