Version 5.2 171 September 2007
SIP User's Manual 5. Web-based Management
Table 5-33: Media Settings -- Fax/Modem/CID Parameters
Parameter Description
CNG Detector Mode
[CNGDetectorMode]
 [0] Disable = The originating gateway doesn’t detect CNG; the
CNG signal passes transparently to the remote side (default).
 [1] Relay = CNG is detected on the originating side. CNG packets
are sent to the remote side according to T.38 (if IsFaxUsed = 1)
and the fax session is started. A Re-INVITE message isn’t sent
and the fax session starts by the terminating gateway. This option
is useful (for example) when the originating gateway is located
behind a firewall that blocks incoming T.38 packets on ports that
have not yet received T.38 packets from the internal network (i.e.,
originating gateway).
 [2] Events Only = CNG is detected on the originating side. The
CNG signal passes transparently to the remote side and a fax
session is started by the originating side using Re-INVITE
message. Usually, T.38 fax session starts when the ‘preamble’
signal is detected by the answering side. Some SIP gatewaya
don’t support the detection of this fax signal on the answering
side, thus, for these cases it is possible to configure the gateway
to start the T.38 fax session when the CNG tone is detected by
the originating side. However, this mode is not recommended.
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