adsl protocols (ipoa pppoa pppoe)
Posted on 2004-09-21
i'd like to know how pppoa and pppoe works (compared to ipoa). I'm currently using an adsl in ipoa (aka Classic IP over ATM aka rfc1483 routed aka many other names) with a static pulbic IP and I like it. It's simple, the modem/router receive IP packets and sends them in ATM frames and viceversa. It's always on for real.
Now they are proposing me different adsl contracts that use PPPoA or PPPoE. But I'm not sure about how these works, so can any of you spread some light please?
Here are some concerns I have:
- PPP implies that a connection can be started and closed, right? So this is no longer always on, or is it? If I start the connection (actually my modem/router starts it becasue it receives outgoing traffic on the ethernet side), then maybe my provider disconnect me for inactivity. At this point I'm not reachable from outside until for some reason the modem decides to reconnect, right? And potentially when I reconnect I may get a different IP!
- What's the difference between PPPoA and PPPoE? If I use an ethernet modem/router that implements both, then on the ethernet side there will be no difference (just tcp/ip traffic) and on the WAN side there will be just ATM frames anyway. So where is the difference? Why doas someone says that PPPoE is for ethernet modems and PPPoA for USB modems?
My understanding is that PPP is used to transport any L3 protocol (IP,IPX,...) over either the ethernet cable (in case of ethernet modem with PPPoE) or ATM (in case of USB modem with PPPoA), but this is a bit confusing. Even if I have an ethernet modem (just a stupid modem that needs a PPPoE client on the pc), the modem will receive IP or IPX packets through PPP over ethernet, de-encapsulate these packets from PPP and then forwards them inside ATM frames, so why should the DSLAM care about my ethernet side, it just receives ATM frames anyway. In other words, from the DSLAM perspective, what's the difference between a client configured in PPPoA mode and another on ein PPPoE mode?