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           tc  qdisc ... tbf rate rate burst bytes/cell ( latency ms | limit bytes
           ) [ mpu bytes [ peakrate rate mtu bytes/cell ] ]
           burst is also known as buffer and maxburst. mtu is also known  as  min-


           The  Token  Bucket  Filter is a classless queueing discipline available
           for traffic control with the tc(8) command.
           TBF is a pure shaper and never schedules traffic. It  is  non-work-con-
           serving  and  may  throttle  itself, although packets are available, to
           ensure that the configured rate is  not  exceeded.   On  all  platforms
           except  for  Alpha, it is able to shape up to 1mbit/s of normal traffic
           with ideal minimal burstiness, sending out  data exactly at the config-
           ured rates.
           Much  higher  rates  are possible but at the cost of losing the minimal
           burstiness. In that case, data is on average dequeued at the configured
           rate  but may be sent much faster at millisecond timescales. Because of
           further queues living in network adaptors, this is often not a problem.
           Kernels  with  a  higher  'HZ'  can  achieve  higher rates with perfect
           burstiness. On Alpha, HZ is ten times higher,  leading  to  a  10mbit/s
           limit  to perfection. These calculations hold for packets of on average
           1000 bytes.


           As the name implies, traffic is filtered based on  the  expenditure  of
           tokens.   Tokens  roughly correspond to bytes, with the additional con-
           straint that each packet consumes some tokens, no matter how  small  it
           is.  This  reflects the fact that even a zero-sized packet occupies the
           link for some time.
           On creation, the TBF is stocked with tokens  which  correspond  to  the
           amount  of  traffic  that  can  be  burst in one go. Tokens arrive at a
           steady rate, until the bucket is full.
           If no tokens are available, packets are  queued,  up  to  a  configured
           limit.  The  TBF  now calculates the token deficit, and throttles until
           the first packet in the queue can be sent.
           If it is not acceptable to  burst  out  packets  at  maximum  speed,  a
           peakrate  can be configured to limit the speed at which the bucket emp-
           ties. This peakrate is implemented as a second TBF with  a  very  small
           bucket, so that it doesn't burst.
           To  achieve  perfection,  the  second  bucket may contain only a single
           packet, which leads to the earlier mentioned 1mbit/s limit.
                  maximum  amount  of time a packet can sit in the TBF. The latter
                  calculation takes into account the size of the bucket, the  rate
                  and  possibly  the  peakrate  (if set). These two parameters are
                  mutually exclusive.
           burst  Also known as buffer or maxburst.  Size of the bucket, in bytes.
                  This is the maximum amount of bytes that tokens can be available
                  for instantaneously.  In general, larger shaping rates require a
                  larger  buffer. For 10mbit/s on Intel, you need at least 10kbyte
                  buffer if you want to reach your configured rate!
                  If your buffer is too small, packets may be dropped because more
                  tokens arrive per timer tick than fit in your bucket.  The mini-
                  mum buffer size can be calculated by dividing the rate by HZ.
                  Token usage calculations are performed using a  table  which  by
                  default  has  a resolution of 8 packets.  This resolution can be
                  changed by specifying the cell size with the burst. For example,
                  to  specify  a  6000 byte buffer with a 16 byte cell size, set a
                  burst of 6000/16. You will probably never have to set this. Must
                  be an integral power of 2.
           mpu    A  zero-sized  packet does not use zero bandwidth. For ethernet,
                  no packet uses less than  64  bytes.  The  Minimum  Packet  Unit
                  determines  the  minimal  token usage (specified in bytes) for a
                  packet. Defaults to zero.
           rate   The speed knob. See remarks above about limits!  See  tc(8)  for
           Furthermore,  if  a  peakrate  is desired, the following parameters are
                  Maximum depletion rate of the  bucket.  Limited  to  1mbit/s  on
                  Intel,  10mbit/s on Alpha. The peakrate does not need to be set,
                  it is only necessary if perfect millisecond timescale shaping is
                  Specifies the size of the peakrate bucket. For perfect accuracy,
                  should be set to the MTU of the interface.   If  a  peakrate  is
                  needed,  but  some  burstiness  is  acceptable, this size can be
                  raised. A 3000 byte minburst allows around 3mbit/s of  peakrate,
                  given 1000 byte packets.
                  Like the regular burstsize you can also specify a cell size.


           To  attach a TBF with a sustained maximum rate of 0.5mbit/s, a peakrate
           Alexey N. Kuznetsov, <>. This manpage maintained by
           bert hubert <>

    iproute2 13 December 2001 TC(8)


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