This paper describes the implementation types of private networks from the viewpoint of equipment and users, and utilization trends from low to high-speed services. Technology trends of private networks from the viewpoint of high-speed and broadband communication, multimedia communication, media access methods and intelligent communication are also examined. A concept for implementing future private networks in the Broadband ISDN (B-ISDN) age, and the major technology and the future efforts to achieve this implementation are discussed. Asynchronous Transfer Mode (ATM) is shown to be the key technology for integrating both various and heavy traffic media communication.

Corporate information communication systems are recently orienting the integration of various kinds of communication services. A PBX and a LAN have been indispensable in the realization of these systems. Some PBXs are orienting towards distributed switching architecture, and LAN systems are increasing their scale. Both requirements can be realized by means of a high speed loop optical fiber network. An integrated LAN should satisfy the required performance as a multimedia LAN and should be provided self-healing functions which heal failures automatically, to enable continuous operation of the entire system. This paper introduces a multimedia LAN, which attaches importance to the self-healing functions, called SHM-LAN. Its system architecture and its characteristics, such as efficient channel allocation are presented. This paper also deals with the self-healing functions and some applications.

This paper presents experiments on a PR4 (Partial Response Class 4) transceiver aimed at using existing telephone-grade twisted pairs. The achievable loop length for typical line codes is first estimated for a wide range of bit rates, assuming that near-end crosstalk (NEXT) is the crucial degrading factor on TTPs. It is shown that a PR4 line code makes it possible to transmit 4 Mbps of data over a loop up to 450 meters long. A low-cost transceiver adopting a newly developed timing extraction method, called LDT (Logically Decided Timing extraction) , is implemented and evaluated. It is experimentally confirmed that 4Mbps transmission over existing TTPs was achieved in the presence of crosstalk and impulse noise.

For providing person-to-person communication as well as improving office work efficiency, demands for multimedia communication services have increased. This paper discusses Integrated Voice/Data LAN (IVDLAN) for handling multimedia communications. First, the IEEE 802.9 IVDLAN working group activities on a user access network which dedicatedly provides a multi-megabit service over an existing unshielded twisted telephone cabling system are summarized. Next, this paper reveals the first commercial IVDLAN product APEX 8000/10 which meets the IEEE 802.9 architecture. A set of an ISDN terminal and an IEEE 802.3 terminal are connected to the node through a terminal adapter. The line rate is 4.096 Mbit/s and the maximum line length is 600m. The IVDLAN node has an 128 Mbit/s burst switching module and a 64 Mbit/s multiple-rate circuit switching module. The flow control in a user-network interface and backpressure control in the burst switching module achieve the data communication with low packet loss.

This paper describes theoretical analyses of a new CRV (Code Rule Violation) collision detection method applicable to an optical CSMA/CD LANs. The new method is based on the ideas combining a partial response (1,0, --1) circuit with the basic CRV collision detection method; the ideas are proposed in IEEE 802.3 committee. The circuit configuration of the new method, however, is different from that proposed in IEEE 802.3 committee. First, the paper outlines the basic CRV collision detection method and shows the problem that it can't detect a collision when identical bits are continuously received. Secondly, a practical circuit configuration of the new method is introduced. To realize large optical dynamic range and stability in collision detection, the circuit is designed not to detect CRVs on noisy zero level signals caused by signal negation with partial response circuits. The calculation formulae are then derived for the basic and the new method to determine the CRV rate with and without signal collision. At a bit rate of 10Mb/s, the CRV rate with and without signal collision is then calculated for the basic and the new method. Finally, the calculation results are compared with each other, and it is clarified that the new method is an effective method to increase CRV rate when signal collision occurs.

This paper proposes a new acknowledgement (ACK) delivery scheme performed in layer two, which gives the highest transmission priority to ACK delivery so as to enable higher ACK transmission speeds in networks using the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access procedure. This scheme is based on the principle of confirming ACK delivery through intentional collision. That is, an ACK is determined to have been received at the source adapter when a packet collision is observed after the end frame delimiter (EFD) of the return-packet. The throughput of a non-persistent CSMA/CD using the new scheme is then analyzed. This throughput is compared to the previously-proposed Acknowledge Ethernet type scheme. The analysis indicates that the new scheme yields a throughput several percent higher than the previous one. Application of the scheme to a 32 Mbit/s fiber-optic passive star network, or SOLARnet, is outlined. The experimental results obtained in a SOLARnet field trial are also reported and discussed.

This paper analyzes the delay performance of 1-persistent CSMA/CD LANs with bus topology and a finite number of heterogeneous stations, each possessing an infinite buffer. The mean waiting time at each individual station is obtained under a light-traffic assumption that the channel is occupied only by successful transmission periods. It is shown that the stations near the heavy-traffic stations gain better performance among light stations and the extent to which the individual delays differ depends on the network configuration as well as the protocol parameters.

In this paper, performance enhancement algorithm in DQDB MAN (Distributed Queue Dual Bus Metropolitan Area Networks) is proposed. DQDB which is standardized by IEEE 802 committee is one of protocols which provide medium access control in metropolitan area networks. In DQDB MAN, a fixed-length slot is a unit for transmission and exchange. Information is transfered by using the slot. The transit delay of the slot has to be small since the slot is not stored in each node. However, the slot having finished information transfer can not be reutilized in downstream nodes. This problem has been discussed by IEEE 802 committee and some societies. This paper proposes new algorithm for improving this point and shows implement scheme to realize it. At first, in this paper, a special node called an erasure node is introduced in a DQDB network and its operation is described. Moreover its implement scheme is shown. In the latter, the performance of this algorithm is evaluated using a queueing model. The result shows the effectiveness of the proposed algorithm.

This paper describes the key areas of support network management in a fiber-optic passive star-configured local area network (SOLARnet) from the view point of lower layer functions. The network manages all network elements including communications control adapters and transmission medium. This is accomplished with a network control terminal that handles management duties such as operation, administration and maintenance. Key areas discussed are architecture and management functions that perform management duties. Management functions used by SOLARnet, together with its systematic outline and protocol are also shown. In a field test, the network operated reliably using the network management functions.

Tohoku University has been constructing the academic information-exchange network TAINS (Tohoku University Academic/All-round/Advanced Information Network System) to link its widely spread campuses and to meet several demands for an intrauniversity network. TAINS, the first network based on OSI, became operational in April 1988. The primary function of TAINS is to connect all the geographically dispersed locations of the university via a high-speed digital network in order to facilitate an easy and efficient interconnection among the various computers, terminals and other scientific equipment. TAINS is constructed as a large-scale local area network of hierarchical structure. In the hierarchical network of TAINS, a backbone network, consisting of two 100 Mbps optical fiber rings, interconnects several small-scale IEEE802.3 networks, each of which span a building or a part of a building. This paper describes the background, the basic design concept and the constitution of TAINS. In TAINS, the inhouse network protocol is OSI-based, and the ring network protocol is based on FDDI. The use of these communication protocols are reviewed and the protocol matching adopted for TAINS is described. Finally, a method for estimating the stable operation of a 2-layer hierarchical network using traffic analysis is given.

This paper is a discussion of the utilization of a campus network at Shinshu University called S-net. S-net was constructed and put into use in 1985, and a total of 48,734 persons made use of S-net in 1990. The structure of S-net is explained and then a description of its current layout is presented. The transmission capabilities of S-net are investigated and the state of utilization of the network is described. The number of S-net users by hour forms a distribution which peaks at 4:00 p.m. and again at 10:00 p.m. Furthermore, a questionnaire survey among S-net users was conducted and the requests and requirements expressed pertaining to the campus network are presented. From these results it can be seen that the demands on the campus network are great. And it was revealed that although a strong desire was voiced on one hand for improvements in the present user environment, requests concerning multi-media networks or connections to off-campus networks exist as well. Finally, the points of improvement of future S-nets based on the opinions and suggestions of the users and six years of actual operating experience with S-net are discussed.

A distributed multiparty desktop conferencing system called MERMAID, is described. This system allows a group of users, seated at their desks, to conduct a meeting from their personal computers (PC). Participants can jointly view and process multimedia conference documents, including text, graphics, scanned images and handwritten figures they are sharing, and they can simultaneously interchange voice and video images through ISDN, IVD-LAN(Integrated Voice and Data LAN which has a common line interface of both ISDN and Ethernet) , satellite network and high speed data network. The MERMAID is implemented by using OS/2 based PCs with electronic writing pads, image scanners, microphone-installed loudspeakers, video cameras, etc. The MERMAID[Sakata90; Watabe90] is designed based on Group Communication Architecture (GCA). GCA is a framework for supporting group cooperative work in a distributed environment. It consists of two models: a function model, which defines hierarchically structured service functions, and a system model, which provides client-server model based service interfaces and multimedia communication protocols. MERMAID has been proven effective and feasible through daily use evaluation by around thirty members, involved in such activities as collaborative software design and development among distributed offices and laboratories.

In this paper we consider the effect of varying routing probability in two parallel M/M/1 queueing systems with dynamic routing under a threshold type scheduling. We also estimate the effect of varying routing probability as well as threshold on the resequencing delay. First we obtain the general expression for state probabilities. Next we estimate the effect of varying routing probability by the numerical calculation and the computer simulation. It is shown that the mean queueing delay can be reduced by varying the routing probability appropriately. Varying the routing probability together with the threshold-type scheduling is more effective to reduce the queueing delay in the variation of the traffic intensity. And besides it is shown that the resequencing delay can be reduced in the wide region of the traffic intensity by employing the optimal threshold and routing probability.

We propose a new multicast ATM switching network, called the Cascade Clos Broadcast Switching Network (CCB-SN). It has the following features. Firstly, the CCB-SN is robust not only for unicast calls but also for multicast calls. Therefore, deterioration of traffic handling performance due to a non-uniform traffic pattern does not occur. Secondly, in the CCB-SN, the cells are replicated after they are partly routed. And so, the delay time caused by the increment of replicas of cells is kept to a minimum.

Generalized expressions for variable transfer functions (VIFs) , v(f,x) , for approximating real transmission chracteristic y₀(f)^u are investigated, which results in several new VTFs that provide error reductions and/or realizations superior to conventional ones. Error reduction is attained through zero forcing (ZF) of errors in terms of u and/or x parameters (ZF- U, ZF-X). It is shown that error reduction for first order VTFs (Linear and bilinear VTFs) depends only on ZF-U. On the other hand, second order VTFs (quadratic and biquadratic VTFs) utilize both ZF-U and ZF-X to attain drastic error reductions. The concept of x range modification is also introduced to contribute design flexibility.

This paper proposes a new service scheme which multiplexes several independent sub-documents onto the main document in a conventional facsimile broadcasting system. These multiplexed facsimile signals are moreover unified besides the voice channels in television system. The scheme does not increase the amount of facsimile signals, thus, it can save the frequency resources and communication channels. In this system, the main facsimile document is open for common subscribers, but the multiplexed sub-documents are delivered only for the special subscribers who are registered to the broadcasting station for each channel.

This paper describes the frequency-domain analysis of a cross polarization interference canceller (XPIC) combined with a waveform equalizer. Analytical formula of the XPIC constructed by a multi-tap transversal filter is described under two-ray fading model. The XPIC performance relative to the correlation between the vertical and horizontal polarizations is also investigated by calculating the post-XPIC residual interference as a parameter of tap numbers. The improvement of disired-to-undesired signal ratio by the XPIC is discussed among three typical fading patterns. When co-polarization is dispersive with the same notch frequency (high correlation) and the cross polarization interference is non-dispersive, the XPIC performance is most degraded. The XPIC performance is better for fading events of non-dispersive co-polarization and dispersive cross polarization interference. Moreover, this paper shows the difference of the XPIC performance between the two types of receiver which obtain the reference signal from either post-equalizer or pre-equalizer.