In ITU-T Recommendation 1.371, the Generic Cell Rare Algorithm (GCRA) is used to define Peak Cell Rate for the ATM network. It is further applied by the TM Forum '93 to define Sustainable Cell Rate and Burst Tolerance so as to facilitate Usage Parameter Control and Network Parameter Control. To judge the validity of a cell according to declared GCRA parameters, the enforcer must read the clock time when the cell arrives. However, the clock of the enforcer would roll over frequently and accordingly the judgment would be incorrect. On the other hand, for a shaper in a customer premise node to dispatch cells conforming to the declared GCRA parameters, the clock would also roll over and the cell would not be dispatched correctly To overcome the problems induced by clock roll-over, based on ''time difference'' concept, we propose two modified GCRA's for the enforcer and shaper, respectively. According to the proposed algorithms, we design a feasible architecture for a multi-connection shaper and simplify it for an enforcer. They are proven to perform well in spite of the inherent clock roll-over characteristics. By simulation, we evaluate the delay in the shaper and the loss in the enforcer. The features of the architectures are also discussed.
