INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS Int. J. Commun. Syst. (2012) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/dac.2333 Performance evaluation of selected Transmission Control Protocol variants over a digital video broadcasting-second generation broadband satellite multimedia system with QoS Elizabeth Rendon-Morales * ,† , Jorge Mata-Díaz, Juanjo Alins, Jose L. Muñoz and Oscar Esparza Department of Telematics Engineering, Universitat Politècnica de Catalunya (UPC), Barcelona, Spain SUMMARY This paper presents an analysis of several Transmission Control Protocol (TCP) variants working over a digital video broadcasting-second generation (DVB-S2) satellite link with the support of the Differentiated Services (DiffServ) architecture to provide quality of service (QoS). This analysis is carried out using the NS-2 simulator tool. Three TCP variants are considered: SACK TCP, Hybla TCP, and CUBIC TCP. These TCP variants are taken as a starting point because they have proven to be the most suitable variants to deal with long delays present in satellite links. The DVB-S2 link also introduces the challenge of dealing with variable bandwidth, whereas the DiffServ architecture introduces the challenge of dealing with different prio- rities. In this paper, we propose a DiffServ model that includes a modified queuing mechanism to enhance the goodput of the assured forwarding traffic class. This modified DiffServ model is simulated and tested, considering the interaction of the selected TCP variants. In addition, we present evaluation metrics, signi- ficant simulations results, and conclusions about the performance of these TCP variants evaluated over the proposed scenario. As a general conclusion, we show that CUBIC TCP is the TCP variant that shows the best performance in terms of goodput, latency, and friendliness. Copyright © 2012 John Wiley & Sons, Ltd. Received 23 July 2011; Revised 30 January 2012; Accepted 30 January 2012 KEY WORDS: DVB-S2; QoS; DiffServ; TCP variants and performance evaluation 1. INTRODUCTION Geostationary (GEO) satellite networks can provide ubiquity and broadband access, being able to reach large and disperse populations around the world. A typical satellite scenario is shown in Figure 1. As it can be observed, there are two elements that manage the physical medium and the data link layer of the satellite link: a satellite forwarder node (hub) and a return channel satellite terminal (RCST). In practice, the hub is located at the operators infrastructure connecting the satellite link to the Internet. On the other hand, each satellite subscriber has an RCST. The link hub-to-RCST is called forward link, and it is defined by the digital video broadcasting-second generation (DVB-S2) standard [1]. The link RCST-to-hub is called return channel, and it is defined by the DVB-return channel satellite (DVB-RCS) standard [2]. Particularly, the DVB-S2 specification [1] specifies as mandatory the implementation of the adaptive code and modulation (ACM) scheme to attain interactive services. This technique reduces the available link bandwidth (transmission rate), if necessary, to achieve a quasi-error-free channel *Correspondence to: Elizabeth Rendon-Morales, Department of Telematics Engineering, Universitat Politècnica de Catalunya (UPC), Campus Nord, Building C3, Office 307, Barcelona, Spain. † E-mail: elizabeth.rendon@entel.upc.edu Copyright © 2012 John Wiley & Sons, Ltd.