Pause Frame is a flow control mechanism to slow down the senders rate.
ROS ignores pause Frames so the mechanism does not work.
You see the pause Frames at lines with different Speeds. So if you send traffic from a 1GBPs Ethernet and
cross a 100MBit or Wireless Segment the router at the border sends pause Frames back to the Sender
when his buffers get filled.
This happens way before the 100MBit in the middle is filled as IP Packets does not arrive evenly spaced.
So a small burst leads to pause Frames. If they are ignored packet drops happen and speeds break down.
I requested flow control from MT. They asked me to ask the Forum if it is needed but there was nearly no Response.
http://forum.mikrotik.com/t/flow-control-in-ros/68224/1
So MT considered flow control as an unwanted feature.