The use of hop-delay for policing in ATM networks

Abstract

The large delay-bandwidth product in wide-area high-speed networks renders conventional control methods, which rely on network feedback in order to react to the network congestion, unusable. This makes preventive control methods, such as policing, essential in maintaining an acceptable quality of services (QoS) offered to user connections. However, existing policing mechanisms which rely purely on source measurements are not effective in policing traffic sources that have large correlations in their output bit rate. In this paper a new approach, which exploits the relative invariability of the cell transfer delay in a long-haul broadband network, is proposed for policing. The idea is to discard from the measurements of the policing function arrival statistics which are no longer related to traffic states inside the network, hence making the policing simpler and more responsive to traffic violations. A new policing mechanism has been developed by applying the new approach in an existing policing scheme—the so-called leaky bucket scheme. Numerical results obtained from the mathematical model developed for the new mechanism show that it has a better cell loss performance than the original leaky bucket. Results from computer simulation substantiate these observations. The results also show that a small increase in the counter size in the new mechanism can yield a large improvement in the cell loss performance, thereby reducing the complexity of policing mechanisms using the new approach. Comparisons in terms of the dynamic characteristics when both mechanisms are policing the effective bandwidth show that the original scheme admits more cells from a violation source before control action takes place. The original scheme is also found to admit more cells from a violation source in the long term.