Abstract
Technological evolution is leading telecommunications toward all-IP scenarios, where multiple services are transported as IP packets. Among these services is the broadcast of video. A possible mechanism for broadcasting multiple video channels over IP is to use IP multicast, and let each client decide about the reception of a channel. The secure IP multicast specified by the IETF MSEC working group is a candidate solution for securing these broadcast services. In this paper we propose a new solution for supporting the broadcast of multiple video channels which can be accessed only by authorized users; besides, when a video channel is not visualized in the last mile its transmission is temporarily suspended, so that the cable can be used for other services such as standard Internet access.

Abstract
We consider the issue of confidentiality in multicast network coding, by assuming that the encoding matrices, based upon variants of random linear network coding, are given only to the source and sinks. Based on this assumption, we provide a characterization of the mutual information between the encoded data and the two elements that can lead to information disclosure: the matrices of random coefficients and, naturally, the original data itself. Our results, some of which hold even with finite block lengths, show that, predicated on optimal source-coding, information-theoretic security is achievable for any field size without loss in terms of decoding probability. It follows that protecting the encoding matrix is generally sufficient to ensure confidentiality of network coded data.

Abstract
Under the emerging network coding paradigm, intermediate nodes in the network are allowed not only to store and forward packets but also to process and mix different data flows. We propose a low-complexity cryptographic scheme that exploits the inherent security provided by random linear network coding and offers the advantage of reduced overhead in comparison to traditional end-to-end encryption of the entire data. Confidentiality is achieved by protecting (or "locking") the source coefficients required to decode the encoded data, without preventing intermediate nodes from running their standard network coding operations. Our scheme can be easily combined with existing techniques that counter active attacks.

Abstract
Discussion forums are presently one of the most important tools in assisting distance education. Web learning is accomplished by using these communication tools and, particularly, by the interactions that take place in these settings. Therefore, students' participations in a discussion forum, the frequency and the way they participate, the types of interactions that they create with their colleagues and with the professor, can and should be analyzed in order to fully understand the group and, consequently, allow a more efficient and student focused education. In this article, suggest graphical representations (the iGraph) of these interactions and by using these tools, we describe forum participation according to the centralization of information, the density and intensity of interactions, and yet the quality of the moderation.

Abstract
We present an architecture that allows the seamless configuration of computer labs to work as dedicated computing clusters during periods of user inactivity. The operation of the cluster is fully automated by making use of differentiated network booting and a job management system. We have prepared it to be plugged to a larger computational grid. We provide some preliminary performance results obtained.

Abstract
The general problem addressed in this paper is the rapid development of web interfaces to software systems using only their command line interface. This kind of system is frequently developed in environments that greatly differ from those where web interface will be implemented. In this setting it is also important to maintain a loose coupling between the web interface and the system it controls since the latter must be able to continue its normal development independently of the former. We propose a framework to develop web interfaces targeted to these systems whose main feature is the fact that it can be extended without requiring code programming. The hot spots of our framework are XML configuration files to define the interface data, how this data is mapped into the system's commands, and how commands output and the interaction state is mapped into web formatting languages. With this approach the web interface is kept separated from the system it controls, it is easy to define and modify, and is able to capture enough domain knowledge to be a real advantage for the novice or sporadic user. In this paper we present the proposed framework architecture, loosely inspired in the MVC pattern, its implementation on Java servlet containers, and its application to the AGILMAT system, a high-school mathematical problem generator developed using constrained grammars.