User's Manual
144
Document #: LTRT-10375
Mediant 500 MSBR
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 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 the 'Always Use Source Address' parameter in the IP Groups table
(see Configuring IP Groups on page 333). If this feature is disabled, the device's NAT
detection is according to the settings of the global parameter, 'SIP NAT Detection'
parameter (see below procedure).
To enable the NAT Detection feature (global):
1.
Open the Transport Settings page (
Setup
menu >
Signaling & Media
tab >
SIP
Definitions
folder >
Transport Settings
).
2.
From the 'SIP NAT Detection' drop-down list (SIPNatDetection), select
Enable
:
Figure
15-5: Enabling SIP NAT Detection
3.
Click
Apply
.
15.2.2.2 Media (RTP/RTCP/T.38)
When a remote UA initiates a call and is not located behind a NAT server, the device
sends the media (RTP, RTCP, and 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. To resolve this NAT traversal problem, the device offers the
following features:
First Incoming Packet Mechanism - see First Incoming Packet Mechanism on page
144
RTP No-Op packets according to the avt-rtp-noop draft - see No-Op Packets on page
146
The figure below illustrates a typical network architecture where the remote UA is located
behind NAT:
Figure
15-6: Remote UA behind NAT
15.2.2.2.1 First Incoming Packet Mechanism
In scenarios where the remote user agent (UA) resides behind a NAT server, it’s possible
that the device, if not configured for NAT traversal, will send the media (RTP, RTCP and
Summary of Contents for Mediant 500 MSBR
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Page 137: ...Part IV General VoIP Configuration ...
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Page 455: ...Part V Gateway Application ...
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Page 757: ...Part IX Maintenance ...
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Page 837: ...Part X Status Performance Monitoring and Reporting ...
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Page 927: ...Part XI Diagnostics ...
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Page 977: ...Part XII Appendix ...
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