25,619 research outputs found
Evaluation and Mission-Specific Optimization of Satellite Packet Telemetry Protocol for Use on DoD Flight Test Ranges
The DoD test range community has come to the realization that its telemetry abilities are obsolete. Efforts are therefore underway to improve telemetry systems at DoD test ranges. The overall objective of this project was to evaluate the practical use of the CCSDS packet telemetry protocol in DoD test ranges and determine the configuration that would maximize performance based on mission requirements. A secondary objective was to compare the CCSDS and ATM protocols in order to substantiate further exploration of using ATM in future DoD telemetry systems. Modeling and simulation of the CCSDS protocol showed a correlation between three CCSDS parameters and the resulting throughput and data quality performance. Flight tests confirmed the correlation between the CCSDS parameters and the resulting protocol performance, and narrowed in on the CCSDS configurations that would maximize data throughput, data quality, or provide a combined \u27best of both worlds\u27 solution. In general, flight test results matched those of the modeling and simulation work. Data collected also indicated that performance of the ATM protocol is sufficiently close to that of CCSDS to warrant further investigation of using ATM on test ranges. ATM offers the military user straightforward interoperability with civilian systems/networks
Performance of voice and video conferencing over ATM and gigabit ethernet backbone networks
Gigabit Ethernet and ATM network technologies have been modeled as campus network
backbones for the simulation-based comparison of their performance. Real-time voice and
video conferencing traffic is used to compare the performance of both backbone
technologies in terms of response times and packet end-to-end delays. Simulation results
show that Gigabit Ethernet has been able to perform the same and in some cases better than
ATM as a backbone network for video and voice conferencing providing network designers
with a cheaper solution to meet the growing needs of bandwidth-hungry applications in a
campus environment
Performance of Bursty World Wide Web (WWW) Sources over ABR
We model World Wide Web (WWW) servers and clients running over an ATM network
using the ABR (available bit rate) service. The WWW servers are modeled using a
variant of the SPECweb96 benchmark, while the WWW clients are based on a model
by Mah. The traffic generated by this application is typically bursty, i.e., it
has active and idle periods in transmission. A timeout occurs after given
amount of idle period. During idle period the underlying TCP congestion windows
remain open until a timeout expires. These open windows may be used to send
data in a burst when the application becomes active again. This raises the
possibility of large switch queues if the source rates are not controlled by
ABR. We study this problem and show that ABR scales well with a large number of
bursty TCP sources in the system.Comment: Submitted to WebNet `97, Toronto, November 9
Empirical exploration of air traffic and human dynamics in terminal airspaces
Air traffic is widely known as a complex, task-critical techno-social system,
with numerous interactions between airspace, procedures, aircraft and air
traffic controllers. In order to develop and deploy high-level operational
concepts and automation systems scientifically and effectively, it is essential
to conduct an in-depth investigation on the intrinsic traffic-human dynamics
and characteristics, which is not widely seen in the literature. To fill this
gap, we propose a multi-layer network to model and analyze air traffic systems.
A Route-based Airspace Network (RAN) and Flight Trajectory Network (FTN)
encapsulate critical physical and operational characteristics; an Integrated
Flow-Driven Network (IFDN) and Interrelated Conflict-Communication Network
(ICCN) are formulated to represent air traffic flow transmissions and
intervention from air traffic controllers, respectively. Furthermore, a set of
analytical metrics including network variables, complex network attributes,
controllers' cognitive complexity, and chaotic metrics are introduced and
applied in a case study of Guangzhou terminal airspace. Empirical results show
the existence of fundamental diagram and macroscopic fundamental diagram at the
route, sector and terminal levels. Moreover, the dynamics and underlying
mechanisms of "ATCOs-flow" interactions are revealed and interpreted by
adaptive meta-cognition strategies based on network analysis of the ICCN.
Finally, at the system level, chaos is identified in conflict system and human
behavioral system when traffic switch to the semi-stable or congested phase.
This study offers analytical tools for understanding the complex human-flow
interactions at potentially a broad range of air traffic systems, and underpins
future developments and automation of intelligent air traffic management
systems.Comment: 30 pages, 28 figures, currently under revie
Hierarchical Models for Relational Event Sequences
Interaction within small groups can often be represented as a sequence of
events, where each event involves a sender and a recipient. Recent methods for
modeling network data in continuous time model the rate at which individuals
interact conditioned on the previous history of events as well as actor
covariates. We present a hierarchical extension for modeling multiple such
sequences, facilitating inferences about event-level dynamics and their
variation across sequences. The hierarchical approach allows one to share
information across sequences in a principled manner---we illustrate the
efficacy of such sharing through a set of prediction experiments. After
discussing methods for adequacy checking and model selection for this class of
models, the method is illustrated with an analysis of high school classroom
dynamics
On-board congestion control for satellite packet switching networks
It is desirable to incorporate packet switching capability on-board for future communication satellites. Because of the statistical nature of packet communication, incoming traffic fluctuates and may cause congestion. Thus, it is necessary to incorporate a congestion control mechanism as part of the on-board processing to smooth and regulate the bursty traffic. Although there are extensive studies on congestion control for both baseband and broadband terrestrial networks, these schemes are not feasible for space based switching networks because of the unique characteristics of satellite link. Here, we propose a new congestion control method for on-board satellite packet switching. This scheme takes into consideration the long propagation delay in satellite link and takes advantage of the the satellite's broadcasting capability. It divides the control between the ground terminals and satellite, but distributes the primary responsibility to ground terminals and only requires minimal hardware resource on-board satellite
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