Russell Stuart wrote: > > On Thu, 2006-02-23 at 10:23 +0100, Andreas Klauer wrote: > > On Thu, Feb 23, 2006 at 06:38:09PM +1000, Russell Stuart wrote: > > > For example, lets say we have a 1000kbit link, and two > > > classes sharing that link: > > > > > > - Voip - ie high prio real time, and > > > - Web - background traffic. > > > > Have you measured this link, i.e. when there is no activity > > and you start some Voip sessions, do they get a constant > > downstream of 1000kbit? > > > > It may very well be that you have to measure the real throughput > > and then go a little lower (since you have to be the bottleneck), > > however having to throw 30% of bandwidth away sounds a bit too > > harsh to me. > > The setup I gave was purely hypothetical. 300kbit > headroom sounds way to high to me as well - any > advice others may have on this would be appreciated. > > > Another way of indirect headroom would be to hard limit the Web class, > > i.e. give the Web class a lower ceil than the other classes. This way, > > there is bandwidth that the Web class can't use no matter what, even > > if the link is completely empty. > > That is the right answer - it would achieve what I want. > In hindsight it seems so obvious I don't know why I > didn't think of it myself. > > Thanks for taking the time to answer my query. Two more things. HTTP is a bursty protocol, so you need to think about the burst and cburst parameters you give it. If you want to squash TCP fast start, use a low burst which will backlog and eventually drop the excessive packets. On the other hand, my experience is that a slow started connection never increases its flow rate much even though the spec says it should. And you can get better precision from HTB by setting HYSTERYSIS (did I just misspell that?), thus dequeueing a single packet rather than a pair. I don't recommend that, but you should know about it. On many ATM links it is a godsend. In terms of headroom, I find that 85 % of real capacity always works, so I start with that and push up until something breaks. YMMV. -- gypsy _______________________________________________ LARTC mailing list LARTC@xxxxxxxxxxxxxxx http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc
