Re: [Make-wifi-fast] 3g/4g with fq_codel & mobility

[Loganaden Velvindron <loganaden@gmail.com>]

On Mon, Nov 21, 2016 at 3:27 PM, Jonathan Morton <chromatix99@gmail.com> wrote:
>
>> On 21 Nov, 2016, at 13:16, Loganaden Velvindron <loganaden@gmail.com> wrote:
>>
>> I have one of those gl.inet 6416a board. It runs fq_codel on the
>> USB-3g dongle modem interface, and it runs very well at rest.
>>
>> I put it inside a car, and while driving, I notice some induced latency:
>>
>> https://www.dslreports.com/speedtest/6354936
>>
>> Can someone who has some understanding of 3g/4g internals shed some
>> light ? Could the 3g/4g modem be buffering due to varying strength of
>> the signal or due to handover in base station ?
>
> Usually such dongles don’t give direct access to the 3G modem interface.  Instead they provide an Ethernet or PPP interface, and do a conversion internally.  Ethernet emulation is more common of late, possibly due to the rise of 4G.
>
> Running fq_codel on such a device without a shaper relies on the buffers in *both* the dongle itself and the driver for the emulated Ethernet device having appropriately sized buffers in aggregate.  This is virtually never the case.  And that’s just for the upload direction.
>
> In the download direction you are relying on buffers in the provider’s network and the cell tower.  Fq_codel on your own hardware has no effect here.
>

I think that reducing the buffer size with NCM might be a good start,
particularly with 4G. THere is a lot of work to be done on the
USB-ethernet stack.