SD,
Don't want to drift this thread any further, PPRuNe isn't really the place for discussing nitty gritty of ISP networks...
Random delays are to be expected on the internet, there are bottlenecks here and there ..... good ISPs know how to use the weapons in their arsenal to take care of routing around it....
However, sort of back on-topic, I should remind you that your most ADSL/Cable type connections do not come with any SLAs, so you get what you pay for in terms of potentially unpredictable performance because you are at the bottom of the ISP customer food chain.