Issue Description
Q:
How is the rule of up & down in VT and Dailer of VRP defined?
Handling Process
A:
1. For MP, when IPCP of all PPP links of bound VT interface is down, VT interface is DOWN. IF IPCP of one PPP link is up, VT interface is up.
2. For PPPoE Server, when there is no session between VT interface and PPPoE Client, VT interface is down. If PPPoE creates one session, VT interface is up.
3. For PPPoE Client, if there is no session between dialer and PPPoE Server, Dialer is down. If PPPoE creates one session, Dialer is up.
4. For non-dial PPPoA, when IPCP of all PPP links on VT is down, VT is down. If IPCP of one PPP link is up, VT is up.
5. For PPPoA Server, if there is no session between VT and PPPoA Client, VT is down. If PPPoA creates one session, VT is up.
6. For PPPoA Client, when there is no session between Dialer and PPPoA Server, Dialer is down. If PPPoA creates one session, dialer is up.
