Research Trials

Description

The SatNEx Community has performed several activities in relation to Research Trials. The philosophy was to develop research tools suited in order to explore relevant aspects of SatComm experimentations, paying attention to the challenges arising at different layers of the OSI protocol stack: Application, Transport, Network and Data Link.

As far as Transport, Network and Data Link layers are concerned, the research performed has been conveniently subdivided into five separated building blocks:

  • Wireless channel modelling (Wichmo)
  • ACM & DRA DVB-RCS simulator
  • VoIP on heterogeneous networks
  • Various cOngestion conTrol protocOl over Satellite (VOTOS)
  • Test beds for Satellite Emulation (MULTESEM)

Wichmo activities were aimed at exploring the challenges posed by the integration of wireless access networks and satellite links. The emphasis is on the characteristics of the wireless link, and a channel model based upon real measurements has been proposed. The added value of this activity was twofold: i) the approach considered showed relevant results with respect to other models commonly used in the literature; ii) most importantly, it exhibited better approximation of the system dynamics. Finally, the explored specifics of such channels were used to evaluate the impact of link errors on the service reliability. These activities are considered as concluded.

The second activity was aimed at designing a simulation tool, capable of reproducing the characteristics and dynamics of a DVB-RCS system at any level, in order to provide the SatNEx community with a unique investigation tool to support the research in the framework of satellite communication. In this perspective, relevant achievements were obtained with respect to the last year, when only a preliminary layout of functionalities was already implemented in the tool. At the present state, the tool implements most of the functionalities of DVB-RCS, especially for what concerns the resource allocation schemes, as well the management policies of layer 2 buffers. Future plans of the activity are expected to include the mobile extensions of DVB-RCS, along with the cross-validation with the NS-2 modules implementing the DVB-RCS, mainly in terms of satellite access schemes. The activity is ongoing.

The third activity aims at consolidating the VoIP experimentation conducted over an experimental satellite platform, namely the regional CNIT one. The research and experimentation efforts have been mostly oriented to an exhaustive comparison of Asterisk and IAX systems in terms of effectiveness, intended as combination of reliability and other QoS metrics. The activity, still ongoing, is temporarily suspended, because of the CNIT platform upgrade operations, which are expected to be accomplished in few months. In consequence of that, the activity will continue its performance validation phase, by taking into account also results of experimentations made in other EU projects around the same themes (i.e., SATLIFE and SATSIX).

VOTOS activities were aimed at exploring the dynamics of different congestion control protocols in DAMA-TDMA satellite networks. After the first phase focused on the performance of TCP start-up in such environments, the second phase has mainly regarded the evaluation of other congestion control protocols, more promising for the benefit they can bring to the transport of multimedia stream. In particular, the use of the TFRC protocol combined with Quick-Start has been considered, by investigating the impact of allocation and access delays on the overall performance. These activities are considered as concluded.

The last point regards emulation tools, test beds and also their integration, when either feasible or necessary, to assess the performance of higher layer protocols, i.e., Network, Transport, and Application protocols. The major added value got in the second year of SatNEx II is undoubtedly the integration of the University of Bologna test bed (TATPA) and the CNIT satellite network. This effort culminated with a huge trial campaign, completed just in July 2007; the tool has captured the interest of UCLA scientists, who have been involved in the measurements. As this action has started in spring 2007, the roadmap for the activities is still under development and it will include the integration of other test beds, such as those possessed by Bradford University, useful for the investigation of IPv6 and multicast issues over satellite. The activity is ongoing.

As far as Application layer trials are concerned, their aim is particularly addressed to the possible extension of the federal platforms suited to tackle security issues and to offer a platform suitable to be used for general-purpose experimentation. For these reason, it is immediate to see a strict relation with other activities, more oriented to the mere use of the platform. In more detail, one point dealt with is the security option that has been investigated and implemented in occasion of the IWSSC 2007 conference. In this case, various protocols have been analysed, in order to identify the most promising solutions, by also taking into account the encoding/decoding complexity that may arise in case of security modules. In addition, also the impact of these solutions on the usability of the platform has been explored, since the selected approach has to be such as to guarantee that the security option does not add further complexity to the platform.

A second relevant point is the integration of federal and regional satellite platforms, which has involved the CNIT one. This activity consisted in the integration on the uplink, while the integration in the reverse direction has been suspended in consequence of the upgrade operations that the CNIT satellite platform is currently undergoing. In this perspective, future plans of integration have been agreed with the other partners involved in the platform extensions. Concerning the benefits arising from the integration achieved so far, it is worth noting that the SatNEx federal platform has been exploited for specific dissemination actions, such as broadcasting the SatNEx Summer School, the INGRID 2007 conference, as well as lectures held in CNIT sites, following the success experienced in the case of the Tele-doctorate lectures’ broadcasting.

Finally, future plans basically consist in the platform extensions suitable to offer the SatNEx community a proper means to conduct application layer trials, provided that the federal platform keeps untouched in its essential functionalities.

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