Evaluation of ABR traffic management under various system time scales

In this paper, the eeects of various time scales on the management of ABR (Available Bit Rate) traac using feedback based control is studied. Since delay tolerable, the ABR applications can be allocated the remaining resources after CBR (Constant Bit Rate) and VBR (Variable Bit Rate) applications have been accommodated. To avoid excessive losses the transmission rate of the ABR applications should be modulated by the amount of remaining resources. That is, the ABR rate should be controlled through a feedback based rate control mechanism. In this paper a network link shared by remote ABR and VBR applications is considered and the impact of various system time scales on the eeectiveness of the feedback based rate control scheme is investigated, by formulating and studying a simple analytical model. These time scales are expressed in terms of the network transmission speed, the minimum tolerable ABR rate and the rate of change of the VBR rate. While the negative impact of a decreased network time scale on the eeectiveness of this control scheme is well established, the impact of the ABR and VBR time scales has not been investigated in the past. It turns out that for a given network time scale, the induced cell losses can be signiicantly reduced for increased ABR and/or VBR time scales and thus, the latter time scales should be taken into consideration when evaluating the eeectiveness of an adaptive feedback based congestion control mechanism. This study also suggests that higher eeciency can be achieved by enforcing large ABR time scales, leading to the introduction of a new class of transmission policies.