This document discusses the token bucket (TB) algorithm and its implementation using hierarchical token bucket (HTB). It provides an overview of key HTB concepts like assured rate, ceil rate, actual rate, and priority. It then describes how link sharing is implemented, with borrowed bandwidth allocated based on priority and quantum. Finally, it walks through a case study example to illustrate how nodes change states and are scheduled at different levels of the HTB tree.

1. htb
Jeromy Fu

2. Agenda
• Parameters
• Tc example
• Link sharing
• Implementation
• Case study

3. Tc Parameters

4. Internal Parameters

5. example1

6. example1

7. example1

8. example2

9. example2

10. example2

11. Basic concepts
• Classful qdisc
• Assured rate(AR)
• Ceil rate(CR)
• Actual rate(R)
• Priority
• Quantum, DRR

12. Basic concepts
• Class mode
HTB_CANT_SEND: red, R>CR
HTB_MAY_BORROW: yellow, AR<R<=CR
HTB_CAN_SEND: green, R<=AR

13. Link sharing
• Rc = min(CRc, ARc+Bc)
- Rc, actual Rate of class c
- CRc, Ceil Rate of class c
- ARc, Assured Rate of class c
- Bc, Borrowed from parent class c
• D(p) – set of nodes
- all nodes are children of p
- all nodes are yellow, which need to borrow bandwidth from parent p

14. Link sharing
• If there are other nodes have higher priority than node c, then those ones
will be scheduled first, thus Bc = 0.
• Otherwise, the bandwidth of parent is divided according to the quantum
of the nodes, which have the same priority with node c.
- Q, quantum
- P, Priority, smaller the higher
- Rp, actual rate of parent p
if min[Pi over D(p)] >= Pc:
Bc = Qc * Rp/sum[Qi over D(p) where Pi=Pc]
else:
Bc = 0

15. Principles
• Red nodes(HTB_CANT_SEND) have to wait
• Yellow nodes(HTB_MAY_BORROW) will try
borrow from parent
• Green nodes(HTB_CAN_SEND) will always
served first for it doesn’t borrow
• Higher priority nodes are served first

16. implementation
• Self feed
each level has one self feed, and every priority has a self slot in self feed(each
slot has the same priority and level).
All classes in the same slot has the same priority and level, and are all green
nodes (HTB_CAN_SEND) of this level.
• Inner feed
every inner class(node) has one inner feed
All classes in the same slot has the same priority and level, and are all yellow
nodes (HTB_MAY_BORROW) that are children of current inner node.
• Wait list
each level has one wait list, which stores the nodes that are yellow
(HTB_MAY_BORROW) and red (HTB_CANT_SENT)

17. implementation
• A htb tree with 3 levels
- red slot (high priority)
- blue slot (lower priority)
- white slot (wait list)

18. implementation
• Start at the lowest level, choose one green
node in the highest priority self slot of this self
feed.
• If it’s leaf, then schedule it.
• If it’s inner node, then check its inner
feed, and choose the highest priority inner
slot, find a yellow node, then schedule it.

19. Case study
• All nodes are initially green
• Pkt arrived for C and D (thick circle)
• C is lower priority (in blue self slot)
• D is higher priority (in red self slot)
• D is scheduled and token is
used

20. Case study
• D exceed AR, but not CR
• D changed to yellow
• D is removed from self slot(red) of level 0
• D is then put to inner slot(red) of B
• D will change back to green in
the future, so it also put into
wait list of level 0
• C is scheduled ( D is higher
priority but C doesn’t need
borrow)

21. Case study
• C exceed CR
• C changed to red
• C is removed from self slot(blue) of level 0
• C can’t borrow so it won’t be put to the parent inner slot
• C will change back to green in
the future, so it also put into
wait list of level 0
• D is scheduled, and borrowed
from B, and B changed to yellow
• B is removed from self slot(red) of
level 1
• B is put to the parent inner slot(red)
and also put to the wait list
• Only A and E are green now

22. Case study
• E has no pkt, so D is scheduled
• A changed to red
• A is removed from self slot(red) of level 2
• A is put to wait list of level2
• Pkt arrived for E (thick circle)
• E is green and lower priority,
so put to self slot(blue) of level 0
• C changed back to green, and
removed from wait list, and put
to self slot(blue) of level 0

23. Case study
• Now both C and E are green and are of the
same priority.
• DRR is used now, they’re scheduled according
to quantum.
• Both C and D are changed to
yellow, removed from self slot,
put to inner slot and wait list
• B is added to both high and
lower priority inner slot of A