Re: [LARTC] HTB Rate and Prio (continued)

[Andy Furniss <andy.furniss@dsl.pipex.com>]

Gael Mauleon wrote:

> I quite don't understand the concept of putting the rate of the line lower
> than it's true value, can you explain me this and do the excess bandwith is
> lost ? What is a good value for a 2m line (SDSL) ?

It depends on what rate you are really synced at and what extra 
overheads/encapsulation your sdsl line has.

It may be a bit different for sdsl  - I only know adsl, but as an 
example, for me, an empty ack which htb will see as 40 bytes (ignoring 
timestamps/sacks) will actually use 2 atm cells = 106 bytes on my line a 
1500 byte ip packet will use 32 cells = 1696 bytes.

Which means that if I tweaked by experementing with my rate using bulk 
traffic and arrived at some figure which seemed OK things could still go 
overlimits when the traffic consists of alot of small packets.

There are patches to work things out per packet and a thesis giving 
various overheads at

http://www.adsl-optimizer.dk/

but for now just back off - 1800 is probably OK for netperf tests.

I am talking about egress here - if you are going to shape ingress 
aswell you need to back off even more as you are trying to shape from 
the wrong end of the bottleneck (which can't be done perfectly anyway) 
to build up queues to shape with.

Andy.

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