Burst with PPPoE Server

Hello guys,
I want to know how to implement rx and tx burst when using PPPoE server. I have read some old topics, but had no luck. I tried modifying the “rate-limit” in /ppp profile set rate-limit=, but I don’t know which argument here.

Any idea?

Thank you

Here you can find format in which to write rate limits
http://wiki.mikrotik.com/wiki/Manual:PPP_AAA#User_Profiles