Short-distance Networks Research Articles

Modeled and experimental results of an omnidirectional free-space optical receiver architecture

Free-space optical (FSO) communications provide point-to-point connectivity while offering many advantages in size, weight, and power as compared to radio frequency. It has the potential to provide fiber-optic data rates without the need for lengthy fiber cables. Omnidirectional FSO, also known as O-FSO systems, provide a non-line-of-sight option for data communications. They are gaining popularity in short-distance networks. Most existing O-FSO links range from 1 to 100 m and present experimental/simulated data rates ranging between 5 kb/s and 1 Mb/s. A 2.5-Gb/s O-FSO system was recently reported with a range of 25 cm. This paper employs a fiber bundle as an O-FSO receiver. The energy collected by the receiver is related to the acceptance cone of each fiber. The fiber bundle integrates the optical power gathered by the individual fibers and couples it to the photodetector. Experimental data rates approaching 100 kb/s over a meter long system are presented, whereas simulated results support a data rate up to 52 Mb/s for distances approaching a kilometer. Theoretical and experimental optical power versus range is also presented for the proposed O-FSO architecture, using on-off keying.

Modeling the Throughput of the Linux-Based Agile-SD Transmission Control Protocol

Agile-SD is one of the latest versions of loss-based congestion control algorithm (CCA), which has been proposed to improve the total performance of transmission control protocol (TCP) over high-speed and short-distance networks. It has introduced a new mechanism, called agility factor mechanism, which shortens the epoch time to reduce the sensitivity to packet losses and in turn to increase the average throughput. Agile-SD has only been tested via simulation; however, it has not been mathematically proven or evaluated. The contribution of this paper is twofold. First, a new mathematical model for the throughput of NewReno and Agile-SD is proposed. This model is designed using the well-known Markov chains to validate the correctness of Agile-SD and to show the impact of buffer size, multiplicative decrease factor, and maximum limit of agility factor ({\lambda}max ) on the total performance. Second, an automated algorithm configuration and parameter tuning (AACPT) technique is employed to optimize and automate the configuration of {\lambda}max . Furthermore, the numerical results for both NewReno and Agile-SD are compared with the simulation results, in which the validity of the proposed model is confirmed. Moreover, the output of the AACPT is exploited to formulate a new equation, which calculates the optimal {\lambda}max from a given \b{eta} in order to conserve the standard interface of the TCP. This equation increases the scalability of Agile-SD and improves its total performance.

Agile-SD: A Linux-based TCP congestion control algorithm for supporting high-speed and short-distance networks

Recently, high-speed and short-distance networks are widely deployed and their necessity is rapidly increasing everyday. This type of networks is used in several network applications; such as Local Area Networks (LAN) and Data Center Networks (DCN). In LANs and DCNs, high-speed and short-distance networks are commonly deployed to connect between computing and storage elements in order to provide rapid services. Indeed, the overall performance of such networks is significantly influenced by the Congestion Control Algorithm (CCA) which suffers from the problem of bandwidth under-utilization, especially if the applied buffer regime is very small. In this paper, a novel loss-based CCA tailored for high-speed and Short-Distance (SD) networks, namely Agile-SD, has been proposed. The main contribution of the proposed CCA is to implement the mechanism of agility factor. Further, intensive simulation experiments have been carried out to evaluate the performance of Agile-SD compared to Compound and Cubic which are the default CCAs of the most commonly used operating systems. The results of the simulation experiments show that the proposed CCA outperforms the compared CCAs in terms of average throughput, loss ratio and fairness, especially when a small buffer is applied. Moreover, Agile-SD shows lower sensitivity to the buffer size change and packet error rate variation which increases its efficiency.

Travellers of the Bronze Age

The aim of this article is to add people to the question of mobility, with a case study in central Macedonia. The traveller, on whose shoulders the long distance connections that network theory and world-systems analysis deal with were carried out, is introduced as an analytical category to add an additional perspective to discussions on mobility. By setting the scale of study at a regional level, encounters and their impacts on people and material culture may both be studied. Both long-distance and short-distance networks are taken into account. The result is an outline of a multi-ethnic trading society which may inspire studies of other sites on routes of communication in the Bronze Age.

Construction and uncertainty evaluation of a calibration system for GPS receivers

GPS is already a main method of positioning measurement in geodesy and is applied widely in many fields. In order to maintain and ensure the accuracy of positioning, an accurate and efficient system for calibrating the GPS receivers must be established. A highly accurate GPS calibration network, tied to the ITRF coordinates of IGS stations, can be effectively used to evaluate the performance of GPS receivers. This study addresses the feasibility of establishing a system for calibrating GPS receivers and the system's traceability in metrology. Uncertainties of the GPS calibration networks were established and maintained by NML (National Measurement Laboratory, Taiwan). Furthermore, the networks are evaluated based on the method suggested by the ISO (International Organization for Standardization). The uncertainties of NML network coordinates are obtained and used as a basis for calibration. The results of the slope distances between pillars measured by the GPS processing units and the precise EDM units are discussed. Analytical results indicate that the 3D expanded uncertainty of the main station TNML of the network in the ITRF system is around 33.2 mm at the 95% confidence level. The 3D expanded uncertainties of the calibration points of the ultra-short distance network and the short distance network are evaluated to be about 2.2 mm and 3.4 mm, respectively in relation to the main station TNML at the 95% confidence level. The precision of the NML network coordinates suffices to calibrate the geodetic and navigational GPS receivers of regional users and is available through the Internet.

Design and characteristics of large displacement optical fiber switch

Plastic optical fiber (POF) is suitable for indoor local area network (LAN), for example, in-home or office networks, because of its flexibility and its ease of connection due to its relatively large core diameter. A 1/spl times/2 optical switch for indoor LAN using POF and a shape memory alloy (SMA) coil actuator with magnetic latches was successfully fabricated and tested. In this paper, the design concept and the characteristics of this switch are described. To achieve switching by the movement of a POF, large displacement is necessary because the core diameter is large (e.g., 0.486 mm). A SMA coil actuator is used for large displacement and a magnetic latching system is employed for fixing the position of the shifted POF. For this design, the insertion loss is 0.40 to 0.50 dB and crosstalk is more than -50 dB without index-matching oil. Switching speed is less than 0.5 s at a driving current of 80 mA. A cycling test was performed 1.4 million times at room temperature. Another optical fiber switch was fabricated and successfully actuated using plastic clad fiber (PCF). PCF also has a large core diameter (e.g., 0.20 mm) and optical switches using PCF will be useful for short distance networks between buildings.

Fluctuations of the auroral zone current system and geomagnetic pulsations

Recordings of Pi 1 and Pi 2 pulsations obtained on a short-distance network of magnetometer stations were used to investigate the relationship between fluctuations of the auroral zone currents and geomagnetic pulsations. During the early part of the substorm expansion phase the pulsations of the D and H components are decoupled from each other at all stations. Similarly, the pulsations of the D components are not significantly correlated at stations with separation distances of approximately 100 km. For this interval the pulsations of the H component are interpreted as being predominantly the magnetic effect of fluctuations of the auroral electrojet, and the pulsations of the D component as being a consequence of fluctuations of Birkeland sheet currents. The conclusion can be drawn from these observations that the Birkeland currents are not directly connected in the north-south direction. Thus a considerable east-west component of the currents is required in order to maintain current continuity in the ionosphere. These effects disappear in the late expansion phase and early recovery phase.