AudioCodes Mediant 800 - Page 1316

CHAPTER72 Configuration Parameters Reference
Mediant 800 Gateway & E-SBC | User's Manual
Parameter Description
■ [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.
configure voip > sip-
definition settings > t38-
use-rtp-port
[T38UseRTPPort]
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.
■ When the device is configured to use V.152 to
negotiate audio and T.38 coders, the UDP port
published in SDP for RTP and for T38 must be
different. Therefore, set the T38UseRTPPort
parameter to 0.
'T38 Fax Max Buffer'
configure voip > sip-
definition settings > t38-
fax-mx-buff
[T38FaxMaxBufferSize]
Defines the maximum size (in bytes) of the device's
T.38 buffer. This value is included in the outgoing
SDP when T.38 is used for fax relay over IP.
The valid range is 500 to 3000. The default is 3,000.
No-Op Packets Parameters
no-operation-enable
[NoOpEnable]
Enables the transmission of RTP or T.38 No-Op
packets.
■ [0] = Disable (default)
■ [1] = Enable
This mechanism ensures that the NAT binding
remains open during RTP or T.38 silence periods.
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