Area Network Access Research Articles

Printed dual‐band monopole antenna for 2.4/5.2 GHz WLAN access point

AbstractA new design of the printed trident monopole antenna for applications in 2.4/5.2 GHz dual‐band wireless local area network (WLAN) access points is presented. The trident monopole antenna comprises a central arm for the 2.4 GHz band (2.4–2.484 GHz) operation and two side arms for the 5.2 GHz band (5.15–5.35 GHz) operation. The obtained impedance bandwidth (1.5:1 VSWR) for a constructed prototype covers the required bandwidths of the 2.4 and 5.2 GHz bands, and the maximum antenna gain reaches about 4.0 and 5.5 dBi across the 2.4 and 5.2 GHz bands, respectively. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 286–288, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10585

A network management architecture for robust packet routing in mesh optical access networks

We describe an architecture for an optical local area network (LAN) or metropolitan area network (MAN) access. The architecture allows for bandwidth sharing within a wavelength and is robust to both link and node failures. The architecture can be utilized with an arbitrary, link-redundant mesh network (node-redundancy is necessary only to handle all node failures), and assumes neither the use of a star topology nor the ability to embed such a topology within the physical mesh. Reservation of, bandwidth is performed in a centralized fashion at a (replicated) head end node, simplifying the implementation of complex sharing policies relative to implementation on a distributed set of routers. Unlike a router, however, the head end does not take any action on individual packets and, in particular, does not buffer packets. The architecture thus avoids the difficulties of processing packets in the optical domain while allowing for packetized shared access of wavelengths. We describe the route construction scheme and prove its ability to recover from single link and single node failures, outline a flexible medium access protocol and discuss the implications for implementing specific policies, and propose a simple implementation of the recovery protocol in terms of state machines for per-link devices.

Remote handling of TEXTOR diagnostics using CORBA as communication architecture

At the Forschungszentrum Jülich, an upgrade of the existing distributed system for data acquisition (DAS) at the fusion experiment TEXTOR94 is under development. DAS is currently restricted to VAX/VMS and DECNET based communications, but it is planned to add UNIX based systems, and to open the local network for an improved wide area network access for remote operations. Therefore, the DAS system is to be equipped with a suitable client/server interface, which is able to cope with the various computer platforms and operating systems involved. For this purpose, the common object request broker architecture (CORBA) will be used. CORBA is an object oriented, standardized architecture for distributed systems, which provides a high degree of modularity in software design and allows for flexible implementations. It is to act as a connecting link between the existing system and new extensions. In order to provide the desired client/server functionality for the data acquisition tasks, the components of the system (diagnostic, database, etc.) are modelled by CORBA interfaces. Processes for diagnostic control and data readout in the existing OpenVMS systems are aimed at to be accessible by CORBA server implementations. The corresponding client implementations will be developed for the operating system platforms most frequently used at TEXTOR94. Communication between clients and server will be based on TCP/IP and are to be managed by CORBA. By this standardized way, remote control of diagnostic instrumentation becomes possible in a multiplatform computer and wide area network environment. At a later stage it is intended to integrate the system into a ‘virtual control room’ environment, which should enable the participation of cooperating institutions in the full experimental program of TEXTOR94.

Optimizing Inquiry Activities in a Corporate Drug Information Department

A system is described which is used by a medium size pharmaceutical company for responding efficiently to professional inquiries and which has been integrated into traditional medical information department activities. Characteristics contributing to its success include structured telephone call handling, closely monitored and frequently updated form letters, response time performance criteria, use of a centralized inquiry database, local area network access to commercial literature databases, and ongoing quality control and assessment of inquirer satisfaction.

Performance of a distributed control LAN access protocol supporting voice and data traffic

This paper describes a local area network access protocol for integrated voice and data communications in a token passing ring. The transmission scheme is decentralized and suitable for both voice and data services. In this system access delay for voice packets can be bounded to a desired upper limit, even at heavy network load. The quality of speech remains unaffected at any level of offered data load and all voice packets are served within the specified delay limit. The protocol provides equal priority to pure data at normal network load while voice is given priority over pure data at heavy network load. The delay-throughput characteristic of both voice and data traffic has been evaluated at a transmission speed of 10 Mb s-1 and it is shown that the mean delay for voice packets, at heavy data load, can be limited to a value equal to half the threshold token rotation time.

Relative Performance Of Two More CD‐ROM Network Access Products

Continues with the second in a series of articles evaluating CD‐ROM local area network access products on the market. The software packages evaluated in this article are: CD Connection and Starport. Describes the comprehensive testing carried out and suggests uses for each package based on its relative merits.

Replacing the Ethernet access mechanism with the real-time access mechanism of Twentenet

The way in which a Local Area Network access mechanism (Medium Access Control protocol) designed for a specific type of physical service can be used on top of another type of physical service is discussed using a particular example. In the example, an Ethernet physical layer is used to provide service to the Twentenet real-time access mechanism. Relevant Ethernet and Twentenet concepts are explained, the approach taken is introduced, and problems encountered, along with the actual synthesis of both networks, are described.

Performance investigation of a token passing access protocol for a multichannel optical fibre LAN

An alternative approach to multichannel local area network access is described. The new multichannel access scheme or protocol is based on a token passing arbitration policy. It is specifically intended for use with a starconfigured optical fibre LAN employing wavelength division multiplexing technology in order to provide a multichannel transmission medium. The multichannel network architecture comprises a single reservation channel and several equivalent speed data channels. Delay versus throughput performance characteristics for the network obtained by both analysis and discrete event simulation are shown. The multichannel token passing protocol is found to significantly improve these characteristics in comparison with a conventional single channel token passing approach using the same overall network transmission rate (i.e. the sum of the individual channel bit rates in the multichannel case). Furthermore, when the end-to-end propagation delay for an individual channel on the network becomes large, the multichannel token passing protocol is shown to exhibit an improved delay versus throughput performance over a multichannel protocol employing carrier sense multiple access with collision detection.

Low‐level programming in modula‐2: An experience with local area network access

AbstractAccess to a computer network, which is currently a topic of some importance to the high‐level language programmer, can be provided in a number of ways. This paper describes one such example, where users of the language Modula‐2 were given access to a local area network. The author discusses the type of problem that needs to be overcome, when a language such as Modula‐2, which was designed as part of an integrated systems architecture, is used for low‐level programming in a different architectural environment.

Scheduled bus protocol for mixed voice and data local communications

This paper discusses a local area network access protocol for voice and data communications in a collision-free bus. The transmission scheme is decentralized and suitable for both voice and data services. In this system, access delays for voice packets can be bounded to a desired upper limit by imposing restrictions on data transmission. The delay-throughput characteristic for both voice and data traffic has been evaluated for various traffic conditions at transmission speeds of 10 and 20 Mbit/s.

Three Typical Blocking Aspects of Access Area Teletraffic

In this paper, an effort is made to represent the military access area grade of service (i.e., probability of blocking) in a more realistic way than before. The circuit switching process is structured into three representative contention phases. The three phases are analytically tractable and are rather typical in existing military networks. All three phases apparently have service properties not accurately described by the conventional Engset, Erlang, and other classical models. Their blocking probabilities also differ from those predicted by the classical models. Given an access area network, the three blocking models may be applied individually or in a variety of combinations. The paper demonstrates several applications to typical access area telephony.