Available online at www.sciencedirect.com Automatica 40 (2004) 729–741 www.elsevier.com/locate/automatica Design of a bandwidth-on-demand (BoD) protocol for satellite networks modelled as time-delay systems  Francesco Delli Priscoli * , Antonio Pietrabissa Dipartimento di Informatica e Sistemistica (DIS), Universit a di Roma “La Sapienza”, Via Eudossiana 18, 00184 Rome, Italy Received 29 July 2002; received in revised form 17 September 2003; accepted 12 December 2003 Abstract Bandwidth-on-demand (BoD) access protocols address the problem of guaranteeing a high exploitation of the valuable satellite bandwidth in the presence of large amount of data trac accessing the satellite network. The novelty of the proposed BoD scheme consists in the use of control theory concepts to model the satellite network as a time-delay system and to generate the bandwidth requests. The proposed scheme, based on the internal model control and on the Smith’s principle, yields the following advantages: (i) when the network is not congested, it provides upper-bounds to the queue lengths and to the queuing delays of the satellite terminal buers; (ii) it is capable of recovering from congested states; (iii) it is independent of the statistical characteristics of the trac entering the satellite network; (iv) the requests are such that the satellite terminals have always enough trac to use all the requested bandwidth (so that no bandwidth is wasted). The paper includes simulations showing the eectiveness of the proposed BoD scheme. The work underlying this paper has been performed within the GEOCAST project belonging to the fth framework Information Society and Technology programme of the European Union. ? 2003 Elsevier Ltd. All rights reserved. Keywords: Bandwidth-on-demand; Internal model control; Smith predictor; Satellite networks; Time-delay systems 1. Introduction The problem of designing an ecient access procedure to a geostationary (GEO) satellite network is crucial in the next generation of satellite systems, due to the necessity to cope withthehighburstiness(i.e.,highratiobetweenpeakandav- erage bit rates) of the multimedia trac. The work presented in this paper has been carried out within the GEOCAST (MultiCAST over GEOstationary satellites) project nanced by European Union. The GEOCAST scenario consists of a GEO satellite network with an on-board asynchronous transfer mode (ATM) packet-switch (ATM Forum, 1996), capable of addressing xed-size ATM packets to the right destination. Although the proposed bandwidth-on-demand (BoD) protocol has been developed in an ATM framework,  This paper was not presented at any IFAC meeting. This paper was recommended for publication in revised form by Associate Editor Hitay Ozbay under the direction of Editor Tamer Ba sar. * Corresponding author. Tel: +39-06-44585972; fax: +39-06-44585367. E-mail addresses: dellipriscoli@dis.uniroma1.it (F.D. Priscoli), pietrabissa@dis.uniroma1.it (A. Pietrabissa). it is suitable for any packet-switching technology, as, for example, the digital video broadcasting (DVB) one (ETSI, 2000). The uplink access technique is MF-TDMA (multi frequency-time division multiple access): the capacity is di- vided into time-slots, each one capable of transporting one packet. Data packets are emitted by single source user ter- minals (UT) or source local area networks (LANs) and are forwarded to the satellite terminals, referred to as source earth stations (ESs). Since the source ESs share common satellite link resources, to prevent uplink collisions between packets emitted by dierent ESs, each source ES has to ask the network control centre (NCC), located on earth, for the reservation of a certain amount of capacity (i.e., of time-slots). Theaccesstoasatellitenetworkcanbeprovidedbymeans of two main approaches: 1 (i) Static capacity assignment: At connection set-up, the NCC assigns a certain amount of capacity to the connection for its lifetime. Since this pre-assigned capacity is always available to the connection, low delays can be granted; the 1 Random access schemes are neglected due to their poor eciency in link utilization. 0005-1098/$ - see front matter ? 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.automatica.2003.12.013