Draytek Vigor2500V Manual page 131

Dialup 64Kbps: Use one ISDN B channel for Internet access.
Dialup 128Kbps: Use both ISDN B channels for Internet access.
Dialup BOD: BOD stands for bandwidth-on-demand. The router will
use only one B channel under low traffic situations. Once the single B
channel bandwidth is filled, the other B channel will be dialed
automatically. For more detailed BOD parameter settings, refer to the
Advanced Setup group > Call Control and PPP/MP Setup.
PPP Authentication:
PAP Only: Set the PPP session to use the PAP protocol to negotiate
the username and password with the ISP.
PAP or CHAP: Set the PPP session to use the PAP or CHAP protocols
to negotiate the username and password with the ISP.
Idle Timeout:
Idle timeout means the router will disconnect after being idle for a
preset amount of time. The default is 180 seconds. If you set the
time to 0, the ISDN connection will remain always connected to the ISP.
IP Address Assignment Method (IPCP)
Fixed IP, and Fixed IP Address:
In most environments, you should not change these settings as most
ISPs provide a dynamic IP address for the router when it connects to
the ISP. If your ISP provides a fixed IP address, check Yes and enter
the IP address in the field of Fixed IP Address.
ISDN Setup
13-4