39,947 research outputs found

    Analysis and optimization of vacation and polling models with retrials

    Get PDF
    We study a vacation-type queueing model, and a single-server multi-queue polling model, with the special feature of retrials. Just before the server arrives at a station there is some deterministic glue period. Customers (both new arrivals and retrials) arriving at the station during this glue period will be served during the visit of the server. Customers arriving in any other period leave immediately and will retry after an exponentially distributed time. Our main focus is on queue length analysis, both at embedded time points (beginnings of glue periods, visit periods and switch- or vacation periods) and at arbitrary time points.Comment: Keywords: vacation queue, polling model, retrials Submitted for review to Performance evaluation journal, as an extended version of 'Vacation and polling models with retrials', by Onno Boxma and Jacques Resin

    Wireless broadband access: WiMAX and beyond - Investigation of bandwidth request mechanisms under point-to-multipoint mode of WiMAX networks

    Get PDF
    The WiMAX standard specifies a metropolitan area broadband wireless access air interface. In order to support QoS for multimedia applications, various bandwidth request and scheduling mechanisms are suggested in WiMAX, in which a subscriber station can send request messages to a base station, and the base station can grant or reject the request according to the available radio resources. This article first compares two fundamental bandwidth request mechanisms specified in the standard, random access vs. polling under the point-to-multipoint mode, a mandatory transmission mode. Our results demonstrate that random access outperforms polling when the request rate is low. However, its performance degrades significantly when the channel is congested. Adaptive switching between random access and polling according to load can improve system performance. We also investigate the impact of channel noise on the random access request mechanism
    • …
    corecore