Abstract: The Available Bit Rate (ABR) service is being designed as a low-cost transport service over ATM networks, which will be using the bandwidth remaining available after servicing connections of a high-priority class [1]. The penalty paid is the lack of QoS guarantees in terms of transport delays figures. Thus, an adaptive shaping mechanism is necessary for the ABR connections at each multiplexing or switching stage for effective bandwidth enforcement and adjusting their traffic profiles according to the prevailing congestion conditions. In this paper, an adaptive shaping mechanism related with the ABR service is analyzed and modeled on the basis of effective rates defined for the multiplexed connections. The traffic shaper is used to enforce the contracted effective rate for the ABR class and to allocate peak rates to the high priority class (burst spacer). The traffic shaper system is presented as an implementation perspective and specific ides concerning its hardware realization are given.