Dorsale (réseau)

vignette|Carte de la dorsale internet des Etats-Unis en 1992 Une dorsale (), aussi appelée cœur de réseau, est le nom de l'interconnexion haut débit entre sous-réseaux qui permet le transit des informations au sein d'un réseau informatique étendu. La dorsale est un élément-clé qui doit être convenablement structuré et dimensionné afin de limiter des effets indésirables tels que la congestion. Dans un réseau, une dorsale peut relier des sous-réseaux correspondant à différentes parties d'un bâtiment, différents bâtiments d'un site voire différents sites d'une implantation. Une grande entreprise avec une large implantation peut ainsi disposer de sa propre dorsale. La dorsale Internet est un autre exemple bien connu, quoiqu'elle soit en réalité constituée d'une multitude de routes majeures aux gérances tout aussi diverses. Historique Fonctionnalités Types Notes et références Voir aussi Articles connexes

Réseau

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L'objectif de ce cours est d'introduire les étudiants à la pensée algorithmique, de les familiariser avec les fondamentaux de l'Informatique et de développer une première compétence en programmation (langage C++).

This course provides a detailed description of the organization and operating principles of mobile and wireless communication networks.

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Réseau informatique

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Topologie de réseau

vignette Une topologie de réseau informatique correspond à l'architecture (physique, logicielle ou logique) de celui-ci, définissant les liaisons entre les équipements du réseau et une hiérarchie éven

Réseau téléphonique commuté

Le réseau téléphonique commuté (RTC) ou réseau téléphonique commuté public (RTCP) (en anglais, public switched telephone network ou PSTN) est le réseau historique des téléphones fixes, dans lequel u

This course provides a detailed description of the organization and operating principles of mobile and wireless communication networks.

Bringing physical layer cooperation closer to practical wireless systems

Emre Atsan

Nowadays the demand for communication over the wireless medium is significantly increasing, while the available wireless spectrum is already limited. In this thesis, we introduce new practical physical layer designs that employ node cooperation for more efficient wireless spectrum utilization. First, a cooperative scheme is introduced that takes advantage of the existence of simultaneous multiple frequency band operation in modern wireless devices. The main idea of this scheme is to use one frequency band for sharing data among collaborating nodes, and another one for cooperatively transmitting to a common destination. The benefits of such a cooperative design across frequency bands are evaluated on a testbed of software-defined radios, where we investigate and identify the possible network conditions under which our scheme enables better throughput compared to the traditional operation. Second, we present a practical design that facilitates physical layer cooperation in Long Term Evolution (LTE) networks. The main idea here is to adapt the inherent Hybrid Automatic Repeat-reQuest (H-ARQ) in standard LTE operation, so that multiple relays can cooperate over the transmission of one encoded block. Performance evaluation of the design reveals significant throughout gains under asymmetric channel conditions for parallel relay networks in LTE framework. Finally, we look at the node cooperation from a privacy perspective in wireless sensor networks. To this end, we design and evaluate a low-overhead message encryption protocol based on network coding. The main idea of the protocol is to employ node cooperation to increase the inherent weak security that network coding offers. Results show up to 60% increase in terms of extra security added on top of the inherent one.

EPFL2015

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Automating the Testing of OpenFlow Applications

Marco Canini, Dejan Kostic, Jennifer Rexford

Software-defined networking, and the emergence of OpenFlow-capable switches, enables a wide range of new network functionality. However, enhanced programmability inevitably leads to more software faults (or bugs). We believe that tools for testing OpenFlow programs are critical to the success of the new technology. However, the way OpenFlow applications interact with the data plane raises several challenges. First, the space of possible inputs (e.g., packet headers and inter-packet timings) is huge. Second, the centralized controller has a indirect view of the traffic and experiences unavoidable delays in installing rules in the switches. Third, external factors like user behavior (e.g., mobility) and higher-layer protocols (e.g., the TCP state machine) affect the correctness of OpenFlow programs. In this work-in-progress paper, we extend techniques for symbolic execution to generate inputs that systematically explore the space of system executions. First, we analyze controller applications to identify equivalence classes of packets that exercise different parts of the code. Second, we propose several network models with increasing precision, ranging from simple traffic models to live testing on the target network. Initial experiences with our prototype, which symbolically executes OpenFlow applications written in Python, suggest that our techniques can help programmers identify bugs in their OpenFlow programs.

2011

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A NICE Way to Test OpenFlow Applications

Marco Canini, Dejan Kostic, Peter Peresini, Jennifer Rexford

The emergence of OpenFlow-capable switches enables exciting new network functionality, at the risk of programming errors that make communication less reliable. The centralized programming model, where a single controller program manages the network, seems to reduce the likelihood of bugs. However, the system is inherently distributed and asynchronous, with events happening at different switches and end hosts, and inevitable delays affecting communication with the controller. In this paper, we present efficient, systematic techniques for testing unmodified controller programs. Our NICE tool applies model checking to explore the state space of the entire system—the controller, the switches, and the hosts. Scalability is the main challenge, given the diversity of data packets, the large system state, and the many possible event orderings. To address this, we propose a novel way to augment model checking with symbolic execution of event handlers (to identify representative packets that exercise code paths on the controller). We also present a simplified OpenFlow switch model (to reduce the state space), and effective strategies for generating event interleavings likely to uncover bugs. Our prototype tests Python applications on the popular NOX platform. In testing three real applications—a MAC-learning switch, in-network server load balancing, and energy-efficient traffic engineering—we uncover eleven bugs.

2012

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