Unattended network operations technology assessment study. Technical support for defining advanced satellite systems concepts

The results are summarized of an unattended network operations technology assessment study for the Space Exploration Initiative (SEI). The scope of the work included: (1) identified possible enhancements due to the proposed Mars communications network; (2) identified network operations on Mars; (3) performed a technology assessment of possible supporting technologies based on current and future approaches to network operations; and (4) developed a plan for the testing and development of these technologies. The most important results obtained are as follows: (1) addition of a third Mars Relay Satellite (MRS) and MRS cross link capabilities will enhance the network's fault tolerance capabilities through improved connectivity; (2) network functions can be divided into the six basic ISO network functional groups; (3) distributed artificial intelligence technologies will augment more traditional network management technologies to form the technological infrastructure of a virtually unattended network; and (4) a great effort is required to bring the current network technology levels for manned space communications up to the level needed for an automated fault tolerance Mars communications network

Re-designing Dynamic Content Delivery in the Light of a Virtualized Infrastructure

We explore the opportunities and design options enabled by novel SDN and NFV technologies, by re-designing a dynamic Content Delivery Network (CDN) service. Our system, named MOSTO, provides performance levels comparable to that of a regular CDN, but does not require the deployment of a large distributed infrastructure. In the process of designing the system, we identify relevant functions that could be integrated in the future Internet infrastructure. Such functions greatly simplify the design and effectiveness of services such as MOSTO. We demonstrate our system using a mixture of simulation, emulation, testbed experiments and by realizing a proof-of-concept deployment in a planet-wide commercial cloud system.Comment: Extended version of the paper accepted for publication in JSAC special issue on Emerging Technologies in Software-Driven Communication - November 201

Second CLIPS Conference Proceedings, volume 1

Topics covered at the 2nd CLIPS Conference held at the Johnson Space Center, September 23-25, 1991 are given. Topics include rule groupings, fault detection using expert systems, decision making using expert systems, knowledge representation, computer aided design and debugging expert systems

Formally Integrating Real-Time Specification: A Research Proposal

To date, research in reasoning about timing properties of real-time programs has considered specification and implementation as separate issues. Specification uses formal methods; it abstracts out program execution, defining a specification that is independent of any machine-specific details (see [I, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14] for examples). In this manner, it describes only the high-level timing requirements of processes in the system, and dependencies between them. One then typically attempts to prove the mutual consistency of these timing constraints, or to determine whether the constraints maintain a safety property critical to system correctness. However, since the model has abstracted out machine-specific details, these correctness proofs either assume very optimistic operating environment (such as a one to one assignment of processes to processors), or make very pessimistic assumptions (such as that all interleavings of process executions are possible). Since neither of these assumptions will hold in practice, these predictions about the behavior of the system may not be accurate. The implementation level captures this operating environment: a real- time system is characterized by such things as process schedulers, devices and local clocks. However, advances here have been primarily in scheduling theory (examples of which are [15, 16]) and language design (examples of which are [15, 16, 17, 18,19,20]). Unfortunately, since formal models have not been used at this level, proofs of time-related properties cannot be made. To construct these proofs, we must show that an implementation is correct with respect to a specification; timing properties that can be shown to hold about the specification will therefore be known to hold for the implementation. We therefore need to represent the implementation formally so as to prove that the implementation satisfies the specification. The proof of satisfaction requires a well-defined formal mapping between the implementation and specification models. We therefore propose to develop an integrated bi-level approach to the problem of reasoning about timing properties of real-time programs. At the specification level, we will use the Timed Acceptances model, a logically sound and complete axiom system which we have recently developed [21]. Using this model, the effect of interaction among time dependent processes can be precisely specified and then analyzed. We will then develop a formal implementation model (similar to the specification model) which captures operational behaviors: for example, the assignment of processes to processors, assumptions about scheduling and clock synchronization, and the different treatment of execution and wait times. A mapping will then be formulated between these two layers. The bulk of our proposed work will be to formulate the implementation layer and define a mapping between it and the specification layer. We also need to continue work on the Timed Acceptances model to facilitate its use as a specification model, and to provide hooks for mappings between the two layers. The rest of this proposal is organized as follows. The next section overviews related work in formal specification models. Section 3 describes our current specification model and proposed enhancements. We also detail the proposed implementation model, and required properties of the mappings between the two models. Section 4 provides a summary of the proposed research, and a yearly plan

Methodology for object-oriented real-time systems analysis and design: Software engineering

Successful application of software engineering methodologies requires an integrated analysis and design life-cycle in which the various phases flow smoothly 'seamlessly' from analysis through design to implementation. Furthermore, different analysis methodologies often lead to different structuring of the system so that the transition from analysis to design may be awkward depending on the design methodology to be used. This is especially important when object-oriented programming is to be used for implementation when the original specification and perhaps high-level design is non-object oriented. Two approaches to real-time systems analysis which can lead to an object-oriented design are contrasted: (1) modeling the system using structured analysis with real-time extensions which emphasizes data and control flows followed by the abstraction of objects where the operations or methods of the objects correspond to processes in the data flow diagrams and then design in terms of these objects; and (2) modeling the system from the beginning as a set of naturally occurring concurrent entities (objects) each having its own time-behavior defined by a set of states and state-transition rules and seamlessly transforming the analysis models into high-level design models. A new concept of a 'real-time systems-analysis object' is introduced and becomes the basic building block of a series of seamlessly-connected models which progress from the object-oriented real-time systems analysis and design system analysis logical models through the physical architectural models and the high-level design stages. The methodology is appropriate to the overall specification including hardware and software modules. In software modules, the systems analysis objects are transformed into software objects

Study of fault-tolerant software technology

Presented is an overview of the current state of the art of fault-tolerant software and an analysis of quantitative techniques and models developed to assess its impact. It examines research efforts as well as experience gained from commercial application of these techniques. The paper also addresses the computer architecture and design implications on hardware, operating systems and programming languages (including Ada) of using fault-tolerant software in real-time aerospace applications. It concludes that fault-tolerant software has progressed beyond the pure research state. The paper also finds that, although not perfectly matched, newer architectural and language capabilities provide many of the notations and functions needed to effectively and efficiently implement software fault-tolerance

Traffic Engineering with Segment Routing: SDN-based Architectural Design and Open Source Implementation

Traffic Engineering (TE) in IP carrier networks is one of the functions that can benefit from the Software Defined Networking paradigm. By logically centralizing the control of the network, it is possible to "program" per-flow routing based on TE goals. Traditional per-flow routing requires a direct interaction between the SDN controller and each node that is involved in the traffic paths. Depending on the granularity and on the temporal properties of the flows, this can lead to scalability issues for the amount of routing state that needs to be maintained in core network nodes and for the required configuration traffic. On the other hand, Segment Routing (SR) is an emerging approach to routing that may simplify the route enforcement delegating all the configuration and per-flow state at the border of the network. In this work we propose an architecture that integrates the SDN paradigm with SR-based TE, for which we have provided an open source reference implementation. We have designed and implemented a simple TE/SR heuristic for flow allocation and we show and discuss experimental results.Comment: Extended version of poster paper accepted for EWSDN 2015 (version v4 - December 2015

A Survey of Monte Carlo Tree Search Methods

Monte Carlo tree search (MCTS) is a recently proposed search method that combines the precision of tree search with the generality of random sampling. It has received considerable interest due to its spectacular success in the difficult problem of computer Go, but has also proved beneficial in a range of other domains. This paper is a survey of the literature to date, intended to provide a snapshot of the state of the art after the first five years of MCTS research. We outline the core algorithm's derivation, impart some structure on the many variations and enhancements that have been proposed, and summarize the results from the key game and nongame domains to which MCTS methods have been applied. A number of open research questions indicate that the field is ripe for future work