VIAVI TestCenter: PAUSE frames sent by Custom Control Plane are not reducing Tx rate as expected

• A PAUSE frame with quanta 65,535 (0xffff) will cause the receiving transmitter to stop transmitting for 512 * quanta bit times. • For a 400Gbps transmitter, this is 83,884.80 nsecs. • To completely stop a 400Gbps transmitter then requires 1 sec / 83,884.8 nsecs PAUSE frames per second = 11,921.1 PAUSE fps ~= 11,922 PAUSE fps. • When STC's Custom Control Plane (CCP) is configured to transmit PAUSE frames at at least this rate, the 400Gbps transmitter (in this case an Spirent TestCenter 400G port) does not completely stop. • Note: the purpose of CCP is to allow the transmission of a very low rate stream amongst other very high rate streams. For example at 400G, test traffic being sent at hundreds of millions of fps versus PAUSE frames being sent at 12,000 fps.This is accomplshed by sending the low rate streams from the CPU rather than from the Generator's FPGA.

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