Draytek 5500 Series Method Ipcp, Check Yes and enter the IP address in the field of Fixed IP

Method (IPCP)	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.

Select Dialing to Dual ISPs if you have more than one ISP. You will be able to dial to both ISPs at the same time. This is mainly for those ISPs that do not support Multiple-Link PPP (ML-PPP). In such cases, dialing to two ISPs can increase the bandwidth utilization of the ISDN channels to 128kbps data speed.

Common Settings	Enable Dual ISPs Function - Check to enable the Dual ISPs
	function. Require ISP Callback (CBCP) -If your ISP
	supports the callback function, check this box to activate the
	Callback Control Protocol during the PPP negotiation.

PPP/MP Setup	Link Type – There are three link types provided here for
	different purpose. Link Disable disables the ISDN dial-out
	function. Dialup 128Kbps allows you to use both ISDN B
	channels for Internet access. Dialup BOD (for detailed
	information of configuration, please refer to section 3.10.5)
	stands for bandwidth-on-demand. The router will use only one
	B channel in low traffic situations. Once the single B channel
	bandwidth is fully used, the other B channel will be activated
	automatically through the dialup.
	PPP Authentication - PAP only allows you to configure the
	PPP session to use the PAP protocol to negotiate the username
	and password with the ISP. PAP or CHAP can configure 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 be
	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 to the ISP will always remain on.
126	VigorPro5500 Series User’s Guide