AudioCodes Mediant 4000 SBC User Manual page 987

CHAPTER 60 Configuration Parameters Reference
configure voip > media
rtp-rtcp > udp-port-
spacing
[UdpPortSpacing]
'T.38 Fax Session'
configure voip > sip-
definition settings > t38-
sess-imm-strt
[T38FaxSessionImmediateStart]
configure voip > sip-
definition settings > t38-
use-rtp-port
[T38UseRTPPort]
Parameter Description
Defines the port spacing ("jumps") of local UDP ports
allocated by the device to media channels (legs) within
the configured port range.
■ [4] = (Default) The device allocates ports in
"jumps" of 4 ports.
■ [5] = The device allocates ports in "jumps" of 5
ports.
■ [10] = The device allocates ports in "jumps" of 10
ports.
Note:
■ A device reset is required for the parameter to take
effect.
■ For more information on configuring the UDP port
range, see Configuring RTP Base UDP
Enables fax transmission of T.38 "no-signal" packets
to the terminating fax machine.
■ [0] Disable (default)
■ [1] Immediate Start on Fax = Device activates
T.38 fax relay upon receipt of a re-INVITE with
T.38 only in the SDP.
■ [2] Immediate Start on Fax & Voice = Device
activates T.38 fax relay upon receipt of a re-
INVITE with T.38 and audio media in the SDP.
The parameter is used for transmission from fax
machines connected to the device and located inside a
NAT. Generally, the firewall blocks T.38 (and other)
packets received from the WAN, unless the device
behind NAT sends at least one IP packet from the
LAN to the WAN through the firewall. If the firewall
blocks T.38 packets sent from the termination IP fax,
the fax fails.
To overcome this, the device sends No-Op ("no-
signal") packets to open a pinhole in the NAT for the
answering fax machine. The originating fax does not
wait for an answer, but immediately starts sending
T.38 packets to the terminating fax machine.
Note: To enable No-Op packet transmission, use the
[NoOpEnable] and [NoOpInterval] parameters.
Defines the port (with relation to RTP port) for sending
and receiving T.38 packets.
■ [0] = (Default) Use the RTP port +2 to
send/receive T.38 packets.
■ [1] = Use the same port as the RTP port to
send/receive T.38 packets.
Note:
■ For the parameter to take effect, you must reset
the device.
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Mediant 4000 SBC | User's Manual
Port.