968 research outputs found
The phase of the crosspolarized signal generated by millimeter wave propagation through rain
Proposed schemes for cancelling rain-induced crosstalk in dual-polarized communications systems depend upon the phase relationships between the wanted and unwanted signals. This report investigates the phase relationship of the rain-generated crosspolarized signal relative to the copolarized signal. Theoretical results obtained from a commonly accepted propagation model are presented. Experimental data from the Communications Technology Satellite beacon and from the Comstar beacon are presented and the correlation between theory and data is discussed. An inexpensive semi-adaptive cancellation system is proposed and its performance expectations are presented. The implications of phase variations on a cancellation system are also discussed
Traffic placement policies for a multi-band network
Recently protocols were introduced that enable the integration of synchronous traffic (voice or video) and asynchronous traffic (data) and extend the size of local area networks without loss in speed or capacity. One of these is DRAMA, a multiband protocol based on broadband technology. It provides dynamic allocation of bandwidth among clusters of nodes in the total network. A number of traffic placement policies for such networks are proposed and evaluated. Metrics used for performance evaluation include average network access delay, degree of fairness of access among the nodes, and network throughput. The feasibility of the DRAMA protocol is established through simulation studies. DRAMA provides effective integration of synchronous and asychronous traffic due to its ability to separate traffic types. Under the suggested traffic placement policies, the DRAMA protocol is shown to handle diverse loads, mixes of traffic types, and numbers of nodes, as well as modifications to the network structure and momentary traffic overloads
CSMA/RN: A universal protocol for gigabit networks
Networks must provide intelligent access for nodes to share the communications resources. In the range of 100 Mbps to 1 Gbps, the demand access class of protocols were studied extensively. Many use some form of slot or reservation system and many the concept of attempt and defer to determine the presence or absence of incoming information. The random access class of protocols like shared channel systems (Ethernet), also use the concept of attempt and defer in the form of carrier sensing to alleviate the damaging effects of collisions. In CSMA/CD, the sensing of interference is on a global basis. All systems discussed above have one aspect in common, they examine activity on the network either locally or globally and react in an attempt and whatever mechanism. Of the attempt + mechanisms discussed, one is obviously missing; that is attempt and truncate. Attempt and truncate was studied in a ring configuration called the Carrier Sensed Multiple Access Ring Network (CSMA/RN). The system features of CSMA/RN are described including a discussion of the node operations for inserting and removing messages and for handling integrated traffic. The performance and operational features based on analytical and simulation studies which indicate that CSMA/RN is a useful and adaptable protocol over a wide range of network conditions are discussed. Finally, the research and development activities necessary to demonstrate and realize the potential of CSMA/RN as a universal, gigabit network protocol is outlined
Extremely high data-rate, reliable network systems research
Significant progress was made over the year in the four focus areas of this research group: gigabit protocols, extensions of metropolitan protocols, parallel protocols, and distributed simulations. Two activities, a network management tool and the Carrier Sensed Multiple Access Collision Detection (CSMA/CD) protocol, have developed to the point that a patent is being applied for in the next year; a tool set for distributed simulation using the language SIMSCRIPT also has commercial potential and is to be further refined. The year's results for each of these areas are summarized and next year's activities are described
Effect of \u3ci\u3eBaculovirus penaei\u3c/i\u3e on Growth and Survival of Experimentally Infected Postlarvae of the Pacific White Shrimp, \u3ci\u3ePenaeus vannamei\u3c/i\u3e
In a series of experiments conducted to investigate age and size-dependent effects of the baculovirus BP on postlarvae of the Pacific white shrimp, Penaeus vannamei, six groups of specific pathogen-free shrimp of different ages (mysis 2–3 through PL 25) were exposed to the virus and cultured for 15 to 21 days. All BP-exposed groups of early postlarvae (PL 9 or younger) became heavily infected within 2–5 days of initial exposure to the virus, and some of those groups experienced high mortalities compared to the noninfected controls. Postlarvae that survived the infection had highly variable and significantly reduced growth, as determined by dry weight, compared to controls. Exposure of older postlarvae to BP produced a high prevalence of infection but with little effect on either survival or growth. One group of shrimp exposed to BP at PL 9 was cultured for 49 days. Postlarvae that survived the infection were significantly smaller than the noninfected controls for the first 4 weeks following exposure to the virus; however, the effect of BP on long-term growth of infected postlarvae appeared minimal. To determine the effect of BP on nutritionally stressed shrimp, groups of noninfected and previously infected postlarvae (PL 13–14) of similar size were deprived of food for 10 days. Less than 2% of the infected postlarvae survived the 10-day starvation period compared to 52% survival of the noninfected postlarvae
Preparation of a geologic photo map and hydrologic study of the Yemen Arab Republic
There are no author-identified significant results in this report
Scalable parallel communications
Coarse-grain parallelism in networking (that is, the use of multiple protocol processors running replicated software sending over several physical channels) can be used to provide gigabit communications for a single application. Since parallel network performance is highly dependent on real issues such as hardware properties (e.g., memory speeds and cache hit rates), operating system overhead (e.g., interrupt handling), and protocol performance (e.g., effect of timeouts), we have performed detailed simulations studies of both a bus-based multiprocessor workstation node (based on the Sun Galaxy MP multiprocessor) and a distributed-memory parallel computer node (based on the Touchstone DELTA) to evaluate the behavior of coarse-grain parallelism. Our results indicate: (1) coarse-grain parallelism can deliver multiple 100 Mbps with currently available hardware platforms and existing networking protocols (such as Transmission Control Protocol/Internet Protocol (TCP/IP) and parallel Fiber Distributed Data Interface (FDDI) rings); (2) scale-up is near linear in n, the number of protocol processors, and channels (for small n and up to a few hundred Mbps); and (3) since these results are based on existing hardware without specialized devices (except perhaps for some simple modifications of the FDDI boards), this is a low cost solution to providing multiple 100 Mbps on current machines. In addition, from both the performance analysis and the properties of these architectures, we conclude: (1) multiple processors providing identical services and the use of space division multiplexing for the physical channels can provide better reliability than monolithic approaches (it also provides graceful degradation and low-cost load balancing); (2) coarse-grain parallelism supports running several transport protocols in parallel to provide different types of service (for example, one TCP handles small messages for many users, other TCP's running in parallel provide high bandwidth service to a single application); and (3) coarse grain parallelism will be able to incorporate many future improvements from related work (e.g., reduced data movement, fast TCP, fine-grain parallelism) also with near linear speed-ups
The Impact of a Parkinson’s Disease Workshop on Student’s Attitudes and Competencies Towards Interprofessional Collaboration
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LTL pricing: Looking back to the future
Numerous LTL carriers struggled during the recent recession as customers demanded lower prices. This study is designed to qualitatively evaluate the data gathered from three industry segments regarding LTL pricing. Researchers used semi-structured interviews to conduct an in-depth investigation with over two dozen industry experts who represented shippers, carriers, and 3PLs. Interview transcripts were analyzed using a grounded theory coding technique. Five major themes emerged from the interview transcripts. These themes are used to describe possible future adjustments to industry pricing structure
A Flexible System for Simulating Aeronautical Telecommunication Network
At Old Dominion University, we have built Aeronautical Telecommunication Network (ATN) Simulator with NASA being the fund provider. It provides a means to evaluate the impact of modified router scheduling algorithms on the network efficiency, to perform capacity studies on various network topologies and to monitor and study various aspects of ATN through graphical user interface (GUI). In this paper we describe briefly about the proposed ATN model and our abstraction of this model. Later we describe our simulator architecture highlighting some of the design specifications, scheduling algorithms and user interface. At the end, we have provided the results of performance studies on this simulator
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