[altq 48] Re: altq-diffserv

[Kenjiro Cho <kjc@csl.sony.co.jp>]

>> I give EF traffic at least 50% of the bandwidth (40 Mbit/s) and BE at
>> least 25% (20 Mbit/s).

>> Since I allow EF and BE to borrow the rest of the bandwidth (20 Mbit/s)
>> from their parent class ("DefaultClass"), I expected that

>> EF would receive: 40 + (40/60)*20 = 53.3 Mbit/s
>> BE would receive: 20 + (20/60)*20 = 26.7 Mbit/s

>> This would be the case with a fair queue.

Unfortunately, CBQ does not define how the excess bandwidth is
shared.  It only says that underlimit classes are served before
overlimit classes.  The current CBQ algorithm employs a heuristic
method.

I have to admit that this is a weak point of CBQ but it is not
simple to share the excess bandwidth among classes with different
priorities, bandwidth assignments, delay requirements, packet sizes...

-Kenjiro