Adding Packet Radio to the Ultrix Kernel

This paper describes the results of a project in which the standard Amateur Packet Radio network link layer protocol, AX.25 (a modified version of X.25), was added to the Ultrix kernel. By implementing AX.25 under Ultrix, and by taking advantage of the IP implementations that already exist for PCs, it is possible for packet radio users with PCs to access IP-based services running on our server and on the Internet. A MicroVAX is being used as an IP gateway for an Amateur Packet Radio network that stretches from Seattle to Tacoma. 1. Introduction Packet Radio is an increasingly active area of experimentation among amateur radio operators. Stations consist of a radio transceiver connected to a terminal or a computer by means of a device known as a Terminal Node Controller (TNC). The TNC is essentially a modem. It "packetizes" data in a manner conforming to the AX.25 link layer protocol, provides a command interpreter, and has a primitive network layer protocol for use with terminals unab..

The influence of protocol choice on network performance

Bibliography: leaves 100-102.Computer communication networks are a vital link in providing many of the services that we use daily, and our reliance on these networks is on the increase. The growing use of networks is driving network design towards greater performance. The greater need for network connectivity and increased performance makes the study of network performance constraints important. Networks consist of both hardware and software components. Currently great advances are being made in network hardware, resulting in advances in the available raw network performance. In this thesis, I will show through measurement that it is difficult to harness all the raw performance and to make it available to carry network services. I will also identify some of the factors limiting the full utilization of a high speed network

Redes mesh basadas en puntos de acceso inteligentes 802.11 open source (III)

El número de redes inalámbricas continúa creciendo sin control debido a que éstas funcionan sobre una banda de frecuencias libre, son de fácil instalación, atractivas al eliminar el cableado además de ser asequibles económicamente. En entornos muy poblados se puede observar la coexistencia de redes inalámbricas de empresas, redes domésticas, hot spots públicos, etc. que comparten la misma banda de frecuencias, que es de hecho un recurso limitado. En muchos casos el número de canales libres para no producir solapamiento con otras redes no es suficiente, por lo que la coexistencia resulta cada vez más problemática debido a la aparición de interferencias entre redes vecinas. La presencia de interferencias afecta al funcionamiento de las redes produciendo errores y colisiones, y como consecuencia se reduce el caudal además de aumentar el retardo de los paquetes. La estructura de este proyecto se basa principalmente en dos grandes bloques que se detallan a continuación: El primero pretende estudiar el impacto que conlleva la coexistencia de diferentes redes WLAN IEEE 802.11 sin una gestión inteligente que permita una óptima distribución de los recursos. Para ello se ha analizado el comportamiento de puntos de acceso meshcubes mediante pruebas en entornos reales. Posteriormente, se han corroborado los resultados obtenidos con dos simuladores de redes: NS-2 y OPNET Modeler. De esta manera se ha realizado una comparación exhaustiva de los resultados obtenidos. A partir de los resultados obtenidos se planteó la necesidad de introducir en las redes inalámbricas mecanismos distribuidos que optimizaran los recursos disponibles con el fin de reducir los efectos negativos de las interferencias. En el segundo bloque se presentan dos alternativas para solucionar la problemática mediante el diseño de protocolos de señalización entre nodos de una red mesh que permiten llevar a cabo diferentes estrategias para le gestión de recursos radio en una red WLAN IEEE 802.11. Uno está elaborado mediante Raw Ethernet Sockets y el otro se ha desarrollado para funcionar sobre el protocolo de encaminamiento OLSR

The Third Annual NASA Science Internet User Working Group Conference

The NASA Science Internet (NSI) User Support Office (USO) sponsored the Third Annual NSI User Working Group (NSIUWG) Conference March 30 through April 3, 1992, in Greenbelt, MD. Approximately 130 NSI users attended to learn more about the NSI, hear from projects which use NSI, and receive updates about new networking technologies and services. This report contains material relevant to the conference; copies of the agenda, meeting summaries, presentations, and descriptions of exhibitors. Plenary sessions featured a variety of speakers, including NSI project management, scientists, and NSI user project managers whose projects and applications effectively use NSI, and notable citizens of the larger Internet community. The conference also included exhibits of advanced networking applications; tutorials on internetworking, computer security, and networking technologies; and user subgroup meetings on the future direction of the conference, networking, and user services and applications

Advancing Operating Systems via Aspect-Oriented Programming

Operating system kernels are among the most complex pieces of software in existence to- day. Maintaining the kernel code and developing new functionality is increasingly compli- cated, since the amount of required features has risen significantly, leading to side ef fects that can be introduced inadvertedly by changing a piece of code that belongs to a completely dif ferent context. Software developers try to modularize their code base into separate functional units. Some of the functionality or “concerns” required in a kernel, however, does not fit into the given modularization structure; this code may then be spread over the code base and its implementation tangled with code implementing dif ferent concerns. These so-called “crosscutting concerns” are especially dif ficult to handle since a change in a crosscutting concern implies that all relevant locations spread throughout the code base have to be modified. Aspect-Oriented Software Development (AOSD) is an approach to handle crosscutting concerns by factoring them out into separate modules. The “advice” code contained in these modules is woven into the original code base according to a pointcut description, a set of interaction points (joinpoints) with the code base. To be used in operating systems, AOSD requires tool support for the prevalent procedu- ral programming style as well as support for weaving aspects. Many interactions in kernel code are dynamic, so in order to implement non-static behavior and improve performance, a dynamic weaver that deploys and undeploys aspects at system runtime is required. This thesis presents an extension of the “C” programming language to support AOSD. Based on this, two dynamic weaving toolkits – TOSKANA and TOSKANA-VM – are presented to permit dynamic aspect weaving in the monolithic NetBSD kernel as well as in a virtual- machine and microkernel-based Linux kernel running on top of L4. Based on TOSKANA, applications for this dynamic aspect technology are discussed and evaluated. The thesis closes with a view on an aspect-oriented kernel structure that maintains coherency and handles crosscutting concerns using dynamic aspects while enhancing de- velopment methods through the use of domain-specific programming languages

Telescience testbed pilot program, volume 3: Experiment summaries

Space Station Freedom and its associated labs, coupled with the availability of new computing and communications technologies, have the potential for significantly enhancing scientific research. A Telescience Testbed Pilot Program (TTPP), aimed at developing the experience base to deal with issues in the design of the future information system of the Space Station era. The testbeds represented four scientific disciplines (astronomy and astrophysics, earth science, life sciences, and microgravity sciences) and studied issues in payload design, operation, and data analysis. This volume, of a 3 volume set, which all contain the results of the TTPP, presents summaries of the experiments. This experiment involves the evaluation of the current Internet for the use of file and image transfer between SIRTF instrument teams. The main issue addressed was current network response times

Conceiving Open Systems

This Article tells the story of the contest over the meaning of open systems from 1980 to 1993, a contest to create a simultaneously moral and technical infrastructure within the computer industry

State of the art survey of network operating systems development

The results of the State-of-the-Art Survey of Network Operating Systems (NOS) performed for Goddard Space Flight Center are presented. NOS functional characteristics are presented in terms of user communication data migration, job migration, network control, and common functional categories. Products (current or future) as well as research and prototyping efforts are summarized. The NOS products which are revelant to the space station and its activities are evaluated

COBE's search for structure in the Big Bang

The launch of Cosmic Background Explorer (COBE) and the definition of Earth Observing System (EOS) are two of the major events at NASA-Goddard. The three experiments contained in COBE (Differential Microwave Radiometer (DMR), Far Infrared Absolute Spectrophotometer (FIRAS), and Diffuse Infrared Background Experiment (DIRBE)) are very important in measuring the big bang. DMR measures the isotropy of the cosmic background (direction of the radiation). FIRAS looks at the spectrum over the whole sky, searching for deviations, and DIRBE operates in the infrared part of the spectrum gathering evidence of the earliest galaxy formation. By special techniques, the radiation coming from the solar system will be distinguished from that of extragalactic origin. Unique graphics will be used to represent the temperature of the emitting material. A cosmic event will be modeled of such importance that it will affect cosmological theory for generations to come. EOS will monitor changes in the Earth's geophysics during a whole solar color cycle

Space and Earth Sciences, Computer Systems, and Scientific Data Analysis Support, Volume 1

This Final Progress Report covers the specific technical activities of Hughes STX Corporation for the last contract triannual period of 1 June through 30 Sep. 1993, in support of assigned task activities at Goddard Space Flight Center (GSFC). It also provides a brief summary of work throughout the contract period of performance on each active task. Technical activity is presented in Volume 1, while financial and level-of-effort data is presented in Volume 2. Technical support was provided to all Division and Laboratories of Goddard's Space Sciences and Earth Sciences Directorates. Types of support include: scientific programming, systems programming, computer management, mission planning, scientific investigation, data analysis, data processing, data base creation and maintenance, instrumentation development, and management services. Mission and instruments supported include: ROSAT, Astro-D, BBXRT, XTE, AXAF, GRO, COBE, WIND, UIT, SMM, STIS, HEIDI, DE, URAP, CRRES, Voyagers, ISEE, San Marco, LAGEOS, TOPEX/Poseidon, Pioneer-Venus, Galileo, Cassini, Nimbus-7/TOMS, Meteor-3/TOMS, FIFE, BOREAS, TRMM, AVHRR, and Landsat. Accomplishments include: development of computing programs for mission science and data analysis, supercomputer applications support, computer network support, computational upgrades for data archival and analysis centers, end-to-end management for mission data flow, scientific modeling and results in the fields of space and Earth physics, planning and design of GSFC VO DAAC and VO IMS, fabrication, assembly, and testing of mission instrumentation, and design of mission operations center