NEC SP5008A - Manual (Page 37)

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3.2 Advanced Configuration
3.2.1 System setting
prack PRACK is defined in RFC 3262: Reliability of
Provisional Responses in SIP. You can
accommodate your softswitch (Proxy Server) to
Enable or Disable this feature.
ROH (FXS only) Receiver-Off-Hook (ROH) Tone
A ROH tone is sent to the subscriber to inform
him that his receiver is off-hook.
You can Enable/Disable this option.
Send billing signal (FXS only) Polarity Reversal for billing signal, you can
enable (Reverse)/Disable the feature.
T.38 NoAttribute No attribute (Fax version, BitRate, Buffer,
Datagram…) indicated in T.38 Re-Invite with
Session Description Protocol (SDP).
You can Enable/Disable this option.
FAX redundancy depth Specify the resend times (0~3)for FAX error
packet,
T.38 FAX Type Select the FAX Type to use, you can choose the
following:
z T.38
z ByPass