Re: [LARTC] patch: HTB update for ADSL users

[Ed Wildgoose <lists@wildgooses.com>]

>So does it just let you be honest about your rated speed, or is there an added 
>performance bonus from being able to specify your true ATM rate?
>  
>

The idea is that your ethernet packets get broken up and encapsulated in 
53 byte ATM packets.  Each ATM packet is fixed size and has a 5 byte 
header = 48 bytes of data.

Straight off that means that the 512Kbit bandwidth you bought is only 
good for 512/53 * 48 = 463 Kbit or 58 Kbytes/s.  However, unless your 
packets are exactly a multiple of 48 then you will be wasting bandwidth 
big time (think about your MTU).  Consider small ack packets which will 
take up two cells, but the second cell is basically empty (bandwidth 
slashed in half).  Unless all your packets are the same size, this is 
why the current mutliply by some fixed constant approach is not working 
perfectly with ADSL.

So the patch simply works out how many cells you will need and 
multiplies up by the real size of those cells to work out bw used. 

It's also more conservative than before.  Previously it was working out 
an effective rate for 8 byte packets, and using that rate for 8-15 byte 
packets.  Now it works out the rate for 15 byte packets and uses *that* 
for 8-15 byte packets.

It's probably not perfect, but it's extremely accurate for me.  I can 
bump up the bandwidth on my interfaces to basically 99% and for stable 
streams there is no queuing.  P2P still seems to cause so many new 
incoming connections that you need to throttle down the incoming to 
leave some space for an unexpected incoming rush - but for most users I 
think it will work nicely

Ed W
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