[Bloat] DSLReports Speed Test has latency measurement built-in

[Jonathan Morton]

> On 19 Apr, 2015, at 21:30, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
> 
>>> Why not? They can be a quite useful measure of how competing traffic
>>> performs when bulk flows congest the link. Which for many
>>> applications is more important then the latency experienced by the
>>> bulk flow itself.
>> 
>> One clear objection is that ICMP is often prioritised when UDP is not.
>> So measuring with UDP gives a better indication in those cases.
>> Measuring with a separate TCP flow, such as HTTPing, is better still
>> by some measures, but most truly latency-sensitive traffic does use
>> UDP.
> 
> Sure, well I tend to do both. Can't recall ever actually seeing any
> performance difference between the UDP and ICMP latency measurements,
> though...

On a LAN, I usually see that ICMP gets a small bonus from being returned by the kernel rather than needing to wake up a userspace process.  That might matter less when the target host is multicore; I’ve often been using an old Thinkpad as a target.  In any case, it’s a constant factor without much dependence on network load.

The one ISP I know of on this side of the pond which does any prioritisation - there are many I don’t know about - prioritises small packets in general, though I don’t know where they set their threshold, specifically to help VoIP and gaming traffic.  I don’t think they treat ICMP specially beyond that.  But they’re a clueful one; there are many others less clueful.

Meanwhile, I’m presently (briefly) in a very rural part of Finland, where old 2G equipment (which I assume was redundant from early populated-area deployments) was relocated to improve coverage.  Twenty miles from any decent-sized town, fifteen miles from the nearest 3G tower, and about 7.5 miles from any worthwhile shops (ie. that sell food).  That means the local coverage is GPRS - not even EDGE.  And I brought some of the more portable components of my lab with me.  This should be fun…

 - Jonathan Morton