Re: [LARTC] Question about htb class

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

Hideaki Nemoto wrote:
> Hi everyone.
> 
> I'm new to this list and I have some questions
> regarding HTB class.
> I was trying to see how tc sets the parameters for
> HTB, but really couldnt understand them.
> So, I thought that I might ask the wizards.
> It's mainly from the source code.
> 
> 1. What is the cell_log ?
> (its everywhere in the code)
> 
> 2. Why does htb calculate its burst(buffer) with
> tc_xmit_time() ? Is opt.rate.buffer supposed to 
> have the time it takes to transmit the packet ?
> (in q_htb.c around 223 lines)

> 3. What does rtab and ctab arrays do ?
> And what kind of value should be in there ?
> (its set in tc_core.c tc_calc_rtable())
> 
> I'd really appreciate your help.
> Thankyou very much in advance.

I can't say about HTB, but I've been playing with Ed Wildgooses patch 
for DSL users -

http://mailman.ds9a.nl/pipermail/lartc/2004q2/012752.html

cell_log is used to look up the delay for a packet to be transmitted at 
a certain rate. A rate table is made using cell_log to give granularity 
- for me using htb it gets calculated with MTU 1600 which means it's 3.

Three means the table has a dispatch time entry for every 8 bytes packet 
size, as a counter gets shifted left by cell_log to generate the table.

HTB / whatever looks up the transmit time for a packet by shifting its' 
length right by cell_log and using the result as an index for the table.

Andy.





_______________________________________________
LARTC mailing list / LARTC@mailman.ds9a.nl
http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/