| 摘要 |
The flow of ATM cells in an ATM network is controlled by signalling to the source to reduce the transmission rate when congestion occurs in a switch in the network. The signalling is carried out by way of insertion into Resource Management Rm cells of a new Explicit Rate (ER) value for the connection. The ER value is obtained as a function of an ABR Output Bandwidth value (AOB). The AOB value is the number of ABR cells output from the buffer within a predetermined time interval. In a simple mode of operation, the new ER value is written to the cell for forward transmission, the changed ER then being signalled back to the source from the destination. In a more complex mode of operation, the cell is passed onwards or forwards with the old ER value unchanged, with a test establishing the lowest value of ER to be written in a DPRAM. In the receiver the ER value stored is written into the next cell only if it is lower than the existing value in the cell. If there is no congestion, the maximum value of ER is put into the DPRAM so that the backward ER in the backward cells is not changed. |
