Modeling the Behavior of a DVB-RCS Satellite Network: an Empirical Validation D. Adami, S. Giordano, M. Pagano, R. Secchi Dipartimento di Ingegneria dell’Informazione - Universit` a di Pisa, Via Caruso, I-56122 Pisa E–mail : {d.adami, s.giordano, m.pagano, raffaello.secchi}@iet.unipi.it Abstract Since satellite networks provide a valuable bandwidth access to vast regions at relatively low costs, recently the interest in Internet access through satellite links has considerably increased. At the same time, the TCP/IP protocols suite is widely used in all the communication environments, encompassing the most important network applications. Thus, the actual exploitation of satellite technology into the global Internet is possible only by moulding satellite access control scheme to the TCP/IP network features. Starting from a set of measurements carried out in a DVB-RCS network, in this paper we propose an analytical model of the RBDC medium access control scheme. The model highlights how bandwidth-on-demand allocation mechanisms may lead to large packet delivery delays when sudden variations in the incoming traffic rate, typical of multimedia traffic flows, occur. Due to the effectiveness of the model, it is possible to use it for improving resources allocation strategies. 1 Introduction In contrast with traditional satellite broadcasting systems, the new generation satellite networks allow the convergence of low-cost broadband connectivity with the technology required for user interaction. Since the satellite links provide Internet access at high bitrate to vast regions, thus allowing a broad portfolio of services with different characteristics and QoS requirements, the broadband satellite networks have been advertised as a significant part of the future global Internet. As a consequence, understanding the behavior of TCP/IP applications in a satellite network is a compelled step for the integration of such networks into the global communication infrastructure. Generally, depending on the service class, the access to a satellite network can be provided by means of static or dynamic capacity allocation schemes. When the static approach is used, during the connection set-up phase, the satellite terminal that submitted the query negotiates the bandwidth with Network Control Center (NCC). This technique, which guarantees a fixed amount of bandwidth to a given traffic terminal (TT) for the whole connection lifetime, is not widespread in satellite networks, because bandwidth is a precious resource and must be cost-effectively used. Therefore, a number of dynamic bandwidth allocation schemes have been proposed and developed [1][2]. In these schemes, the NCC dynamically assigns a certain amount of bandwidth to each TT on the basis of explicit capacity requests according to a specific Demand Assignment Medium Access (DAMA) scheme. This way, the NCC is able to keep track of the actual traffic generated by the TTs and to modify the bandwidth assignment in order to better exploit the satellite link capacity. On the other hand, since the TTs have to wait for an explicit capacity assignment from the NCC, the connections traversing the satellite link may experience long delays before gaining access to the satellite network. This phenomenon may reduce the throughput mainly for short-lived connections. Unlike traditional approaches, which aim to describe the satellite link only in terms of delay and losses, in this paper we propose a model for a satellite connection that explicitly accounts for the rate-based bandwidth- on-demand (BoD) allocation scheme. Many reasons motivated our choice to develop the theoretical model. First, an analytical approach is useful to have a better understanding of satellite system behavior at IP layer and to identify the most critical aspects of BoD schemes in TCP/IP traffic management. Moreover, we believe P55/1