Samsung Ubigate iBG3026, Configuration Manual

Page: 238 / 718

CHAPTER 19. QoS
200
© SAMSUNG Electronics Co., Ltd.
Minth is given a default value of N packets, where N corresponds to 2xTs
msec of buffering, for 200 byte packets, at a rate of CR Kbps or Ts msec of
buffering at BR Kbps or N = 5, whichever is greater.(For larger packets, this
will result in larger amount of buffering). This means that, if a class is
receiving not more than it’s CR, on an average at least(2*Ts) msec of traffic
will be buffered before RED starts dropping. Note that these buffering
requirements are calculated for 200 byte packets which are conservative.
The average internet packet size is probably between 200-300 bytes, for which
the buffering would be up to twice the amount mentioned above.
The minimum permissible value for minth is L, where L corresponds to Ts
msec of buffering(for 200 byte packets) at CR Kbps or L = 3, whichever is
higher.
Maxth is given a default value of 3 times the minTh. However it is
recommended to set maxth to at least 2 times the minth. Too small a
difference between minth and maxth will reduce the effectiveness of RED by
causing frequent tail drops. The maximum permissible value for maxth is a
value slightly less than the maximum queue buffers by worth of Ts msec of
buffering at BR Kbps. The permissible range for minth and maxth values will
be displayed in the CLI. Minth can never be greater than maxth.
Statistics
The following RED statistics will be collected for interface and class queue RED.
Packets dropped above maxth
packets dropped between minth-maxth
packets allowed between minth-maxth
Total RED drops
Current average queue size
Maximum recorded average queue size
Maximum recorded queue size