LARTC - Jan 2005 - Sharing/splitting bandwidth on a link while bandwidth of the link is variable (or unknown) ?

Hello,
 
I want to  share/split bandwidth on a link with unknown bandwidth. I want to
exactly
share/split bandwidth (for example : FTP 30% , HTTP 20% or 30% for a group of
PCs and so forth.)
 
"Traffic-Control-HOWTO" talk that PRIO scheduler is an ideal match for
"Handling a link with a variable (or unknown) bandwidth".
 
But PRIO scheduler can not exactly share/split bandwidth .
 
Could you tell me if  I can exactly share/split bandwidth on a link with a
variable (or unknown) bandwidth?  If it is possible, how can I do that ?
 
Thanks in advance!
nhgiang.
 

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Hello,
> I want to  share/split bandwidth on a link with unknown bandwidth. I 
> want to exactly
> share/split bandwidth (for example : FTP 30% , HTTP 20% or 30% for 
> a group of PCs and so forth.)
>  
> "Traffic-Control-HOWTO" talk that PRIO scheduler is an ideal
match for
> "Handling a link with a variable (or unknown) bandwidth".
>  
> But PRIO scheduler can not exactly share/split bandwidth .
>  
> Could you tell me if  I can exactly share/split bandwidth on a link with 
> a variable (or unknown) bandwidth?  If it is possible, how can I do that ?
[Warning irony ahead]
I''ll give you a complete script if you tell me how many bits/sec
exactly
30% of unknown is.
[/irony]

In other words: You don''t know how much there is available, I
don''t know
  it, the list doesn''t know it and your computer can''t know it
either.
So no - that''s not possible (and should be evident, hopefully)

What you CAN do is let some ping run alongside and react to changes in 
the latency it sees across the link - then adapt the script and thus 
changing the parameters. This needs lot of experimentation, is a bad 
hack but maybe it is sufficient for what you are trying to achieve.

Otherwise, find a minimum value of bandwidth you never drop below and 
set that as the maximum bandwidth available for your root qdisc. This 
gives you the predictability.

Or : find a better line/ISP. Find and drop abusive users/applications.

But all in all, there''s not much you can actually do in your situation.
-- 

C U

      - -- ---- ----- -----/\/  René Gallati  \/\---- ----- --- -- -

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In the past, people played with routing protocols such
as HELLO and FUZZBALL which reacted to the latency on
each link. They gave up. It turns out that overly
reactive systems are not that useful. The gains are
dubious, and the costs on resources are high.

The other factor is in what the original poster meant
by an "exact" split. Exact over what timeframe? Over
any given instant, only one packet is being sent (it''s
a serial stream) so the split over that amount of time
is always 100% of whatever it''s doing.

On the other hand, if it''s an exact split over a
fairly long timeslice, you use a class-based queueing
system and measure what''s been sent out of each queue.
You then predict what the net bandwidth is over the
whole timeslice, by looking at what gets sent and what
gets dropped. Each time you adjust the prediction, you
adjust the hard limits for the queues to allow out
whatever is left of that class'' net bandwidth.

A third approach is to see what you can do with ECN
and other back-propogating QoS protocols to throttle
given queues that reach or exceed their limits. That
way, you don''t need to care what the bandwidths are at
any given time, because the primary router that
divvies up the bandwidth can throttle in proportion to
how it does that division.

--- Rene Gallati <lartc@draxinusom.ch> wrote:
> Hello,
> 
> > I want to  share/split bandwidth on a link with
> unknown bandwidth. I 
> > want to exactly
> > share/split bandwidth (for example : FTP 30% ,
> HTTP 20% or 30% for 
> > a group of PCs and so forth.)
> >  
> > "Traffic-Control-HOWTO" talk that PRIO scheduler
> is an ideal match for 
> > "Handling a link with a variable (or unknown)
> bandwidth".
> >  
> > But PRIO scheduler can not exactly share/split
> bandwidth .
> >  
> > Could you tell me if  I can exactly share/split
> bandwidth on a link with 
> > a variable (or unknown) bandwidth?  If it is
> possible, how can I do that ?
> 
> [Warning irony ahead]
> I''ll give you a complete script if you tell me how
> many bits/sec exactly 
> 30% of unknown is.
> [/irony]
> 
> In other words: You don''t know how much there is
> available, I don''t know 
>   it, the list doesn''t know it and your computer
> can''t know it either. 
> So no - that''s not possible (and should be evident,
> hopefully)
> 
> What you CAN do is let some ping run alongside and
> react to changes in 
> the latency it sees across the link - then adapt the
> script and thus 
> changing the parameters. This needs lot of
> experimentation, is a bad 
> hack but maybe it is sufficient for what you are
> trying to achieve.
> 
> Otherwise, find a minimum value of bandwidth you
> never drop below and 
> set that as the maximum bandwidth available for your
> root qdisc. This 
> gives you the predictability.
> 
> Or : find a better line/ISP. Find and drop abusive
> users/applications.
> 
> But all in all, there''s not much you can actually do
> in your situation.
> -- 
> 
> C U
> 
>       - -- ---- ----- -----/\/  Ren Gallati 
> \/\---- ----- --- -- -
> 
> _______________________________________________
> LARTC mailing list / LARTC@mailman.ds9a.nl
> http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO:
> http://lartc.org/
> 


		
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On Wednesday 05 January 2005 11:59, Jonathan Day wrote:
<snip>
> On the other hand, if it''s an exact split over a
> fairly long timeslice, you use a class-based queueing
> system and measure what''s been sent out of each queue.
> You then predict what the net bandwidth is over the
> whole timeslice, by looking at what gets sent and what
> gets dropped. Each time you adjust the prediction, you
> adjust the hard limits for the queues to allow out
> whatever is left of that class'' net bandwidth.
I wish there was something like that available for PPP over ATM links.  My 
ADSL connection varies between 160Kbps and 224Kbps depending on how many ATM 
cells are wasted by mostly null cells.  I''m stuck with a rate of
160Kbps
since that''s the lowest stable rate I could find that works under the
worst
case scenario of many, small Ethernet packets.  Sadly I miss out when my 
connection is not in that worst state.

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