Still vague, and you have the bad habit of specifying implementation
mechanisms when asked for requirements. Users who specify
implementation methods to engineers end up with bad designs 
With
sincere respect, I point out you are asking a question to which you do
not know the optimal answer and then supplying your best answer so far
as if it is the only answer. You might learn more if you sincerely
asked the question and listened...
Quick review:
The Ethernet protocol was designed to adjudicate and route packets
internal to one homogeneous, physical network. It handles media
access, security, reliablity and routing in that one physical network.
What does Ethernet have to do with routing ?
It appears to me that your problem here is at the physical network
level. You only have one physical network. Your Ethernet hardware
should handle the routing to the proper ISP. If it were me, I would
also expect my Ethernet hardware to be able to filter, load-balance
and meter based on MAC address so that I could gaurantee no ISP could
see another's traffic and accurately charge the ISP for bandwidth.
The problem you dont really have one physical network. We are trying
to extend Ethernet into a logical network. The physical link to the
customer is the same, but the customer is terminated logically. The reason
that I
like PPPoATM is that the end device requires littel intelligence , it knows
one
PVC, and all changes (linking them to the ISP of choice, propogate easily
downstream).RFC
1483 (Ethernet over ATM, used in DSL and plausibly in cable ) is a great
idea
for business but not suitable for home users. Hardware that you speak of
becomes just too expensive.
I think I hear you saying you must use hardware that does not use
Ethernet. In which case, you have steered the conversation away from
the original IPoE public network arena. You also have my condolences.I strongly recommend you spend some quality time with the DOCSIS
spec... Personally, I think DSL and wireless modems would benefit from
using DOCSIS. I have not thought hard about this issue and am
interested in other opinions...
It appears as if someone has thought of this before Someone is apparently
doing this already (I don't know the name of the company), taking regular
cable
modems and using wireless for intramodem communication (why re-invent the
wheel)
instead of copper.
[ On Tuesday, June 26, 2001 at 13:05:40 (-0400), Fletcher E Kittredge wrote: ]
Subject: Re: Cable Modem [really good network design]
I strongly recommend you spend some quality time with the DOCSIS
spec... Personally, I think DSL and wireless modems would benefit from
using DOCSIS. I have not thought hard about this issue and am
interested in other opinions...
You do learn fast! 
However you'd better watch out. DOCSIS-1.0 is an implementer's worst
nightmare. At best it provides a low-level physical layer spec. and the
rest of it is pretty much useless in prodcution. 2.0 solves some of the
problems, but introduces more.