Re: [OT] traffic shaping (Was: Re: [Mldonkey-users] 1/ Solving latency pb - 2/download/connect_to_server pb)

[Lionel Bouton]

Jarek Hirny wrote:

> Hi.
>
>  
>
> > Forgot to add : UPLINK must be set to a value slightly less than your
> > actual upload bandwidth in kbit/s (mine is 128 kbit/s).
> >    
>
> Talking about this, do you accidentally now what I should do if my bandwidth
> depends  on  a)  network,  where the other host/client is, b) period of day?
> Normally  I have 128kbps, but in the night (or if I connect to somebody from
> www.wix.net.pl)  it  increases  to 512kbps. And I have no idea how my shaper
> should look like...
>  
Virtually no impact on UPLINK. This should be set like said above (it is 
used to make sure there's no huge buffer between you and the Net that 
would prevent low latency queuing). You may have a look at the wonder 
shaper doc on lartc.org.

To sum up, most ADSL/cable 'modems' do buffer incoming and outgoing 
transfers in order to maximize your throughput. So one request can be 
queued in this buffer for a relatively long time when the buffer is 
already full with upload data. The solution is to feed the modem with a 
slower rate than the one sustainable by the link between your modem and 
your ISP's router.
- Today an Unix personnal computer is fast enough to use small buffers, 
some high latency OSs don't have this opportunity -
This speed is a constant. What changes is the bandwidth on the ISP's 
internal network. If it's too low, its routers will drop packets or use 
ECN (explicit congestion notification) and your TCP stack will adapt and 
slow the transfer connexion by connexion (TCP really is clever).
You don't need to take the actual bandwidth of the ISP's internal 
network as the first router you see should always be able to empty your 
modem's queue at the advertised link speed (or there's something really 
odd with this link).

LB