I am wondering what is the general use of authentication of clients on a WISP or FISP (fixed line) Network. What are operators usually using, and where?

We ever started with simple dhcp server and assigned an IP to the client antenna.
Then we moved to use a more centralized system with the use of a PPPoE concentrator/server (with User Manager as radius) and the PPPeE client residing in the CPE.

I know many cable and adsl operators in EU use PPPoE in the clients device at home. the wifi router or modem (old days!)
According the suggestion of some hardware vendors in Russia and other east European countries other forms are used as well.
Then we have operators using vlans to separate different kind of services from others.

I am just wondering what is common, what are the pro's and con's and why are some systems used by some where others choose to specifically do it different...

The fact is that large providers have historically been able to provide services via the PPPoE protocol and vendors that sold them hardware should support it. In fact: vendors got money, providers don't need to change something in their network. Over time, it has not become worse, and cold patches can improve it, if something went wrong. But in general, you can connect your subs as you want I work for a large Internet provider and I can only say one thing: the simpler the design, the more stable services you can provide to customers. And technical support can handle it better.

In the old days, PPPoE was used to terminate the subscriber traffic through the phone line! It worked much better than coaxial cable with constant signal loss.

The fact is that large providers have historically been able to provide services via the PPPoE protocol and vendors that sold them hardware should support it. In fact: vendors got money, providers don't need to change something in their network. Over time, it has not become worse, and cold patches can improve it, if something went wrong. But in general, you can connect your subs as you want I work for a large Internet provider and I can only say one thing: the simpler the design, the more stable services you can provide to customers. And technical support can handle it better.

In the old days, PPPoE was used to terminate the subscriber traffic through the phone line! It worked much better than coaxial cable with constant signal loss.

Basically all I would like to know is if you only need to do a simpel authentication of a client (we'd use User Manager) and we have a gateway router performing the client limiting based upon his radius (UM) setting what would give you the most stable solution in respect to the network?
I have the 'feeling' our PPPoE use is at time giving more issues then it solves. (MTU comes in mind here..)
And 'where' is it best done, the authentication? At the client's Wifi router? (So when he/she resets it he has no more internet access and calls us to set it up again which we can't without going there.
Or best done in our CPE so if the clients has no internet we can check up towards our antena but have little idea what happens behind that. But now my CPE has to have a PPPoE 'tunnel' and probably a management IP which give the CPE more work and make the config more complicated and thus the possibility for errors bigger...

I don't know what is best. And maybe there are some real good other alternatives....