On improving CBR service playback buffer mechanism in WATM networks

Abstract

AbstractThe commonly recommended approach to meet the Constant Bit Rate (CBR) service requirements in ATM networks is to use the playback buffer mechanism implemented at the AAL layer [1],[2],[3]. This solution was originally proposed for the fibre optics ATM networks, where cell loss ratio is negligible (e. g. 10—9). However, for the wireless ATM network concept the designers have to take into account the fact that an essential part of sending cells can be simply lost due to transmission errors and these losses can also occur in bursts (despite applying error protection mechanisms). Moreover, the variation of cell transfer delay is expected to be significantly larger and this is mainly due to radio access protocol behaviour. As a consequence, the above leads to a need to modify the playback buffer mechanism in order to improve its functionality in the wireless ATM network environment. The solution proposed in this paper is based on some enhancements of the dummy cell insertion (instead of lost cells) algorithm and on the K times extension of AAL1 PDU numbering range, by assigning the same number to K consecutive cells. The justification of the approach is provided in terms of theoretical considerations and simulation results.