[Cake] Getting Cake to work better with Steam and similar applications

[Sebastian Moeller]

Hi David,

> On Apr 23, 2017, at 14:32, David Lang <david at lang.hm> wrote:
> 
> On Sun, 23 Apr 2017, Sebastian Moeller wrote:
> 
>>> About the per-host fairness download issue: while it's kinda resolved I still feel like it's mainly related to Steam, as normally downloading files from PC1 and PC2 halved the speed as expected even at full bandwidth (so no overhead, no -15%).
>> 
>> 	This might be true, but for cake to meaningfully resolve bufferbloat you absolutely _must_ take care to account for encapsulation and overhead one way or another.
> 
> well, one way to account for this overhead is to set the allowed bandwidth low enough. Being precise on this overhead lets you get closer to the actual line rate, but if you have enough bandwidth, it may not really matter (i.e. if you have a 100Mb connection and only get 70Mb out of it, you probably won't notice unless you go looking)

	Violent agreement. But note that with AAL5’s rule to always use an integer number of ATM cells per user packet the required bandwidth sacrifice to statically cover the worst case gets ludicrous (theoretical worst case: requiring 2 53 byte ATM cells for on 49 Byte data packet: 100 * 49 / (53 * 2) = 46.2% and this is on top of any potential unaccounted overhead inside the 49 Byte packet). Luckily the ATM padding issue is not as severe for bigger packets… but still to statically fully solve modem/dslam bufferbloat the required bandwidth sacrifice seems excessive… But again you are right, there might be users who do not mind to go to this length. For this reason I occasionally recommend to start the bandwidth at 50% to certainly rule out overhead/encapsulation accounting issues (mind you take 50% as starting point from which to ramp up…)

Best Regards
	Sebastian.


> 
> David Lang