Thanks for your response which I find disturbing more than anything else.
“All perfectly normal on ADSL/ADSL2+”. Here’s the really frustrating thing, with a sensible packet shaper in place the ISP can ensure the downlink isn’t overloaded. Andrews & Arnold make a point of running a shaper on the downlink either at or just below (95%) of the BRAS rate, thus they can achieve good latency figures even under load.
In other words it doesn’t and shouldn’t be this way. To regard it as normal is unacceptable, we should be trying harder and doing better. 1.3 seconds of additional latency under load is the equivalent of the downlink side of the exchange being on the moon!
The upstream latency is relatively well controlled by the supplied router (D-link) being around 100ms - not a perfect score but certainly an order of magnitude better than the downlink.
“With faster services you have more options e.g. operate QoS which reserves some bandwidth to allow for prioritising certain traffic”
Lower capacity links are much more in need of QoS functionality. There are some excellent shapers and active queue management algorithms out there that can maintain low latency and flow fairness. Have a look at fq_codel (and for the really brave ‘cake’)
For ‘fun’ I artificially limited my own connection from 78/20 to 2/.6 with a shaper, in combination with an AQM this kept latency down to 20ms and flow fairness good. Yes there was less data flowing so downloads/uploads took more time (were slower) but general browsing was acceptable because latency was still low. Latency has much more impact on the ‘interactivity’ of a connection than pure ‘speed’…by which we really mean link capacity.
“Solution is two get two lines, so if a big download is using up one they can do latency sensitive stuff on the other.” There are so many practical problems with that that I’m not going to get started.
Like I said at the start, I find “All perfectly normal on ADSL/ADSL2+” to be the most disturbing of all of this. It shouldn’t and doesn’t have to be this way, if only we could get ISPs to listen.