Draytek Vigor2925 Series User Manual page 429

The major benefit of this mode is that you don't have to memorize your friend's IP
address, which might change very frequently if it's dynamic. Instead of that, you will
only have to use dial plan or directly dial your friend's account name if you are with
the same SIP Registrar.

Peer-to-Peer
Before calling, you have to know your friend's IP Address. The Vigor VoIP Routers will
build connection between each other.

Our Vigor V models firstly apply efficient codecs designed to make the best use of
available bandwidth, but Vigor V models also equip with automatic QoS assurance.
QoS Assurance assists to assign high priority to voice traffic via Internet. You will
always have the required inbound and outbound bandwidth that is prioritized exclusively
for Voice traffic over Internet but you just get your data a little slower and it is tolerable
for data traffic.
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Vigor2925 Series User's Guide