Modem Link Research Articles

A Methodology for Creating RTK Positioning Coverage Maps via a Radio Modem Link to CORS Stations

The Andalusian Positioning Network (RAP) is a real-time kinematic (RTK) GPS-based network that covers the Autonomous Community of Andalusia (southern Spain) homogeneously and offers, amongst other services, radio modem-based differential corrections for accurate real-time positioning (RAP-RTK). The institutions responsible for permanent GPS networks do not currently provide information regarding the radio coverage of their stations. In this communication we therefore present a methodology for creating RTK positioning maps via a radio modem link to continuously operating reference stations (CORS). We have applied this methodology to the University of Jaén (UJAE)'s permanent GPS station and present, for the first time, two coverage maps for this service. One of these maps is based on field data and the other on a combination of field data and computerized applications that generate viewshed maps, thus offering relevant information regarding the areas where users can make use of this service. This type of application is shown to be an excellent tool for estimating beforehand the possibility of using the radio modem-based differential correction service without having to visit the site.

Dealing with DirectPlay Environments under DirectX

The idea of this project is based on programming the functions of DirectX, which will connect the last one with the windows, this work is needed because DirectX deals with the hardware and the buffers of the memory while the windows does not directly deal with it. The work focuses on programming the DirectPlay function, which is considered as an interface programming to guarantee the arrival of the applications to the communication services. DirectPlay supports the facilities of connecting the game with the internet directly by the Modem Link or indirectly by the Ethernet. Actually the game becomes more flexible and enjoying if it is played against a real player (or another user of the computer) instead of playing with the computer itself. Also DirectPlay supports a group of users connected with each other in an active way at the same time (for example, the Internet chatting or Ethernet chatting). In this work, an Ethernet chatting is done by using a Client/Server applications to see the working of DirectPlay, then, we try to use an active and strong language to make this is possible, and therefor we use the Visual C++ language.

Wireless Teleradiology for Renal Colic and Renal Trauma

Image transmission is an integral part of telemedicine, allowing evaluation of patients at remote sites. We developed a simple method of wireless transmission of digital images to a hand-held computer (PDA) and evaluated its feasibility and diagnostic accuracy in patients with acute renal colic or renal trauma. The CT images from 11 patients with suspected renal colic and one patient with renal trauma were transmitted using a cellular telephone with a wireless modem link to a PDA (Sony Clie 615C). A diagnostic interpretation was recorded for the presence/absence of an upper-tract stone, stone location, estimated stone size, and signs of upper-tract obstruction. Radiologic staging of trauma was provided in the patient with a renal injury. Comparison was made with the final dictated report of a staff radiologist. Ten CT sets of patients with renal colic were used for comparison, the remaining one being excluded because of ambiguity in the final radiology report. An average of 5.9+/-1.6 images, average size 32.2+/-5.2 kb (range 21-42 kb) for each patient were sent at an average speed of 1 kb/sec. Interpretation correctly identified stone presence in 80%, hydronephrosis in 100%, and perinephric stranding in 80% and stone size within 1+/-1 mm. A stage-3 renal trauma was correctly identified and staged. Wireless teleradiology to PDA units provides image quality sufficient for diagnostic interpretation. Anticipated improvements in wireless transmission and PDA screen image resolution will enhance the speed, quality, and quantity of images transmitted. Wireless teleradiology may facilitate convenient rapid evaluation of patients at remote sites.

Delay analysis for CBR traffic under static-priority scheduling

We examine the delay performance of packets from constant-bit-rate (CBR) traffic whose delay is affected by non-real-time traffic. The delay performance is analyzed by solving the nD/D/1 queue with vacations. We obtain an exact and closed form solution, hence obviating the need of any approximations or numerical Laplace inversions. We then provide various numerical results for low-bit-rate transmission links, in which packets can experience large delay. From our quantitative evaluation, we conclude that there exists an optimum packet size for a given delay bound. In extremely slow links, such as modem links, transmission control protocol (TCP) packets should be segmented to reduce the CBR delay. We therefore investigate the delay impact of TCP packet sizes as well.

ATM over ADSL probe in Telecom Italia environment

This paper covers access network performance analysis by deploying asynchronous transfer mode (ATM) over ADSL within the Telecom Italia experimental department “EXANET” (experimental ATM network). In this scenario, data traffic leaves customer site as ATM traffic running over ADSL modem links, it is aggregated via digital subscriber line access multiplexer (DSLAM) at the central office (CO) and then dropped onto the high-speed ATM switching fabric. The Italian telephone company was eager to use ADSL as a way to relieve congestion on their circuit-switched voice telephony system, increasingly bogged down by the growth of the Internet and by long data transmissions.

A demonstration of instant pocket wireless CT teleradiology to facilitate stat neurosurgical consultation and future telemedicine implications

To show the feasibility of wireless pocket teleradiology, brain computed tomography scan images of five neurosurgical emergency cases were received on a pocket computer via a wireless modem link. Viewing times from turning on the pocket computer to viewing the entire image ranged from 4 to 6 minutes. The quality of the images was satisfactory. Reliability in obtaining a wireless internet connection was good, but not perfect. Wireless pocket telemedicine devices carried by specialists may improve the ability of telemedicine systems to gain access to the expertise of specialists. (Am J Emerg Med 2000;18:423-426.

Streaming Multimedia for the Internet

Multimedia streaming enables Web sites to be enhanced with real-time audio and video content. Through the appropriate use of video compression technologies, audio and video content can be delivered directly into the Web browser environment to create a rich mix of text, graphics and multimedia. The audio quality and video window size available to viewers is primarily determined by network access speeds. For the Internet, audio and video can be successfully streamed at rates between 20 kbit/s and 37 kbit/s over a PSTN modem link. In the corporate intranet environment, where higher end-to-end network speeds exist, audio and video can easily be streamed at rates between 56 kbit/s and 450 kbit/s. This paper illustrates how commodity video compression techniques facilitate the introduction of real-time multimedia streaming over IP networks. It describes the technology components within a basic video streaming system and provides an overview of two applications that utilise this technology, namely Intranet TV and BT Results Webcast. The underlying network protocols required to support real-time Internet applications are also discussed and network measurement statistics obtained from Intranet TV and BT Results Webcast are also presented.

Modem link brings benefits

Modem link brings benefits

An evaluation of TCP with larger initial windows

TCP's slow start algorithm gradually increases the amount of data a sender injects into the network, which prevents the sender from overwhelming the network with an inappropriately large burst of traffic. However, the slow start algorithm can make poor use of the available bandwidth for transfers which are small compared to the bandwidth-delay product of the link, such as file transfers up to few thousand characters over satellite links or even transfers of several hundred bytes over local area networks. This paper evaluates a proposed performance enhancement that raises the initial window used by TCP from 1 MSS-sized segment to roughly 4 KB. The paper evaluates the impact of using larger initial windows on TCP transfers over both the shared Internet and dialup modem links.

The potential of Web-based mapping and virtual reality technologies for modelling urban environments

The paper will consider the potential of interactive mapping and virtual reality technologies being developed on the World Wide Web (WWW) for the visualisation, modelling and analysis of urban environments. A range of innovative technologies are being developed that offer different ways of modelling and representing built-form and associated urban information with real-time interaction over the Internet. We shall present a review of the capabilities of the technologies and how they can be applied in the field of planning and design of urban environments. The WWW offers both an interface to, and a delivery channel for, the built environment information as well as being a medium for linking distributed users. We are interested in affordable “off-the-shelf” software that is relatively easy to set-up and use and which requires standard PC-computing power preferable to a home user with a modem link (i.e., not high-end graphics workstations). The advantages and disadvantages which these technologies offer will be considered in terms of the level of realism and interactivity available to the end user. Working examples of these technologies which are being developed by the authors will be demonstrated and discussed throughout so as to qualify this review. The paper will also consider the applications of these technologies in a range of contexts, such as in local planning, urban design, development control, community participation, education and training. The implications for a wide range of potential users including planners, infrastructure managers, built environment students, community groups and interested members of the general public will also be discussed.

Low-loss TCP/IP header compression for wireless networks

Wireless is becoming a popular way to connect mobile computers to the Internet and other networks. The bandwidth of wireless links will probably always be limited due to properties of the physical medium and regulatory limits on the use of frequencies for radio communication. Therefore, it is necessary for network protocols to utilize the available bandwidth efficiently. Headers of IP packets are growing and the bandwidth required for transmitting headers is increasing. With the coming of IPv6 the address size increases from 4 to 16 bytes and the basic IP header increases from 20 to 40 bytes. Moreover, most mobility schemes tunnel packets addressed to mobile hosts by adding an extra IP header or extra routing information, typically increasing the size of TCP/IPv4 headers to 60 bytes and TCP/IPv6 headers to 100 bytes. In this paper, we provide new header compression schemes for UDP/IP and TCP/IP protocols. We show how to reduce the size of UDP/IP headers by an order of magnitude, down to four to five bytes. Our method works over simplex links, lossy links, multi‐access links, and supports multicast communication. We also show how to generalize the most commonly used method for header compression for TCP/IPv4, developed by Jacobson, to IPv6 and multiple IP headers. The resulting scheme unfortunately reduces TCP throughput over lossy links due to unfavorable interaction with TCP's congestion control mechanisms. However, by adding two simple mechanisms the potential gain from header compression can be realized over lossy wireless networks as well as point‐to‐point modem links.

Design of an integrated shallow water wave experiment

The experimental design and instrumentation for an integrated shallow-water surface gravity wave experiment is discussed. The experiment required the measurement of the water surface elevation, meteorological parameters, and directional spectra at a number of locations on a shallow lake. In addition, to acquire data under a wide range of conditions, an experimental period of three years was required. A system of telephone and radio modem links were installed to enable real-time monitoring of instrument performance at eight separate measurement locations on the lake. This system also enabled logging sessions to be optimized to ensure the maximum possible data return from this extended experiment.

Implementation of a World Wide Web Server for the Oil and Gas Industry

Summary The Gas and Oil Technology Exchange and Communication Highway (GO-TECH) provides an electronic information system for the petroleum community for exchanging ideas, data, and technology The PC-based system fosters communication and discussion by linking the oil and gas producers with resource centers, government agencies, consulting firms, service companies, national laboratories, academic research groups, and universities throughout the world. The oil and gas producers can access the GO-TECH World Wide Web (WWW) home page through modem links, as well as through the Internet. Future GO-TECH applications will include the establishment of "virtual corporations" consisting of consortia of small companies, consultants, and service companies linked by electronic information systems. These virtual corporations will have the resources and expertise previously found only in major corporations.

Home reporting for the nuclear clinician?

The computer-based 'home office' is becoming a widely accepted mode of operation for modern businesses. It is implausible to believe that a nuclear medicine department can be covered permanently at a distance by a single physician, but it should be possible to provide cover for colleagues during sickness or at night or weekends. We have used a 486 PC with a high-resolution screen and software provided by LINK Medical Ltd to obtain images from hospital sites using a modem link to ADAC, Bartec and Nuclear Diagnostic SUN workstations. The data were transferred via standard telephone lines to the homes of two of the authors. During a trial period lasting several months, 60 lung scans, 20 bone scans, 1 gastrointestinal bleeding study, 4 leukocyte scans, 5 bone tomograms, 9 renograms, 6 myocardial perfusion tomograms and 2 gated cardiac studies were transferred. The system allowed transfer of a 128 x 128 eight-view lung scan to be completed in approximately 2 min. The program on the PC allowed alteration of individual image contrast, image rotation, cine display and a variety of colour scales to enhance image interpretation. A system to transfer chest X-rays has been developed and typical transfer times are approximately 3.5 min. Within the viewing protocol on the PC, a reporting window was available with the ability to fax the report directly to the hospital. The system allowed consultants who live at a distance from their nuclear medicine departments to provide cover and is now used as an integral part of our out-of-hours service. The system also allows cover of satellite units or to provide cover for junior staff at night or weekends.

Wheel impact load monitoring

The WILD system, which was Introduced to monitor and control damaging track forces by identifylng defective wheels in passing trains accordlng to pre-set limits and reporting immediately by a modem link, is described. Associated cost savings are estimated, recent Improvements are described and future developments are outlined.

New home-delivered training prospects for people with disabilities.

The 'Home-Delivered Training Project' set out to test the viability of providing training in Information Technology to people with physical disabilities in their homes, using computers and modem links. The course included core modules on business applications software and optional modules on more specialist applications. The computer-based approach to instruction included computerized monitoring of student progress, the provision of on-line tutorial support as well as computerized test administration and marking. The 20 course participants, who lived in locations throughout Ireland, were unable to attend conventional training centres because of their limited mobility or other restrictions arising from their disabilities. They differed considerably in terms of disability type, educational qualifications and experience with computers. All but one of them completed the course successfully and were awarded certificates which are recognized in Ireland and the United Kingdom. Overall, they were very positive about the course, mainly because they could undertake it in their homes at a flexible pace to suit their learning patterns and the requirements of their disabilities. They recognized, however, that studying at home required a self-disciplined study routine which was not always easy to maintain. The fact that they were awarded an internationally recognized qualification on completion of the course was an important motivating factor, as it made the course relevant in terms of their employment aspirations.

A continuous UHF monitor for gas-insulated substations

Assessing the condition of a GIS by measuring the UHF signals generated in it by partial discharges gives warning of developing faults. The signals are taken from couplers built into the equipment. The couplers are continuously monitored using special amplifying and detection units connected in a digital optical fiber network. The data collected can also be interpreted by an expert system and an analysis of the situation sent via a modem link to a PC. Laboratory trials of the continuous monitor have been carried out on a test rig of 400-kV GIS chambers. The basic principles of the monitor and the results of its trials are given. >

Intelligent aircraft noise monitoring terminals

Current technology airport monitoring units using, “short Leq” as the data transfer units, allow much more and better data than has been previously possible. With very large internal stores, in the order of 2 megabytes, the new generation of units can simultaneously store raw data elements and full environmental information as well as each aircraft event. The pattern recognition built into the units will allow each noise monitoring terminal on the system to recognize aircraft flying over. Then, by a template comparison technique, it both stores the resultant data and transfers it to a remote hoist for correlation. The terminal incorporates some learning capability to increase the “hit rate” of recognition. Any, or all, of the acquisition parameters in each terminal can be configured from the host using a modem link. In a similar way, diagnostics can be performed from the host without visiting each terminal. Typically, 1 to 2 weeks of raw data and up to 10 000 aircraft events are stored in each terminal. This allows for unattended operations as well as security backup for the host.

Cellular telephone transmission of 12-lead electrocardiograms from ambulance to hospital

Currently, only single-lead, serial telemetry rhythm strips can be transmitted from ambulances. Triage of patients with chest pain and administration of thrombolytic therapy in ambulances is limited by the lack of specific electrocardiographic (ECG) diagnosis. A new technique is described using cellular telephone transmission of simultaneous 12-lead ECGs from ambulance to hospital to overcome this limitation. A portable 12-lead ECG installed in an ambulance was connected via modem link to a cellular telephone and digitized ECG information was transmitted to an ECG device in the hospital emergency room. Paramedics in the field placed adhesive patch electrodes and attached ECG wires. Field ECGs from 23 patients were compared with corresponding transmitted ECGs. There were no differences in heart rate, PR interval, QRS duration, QT interval or R- and T-wave axes. Baseline and transmitted ECGs had identical morphologic characteristics. Differences in R-wave amplitude in 5 transmitted tracings compared with hospital-recorded ECGs resulted in computer diagnosis of left ventricular hypertrophy by voltage, possibly due to differences in patient position. Twelve-lead ECGs can be easily transmitted from a moving ambulance using cellular telephones. This allows diagnosis before hospital arrival, improves prehospital triage of patients and may facilitate prehospital therapy with lidocaine or streptokinase. In addition, the cellular telephone link can convey both verbal and digitized information and thus improve on current telemetry systems.