Valcom IP bold series Installation & Operation Instructions page 36

RTP. After sends data to same adress:port from which message
arrived. It is trick used for bridging NAT.
In active mode - P2P is possible to operate device, which require for
their function registration at the SIP server. This option will use new SIP
phones, which generally do not support P2P mode, as well as applications for
iOS - Apple.
The principle of setting SIP phones and UDV guard, UDV Panel with IP BOLD:
1. Mode of phone is SIP server registration is IP address IP BOLD
(registration or SIP server = IP address IP BOLD)
2. Name and password is the line number (we choose a numbering plan
so that each number occurred in the network only once, then for each
device, fill in name and password to register with this number).
Example:

IP address of IP BOLD is 192.68.1.250 and the name (page SIP
parameters) is 250

The IP address of SIP phone 1 is 192.168.1.200, fill in the registration
here - SIP server = 192.168.1.250 and name = password = 230

The IP address of SIP phone 2 is 192.168.1.201, fill in the registration
here - SIP server = 192.168.1.250 and name = password = 231
Call to SIP Phone 1 is 230, calls to SIP phone 2 is 231 and calls to
IP BOLD is 250
36 IP BOLD
- installation and operating instructions