QoS-oriented Traffic Management in on-board switches

The use of on-board switches for space applications is not yet widespread because efficient switches for space applications do not exit yet. Unlike terrestrial switches, basically gigabit switches with almost unlimited buffer capacity, switches used inside a satellite payload suffer from the constraints of the space environment and from the following limitations: weight, power consumption, buffer capacity, frequency and temperature of functioning, available technology. Therefore, the architecture of the on-board switch should remain quite simple, and simultaneously the switch should provide some good performance. Moreover interoperability between the satellite system and the terrestrial networks should be provided. The satellite system possibly acts as an access network for the terminal (e.g. Satellite UMTS) or as a portion of the backbone. In any cases, it should be transparent to the top level applications and end-to-end Quality of Service (QoS) should be provided. It means that the satellite system should support efficiently and transparently the QoS mechanisms implemented in all the overlying terrestrial networks. Especially, the satellite system should provide compatibility with connection oriented QoS mechanisms such as Integrated Services (Intserv [2]) and aggregated QoS mechanisms such as Diffserv [3] for Internet Protocol (IP) networks. Therefore, it is quite straightforward that the on-board switch should fulfil two opposite requirements: on the one hand, as a key component of the satellite system, it should contribute to the QoS support for the high layer applications but on the other hand as a physical part of the payload its architecture should remains simple. The aim of this article is therefore to study such a switch’s architecture and to give an overview of the mechanisms that can be implemented inside the switch to support QoS as well as their performance. The article will be divided into the following parts: First, an overview of the protocols used in the terrestrial networks with which the satellite system should interoperate will be given. Special emphasis will be put on the QoS mechanisms implemented in these protocols. Second, the satellite system architecture considered in this article will be described. Special emphasis will be put on the elements of the satellite system providing QoS and on the interaction between these elements and the terrestrial networks elements. Third the on-board switch architecture and the different QoS mechanisms implemented in it will be described. Then, simulation results showing the performance of the switch when loaded with a peculiar traffic pattern will be displayed. Finally, a conclusion will be drawn.