There are no upper boundaries when it comes to latency, but at some point your browser/whatever will start to resend the information, thinking it's lost. Typically you should have around 20-30ms within the same country, depending on peering and such.
When you start to factor in things like the fact that light travels 1/3 as fast in a glass fiber as it does in vacuum, routing overhead, and the fact that ping is a round-trip measurement, 60-100ms is about normal.
15 milliseconds * 2 (ping = round trip time) * 1.52 (~index of refraction in fiber) = 45.6ms straight line. Add in routing dilays and less than optimal paths and your quickly hit 60-100 ms.
> The high latency with dsl usually comes hand in hand with interleaving enabled.
Interleaving doesn't add huge amounts of latency. To the LNS with the ISP I'm on, I usually see about 11-16ms to the first hop, maybe 5ms to a game server on their network a most. Without interleaving, I see about 5-7ms less on a good day.
Now, saying that, there are different levels of interleaving that can be applied on modern DSLAMs, but we're not really talking tens of milliseconds here.
It's also worth keeping in mind that your pings won't be truly representative of latency. Plenty of ISPs de-prioritise ICMP traffic.
My pings are really similar to my latency measured with different sources.
My isp (Qwest) uses interleaving and it adds quite a bit to my first hop (it usually is about 60ms) and from what I've seen those people actually living in a more populated area the interleaving latency added is about the same (>30ms first hop and usually closer to 60). So of course it depends on the ISP and qwest is notoriously bad for this but is my only option, and occurs with plenty of other ISPs with interleaving.
Which residential fiber products have huge latency?