Nagra Seven Operating Instructions Manual page 74

Method 1: (Preferable choice) is a direct audio communication between devices without going
through a dedicated SIP server. A SIP server is required to initially establish the connection but is
subsequently bypassed once the connection is made. The direct audio connection using the RTP
protocol induces lower delays since the data does not pass through a relay point.
In case an (asymmetric) NAT / Firewall is present a STUN server is used to configure the
communication across the NAT (Firewall).
Chapter IV 73 September 2014