Satellite Independent – Service Access Point for QoS Interworking Mario Marchese, Maurizio Mongelli DIST - Department of Communication, Computer and System Sciences University of Genoa, Via Opera Pia 13, 16145 Genova, (Italy) Abstract-The paper deals with protocol architectures to support mapping of Quality of Service (QoS) between protocol layers of telecommunication networks. The Technology Independent – Service Access Point studied to this aim within the ETSI committee is summarized and analyzed. Inherent QoS mapping operations introduce the generalization of the regular concept of equivalent bandwidth (EqB). Some performance evaluation is proposed to highlight EqB dimensioning. I. INTRODUCTION Protocol stacks in telecommunications networks are composed of functional layers. Quality of Service (QoS) provision depends on the performance achieved at each layer and is based on functions performed at layer interfaces. Having in mind the OSI paradigm, QoS derives from reliable physical and link layers that can offer specific transport services to the upper network layers. The flows generated by the network layers (or bundles of them) are forwarded down to a physical interface that transports the information along a channel. Even if network layer implements efficient QoS mechanisms (IP IntServ, IP DiffServ, MPLS), it is topical that layers below can assure connection to the channel with specific degrees of performance. Otherwise the implementation of complex QoS mechanism is useless. As a consequence, the QoS requirements must flow vertically and need to be received and satisfied by all the layers of the protocol stack. More specifically, the link layer must implement appropriate mechanisms to support the Service Level Agreement (SLA) defined at the network layer. In some cases, in particular in wireless environments, the link layer acts in cooperation with the physical layer through the application of specific cross-layer design solutions. The interaction between the layers in this context is called here “QoS Mapping”. It leads to some technological problems that nowadays constitute open areas of standardization and research. The paper proposes an insight into QoS Mapping issues from different viewpoints. A detailed analysis is reported for the protocol architectures necessary to support QoS Mapping. Recent results of the European Telecommunications Standardization Institute (ETSI) are considered in detail. The remainder of the paper is organized as follows. The remainder of the paper is organized as follows. The next two sections introduce the technological elements of the ETSI architecture at both user and control plane levels. Section IV specifies the abstraction methodology used to hide the local implementation of the QoS within the satellite core. Section V outlines the technological problem inherent to this solution. Performance analysis is proposed in section VI to highlight how bandwidth dimensioning is a hard task in the presence of QoS mapping operations. Conclusions are summarized in section VII together with possible directions of future research. II. THE CONCEPT OF TECHNOLOGY INDEPENDENT SERVICE ACCESS POINT The protocol stack considered here is the ETSI BSM (Broadband Satellite Multimedia) architecture [1]. It is related to satellite communication, but it may have a wider application. This is the motivation to choose it as reference for the investigation of QoS mapping. The considered protocol stack separates the layers between Satellite Dependent (SD) and Satellite Independent (SI). The interface between SI and SD is defined as Satellite Independent – Service Access Points (SI-SAPs). QoS requirements must flow through SI-SAPs and be implemented at SD layers. An appropriate set of primitives (called Satellite Independent Adaptation Functions, SIAF, and Satellite Dependent Adaptation Functions, SDAF) is defined to support resource reservation invocation at the different levels of the protocol stack. It allows decoupling responsabilities of resource control for each independent component of the system. A detail description of the approach is reported in the following. Some issues are topical when traffic is forwarded from SI to SD: the change of encapsulation format, the possible need of aggregating traffic with heterogeneous performance requirements and satellite channel fading counteraction. On one hand, there is the need that SD layers provide a service to the SI layers, but, on the other hand, it should be done with the minimum information SD-SI bi-directional exchange. Ideally, the exchange should be limited to the performance requirements and its matching or not to simplify the structure of SIAF and SDAF primitives. The problem is therefore connected to automatic bandwidth adaptation. SD layer needs