[LARTC] Fair shaping over link with variable parameters

[Andy Furniss]

Rafal Krypa wrote:
> Hi.
> I would like to ask you for advice.
> I am trying to construct following shaping solution:
> * several users are using one link to the Internet
> * all of them have equal priority and should be given fair amount of bandwidth
> * no kind of traffic is considered more important than other
> * our Internet connection has no CIR, only "maximum dl/ul speeds" given by
>   provider

What you can or can't do will depend on the exact nature and behavior of 
the link.

> * most important: our outgoing and incoming traffic must be shaped to some rate
>   that will provide possibly low latency. For users that do not have active
>   connections I'd like to ensure no more than 100ms latency for ping or any
>   other low-traffic connections

100ms - that would be hard to guarantee on a slow fixed rate link, in 
some situations you may need to sacrifice 50% of ingress bandwidth.

It depends on how fast the link is and how slow it gets and how it is 
slowed.

>   
> 
> For several years of my experiments with traffic shaping over Linux I found no 
> tool for creating such system. For example, HTB require given, constant 'ceil' 
> parameter. I would like to have some qdisc that can automatically adjush its 
> rate/ceil parameter depending on achieved latency. The rest of the job would be 
> quite pretty done by ESFQ.
> Could you point me to anything adequate to my needs?
> 

There is no qdisc that has variable rates.

I've just got a link with variable down speed and have played around 
with policers to see what's possible. I haven't done much and it doesn't 
work too well - though it works enough to carry on trying to see what's 
possible. I still don't know whether it can ever work enough to be left 
"unnatended".

If you have few users and know your traffic and have a fairly fast link 
and know how it behaves there may be a way - at least to do alot better 
than doing nothing.

Andy.