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VCX V7111 VoIP Gateway User Guide
285
On startup the gateway sends a STUN Binding Request. The information received in the
STUN Binding Response (IP address:port) is used for SIP signaling. This information is
updated every NATBindingDefaultTimeout.
At the beginning of each call, if STUN is needed (that is, not an internal NAT call), the media
ports of the call are mapped. The call is delayed until the STUN Binding Response (that
includes a global IP:port) for each media (RTP, RTCP and T.38) is received.
To enable STUN:
Set the parameter EnableSTUN to 1
Define the STUN server's address by performing one of the following:
Define the STUN server's address by assigning it a domain name. The STUN client
can perform the required SRV query to resolve it to an IP address and port, sort the
server list, and use the servers according to the sorted list.
Determine the IP address of the primary and (optionally) the secondary STUN
servers using the parameters STUNServerPrimaryIP and STUNServerSecondaryIP.
If the primary STUN server is not available, the gateway tries to communicate with
the secondary server.
Use the parameter NATBindingDefaultTimeout to determine the default NAT binding
lifetime in seconds. STUN is used to refresh the binding information after this time
expires.
•
STUN only applies to UDP (doesn’t support TCP and TLS).
•
STUN can’t be used when the gateway is located behind a symmetric NAT.
•
For defining the STUN server's address, either use the
stunServerPrimaryIpAddress or the StunServerDomainName method, with
priority to the first one.
First Incoming Packet Mechanism
If the remote gateway resides behind a NAT device, it is possible that the Gateway can
activate the RTP/RTCP/T.38 streams to an invalid IP address / UDP port. To avoid such
cases, the Gateway automatically compares the source address of the incoming
RTP/RTCP/T.38 stream with the IP address and UDP port of the remote gateway. If the two
are not identical, the transmitter modifies the sending address to correspond with the
address of the incoming stream. The RTP, RTCP and T.38 can thus have independent
destination IP addresses and UDP ports.
Users can choose to disable the NAT mechanism by setting the
ini
file parameter
DisableNAT
to 1. The two parameters
EnableIpAddrTranslation
and
EnableUdpPortTranslation
enable users to specify the type of compare operation that takes
place on the first incoming packet. To compare only the IP address, set
EnableIpAddrTranslation = 1
and
EnableUdpPortTranslation = 0
. In this case, if the first
incoming packet arrives with only a difference in the UDP port, the sending addresses won’t
change. If both the IP address and UDP port need to be compared, then both parameters
need to be set to 1.
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