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CPE Signaling Model
November 2009 338
Table 17. Line Signaling Model
State CAS Bits Notes
Outbound AB Inbound AB
Idle 10 10 Both outbound and inbound
channels are sending idle signal.
Seize 00 10 Outbound channel seizes the line.
Seize Acknowledge 00 11 Inbound channel initializes MFC
inter-register signaling and sends
the seize acknowledgment. When
the seize acknowledgment is
recognized by the outbound
channel, inter-register signaling
begins with the transmission of the
first DNIS digit.
If the call is accepted by the inbound side via the inter-register signaling, the answered state
is entered.
Answer 00 01
Answer 00 11 Metering pulses are possible. In
this example the pulse is
transmitted on the A bit. The
outbound side must not confuse
this with a clear back signal.
Answer 00 01 Metering pulse over, inbound
resumes transmission of the
answer signal.
If the call is rejected by the inbound side via the inter-register signaling, the outbound side is
responsible for clearing the call.
Clear forward 10 11 Outbound side sends clear forward.
Idle 10 10 Inbound side sends the idle signal.
Disconnection initiated by the inbound side.
Clear back 00 11 or 00 The hang-up might be signaled by a
clear back (AB=11) or by a forced
release (AB=00), as indicated by
network specifications.
Clear forward 10 11 or 00 Outbound side sends the clear
forward signal.