[e2e] Congestion control and avoidance - QoS?

[demir]

Can I view congestion control and avoidance as one of the QoS
mechanisms? If so, I assume the Internet has evolved from best-effort
service to "congestion controlled and avoided best-effort
service" (assuming all end-systems are deployed with TCP-friendly
algorithms) ???
What was the reason that TCP was chosen to control and avoid congestion
whereas UDP was left to be free from congestion control and avoidance then
TCP-friendliness became an issue? If the answer to above question is yes,
then I assume current Internet offers two types of service: one of them is
"TCP-friendly throughput guarated best-effort service" and the other one
is "better-than TCP-friendly throughput guaranteed best-effort service".
Can a AQM algorithm deployed throughout a network change the meaning of
"best-effort" service? 

Although the network offers only "best-effort service" from network point
of view, I think when a QoS is defined from "end-system" point of view,
the service observed will differ. 

For a future QoS network, shall congestion control and avoidance be
protected by co-operative end-systems or by the network? I assume
"end-to-end argument" is very important here. However, if
"end-systems" are not trustfull, is it possible at all  that network can
achieve the goal correctly in a distributed fashion? If so, I assume
this should be at IP level? Is there any reserach on this? Thank you very
much.

Alper K. Demir