To minimize latency, (which is probably what you want for voip traffic), give the class a high priority.
Make sure it never reaches its configured rate.  If it does, you will see that the latency increases.
If you think it might reach its configured rate, than use a policing filter before the class to place an upper limit on the rate.
And, as Steph memtionned, a FIFO is a good thing.  Just make sure it is big enough to handle your expected burst, but not too big because it could increase the latency.

Good luck,

Mathieu.

> Yep i missunderstood the quantum concept (it´s clear
> now), but since my voip class was configured with
> enough bw this doesn´t matter
>
> Reading more on docum.org, i find hte possible cause
> of the delays i was using sfq (128p queue) on the leaf
> i removed sfq from the voip class
>
> I will try also with other disciplines.. like tbf
> just to have a deeper understanding of queuing in real
> life applications
Tbf will not change nything.  Htb is acutally a tbf but with classes.

> Are there any recomendation on which queuing
> discipline to use with voip?
> (my stats show 100 bytes per packet average in voip)
Why not a simple fifo?  You can adapt the size of it from the command line.

> i´m doing more tests now and i´ll re re-read the full
> lartc. doc