Re: monitoring queue length

[Jonathan Morton <chromatix99@gmail.com>]

> On 1 Dec, 2018, at 9:37 am, Azin Neishaboori <azin.neishaboori@gmail.com> 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