User's Manual 132 Document #: LTRT-42060
Mediant 2600 E-SBC
Parameter Description
Target End Port
CLI: TargetEndPort
[NATTranslation_TargetEndPort]
Defines the optional, ending port range (0-65535) of the global
address. If not configured, the ports are not replaced. Matching
source ports are replaced with the target ports. This address is
set in the SIP Via and Contact headers, as well as in the o= and
c= SDP fields.
12.9.2 Remote UA behind NAT
12.9.2.1 SIP Signaling Messages
By default, the device resolves NAT issues for SIP signaling, using its NAT Detection
mechanism. The NAT Detection mechanism checks whether the endpoint is located behind
NAT, by comparing the incoming packet's source IP address with the SIP Contact header's
IP address. If the packet's source IP address is a public address and the Contact header's
IP address a local address, the device considers the endpoint as located behind NAT. In
this case, the device sends the SIP messages to the endpoint, using the packet's source IP
address. Otherwise (or if you have disabled the NAT Detection mechanism), the device
sends the SIP messages according to the SIP standard RFC 3261, where requests within
the SIP dialog are sent using the IP address in the Contact header, and responses to
INVITEs are sent using the IP address in the Via header. To enable or disable the device's
NAT Detection mechanism, use the 'SIP NAT Detection' parameter.
If necessary, you can also configure the device to always consider incoming SIP INVITE
messages as sent from endpoints that are located behind NAT. When this is enabled, the
device sends responses to the INVITE (to the endpoint), using the the source IP address of
the packet (INVITE) initially received from the endpoint. This is especially useful in
scenarios where the endpoint is located behind a NAT firewall and the device (for whatever
reason) is unable to identify NAT using its regular NAT Detection mechanism. This feature
is enabled per specific calls using IP Groups. To configure this feature, use the 'Always
Use Source Address' parameter in the IP Group table (see ''Configuring IP Groups'' on
page 260). If this feature is disabled, the device's NAT detection is according to the settings
of the global parameter, 'SIP NAT Detection' parameter.
12.9.2.2 Media (RTP/RTCP/T.38)
When a remote UA initiates a call and is not located behind a NAT server, the device
sends the RTP (or RTCP, T.38) packets to the remote UA using the IP address:port (UDP)
indicated in the SDP body of the SIP message received from the UA. However, if the UA is
located behind NAT, the device sends the RTP with the IP address of the UA (i.e., private
IP address) as the destination, instead of that of the NAT server. Thus, the RTP will not
reach the UA.
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