Gigabit Satellite Network for NASA\u27s Advanced Communication Technology Satellite (ACTS): Features, Capabilities, and Operations

This paper describes the Gigabit Satellite Network (GSN) being developed under joint sponsorship of NASA and ARPA. The system will use the wide-band Satellite Switched Time Division Multiple Access (SS-TDMA) capability and hopping beam antennas of NASA\u27s Advanced Communications Technology Satellite (ACTS). The GSN network will provide full-duplex SONET services over satellite at OC-3 (155.54 Mb/s) and OC-12 (622.078 Mb/s) rates. Typical applications will include connection of distributed SONET/ATM fiber islands over satellite, wide-area distributed supercomputer networking, high-definition digital TV, and high-speed file transfer. The RF link consists of 30 GHz uplink and 20 GHz downlink signals transmitted using a 3.4 meter offset-fed antenna and 120 Watt helix-type TWTA. The burst modem uses offset QPSK or offset-BPSK modulations for transmission at 696 Mb/s and 348 Mb/s, respectively. Transmissions to the satellite are protected using Reed-Solomon encoding, providing almost error-free clear-sky performance and, in the case of rain-fade, bit error rates better than 1099% of the time. The terrestrial side of the ground station will function as standard SONET Line Terminating Equipment (LTE), with OC-3 and OC-12 fiber interfaces, and is capable of multiplexing and demultiplexing the SONET signals down to the STS-1 (51.84 Mb/s) level. These STS-1 signals can be routed independently through the satellite between various ground stations. Management of the network is performed using a Network Management Terminal (NMT) and is based on standard SNMP and Internet protocols. The earth stations can also be remotely monitored and controlled via the satellite channel or via the terrestrial Internet

A Ka-Band High Data Rate Shipboard Satellite Terminal

A fully articulated steerable shipboard satellite antenna system operating at Ka-band was developed by engineers from the Naval Research Laboratory (NRL), NASA\u27s Glenn Research Center, and a number of industry partners. A series of tests conducted in October of 1998 on Lake Michigan achieved an unparalleled data rate transmission of 45 megabits per second (Mbps) between a moving vessel at sea and a fixed-earth station using NASA\u27s Advanced Communications Technology Satellite (ACTS). Network and application layer tests ran concurrently with the data rate transmission trials, examining TCP/IP file transfers, video and voice transfer technologies, and Asynchronous Transfer Mode (ATM) techniques. This experiment, called the Shipboard ACTS Ka-band Experiment (SHAKE), collected a data set of time-correlated measurements. The samples, collected at one-second (or faster) intervals, included vessel motion, RF and IF (modem) measurements. DS-3 layer port statistics, ATM layer statistics, TCP/IP statistics, and application performance. This data set (discussed herein) represents the one of the most comprehensive collections of its type ever recorded on a vessel. Tracking was measured at various sea states and weather conditions, including seas that generated peak pitch variations on the vessel of + 12 degrees, and peak roll variations of + 24 degrees. The SHAKE experiment, utilizing a combination of commercial-off-the-shelf (COTS) and government hardware, clearly illustrated the viability of high data rate (HDR) Ka-band systems for ship-to-shore communications. The system, which was developed over a period of four months, was tested during a two-week period on Lake Michigane on a 45-foot Bayliner Motor Yacht. Entropy. Underlying networking, protocol, terminal, and bandwidth-on-demand issues, combined with variable bit rate servive and HDR capabilities, present challenges not typically addressed in current Naval SATCOM systems. Through this study, numerous system optimizations were documented, which are presented as work remaining in order to realize reliable services that would support Naval HDR shipboard SATCOM requirements using commercially-available Ka-Band satellite systems

Extended reaction kinetics model for non-thermal argon plasmas and its test against experimental data

An extended reaction kinetics model (RKM) suitable for the analysis of weakly ionised, non-thermal argon plasmas with gas temperatures around 300 K at sub-atmospheric and atmospheric pressures is presented. It considers 23 different species including electrons as well as the ground state atom, an atomic and molecular ion, four excited molecular states, and 15 excited atomic states of argon, where all individual 1s and 2p states (in Paschen notation) are included as a separate species. This 23-species RKM involves 409 collision processes and radiative transitions and recent electron collision cross section data. It is evaluated by means of results of time- and space-dependent fluid modelling of argon discharges and their comparison with measured data for two different dielectric barrier discharge configurations as well as a micro-scaled atmospheric-pressure plasma jet setup. The results are also compared with those obtained by use of a previously established 15-species RKM involving only the two lumped 2p states 2p10…5 and 2´p4 … 1. It is found that the 23-species RKM shows generally better agreement with experimental data and provides more options for direct comparison with measurements than the frequently used 15-species RKM

The JKind Model Checker

JKind is an open-source industrial model checker developed by Rockwell Collins and the University of Minnesota. JKind uses multiple parallel engines to prove or falsify safety properties of infinite state models. It is portable, easy to install, performance competitive with other state-of-the-art model checkers, and has features designed to improve the results presented to users: inductive validity cores for proofs and counterexample smoothing for test-case generation. It serves as the back-end for various industrial applications.Comment: CAV 201

ACTS 118x Final Report High-Speed TCP Interoperability Testing

With the recent explosion of the Internet and the enormous business opportunities available to communication system providers, great interest has developed in improving the efficiency of data transfer using the Transmission Control Protocol (TCP) of the Internet Protocol (IP) suite. The satellite system providers are interested in solving TCP efficiency problems associated with long delas and error-prone links. Similarly, the terrestrial community is interested in solving TCP problems over high-bandwidth links. Whereas the wireless community is intested in improving TCP performance over bandwidth constrained, error-prone links. NASA realized that solutions had already been proposed for most of the problems associated with efficient data transfer over large bandwidth-delay links (which include satellite links). The solutions are detailed in various Internet Engineering Task Force (IETF) Request for Comments (RFCs). Unfortunately, most of these solutions had not been tested at high-speed (155+ Mbps). Therefore, the NASA\u27s ACTS experiments program initiated a series of TCP experiments to demonstrate scalability of TCP/IP and determine how far the protocol can be optimised over a 622 Mbps satellite link. These experiments were known as the 118i and 118j experiments. During the 118i and 118j experiments, NASA worled closely with SUN Microsystems and FORE Systems to improve the operating system, TCP stacks, and network interface cards and drivers. We were able to obtain instantaneous data througput rates of greater than 529 Mbps and average throughput rates of 470 Mbps using TCP over Asynchronous Transfer Mode (ATM) over a 622 Mbps Synchronous Optical Network (SONET) OC12 link. Following the success of these experiments and the successful government/industry collaboration, a new series of experiments, the 118x experiments, were developed

Verifying the Safety of a Flight-Critical System

This paper describes our work on demonstrating verification technologies on a flight-critical system of realistic functionality, size, and complexity. Our work targeted a commercial aircraft control system named Transport Class Model (TCM), and involved several stages: formalizing and disambiguating requirements in collaboration with do- main experts; processing models for their use by formal verification tools; applying compositional techniques at the architectural and component level to scale verification. Performed in the context of a major NASA milestone, this study of formal verification in practice is one of the most challenging that our group has performed, and it took several person months to complete it. This paper describes the methodology that we followed and the lessons that we learned.Comment: 17 pages, 5 figure

A simple abstraction of arrays and maps by program translation

We present an approach for the static analysis of programs handling arrays, with a Galois connection between the semantics of the array program and semantics of purely scalar operations. The simplest way to implement it is by automatic, syntactic transformation of the array program into a scalar program followed analysis of the scalar program with any static analysis technique (abstract interpretation, acceleration, predicate abstraction,.. .). The scalars invariants thus obtained are translated back onto the original program as universally quantified array invariants. We illustrate our approach on a variety of examples, leading to the " Dutch flag " algorithm

Automatic Abstraction in SMT-Based Unbounded Software Model Checking

Software model checkers based on under-approximations and SMT solvers are very successful at verifying safety (i.e. reachability) properties. They combine two key ideas -- (a) "concreteness": a counterexample in an under-approximation is a counterexample in the original program as well, and (b) "generalization": a proof of safety of an under-approximation, produced by an SMT solver, are generalizable to proofs of safety of the original program. In this paper, we present a combination of "automatic abstraction" with the under-approximation-driven framework. We explore two iterative approaches for obtaining and refining abstractions -- "proof based" and "counterexample based" -- and show how they can be combined into a unified algorithm. To the best of our knowledge, this is the first application of Proof-Based Abstraction, primarily used to verify hardware, to Software Verification. We have implemented a prototype of the framework using Z3, and evaluate it on many benchmarks from the Software Verification Competition. We show experimentally that our combination is quite effective on hard instances.Comment: Extended version of a paper in the proceedings of CAV 201

ACTS 118x: High Speed TCP Interoperability Testing

With the recent explosion of the Internet and the enormous business opportunities available to communication system providers, great interest has developed in improving the efficiency of data transfer over satellite links using the Transmission Control Protocol (TCP) of the Internet Protocol (IP) suite. The NASA's ACTS experiments program initiated a series of TCP experiments to demonstrate scalability of TCP/IP and determine to what extent the protocol can be optimized over a 622 Mbps satellite link. Through partnerships with the government technology oriented labs, computer, telecommunication, and satellite industries NASA Glenn was able to: (1) promote the development of interoperable, high-performance TCP/IP implementations across multiple computing / operating platforms; (2) work with the satellite industry to answer outstanding questions regarding the use of standard protocols (TCP/IP and ATM) for the delivery of advanced data services, and for use in spacecraft architectures; and (3) conduct a series of TCP/IP interoperability tests over OC12 ATM over a satellite network in a multi-vendor environment using ACTS. The experiments' various network configurations and the results are presented