User`s manual

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3.4 Advanced Configuration
3.4.1 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 Tone(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.
Enable: using default setting or custom
setting.
Send billing signal (FXS only)
Enable Polarity Reversal for FXS as billing
signal or not. When a FXS calls to VOIP
and answered by the VOIP, SP50X8A will
generate reverse signal to FXS as billing
start. When VOIP side disconnect first,
SP50X8A will reverse back as billing stop
signal.