ATM TRAFFIC ENGINEERING FOR ABR SERVICE PROVISIONING

The Available Bit Rate (ABR) service is being designed as a low-cost t ransport service over ATM, which will be using the bandwidth left avai lable after servicing connections of another, high-priority class. The implementation of the ABR service requires large buffers at each mult iplexing/switching stage to keep cell-loss rates down to a minimum, an d a feedback mechanism from the network to the terminals in order for the latter to adjust their traffic profiles according to the prevailin g congestion conditions. Thus, an enhanced set of traffic control func tions is necessary to support this new service. In this paper the main traffic analysis and control problems related with the ABR service ar e addressed, modelled and answered on the basis of effective rates def ined for the multiplexed connections. Emphasis is given to a simple CA C scheme which consists in allocating peak rates to the high-priority class and effective rates to the ABR class. An adaptive shaping mechan ism is then required to enforce the contracted effective rates for the ABR streams. Producing ON/OFF streams facilitates the control functio ns by allowing the use of approximate closed-form calculations.