[Cake] Cake over satellite

Kevin Darbyshire-Bryant kevin at darbyshire-bryant.me.uk
Mon Oct 19 11:48:26 EDT 2015

On 19/10/15 16:15, Sebastian Moeller wrote:
> Hi Noven,
> On Oct 19, 2015, at 09:55 , Noven Purnell-Webb <noven at liberant.com.au> wrote:
>> I'm about to go on a mission to the outback, with one objective being to tune a disappointing satellite link. Theoretically 6/1mbps, with RTTs ranging from 700 - 1200ms. From the cake technical page 
>> "The AQM layer has no configuration options. However, it is planned to add simple tuning options for different prevailing RTTs that may be significantly different from the Internet-scale 100ms currently assumed. Satellite links tend to impose longer RTTs, and enclosed LANs tend to have much shorter RTTs." Does this imply cake is not yet ready for use on satellite links? Or merely that I'll get sub-optimal results but it's still worth testing? 
>> I see I could set the interval in sch_cake.c and recompile - is there any reason why this would be a bad idea? Am I right in thinking with such observed variation I'll get better results setting for the lower limit (700) rather than the upper (1200)?
>> Any suggestions for a more sane target to set while I'm doing this?
>> Has anyone here already done testing on satellite links?
> 	I believe that interval/rtt is now settable via tc, BUT target is clamped to a max of 5ms, while in theory it should be 5-10% of rtt, so current cake might work well out of the box, or might require fiddling with target. It would be most excellent if you could actually test that aspect of cake for us ;)
hi Noven,

The interval value is exposed as an rtt parameter, either as a time (say
700ms) or as some hopefully relevant pre-set keywords, may I suggest
'satellite' is suitable in your case (1000ms)   The target value is not
directly available from tc, however an API interface for it does exist
(like interval alias rtt and other parameters)   Target max is 5ms,
except for 'slow' links where a calculation using the time for an MTU
sized packet + overhead is used (there's little point in trying to
control latency to 5ms when it takes longer than that to actually send
the bytes out), other than that target is set to 5% of rtt.

Tell it the link bandwidth, any overhead bytes (PPP, ether-FCS, VLan and
the like) and the rtt 1000ms and she'll be right mate ;-)


> Best Regards
> 	Sebastian
>> - Noven
>> -- 
>> - Noven Purnell-Webb
>> Creative Technology Consultant
>> +61 448 841 091
>> http://onecardme.com/NovenPWebb
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