Hi Jonathan Thank you for your very helpful insight. I can see the effect of bufferbloat in increased RTT, but when trying to further support the data with the queue size, I encountered the zero-backlog data which was very confusing to me. So now I know :) Thanks a lot for taking time, reading my message and providing helpful insight. Best Azin On Sat, Dec 1, 2018 at 2:47 AM Jonathan Morton wrote: > > On 1 Dec, 2018, at 9:37 am, Azin Neishaboori > wrote: > > > > So based on the dumbbell topology you described, I should see queue > buildup at the egress cellular interface of the router, right? > > Yes - but the actual cellular interface is on the far side of a > translation device, and so its queue is hidden from Linux. That's > unfortunately true of *every* 3G or LTE interface I've yet seen. Older > devices have a virtual serial PPP interface to the translator, newer ones > pretend to be Ethernet devices on the near side of the translator - in both > cases with much more bandwidth than the cellular interface itself. > > This is actually quite a serious problem for people trying to improve the > quality of cellular Internet connections. All of the low-level stuff that > would be useful to experiment with is deliberately and thoroughly hidden. > > If you put in an artificial bottleneck of 10Mbps on the outgoing > interface, you should be able to develop a queue there. You can use HTB or > HFSC, with the qdisc of your choice as a child on which the actual queuing > occurs. > > A better way to measure the impact of queuing in the raw device is to > observe the increase of latency when the link is loaded versus when it is > idle. I recommend using the Flent tool for that. > > - Jonathan Morton > >