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.TH HTB 8 "10 January 2002" "iproute2" "Linux"
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HTB \- Hierarchy Token Bucket
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HTB is meant as a more understandable and intuitive replacement for
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the CBQ qdisc in Linux. Both CBQ and HTB help you to control the use
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of the outbound bandwidth on a given link. Both allow you to use one
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physical link to simulate several slower links and to send different
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kinds of traffic on different simulated links. In both cases, you have
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to specify how to divide the physical link into simulated links and
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how to decide which simulated link to use for a given packet to be sent.
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Unlike CBQ, HTB shapes traffic based on the Token Bucket Filter algorithm
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which does not depend on interface characteristics and so does not need to
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know the underlying bandwidth of the outgoing interface.
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Shaping works as documented in
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Within the one HRB instance many classes may exist. Each of these classes
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contains another qdisc, by default
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When enqueueing a packet, HTB starts at the root and uses various methods to
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determine which class should receive the data.
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In the absence of uncommon configuration options, the process is rather easy.
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At each node we look for an instruction, and then go to the class the
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instruction refers us to. If the class found is a barren leaf-node (without
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children), we enqueue the packet there. If it is not yet a leaf node, we do
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the whole thing over again starting from that node.
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The following actions are performed, in order at each node we visit, until one
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sends us to another node, or terminates the process.
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Consult filters attached to the class. If sent to a leafnode, we are done.
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If none of the above returned with an instruction, enqueue at this node.
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This algorithm makes sure that a packet always ends up somewhere, even while
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you are busy building your configuration.
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.SH LINK SHARING ALGORITHM
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The root of a HTB qdisc class tree has the following parameters:
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parent major:minor | root
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This mandatory parameter determines the place of the HTB instance, either at the
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of an interface or within an existing class.
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Like all other qdiscs, the HTB can be assigned a handle. Should consist only
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of a major number, followed by a colon. Optional, but very useful if classes
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will be generated within this qdisc.
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Unclassified traffic gets sent to the class with this minor-id.
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Classes have a host of parameters to configure their operation.
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Place of this class within the hierarchy. If attached directly to a qdisc
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and not to another class, minor can be omitted. Mandatory.
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Like qdiscs, classes can be named. The major number must be equal to the
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major number of the qdisc to which it belongs. Optional, but needed if this
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class is going to have children.
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In the round-robin process, classes with the lowest priority field are tried
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for packets first. Mandatory.
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Maximum rate this class and all its children are guaranteed. Mandatory.
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Maximum rate at which a class can send, if its parent has bandwidth to spare.
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Defaults to the configured rate, which implies no borrowing
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Amount of bytes that can be burst at
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speed, in excess of the configured
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Should be at least as high as the highest burst of all children.
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Amount of bytes that can be burst at 'infinite' speed, in other words, as fast
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as the interface can transmit them. For perfect evening out, should be equal to at most one average
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packet. Should be at least as high as the highest cburst of all children.
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Due to Unix timing constraints, the maximum ceil rate is not infinite and may in fact be quite low. On Intel,
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there are 100 timer events per second, the maximum rate is that rate at which 'burst' bytes are sent each timer tick.
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From this, the mininum burst size for a specified rate can be calculated. For i386, a 10mbit rate requires a 12 kilobyte
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burst as 100*12kb*8 equals 10mbit.
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HTB website: http://luxik.cdi.cz/~devik/qos/htb/
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Martin Devera <devik@cdi.cz>. This manpage maintained by bert hubert <ahu@ds9a.nl>
added
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debian/manpages/tc-htb.8
