Mesa structures have been investigated to optimize a buried-heterostructure (BH) for a GaInAsP/InP surface-emitting (SE) laser regrown by metalorganic chemical vapor deposition (MOCVD), and it has been found that a square mesa top pattern of which the sides are at an angle of 45 to the 011 orientation is suitable. A 1.3-µm GaInAsP/InP square buried heterostructure (SBH) SE laser with this mesa structure has been demonstrated and low-threshold CW oscillation (threshold current Ith=0.45 mA) at 77 K and low-threshold room-temperature pulsed oscillation (Ith=12 mA) have been obtained.

A GaAs defferential oscillator IC with on-chip LC resonator has been developed for suppressing the relative intensity noise (RIN) of a laser diode. The relationship between the Q-factor and minimum supply voltage for oscillation is fully described. In view of reducing the present LC resonator, we made use of BST (Barium Strontium Titanate) capacitor to make the resonator without increasing the chip area. The oscillation frequency is stable since it's determined by the geometry of the resonator. The experimentally fabricated oscillator IC achieved the output power of 12 dBm at the frequency of 600 MHz with voltage/current conditions of 2 V/20 mA. The present IC keeps quite stable RIN value less than -138 dB/Hz under the light-feedback condition up to 10%.

This paper proposes a requirement description and elicitation approach for communication services. Requirements are described in natural language, refined with a knowledge base, and converted to a formal language for program generation. A model for communication services is made as a set of three items: terminal state, terminal action and the response of the communication system to the action. This set, in turn, corresponds to natural language syntax that expresses two conditions (terminal state and action) and their result. These conditions and result are expressed as a sequence of simple sentences that describe the relationship between a terminal and a communication system. Thus, by defining such a description style to reflect the features of communication services, it should be possible to achieve both a high level of description and mechanical processing capabilities at the same time. However, requirement descriptions usually include omission and inconsistency. This problem cannot be solved by merely introducing natural language for the descriptions. Knowledge about the target domain of requirements is needed to resolve it. This paper reports on a knowledge base that stores constraints existing between conditions and results in communication services. This knowledge base is shown to be effective in supplementing omissions and resolving inconsistency. This paper also presents a technique for converting the elicited requirements in natural language to descriptions in a formal language that can be used to generate a program.

In this paper, we analyze the traffic data management requirements of the customers, describe the functions of the traffic database needed to satisfy their requirements, and propose a highly distributed database system which can efficiently implement these functions. Finally, we report the results of system performance evaluations.

In this paper we propose a two-stage address coding scheme to transmit two data symbols at once within a frame in a MFSK/FH-CDMA system. We compare it with the conventional system using single-stage address coding. Assumed that the address codes of all users are known in the receiver. A multiuser detection scheme is applied and the performance is evaluated by computer simulations to show the improvement in bit error rate (BER) compairing to the conventional system. We also investigate the performance of error-correcting coding and decoding in the two-stage address coded MFSK/FH-CDMA system. An erasure decoding scheme is modified for the two-stage address coded system and is utilized to improve spectral efficiency or to increase user capacity in the MFSK/FH-CDMA system. Finally, we investigate a hybrid scheme of combining the multi-user detection scheme and the error-correcting decoding scheme for the two-stage address coded MFSK/FH-CDMA system. The performance is evaluated by computer simulations.

This paper gives several explicit formulas for the waiting times in each stage in an alternating-service, two-stage tandem queue (M/G/1 type queue) with a gate in the first stage and server vacations (or setup time). These formula are obtained by using simple conversion relationships between the performance measures. This study has been motivated by the performance evaluation of call (packet or message) processing in telecommunication switching systems.

This paper presents the concept of k-FR circuits. The controllability of such a circuit is high due to its special structure. It is shown that all stuck-at faults and stuck-open faults in a k-FR circuit can be detected and located by k(k1)1 test vectors under the highly observable condition which assumes the output of every gate to be observable. k is usually two or three. This paper also presents an algorithm for converting an arbitrary combinational circuit into a k-FR circuit. A k-FR circuit is easy to test when using technologies such as the electron-beam probing, the current measurement, or the CrossCheck testability solution.

In the course of the development of the "Hyper Hospital," a novel medical care system constructed in the computerized information network using virtual reality as its human interface, we devised a virtual reality world creating system which allows users to con figure the world interactively. The re-configuration of the virtual world was designed to be carried out without interruptions of activity and the world can continue to exist during the reconfiguration process. This facility comprises an important part of our Hyper Hospital system because one of our major goals of this proposal of the Hyper Hospital is to restore maximum freedom for patients in the medical care system. Discussion was given in the present study with respect to the basic requirements of the system to be realized, including discussions on the permission given to the participants of different levels, and means by which to modify the structure of the virtual world. A preliminary implementation was described following this general consideration. The developed prototype was shown to be practically suitable to the test of our virtual environment applied to realistic medical scenes.

Currently there is considerable world-wide speculation regarding the introduction of optical fiber cable into access networks, because optical fiber has a big potential for providing attractive multimedia services. Since optical fiber cable can provide a variety of grade of services, high-reliability of cable networks would be required compared with the conventional copper cable networks. To develop multimedia telecommunication networks as an infrastructure, it is urgent to clarify the highly reliable optical fiber cable network architecture. Since cable network architecture deeply depends on regional conditions such as demand, area size, duct layer networks (consisting of ducts, manholes, tunnels, feeder points etc.), it is necessary to develop a cable network designing tool with user-friendly interfaces for efficiently evaluating cable network architectures. This paper firstly proposes the heuristic algorithms enhanced by the disjoint-shortest-path and the depth-first-search methods that would be applicable for real access networks. Secondly, the design method of highly reliable optical fiber cable network based on the heuristic algorithms in terms of network cost and unavailability caused by cable breakdown is proposed. It can design the combination of star- and loop-shaped (where two diversified routes exist between a feeder point and central office) cable network. Furthermore, comparison with the conventional design method which simply applies star- or loop-shaped cable network is done in terms of economy and reliability on real access networks in the Tokyo metropolitan area. It is concluded that the proposed method can reduce the network cost further and realize a short unavailability value compared with the conventional method.

This paper studies routing methods for the complete broadcast multipoint-to-multipoint communication. For a Z-node (Z-site) of the participants of the connection, each site transmits one signal and receives Z-1 signals. The routing method based on connecting each participant by multiple directed point-to-point circuits uses wasteful bandwidth that the source-to-destination data may be duplicated needlessly. We propose routing methods that the connection approach is based on setting multicast tree routes that each participant (site) has one own multicast tree connecting to the other participants under two constraints: the delay-bounded constraint of source-destination path and the available constrained bandwidth for the service of links. For this routing approach, we propose both heuristic algorithm finding approximate solution and search enumeration based algorithm finding optimal solution, and compare the approximate solution with the optimal solution. This approach can lower costs for the subscribers and conserves bandwidth resources for the network providers.

The intermodulation distortion (IMD) due to laser diode (LD) nonlinearity of an asynchronous direct-sequence code division multiple access (DS/CDMA) system in optical transmission is analyzed. A third-order polynomial without memory is used to present LD nonlinearity. In DS/CDMA systems, only one harmonic of the third-order inter-modulation term falls on the signal frequency band and influences the system performance. The average distortion is derived with only the information of autocorrelation functions. The results are useful for CDMA system design and performance analysis. With LD nonlinearity it is necessary to select an optimal modulation index that provides a maximum signal-to-noise ratio (SNR). The analytical method is applicable to other general nonlinearities in CDMA systems.

When communication network planning-design is performed, especially in a short-term case, it is important to utilize existing facilities in the construction of the new network. In this paper, link capacity assignment problem (CA problem) for packet-switched networks is investigated with the consideration of the existing network. To deal with this, per-unit cost of existing link capacity is thought to be less than that of newly installed capacity and a link cost function is modeled by a non-linear, non-differentiable one which is composed of two portions of capacity cost. After formulating the CA problem, two optimum algorithms derived from Lagrange multiplier method are presented and a modified algorithm is used for solving the CA problem in order to reduce the computation time. Some numerical results show that according to the values of link traffic flows, there will be links whose capacities must be set equally to the existing values. Moreover, when link cost difference is introduced in the CA problem, the number of links that the capacities of which have to be changed from existing values is less than that of linear cost function case, i.e., the case without consideration of the cost difference in link capacity.

Next generation personal communication systems will provide a range of different services to moving users. In parallel, packet switching is being proposed as a way to statistical multiplexing and hence to better resource exploitation. The co-existence of different services may prove difficult due to the different requirements on quality of service parameters like packet loss, delay, and so on. This requires a careful design of Call Admission Control policies, which are to be quite different from those used in fixed network, due to two phenomena which are typical of mobile systems, namely co-channel interference and handovers. In this paper we address these complex topics, and propose some basic rules for Call Admission Control policies suitable in this context.

We propose a new concept of network dimensioning, which is based not only on the grade of service but also on profit. In traditional network dimensioning methodology, the number of circuits on links is designed under a cost-minimization concept with grade of service constraints. Recently, telecommunication markets have become very large and competitive; therefore, we believe that a profit viewpoint is now essential. However, it is difficult to calculate profit in almost all the dimensioning methods currently used, because they mainly employ peak-hour traffic data, while profit depends on all the hourly traffic data which contain both peak and off-peak data. In this paper, we propose using all the hourly traffic data in network dimensioning. From these data and telephone charges for each hour, revenues will be estimated. On the other hand, facility costs will be estimated from the number of circuits. Finally, we can estimate profit from the difference between revenues and facility costs. Focusing on both quality and profits in network dimensioning leads to more advanced quality management and quality control in telecommunications networks than with traditional methodology. This paper outlines a dimensioning method based on profit, and describes its properties, some applications of it, and summarizes further studies.

This paper proposes a hybrid access control scheme for broadcast-based ATM-LANs. Broadcast-based ATM-LANs are shared media networks with star topology. In this network, packets are broadcast to all subscriber terminals by a CPYF (Cell COPY Function) node located in the ATM network and only relevant packets are extracted and sent to the destined user layer function by packet filtering functions in the terminals. The simplicity of the packet transfer mechanism makes the network very economical. In broadcast-based ATM-LANs, the hybrid access control scheme is effective in improving performance. In this scheme, short packets and long packets are transmitted respectively by means of a back-pressure type and a CSMA/CD type access control scheme. Throughput evaluation was performed by computer simulation and the results show that the proposed scheme achieves a high throughput characteristic.

This paper studies congestion control schemes for integrated variable bit-rate (VBR) video and data communications, where the quality of service (QOS) of each medium needs to be satisfied. In order to control congestion, we exert here either dynamic resolution control or QOS control. The dynamic resolution control scheme in this paper dynamically changes the temporal or spatial resolution of video according to the network loads. The QOS control scheme here assigns a constant capacity of buffer to each connection and determines the video resolution in order to guarantee the QOS of each medium at the connection establishment. The performance of these schemes is evaluated through simulation in terms of throughput, video frame delay probability distribution, and video frame loss rate. We also examine the effects of priority scheduling and packet discarding on the performance. Numerical results indicate that both dynamic resolution and QOS control attain low delay jitters as well as large video and data throughput. In particular, the QOS control is shown to be more suitable for integrated VBR video and data communications.

This paper reports an overload control method for the Intelligent Network (IN). The IN, which is being investigated as a future communication network, facilitates both rapid introduction of new services and easy modification of existing services. In the IN, the call processing functions and data needed to achieve IN services are distributed over several nodes. Therefore, traffic demand for the various services may cause varying patterns of node overloads. It is therefore important to develop effective overload control methods and to evaluate their characteristics. We propose an overload control method and evaluate its characteristics in comparison with other methods under various overload traffic patterns with a network simulator that models all nodes and their relationships in the IN. In particular, we focus on three aspects of overload control: how can high throughput be maintained, how can an overloaded node be stabilized, and how can fair access be guaranteed.

The recent progress of B-ISDN signaling systems has enabled networks to handle calls which require a wide variety of ATM connection sets. This paper is concerned with the circuit group which handles calls requesting asymmetric forward and backward multi-connections, and has the capability of both bandwidth negotiation and bandwidth reservation as a traffic control for enhancing call blocking performance. A model of the circuit group is first established focusing on the call level characteristics of the group, and then a method based on the reduced load approximation and an approximate analysis of a multirate group is proposed for calculating approximate blocking probabilities. The accuracy of the approximation method is evaluated numerically by comparing with an exact method and simulation. Further the impact of bandwidth negotiation and reservation on call blockings is examined based on numerical examples.

Data communication by using TCP/IP is one of important services on ATM networks. At one approach in traffic control of this service, the dedicated bandwidth for data transfer is not guaranteed and the feedback congestion control to prevent cell loss is performed in the congestion case. However, when a large quantity of data is transferred within a short period, this traffic control cannot be expected to achieve high efficiency. In this case, it is suitable that the dedicated bandwidth is guaranteed by FRP (Fast Reservation Protocol) before the data is transferred. This paper describes that FRP is superior to the feedback congestion control for large size data transmission. Next, it proposes a selectable traffic control which selects adaptively one of the feedback congestion control and FRP.

This paper discusses two approaches to statistical multiplexing: rate envelope multiplexing, allowing resource sharing with small delays for low peak rate connections, and rate sharing, based on the use of large multiplexer buffers to ensure high link utilization for high speed data traffic. We argue that the weighted fair queueing scheduling algorithm provides an efficient means for combining both kinds of multiplexing in the B-ISDN. A feasible implementation known as Virtual Spacing is outlined. We illustrate the flexibility of the proposed scheme by showing how different service categories could be provided.