VoIP QOS best practices

[Jason Lixfeld <jlixfeld () andromedas com>]

Looking for some links to case studies or other documentation which 
describe implementing VoIP between sites which do not have point to 
point links.  From what I understand, you can't enforce end-to-end QoS 
on a public network, nor over tunnels.  I'm wondering if my basic 
understanding of this is flawed and in the case that it's not, how is 
this dealt with if the ISPs of said sites don't have any QoS policies?

-jL