The Coherent File Distribution Protocol

CFDP is a protocol that takes advantage of the broadcast nature of CSMA networks to speed up simultaneous one-to-many file transfers (e.g., when booting diskless workstations). The CFDP server listens and services requests for entire files or portions thereof. CFDP clients first determine whether the file they are interested in is already being transferred, in which case they "eavesdrop" and load as much of it as they can, or they initiate a new transfer. The clients timeout when the server stops transmitting, and if they are still missing parts of the file they request them with a block-transfer request. CFDP is a back-end protocol a front end is needed to handle naming and security issues. A simple such front end is also presented here

Sistema de control de acceso a redes (NAC) basado en SNMP y VLAN

El control de acceso a red es un concepto del ámbito la seguridad de redes de computadoras que consiste en la aplicación de los mecanismos y técnicas necesarias para controlar el acceso a la red y prevenir posibles ataques. Hay múltiples soluciones comerciales que tratan este asunto, pero en su mayoría son demasiado generalistas y consumen una cantidad bastante alta de recursos computacionales. Por este motivo, se decide crear una herramienta que separe a los diferentes usuarios conectados a un switch en diferentes redes en función de su rol dentro de la red, incluyendo un mecanismo para que el administrador de red pueda consultar el estado del switch y quién está conectado en cada momento. Para lograr este cometido, hay dos tecnologías que resultan fundamentales: SNMP y VLAN. SNMP es un protocolo de gestión de red que, en este caso, va a servir para notificar cuándo se produce un cambio en el estado de uno de los puertos del switch. Mediante la creación de VLAN, sería posible tener a los usuarios en diferentes redes en función de su rol y aplicar políticas de cortafuegos de forma más fácil.Network access control is an aproach to computer network security that involves the application of the mecanisms and techniques needed to control the access in a network and prevent potential attacks. There are multiple commercial solutions that address this issue, but the most part of them are too general and consume a lot of computational resources. For this reason it is decided to create a tool that separetes the diferent users connected to a switch in diferent networks, based on their role whitin the network, that includes a mechanism for the network administrator to check the switch status and who is currently connected. To achieve this task, there are two technologies that are fundamental: SNMP and VLAN. SNMP is a network management protocol that, in this case, will notify when there is a change in the state of one of the switch ports. By creting VLANs, it will be possible to have users in diferent networks based on their role and apply firewall policies more easily.Grado en Ingeniería de Tecnologías Específicas de Telecomunicació

Standards as interdependent artifacts : the case of the Internet

Thesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2008.Includes bibliographical references.This thesis has explored a new idea: viewing standards as interdependent artifacts and studying them with network analysis tools. Using the set of Internet standards as an example, the research of this thesis includes the citation network, the author affiliation network, and the co-author network of the Internet standards over the period of 1989 to 2004. The major network analysis tools used include cohesive subgroup decomposition (the algorithm by Newman and Girvan is used), regular equivalence class decomposition (the REGE algorithm and the method developed in this thesis is used), nodal prestige and acquaintance (both calculated from Kleinberg's technique), and some social network analysis tools. Qualitative analyses of the historical and technical context of the standards as well as statistical analyses of various kinds are also used in this research. A major finding of this thesis is that for the understanding of the Internet, it is beneficial to consider its standards as interdependent artifacts. Because the basic mission of the Internet (i.e. to be an interoperable system that enables various services and applications) is enabled, not by one or a few, but by a great number of standards developed upon each other, to study the standards only as stand-alone specifications cannot really produce meaningful understandings about a workable system. Therefore, the general approaches and methodologies introduced in this thesis which we label a systems approach is a necessary addition to the existing approaches. A key finding of this thesis is that the citation network of the Internet standards can be decomposed into functionally coherent subgroups by using the Newman-Girvan algorithm.(cont.) This result shows that the (normative) citations among the standards can meaningfully be used to help us better manage and monitor the standards system. The results in this thesis indicate that organizing the developing efforts of the Internet standards into (now) 121 Working Groups was done in a manner reasonably consistent with achieving a modular (and thus more evolvable) standards system. A second decomposition of the standards network was achieved by employing the REGE algorithm together with a new method developed in this thesis (see the Appendix) for identifying regular equivalence classes. Five meaningful subgroups of the Internet standards were identified, and each of them occupies a specific position and plays a specific role in the network. The five positions are reflected in the names we have assigned to them: the Foundations, the Established, the Transients, the Newcomers, and the Stand-alones. The life cycle among these positions was uncovered and is one of the insights that the systems approach on this standard system gives relative to the evolution of the overall standards system. Another insight concerning evolution of the standard system is the development of a predictive model for promotion of standards to a new status (i.e. Proposed, Draft and Internet Standards as the three ascending statuses). This model also has practical potential to managers of standards setting organizations and to firms (and individuals) interested in efficiently participating in standards setting processes. The model prediction is based on assessing the implicit social influence of the standards (based upon the social network metric, betweenness centrality, of the standards' authors) and the apparent importance of the standard to the network (based upon calculating the standard's prestige from the citation network).(cont.) A deeper understanding of the factors that go into this model was also developed through the analysis of the factors that can predict increased prestige over time for a standard. The overall systems approach and the tools developed and demonstrated in this thesis for the study of the Internet standards can be applied to other standards systems. Application (and extension) to the World Wide Web, electric power system, mobile communication, and others would we believe lead to important improvements in our practical and scholarly understanding of these systems.by Mo-Han Hsieh.Ph.D