Network management technologies based on network-wide real-time control schemes have become significant in ensuring both high throughput and GOS fairness and maintaining high usage of network facilities. The first part discusses the roles of network control schemes in the network resource hierarchy. With respect to the layering concept for network resources, it is clarified as to why each network control scheme should maintain its autonomy in each corresponding network resource layer, as well as cooperate with the other control schemes. Examples of cooperative control are presented to show that both dynamic routing in the circuit layer networks and path assignment control in the path layer networks can mutually compensate each other for any insufficient control. In the second part, an advanced routing scheme called "State- and Time-dependent Routing (STR) " is proposed. The principle of STR is a combination of routing-domain definition on a time-dependent basis and call-level routing on a state-dependent basis. Performance evaluation examples of STR through large-scale call-by-call computer simulations are presented to show its high throughput performance as well as high adaptability to real-time traffic fluctuations. A system configuration example featuring the STR algorithm which is currently under development for use in NTT's transit networks is also shown.

There is a rapidly growing need for making high capacity digital global networks resilient to variations in traffic load and network element failures. This can be accomplished by robust network engineering and greater network flexibility. The primary vehicles for achieving network flexibility objectives are dynamic routing and/or dynamic capacity allocation techniques. This paper presents an overview of the recent progress and new challenges in developing those advanced network control methodologies for global networks that exploit revolutionary new telecommunications technologies.

The telecommunication network is a complex system. So, it needs an enormous computation to control a network optimally. The fuzzy control is a very useful method to deal with such a complex problem. This paper discusses an application of hierarchical fuzzy system to dynamic routing. The performance is compared with some other control methods, and it is shown that the hierarchical fuzzy system has a good performance for a wide range.

In this paper, we study an algorithm of route optimization using the first-derivative length (FDL) path in a hybrid-switching network with movable-boundary for heterogeneous traffics, and investigate the interactions among four different classes of traffics in a time division multiplexing (TDM) network. This algorithm has some desirable properties compared with the gradient projection method or the flow deviation method. That is, it requires no initial specification of traffic flow, and the convexity of the objective function is not required. The numerical results show that the solution is close to the optimal solution and this method yields a substantial improvement in convergence time over the gradient projection method.

Several advanced call routing systems have been proposed for transit planes of PSTN. The paper addresses the question to what extent the routing sophistication increases the traffic handling capability of these planes. Situations with nominal traffic, its fluctuations, equipment failures and overloads are discussed. It turns out that a simple alternative routing system with a routing patterns reconfiguration facility will ensure a major percentage of the benefits achievable with more sophisticated routing systems.

A hybrid controlled dynamic routing scheme called State- and Time-dependent Routing (STR), has been proposed for telephone networks. The STR is characterized by two-level control processes: routing domain definition and call-level routing. In the routing domain definition, a set of possible alternate routes for each origin-destination node pair for each time period of the day is determined once a week by a centralized control method. In the call-level routing, each exchange determines a near-optimum alternate route from the set of possible alternate routes, which is determined in the routing domain definition process according to only the network information obtained in the call-connection processes. This paper proposes advanced call-level routing schemes for improving the performance of the basic STR. Call-by-call computer simulation of call-level routing schemes under unbalanced traffic conditions and focused overload conditions shows that the advanced schemes can achieve high performance with minimal changes of existing exchange software and operations systems. The performance of the advanced scheme based on isolated control capabilities built into each exchange is close to that of an ideal state-dependent scheme that is based on centralized control capabilities and uses data on the status of the entire network.

This paper proposes an algorithm for cooperative control over both logical (switching) and physical (transmission) networks for multiservice environments. The control of the logical networks, which conduct traffic routing in response to demands for grades of service, is cooperatively performed with the control of the physical network, which allocates capacity based on the network topology and its resources. A case study is carried out to evaluate the usefulness of the proposed cooperative control method. The case study results show the proposed method provides grade of service satisfaction for a wider range of network condition and improvements in throughput compared with the separate logical or physical network control method. In addition, the application of the proposed control method to ATM networks is discussed.

Cost minimization and enhancement of robustness are the major objectives in the design and control of corporate networks. The trade-off between private facility cost and expense for public network use is an important cost-effectiveness criterion. In this paper, we propose a traffic control method which minimizes cost for public network usage in the international corporate networks under both normal and abnormal conditions. The method is a combination of alternative routing and dynamic trunk reservation in which the number of reserved trunks at a link vary with 24-hour profiles of traffic and public network charges between nodes. An analytical performance evaluation method is described, and the effectiveness of the control method is evaluated based on numerical examples.

Multicast routing problem is one of the essential problems for supporting multicast and broadcast communication service which is the most important service of the multimedia information networks. Multicast routing is the problem of finding out an adequate path which connects one source node and more than one destination node, i.e. a tree shaped path. In packet type networks, a packet for multicast communication should go through the tree shaped path as making its copies at a branching node for efficient use of network resources. However, concentration of packet copy operations at a particular node leads to performance degradation of other calls which go through this node. In this paper we propose two multicast routing algorithms which distribute packet copy operations through whole nodes in the multicast path; a link added type algorithm and a loop constructed type algorithm. Both algorithms, at first, find out an approximate solution for minimum cost path, and avoid concentration of packet copy operation at a little sacrifice of total cost in the path. Computer simulation results show that these algorithms can decrease the burden of packet copy operation per a node at the sacrifice of increase in average distance (cost) of a source-destination pair but the sacrifice of total cost is very small.

Asynchronous Transfer Mode (ATM) technology is expected to be used in constructing a B-ISDN. ATM networks must support a variety of services, e.g., voice, data, and image communications with different grade of service requirements. The demand for these services and their traffic characteristics, however, are not yet clear. To implement B-ISDN under this situation, it is necessary to establish a network control scheme that can' absorb the difference between the estimated traffic and the traffic that is actually offered. In ATM networks, virtual path bandwidth control is a key control scheme for absorbing this traffic estimation error, and several control algorithms have already been proposed. When we try to further utilize the VP resource by dynamically reallocating the bandwidth according to the short-term traffic variation, however, we need control schemes that are highly responsive. This is achieved by using control intervals that are shorter than the intervals over which traffic fluctuates. Control algorithms based on central controllers generally need to collect a large amount of information from geographically widespread network facilities and solve a large optimization problem. This can make them difficult to use with short control intervals in large networks. An alternative enabling the shorter control periods is to use multiple distributed controllers that use only local information. This paper proposes two new VP bandwidth control algorithms suitable for this distributed implementation. In these algorithms, decentralized controllers are located at network nodes including ATM switch (ATM-SW) or ATM cross connect (ATM-XC) function, and each controller observes the quality of the VPs relevant to it. The bandwidth is modified successively as these distributed controllers communicate with each other. We therefore call this method "successive modification method" (SMM). Numerical evaluation using a model network shows the effectiveness of these algorithms for preventing the performance degradation caused by large-scale traffic imbalance within a network. Comparison with the batch modification method (BMM), which has no feedback effect, shows that the proposed SMM with approprate control intervals can be more responsive to traffic variation over time, but is slightly inferior when network conditions are static.

This paper evaluates the performance of the statistical multiplexer with selective cell discarding (SCD) control in asynchronous transfer mode (ATM) networks. The multiplexer integrates delay-sensitive traffic such as voice or video and loss-sensitive traffic such as data, for which cell arrival processes are of bursty nature. The SCD control scheme is incorporated to prevent the systems from congestion as well as improve the system efficiency. It is based on the embedded ADPCM coding technology to packetize the delay-sensitive (voice & video) information into two kinds of cells: more significant part (MSP) cells and less significant part (LSP) cells, and priority is assigned to the MSP cells. When the system congestion occurs, the LSP cells are selectively discarded to reduce the congestion. In this paper, by approximating the two types of bursty inputs with respective Markov modulated Poisson processes (MMPP) and the fixed cell service time with k-Erlang distribution, we model the system under consideration as a queueing model MMP₁^[x]+MMPP₂/E_k/1/m(m₁), . Such a queueing model is analyzed by means of the matrix-analytic method, and the individual performance measures are derived. Numerical examples are shown to demonstrate the effectiveness of the SCD control scheme.

The cutoff rate of Multi-pulse Pulse Position Modulation (MPPM) is evaluated in noiseless photon counting channel. The cutoff rate per slot and the cutoff rate per photon are shown for MPPM. It is found that MPPM performs better than PPM in the practical range of average number of photons per pulse. Moreover, it is shown that, in the case with binary digit, MPPM can be seen as the parallel combination of completely correlated binary erasure channels (BECs). From this perspective, both the capacity and the cutoff rate are investigated. It is shown that the capacity of MPPM is larger than the sum of the capacities of BECs, but that the cutoff rate of MPPM is smaller than the sum of the cutoff rates of BECs when a large number of bits are transmitted in one frame. Therefore, it is found that, when large number of bits are transmitted in one frame, coding/decoding on each BEC independently has advantages in system complexity rather than coding/decoding over BECs jointly to achieve a given bit error probability.

The static and dynamic characteristics of a zero-voltage-switched half-bridge converter are analyzed quantitatively. This converter is controlled by Pulse-Width Modulation with the asymmetrical drive of a pair of semiconductor switches, and. the zoro-voltage switching is maintained by the partial resonance during the OFF interval of both switches. The effects of circuit parameters such as the input capacitance, the resonant inductance and capacitance, and the transformer leakage inductance are discussed through the comparison of analytical and experimental results.

Characteristics of a cavity-backed annular slot antenna with one point shorted are investigated. Resonance frequencies, bandwidths and radiation patterns with respect to a slot width and a slot shorting position are studied experimentally. By selecting a slot shorting position, the bandwidth of more than 10% for the input impedance and circular polarization of the bandwidth of about 3.2% for the axial ratio are obtained.