[Cake] Cake over satellite

Kevin Darbyshire-Bryant kevin at darbyshire-bryant.me.uk
Tue Oct 20 13:32:38 EDT 2015

On 19/10/15 20:05, Sebastian Moeller wrote:
> Hi,
> On October 19, 2015 10:24:01 AM CDT, Dave Taht <dave.taht at gmail.com> wrote:
>> well, yes, but we can do it in the lab *this week*, before he takes
>> the dingos on....
> Good idea, als I am at A conference right now and will not find the time to make the changes to TC in time. I believe that cake should certainly A) set A reasonable target by default and B) still allow the user to explicitly request something else. Currently, I believe cake does only A)...
> Besteht Regards
>         Sebadtian

As an FYI:

tc has a number of calculations for interval & target

If an rtt is specified then target is 5% of interval with 1uS
(microsecond!) and 5mS (millisecond) lower & upper bounds.

The keyword predefined rtt values are:

datacentre (100uS), lan (1mS), metro(10mS), regional(30mS),
internet(100mS), oceanic(300mS), satellite(1000mS), interplanetary(1hour!)
Corresponding targets are 5uS, 50uS, 500uS, 1.5mS and everything from
internet onwards as a 5mS target.

Although these are the values passed into cake from tc, that isn't the
final story with regard to calculations as cake qdisc has some further
sanity checks.

If a link bandwidth is specified then the target is set to the max of
'1.5 MTU's worth of link time' and the target value passed by tc.  The
interval is set to max of '8 times the calculated target' and interval
value passed by tc.

So whilst tc supplies an rtt/interval and a 5% calculated target, cake
itself will override this with sensible values if that makes sense for a
'slow' link.


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