User guide

126 RealCT Direct API Developer Guide
Chapter 4: E1 Networking
The main reason to run PCPM algorithms in R2 systems would
be detecting special tones such as Fax tones or operator
intercept not accompanied by an R2 register signal. However,
proprietary protocols running on E1 lines might require PCPM.
RHT_START_PCPM only monitors audible signals on the line
and runs independently of the type of line being used.
Since PCPM uses only sound or silence to determine the call
status, it cannot be absolutely accurate in detecting answer. For
example, if a busy switch plays a recording saying that all
circuits are busy, the PCPM algorithm might recognize the
human voice and determine that the call has been answered.
For this reason, you should run RHT_WAIT_ANSWER and
RHT_START_PCPM simultaneously. RHT_WAIT_ANSWER
provides accurate answer detection while RHT_START_PCPM
provides other information about the status of the call.
If the application starts RHT_START_PCPM with
VPstartStop_s.LineTerm0 set, the VP driver automatically
requests that the E1 device run RHT_WAIT_LINE_OFF.
RHT_WAIT_LINE_OFF monitors the line for a disconnect, but
it also detects answer. When RHT_WAIT_LINE_OFF detects
an answer or disconnect, it terminates RHT_START_PCPM.
The application then calls RHT_GET_STATUS to determine
the status of the line.