Snom ONE IP, Техническое руководство, Страница: 76 / 237

Deploying the snom ONE IP Telephone System
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be consulted by the system before consulting/using the operating system).
Whenever the system wants to find the IP address that is being used when
sending a SIP packet, it steps through the list and looks for a match (using
the netmask mask) to a destination address (DAdr). If a match is found, the
system uses the provided IP address (LAdr). The mask must be in the form of
an IP address, e.g., 255.255.255.0 .
RTP Ports
The Real Time Protocol (RTP) ports are used for sending and receiving media. Be sure
to specify a reasonable port range so that you have enough ports for all open calls. A
port range of 100 ports is not unusual.
Most user agents send RTP media data from the same port on which they expect to re-
ceive data. This is useful when a user agent sends media from behind NAT. The system
can use this mechanism to establish a two-way media path, even if the user agent is not
able to determine its public IP address for media and is behind NAT.
•
Port Range Start: This setting represents the starting RTP port that the sys-
tem will use for media sessions. If the system is behind a firewall, these ports
should be open.
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Port Range End: This setting represents the end RTP port that the system
will use for the media sessions. RTP uses UDP for transport, whereas SIP can
use UDP, TCP, and/or TLS.