QoS of IP over ATM: the PCR and ACR policing issue

Many solutions to integrate IP with ATM and to map IP on ATM service categories have already been presented. Yet how to police the chosen ATM service category is still an open issue. We present the IP over ATM policing issue. Since the loss of a single ATM cell would cause the loss of an entire IP packet, no cell of a well-behaved user should be rejected. At the same time in order to protect all network resources and the QoS of the other services, any violating user should be policed as rigidly as possible, independently of the background traffic. To this end we refer to ATM Usage Parameter Control standards and dimension the standardized ATM rate policer, the GCRA. We provide an upper-bound analytic GCRA parameters dimensioning able to ideally police the PCR of IP over CBR and VBR applications and the ACR of IP over ABR applications. For any background traffic no cell of a well-behaved user will be discarded whereas any violating user will be policed as rigidly as possible. In the case of IP over ABR policing we present a solution able to ideally police the ACR even during the updating phases of the current ACR.