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Communications, IEE Proceedings-

Issue 56 • Date 2002

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Displaying Results 1 - 10 of 10
  • Multiple additively constrained path selection

    Publication Year: 2002 , Page(s): 237 - 241
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (417 KB)  

    Finding a feasible path subject to multiple constraints in a network is an NP-complete problem and has been extensively studied. However, current algorithms suffer either high computational complexity or low success ratio in finding feasible paths. The authors propose a novel extended Bellman-Ford algorithm (EB), from which they present a high-performance algorithm with low computational complexity in finding feasible paths with multiple additive constraints. Through analysis and simulations, it is shown that the algorithm outperforms its contenders in the success rate of finding a feasible path as well as in terms of scalability; the proposed algorithm can achieve almost 100% success ratio as long as a feasible path exists. Furthermore, the worst case computational complexity is only twice that of the Bellman-Ford algorithm. View full abstract»

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  • Neural approach to detecting communication network events

    Publication Year: 2002 , Page(s): 257 - 264
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (540 KB)  

    The Internet and associated network technologies are an increasingly integral part of modem day working practices. With this increase in use comes an increase in dependence. For some time, commentators have noted that given the level of reliance on data networks, there is a paucity of monitoring tools and techniques to support them. As this area is addressed, more data regarding network performance becomes available. However, a need to automatically analyse and interpret this performance data now becomes imperative. The paper takes one-way latency as an example performance metric. The term 'data exception' is employed to describe delay data that is unusual or unexpected. Data exceptions can be used by network operators to assess the effect of network modifications, failures and usage, and can also help in the diagnosis of intermittent network faults. Automating the detection of data exceptions is a non-trivial process that is not well suited to a rule-based solution. The paper shows that data exceptions can be identified by the use of a two-stage approach. The Kolmogorov-Smirnov test can initially be applied to detect general changes in the delay distribution, a neural network can then be used to categorise the change. The approach is evaluated using a network simulation. View full abstract»

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  • Fault localisation and recovery in multichannel ATM switches

    Publication Year: 2002 , Page(s): 283 - 291
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (617 KB)  

    One of the important advantages of multichannel switches is the incorporation of inherent fault tolerance into the switching fabric. For example, if a link which belongs to the multichannel group fails, the remaining links can assume responsibility for some of the traffic on the failed link. On the other hand, faults occurring in the switching elements can lead to erroneous routing and sequencing in the multichannel switch. The authors investigate several fault localisation algorithms in multichannel crossbar ATM switches with a view to early fault recovery. The optimal algorithm gives the best performance in terms of time to localisation but is computationally complex, which makes it difficult to implement. The authors develop an online algorithm which is computationally more efficient than the optimal algorithm. They evaluate its performance through simulation. The simulation results show that performance of the online algorithm is only slightly sub-optimal for both random and bursty traffic. Finally, a fault recovery algorithm is described which utilises the information provided by the fault localisation algorithm. The fault recovery algorithm provides additional rows and columns to allow cells to be routed around the faulty element. View full abstract»

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  • Multirate asynchronous optical CDMA system with product code

    Publication Year: 2002 , Page(s): 299 - 304
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The authors propose a new architecture for a multirate asynchronous optical CDMA (code division multiple access) system. An optical orthogonal code (OOC) is employed as the signature sequence. The serial multirate data is converted into parallel information bits and then transmitted simultaneously via spatial channels. Exploiting the essence of parallel transmission of spatial channels, the product code (i.e. rectangular code) through an extra protection channel performs error control, which can significantly improve the system performance. The authors' proposed scheme requires only one laser diode, sequence encoder and product-coded encoder/decoder. Moreover, the adverse impact of multiple access interference, APD (avalanche photodiode) noise and thermal noise are taken into consideration in system performance analysis. View full abstract»

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  • Modelling of a VSAT link physical layer fade countermeasure controlled at the data link layer

    Publication Year: 2002 , Page(s): 277 - 282
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (493 KB)  

    A satellite data communication link with fade countermeasures applied at the physical layer, in the form of adaptive modulation and forward error correction coding, will only perform as well as governed by the way in which the inherent system adaptivity is controlled. By considering the controlled quality attribute to be the error-free frame throughput of the link, the place where the control happens has to move from the physical layer to the data link layer. Following earlier research which produced excellent results when the OSI HDLC protocol was simulated, the authors have embarked on the development of a fast executing simulator based on a Markov chain architecture. The basic model has been modified by application of adaptive filtering techniques in the calculation of the state change probability values. This refined the model to perform within 2% of the original simulator in the case of the selective repeat continuous ARQ. The paper presents the development philosophy of the new model and some of the results obtained using both deterministic test fades and propagation fades previously recorded by satellite beacon receivers. The good accuracy of the model, coupled with its computation efficiency, makes it suitable for application in future work where a potentially large number of links would have to be simultaneously considered. View full abstract»

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  • Collision resolution in contention access local area networks using concatenated prime sequences

    Publication Year: 2002 , Page(s): 249 - 256
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    A new back-off algorithm for collision resolution in CSMA/CD local area networks is introduced. The algorithm, called the 'concatenated prime sequence back-off algorithm', is a code-division multiple-access technique based on multilevel prime sequences. Preliminary simulation results have shown the superiority of the proposed algorithm over the binary exponential back-off algorithm used in Ethernet. Three possible modes of operation for a LAN adopting the proposed algorithm are suggested. View full abstract»

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  • Markov decision theory framework for resource allocation in LEO satellite constellations

    Publication Year: 2002 , Page(s): 270 - 276
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    The authors address the problem of call admission and route selection for connection-oriented networks with deterministically varying topology, such as low-Earth orbit (LEO) satellite constellations. They direct their study to non-reservation routing schemes, i.e. where the use of channel reservation strategies for handover calls is omitted. The problem is formulated as a semi-Markov decision process (SMDP), where the objective is to maximise the long term network revenue, which is a combination of the revenue, earned from accepted new calls and the costs of forced terminated calls. The framework, which is novel in applications to LEO satellite networks, extends from the call admission control problem formulated as an SMDP in wireless networks to an end-to-end route allocation problem. The performance of the SMDP policy is compared with existing non-reservation-based routing algorithms. A set of results obtained from simulations in symmetric and asymmetric traffic demand regimes shows that the SMDP framework outperforms the previously proposed algorithms. View full abstract»

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  • QoS-guaranteed fuzzy transmission controller for dynamic TDMA protocol in multimedia communication systems

    Publication Year: 2002 , Page(s): 292 - 298
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (550 KB)  

    The paper proposes a QoS-guaranteed fuzzy transmission controller (FTC) for the dynamic TDMA protocol in multimedia communication systems. The the dynamic TDMA protocol adopts a mini-slot technique for reducing contention cost, and the mini-slots are further partitioned into multiple MAC regions that users can access with their respective quality-of-service (QoS) requirements. The FTC mainly contains a Sugeno self-tuning fuzzy MAC threshold controller and a fuzzy access controller. The former applies a position-gradient-type reasoning method to properly determine the MAC regions; the latter employs max-min inference fuzzy logic to determine the access probabilities of users for enhancing dynamic TDMA efficiency under the QoS constraint. Simulation results show that the dynamic TDMA protocol with FTC can always guarantee the QoS requirement of real-time packet loss probability, regardless of the non-real-time traffic loads. Furthermore, it achieves higher system utilisation and less non-real-time packet delay compared to previously proposed PRMA, IPRMA and FRMA protocols. View full abstract»

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  • Subsets of the STM-1 frame-alignment signal: a monitoring analysis

    Publication Year: 2002 , Page(s): 242 - 248
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    A novel approach to frame-alignment monitoring considers splitting the frame-alignment signal into its independent subsets, making the evaluation of the out-of-frame detection time within the overlap zone quite complex. The paper proposes a simplified model for this evaluation. An STM-1 framing signal is used as an illustrative example and it is pointed out that its repetitive structure is not suitable for splitting. Framing signals optimised specifically for splitting into subsets are introduced. View full abstract»

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  • IP routing by an optical spectral-amplitude-coding CDMA network

    Publication Year: 2002 , Page(s): 265 - 269
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (458 KB)  

    An optical spectral-amplitude-coding CDMA network is proposed as a solution to the IP routing bottleneck in the global Internet. Its performance has been analysed for two different cases. For a given peak bit rate the network performance can be improved by reducing channel utilisation. However, when each user in the network has a fixed average bit rate, an optimal utilisation exists for the overall network performance. Analytical results clearly indicate that optical spectral-amplitude-coding CDMA technology may be a good candidate for the future IP backbone. View full abstract»

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