http://i3xi5qxvbrngh3g6o7czwjfxwjzigook7zxzjmgwg5b7xnjcn5hzciad.onion/tor-spec/flow-control
To ensure unpredictability, random bytes should be added to at least one
RELAY_DATA cell within one increment window. In other word,
at every 100 data-bearing cells (increment),
random bytes should be introduced in at least one cell.