Bert - in answer to your question about DSL, they are run through concentrators at the CO (telco facility), and DSL circuits are routinely oversubscribed using the concentrator. You may not see it all the time, but if you run a trace-route device over time, DSL circuits are much more prone to mid-course congestion and latency. First ran into this ~ 15 years ago doing VOIP implementations.
Because they are carried over copper pair to the CO, they are also more prone to interference and episodic grounding.
