Vigor Router broadband models, such as Vigor2100V; Vigor2110V; Vigor2901V, connect to the internet via an external modem connected by 10 or 100Mbps Ethernet cable; and hence do not know how much bandwidth is actually available from the modem to the ISP. Normally this isn’t a problem, but when the bandwidth starts to become congested the Vigor’s QoS needs to start prioritising traffic to ensure that VoIP quality does not degrade.
DrayTek recommend setting the WAN Inbound and WAN Outbound Bandwidths to 80% of the bandwidth provided by your ISP.
Commonly ISP bandwidth is referred to as two numbers (e.g. 1.5M/256, 512/128 or 256/64), with Downstream bandwidth (pages and files coming “in” to you) the first number, and Upstream bandwidth (your page request going “out” to the second (and usually smaller) number. For example a 512/128 ADSL account has 512Kbps downstream and 128Kbps upstream bandwidth, and Draytek recommends you enter 410 into “WAN Inbound Bandwidth” and 102 into “WAN Outbound Bandwidth”.
Note that the default value of 10,000 represents the speed (10Kbps=10,000Kbps) of the Ethernet cable between your Vigor router and the external modem – which is a lot faster than the modem’s connection to your ISP.