| 摘要 |
A switch in an asynchronous transfer mode system utilizes an early packet discard (EPD) scheme and discards all but the end-of-packet cell of packets that are expected to prevent other partially transmitted packets from being transmitted through the switch. The switch also utilizes an integrated tail packet discard (I-TPD) scheme and, once a cell of a packet has been discarded for any reason, discards all of the remaining cells of the packet except the end-of-packet cell. Each of the EPD and the I-TPD schemes retain the last cell of a packet in order to maintain packet boundaries. Further, they each set the loss-priority of the end-of-packet cell to high, to increase the likelihood that the cell will be transmitted through the remaining switches in the route to the station to which the packet is directed. When the end-of-packet cell is received, the switch retains the cell unless its maximum queue limit is exceeded, and resets any associated early or tail packet discard flag. When the beginning of the next packet is received, the switch checks its queue length against an associated queue limit and against a CLP and an EPD threshold to determine whether or not to retain the cell. If the cell is discarded, the switch invokes, as appropriate, either the EPD or I-TPD and thereafter discards cells of the same packet. It invokes EPD when the queue limit exceeds the EPD threshold, and invokes I-TPD if it discards this or any cell when (a) it is policing a usage or network parameter control violation, (b) its associated queue exceeds an applicable queue limit, or (c) it selectively discards low-priority cells.
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