Considering digital multimedia broadcasting (DMB) with reverse channels, we propose a novel scheduling algorithm for data dissemination as a combination of push and pull schemes. Collecting statistics of requests from clients, the server partitions the data items into hot and cold sets, according to the number of requests. The broadcast server schedules and broadcasts hot items periodically based on a push algorithm. On an empty slot between hot items scheduled, the server broadcasts a cold item in an on-demand manner based on a pull mechanism. Simulations show that our proposed algorithm allows the server to reach high successful response ratio with practically small response time.

First, we propose a new modeling method for superposed ATM traffic by the MMPP(2), which is a special case of the MAP(2). In this new method, we measure the mean and autocorrelation of cell interarrival times, and the histogram of the number of arrivals during measurement windows of fixed size. The MMPP(2) has interarrival times with a second-order hyper-exponential distribution with coefficient of variation c/sub /spl nu// > 1. However, superposed traffic is often observed to have c/sub /spl nu// < 1. To cover this situation, we extend the MMPP(2) to a MAP(3) by adding a new state with inter-state transition accompanied by an arrival. For the MAP(3) model, we take into account the second moment of the interarrival times. From numerical examples, we observe that both the proposed MMPP(2) and MAP(3) yields very good estimation of the cell loss ratio (CLR) for usual superpositions of voice and/or VBR video sources. However, when we have superpositions from CBR video sources together with other VBR sources, c/sub /spl nu//. is much less than 1, and the MAP(3) outperform the MMPP(2), as expected. The proposed MAP(3) well characterizes the cell scale component as well as the burst scale component of superposed traffic streams.

We consider a common-memory (CM) type N /spl times/ N ATM switch, where CM block consists of K (K /spl ges/ N) separated submemories. We propose an address assignment algorithm to avoid input/output contentions so that we can have the read/write speed of submemories as low as the interface (input/output) port speed. Taking a replication-at-sending approach to multicast, we pursue memory efficiency and maximum throughput. We develop an analytical model to evaluate the system in terms of cell loss ratio and average delay time. In the analysis, we take into account two loss factors causing losses of incoming cells: (1) the failure of scheduling to avoid the input/output contentions and (2) overflow in the CM block. The first factor is dominating and can be significantly reduced by increasing K. From our analytical results compared with simulations, it is observed that we can take K /spl ap/ 3N as a guide of system design.

For the superposition of on/off sources, we propose a real-time computable two-state Markov modulated Poisson process [MMPP(2)] modeling method characterizing the aggregate cell arrival rate and the variance-time curve for cell counts. Numerical examples show that the proposed method yields a good estimation of the cell loss ratio (CLR) in asynchronous transfer mode (ATM) multiplexers. Then, we propose an approximation method for calculating the workload for the MMPP(2)/D/1 system. By considering the workload as an upper bound of CLR of ATM multiplexers, we propose a connection admission control (CAC) algorithm utilizing peak cell rate, sustainable cell rate, and maximum burst size as user traffic descriptors. Using the proposed CAC algorithm, an acceptance decision is made with computational complexities of less than 3000 floating point operations. It is also observed from numerical evaluations that the proposed CAC algorithm yields a high multiplexing gain, compared with other methods in the literature.

We are concerned with a real-time quality of service (QOS) estimation method for ATM statistical multiplexers with heterogeneous ON/OFF sources. We propose a real-time modeling method for the superposed traffic by a two-state MMPP by approximating the density function of aggregate cell arrival rate as a Bellows-like Poisson process. We also investigate a real-time calculation of the waiting time distribution for MMPP(2)/D/1 system to consider an upper bound of the cell loss ratio (CLR) for the finite-buffer system. Numerical examples show that the proposed QOS estimation method gives a good estimation of CLR.

Advanced satellite on-board baseband switching processors have time-space-time (T-S-T) structures which are similar to the terrestrial switching networks (Sw-Nw). Generally, the satellite systems require higher reliability than ground equipment because of more severe environment and lack of repair. This paper proposes fault-tolerant satellite on-board T-S-T Sw-Nw with multiple separated space switches instead of a single spare switch. The authors analyze the mean time to unreliable operation (MTUO), as a performance and reliability index for the T-S-T systems with multiple separated space switches as well as conventional T-S-T systems. The MTUO varies depending on the threshold level of blocking-probability and the offered traffic. In general, T-S-T Sw-Nw with multiple space switches have better performance and reliability than those with the single space switch, and their performabilities are appreciably improved, especially for one additional spare space switch. This study can be extended to analyze the performance and reliability of entire satellite communication systems including the on-board baseband Sw-Nw, Rx interfaces, and Tx interfaces.