[Cerowrt-devel] routers you can throw off the back of a truck

[Alan Jenkins]

On 18/01/2016, Valent Turkovic <valent at otvorenamreza.org> wrote:

> @everybody any ideas how to tweak current "simple.qos" and
> "simplest.qos" scripts in OpenWrt for 3G and fiber optics? On fiber
> optic connection idle latency is around 30ms and on 3G connection is
> around 60ms, do I need to change 5ms default in fq_codel to these
> values? How?

Target should stay at 5ms, unless bandwidth is low ( < 2Mbit).
qos-scripts will tweak it according to the bandwidth you set.

Interval needs to match the expected round-trip-time, as a maximum
across most endpoints.  The 100ms default interval works well in many
cases... a base of 60ms might argue to increase it slightly for 3G, if
you expect some trans-continental destinations.[1]

Source: an update from the original Codel author.  Might not sound
directly related to your question, but I guess 3G falls under their
definition of a "bursty MAC".

"Many experimenters believe the value of target needs to be increased
independently of interval in this case. This note is to help explain
why this is not so."  http://pollere.net/Pdfdocs/noteburstymacs.pdf

The problem is that you need either a fixed rate you can use, or an
underlying connection that isn't itself horribly over-buffered.
(Ethernet with BQL, or dialup modems in the era of wondershaper...)
3G doesn't guarantee either :(.  I assume it also has the wireless
problem, of retry-induced latency on poor signal.  (ala Taht's
"infinite retry" bug).

If Johnathans new "autorate_ingress" solves or mitigates it for
ingress, that would be miraculous.  I had assumed it was most
applicable to point-to-point links which change the bitrate they use
over time due to changing signal quality, e.g. point-to-point wireless
v.s. weather.  (IIRC he had this clever idea of measuring the maximum
bitrate of two packets received back-to-back).

Btw make sure you've measured the idle latency during the busiest
period for the 3G network (for which it is still usable).  People
observe high variations during the day.

Regards
Alan

[1] E.g. from Europe you might expect some US endpoints, but not worry
about performance degradation to Australian-only servers.  You can try
pinging the world from your browser with
http://www.dslreports.com/tools/pingtest :).