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Communications, IEE Proceedings-

Issue 1 • Date Feb 1998

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Displaying Results 1 - 8 of 8
  • Throughput analysis of input-buffered ATM switch

    Page(s): 15 - 18
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    The limiting throughput of an ATM (asynchronous transfer mode) switch with input queueing under the FCFS (first-come-first-served) scheme is 0.59. Three policies are proposed in the literature to improve the throughput of the switch: policy A (input expansion policy), policy B (window selection policy) and policy C (cell discarding policy). The author considers, for policy C, correlated traffic where all cells belonging to a burst are routed to the same output port and each traffic source is modelled by an interrupted Bernoulli traffic process (IBP). The results for policy C show that the destination correlation does not affect the throughput, and that the throughput is higher when all input traffic is balanced. Better results for policy B are obtained compared with the simulation results found in the literature. Results show that policy A achieves the highest throughput. The throughput obtained by policy A is higher by 0.07 than that obtained by policy B. For example, with expansion size s=8, the achievable throughput obtained by policy A is 0.94. With window size w=8, the throughput obtained by policy B is 0.87. The throughput obtained by policy C exceeds 0.8 when the input traffic rate is less than 0.5. The throughput, for policy C, is ρ=1-(1-p/N)N whether the input is an IBP or Bernoulli and whether there is destination correlation or not. Simulation data, which are available in the literature for policy B, show better agreement with the author's analytical results than with other analytical results in the literature View full abstract»

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  • Analysis of a leaky bucket control scheme in the signalling system no.7 network

    Page(s): 25 - 32
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    Bursts of correlated messages can be sent through the SS7 network if access is available to user signalling bearer capabilities as specified in the CCITT Q.931 standard. These user-to-user correlated messages would cause an increase in the delay of background telephone traffic consisting of ISDN user part (ISUP) and transaction capability application part (TCAP) which has been primarily transferred through the SS7 network. A leaky bucket (LB) controller is introduced to prevent the correlated messages from degrading the link delay performance of background telephone traffic (BTT). The main purpose of the LB controller is to give appropriate time separation between the correlated messages during which BTT messages can be sent. The authors model the system as a Markov chain and analyse the effect of time separation on the delay performance of BTT at the link transmit queue View full abstract»

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  • Delay spread profiles and receiver performance in a dense multipath environment

    Page(s): 47 - 52
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    Delay spread in communication systems is due to the abundance of multipath reflections. The classical model of wide-sense stationary uncorrelated scatterers (WSSUS) is adopted for the derivation of the received power profile. It is found that there is a gain G(D) in the total received power relative to the direct ray received power in a free-space environment, that increases with transmitter-receiver distance D. The delay spread also increases with D. Using the derived power profile, the performance of a receiver that optimally combines the multipath rays, using side information about the sample channel impulse response, is analysed under Rayleigh statistics for both narrow and broadband signalling. An upper bound on the error rate indicates an improvement by a factor of e-G(D) owing to the multipath diversity combined with spread spectrum transmission. The possible application of these results to indoor communications is discussed View full abstract»

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  • Cell-access control for multiple cell-loss classes in shared ATM output buffer

    Page(s): 8 - 14
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (712 KB)  

    A cell-access control scheme is described for guaranteeing multiple classes of cell-loss quality-of-service (QoS) requirements in an output buffer of an ATM switch shared by multiple connections. A class acceptance controller is proposed which regulates the acceptance of cells of QoS classes based on the state of the queue. Decision functions for the class-acceptance controller are considered with a view to comparing their effects on QoS performance. A queueing analysis uses a discrete-time finite-capacity queueing model and derives important performance measures. The implications of the work are discussed using numerical experiments View full abstract»

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  • Selection of multi-h modulation sets using a stochastic search algorithm

    Page(s): 41 - 46
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    Multi-h CPFSK modulation is simple to implement, spectrally efficient, and has inherent error correction properties. Multi-h requires large parameter sets to obtain high coding gain. Large numbers of combinations may need to be investigated. A fast efficient and thorough search needs to be performed. A search method based on a genetic algorithm known as `population based incremental learning' (PBIL) is described. A number of sets of modulation indices are shown and their performance is evaluated View full abstract»

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  • Bandwidth allocation of virtual paths using neural-network-based genetic algorithms

    Page(s): 33 - 39
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    The concept of virtual paths has become the key technology in ATM networks. A control scheme based on genetic algorithms and neural networks is proposed and applied to the bandwidth allocation of virtual paths in ATM networks. The proposed control scheme is capable of selecting adaptively optimal step sizes of virtual paths according to the traffic characteristics and network environment. As the optimisation problem is constrained, traditional genetic algorithms are no longer applicable to this problem. The authors propose the masked genetic algorithms with seeds (MGAS) to solve the optimisation problem. Simulation results demonstrate the superiority of the MGAS algorithm. To achieve better performance, the relationships among the QOS measures, the evaluation of seed scores, and the selection of relearning data records are discussed. Finally, a simplified control scheme is proposed to reduce not only the complexity of the neural networks but also the processing time View full abstract»

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  • Integration of optimal routing and flow control in ATM networks

    Page(s): 1 - 7
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (652 KB)  

    An integrated approach to routing and flow control in ATM networks is proposed. Traditionally, routing and flow control are carried out relatively independently of each other, however, in the reported approach they are integrated and are strongly coupled in the sense that routing is done according to information obtained by the optimal flow control protocol. The flow control protocol NOBEL is extended to include the routing function. The resulting protocol is computationally attractive and results in improved network performance View full abstract»

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  • Blocking analysis of time-division multiplexed multicast switch with intermediate channel grouping

    Page(s): 19 - 24
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    The blocking performance of circuit switched traffic in a multicast switch with intermediate channel grouping is investigated. The particular switch concerned here is a three-stage time-space-time (TST) interconnection network and performs time-division circuit switching. The input and output stages are time slot interchangers (TSI). The central stage is a time-multiplexed switch with two ports per address. By exploiting the channel grouping at the central stage as well as reducing the average loading at each internal frame, the three-stage multicast switch has potential to remove almost all slot contention blocking View full abstract»

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