Quite a bit of overhead. Good article here:
http://blog.ioshints.info/2009/03/adsl-overhead.html
Curtis Maurand wrote:
I don't understand why DSL providers don't just administratively down
the port the customer is hooked to rather than using PPPoE which costs
bandwidth and has huge management overhead when you have to disconnect a
customer. I made the same recommendation to the St. Maarten (Dutch)
phone company several years ago. They weren't listening either. That
way you can rate limit via ATM or by throttling the port administratively.
Just a suggestion