On Wednesday 11 June 2003 12:26, Emmanuel SIMON wrote:
> First, thank you Stef for answering.
> That's what I understood. I think my question was not enough precise (??)
>
> My reel question/problem is why are parameters of the bandwidth (such as
> rate, burts ...) set on classes rather than on qdiscs ?
You have to see a class as a virtual channel. Each class is responsible for
the packets that it holds. So the rate / burst / ceil and so one are only
valid for that class. So you have to put packets in the same class that
somehow are the same. Like all telnet/ssh packets. So you can give that
class a small burst and a low latency. Or you put the packets from 1 client
in 1 class so all the traffic to the client is one 1 big channel and he is
reponsible for this.
> I guess a class should only map a flow and should not know how this flow
> will be sent. Especially that classes don't send packets. What is the
> reason why it is done so ? And what if i don't specify parameters fir a
> leaf class ? Does it herit from the parent ?
A class is not reponsible for sending the packets because the class is only
used to create the virtual channels (and so to limit the packets in that
class). Once a packet is dequeued from a virtual channel (and so is dequeued
form a class) it's give to the qdisc attached to that class. So you can add
a small fifo qdisc to that class so packets are send fast. Or you can add a
sfq qdisc so each flow has his own little queue. So you have a lot of
flexibility.
You can even add a classfull qdisc to a class, but that's just a waste of CPU
cycles and will only add extra delays.
Each class needs it's own parameters when you create it. It will not inheret
something from its parent.
> Thanks once more
This is even for more confusing when I have to think about ut. This is in no
docs explained, but I don't think that I'm telling big lies.
Stef
--
stef.coene@xxxxxxxxx
"Using Linux as bandwidth manager"
http://www.docum.org/
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