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It is retained for the value of any residual information contained in it.


PPPoE stands for point to point protocol over ethernet. It is a method of encapsulating your data for transmission to a far point.
PPPoA is PPP over ATM.. from a software point of view, this is very similar to PPPoE .. in this case though, a DSL modem pumping ATM is internal to the computer, rather than being a short ethernet cable away.
Originally designed for dialup lines, it is being used by DSL providers to solve the problems they get managing an open DSL network, viz: IP address shortages, broadcasts not meant for you appearing on your local IP address (because you are on a giant ISP centered virtual net), and other (mainly ISP-end) difficulties inherent in large bridged networks.
Some heavy duty DSL back-end suppliers are promoting PPPoE as a way of helping ISPs cope with these difficulties. Redback, for example, is promoting PPPoE (PPP over ethernet), with a lot of success.
With a PPPoE setup, your computer (or in some cases, DSL hardware) needs to run a PPPoE protocol stack (software). This will be recommended by your DSL supplier. One of the more common PPPoE stacks is WinPOET. There may be difficulties combining NAT and PPP or PPPoE implementations.. it generally makes things more complex. Check the FAQ for common problems with PPPoE, DHCP and other issues. If you have a choice, try to get a bridged static IP.
An argument from a large DSL ISP, in favor of PPPoE follows:

One of the biggest complaints with dial-up, is that unless my company runs L2TP tunnels or some kind of IPSec, there's no way to access my work files from home. BSG's, with or without PPPoE allow the service provider to manage many seperate networks. For instance, ibm.com, bigDSLisp.net, ba.com could all be accessed from your desktop provided your service provider had agreements with these companies. This is only the first step. In 5 years you could see a consolidation, whereby there are only 2-3 facilities providers in New York, with many service companies providing value adds. Can you imagine FOX being a reseller with all of their programming offered at 500kb/s streaming! Sure there are bumps in the road. The whole PPPoE issue is only an issue because the software is still in it's infancy.

Why don't I like the static/DHCP model? Well mainly because it is so inflexible. Your router becomes the termination point, and running any advanced services reduces its ability to forward packets. The irony is that the SMS-1000 (Redback) BSG which Bell Canada and Bell Atlantic have deployed was designed by former Cisco developers. Essentially the redback emulates a bank of routers, and the customer is connected to one of those routers based on their domain name.

What will happen 3-5 years? Only backbone routers will remain packet workhorses, the access routers will be replaced by BSG's capable of "seeing" every single customer. Access providers will realize that their value is in the proximity to users, which equates to large amounts of revenue from new broadcasters. By users, I mean consumers, because the power workers will be starting to convert to mass wireless services, as yet too expensive for consumer.

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