RG         UP(LAC)      CP(LAC)     AAA        LNS
     |    PPPoE   |    PPPoE     |        |          |
     |  Discovery |   Discovery  |        |          |
    1|<---------->|<---via Si--->|        |          |
     |            |              |        |          |
     |  PPP LCP   |   PPP LCP    |        |          |
    2|<---------->|<---via Si--->|        |          |
     |            |              |   AAA  |          |
     |PPP PAP/CHAP| PPP PAP/CHAP | Req/Rep|          |
    3|<---------->|<---via Si--->|<------>|          |
     |            |              |        |          |
     |  PPP IPCP  |  PPP IPCP    |        |          |
    4|<---------->|<---via Si--->|        |          |
     |            |              |        |          |
     |            | L2TP Tunnel  |        |          |
     |            | Negotiation  |        |          |
     |            |   SCCRQ/     |        |          |
     |            |   SCCRP/     |        |          |
     |            |   SCCCN      |        |          |
     |           5|<---via Si--->|        |          |
     |            | /\                               |
     |            | || Forward                       |
     |            | \/                               |
     |            |<-----------via Routing---------->|
     |            |                                  |
     |            | L2TP Session |        |          |
     |            | Negotiation  |        |          |
     |            |    ICRQ/     |        |          |
     |            |    ICRP/     |        |          |
     |            |    ICCN      |        |          |
     |           6|<---via Si--->|        |          |
     |            | /\                               |
     |            | || Forward                       |
     |            | \/                               |
     |            |<-----------via Routing---------->|
     |            |                                  |
     |            |    Create    |         |         |
     |            |  Subscriber  |         |         |
     |            |  Session Req |         |         |
     |           7|<---via Ci----|         |         |
     |            |    Create    |         |         |
     |            |  Subscriber  |         |         |
     |            |  Session Rep |         |         |
     |           8|----via Ci--->|         |         |
     |            |              |         |         |
     |                                               |
     |         PAP/CHAP (Triggered by LNS)           |
    9|<-----------------via Routing----------------->|
     |                                               |