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Packet Performance and Throttling


Because there is no way to prevent large numbers of small packets from arriving at the packet-bearing serial (PBS) interfaces, policing is performed on the CTP system. Bridged packets are identified and throttled before they exit the CTP system onto the Ethernet line, and offending packets are dropped.

This action is done with a throttling mechanism implemented in the serial driver. At the beginning of every second, the driver is deposited with a fixed number of tokens. For each token, a packet may be received by the driver and sent to the system for forwarding. After the tokens have been used up, no more packets may be received, and any subsequent packets that arrive are discarded (and the dropped counter incremented). At the beginning of the next second, that driver receives another allotment of tokens, and packet reception resumes. If there are any unused tokens at the end of the second, they are discarded.

The overall bridged packet forwarding budget of a CTP2000 system is 25,000 packets/sec.