Name: Juniper CTP2024
Brand: Juniper
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call, the CTP device sends A = B = 1 signaling bits. At the end of the call, the FXO device

goes back to on-hook, the CTP detects the on-hook, sends out A=0 and B=1 signaling

bits, and the circuit returns to the idle state.

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For an analog CTP FXO interface, before the call starts the FXO is on-hook and no

ringing is generated by the attached FXS device. In this, the idle state, the CTP interface

generates B=1 and sends both A=0 and B=1. When the call comes in from the CO, the

CTP FXO interface detects ring voltage and starts toggling the B bit. When the other

end of the VCOMP bundle goes off-hook, it sends A=1 to the CTP. In response, the CTP

FXO interface closes the loop, going off-hook. With ringing stopped, the CTP interface

sends A = B = 1 during the call. At the end of the call the interface is again idle, and the

CTP interface sends A=0 and B=1 signaling bits.

Digital FXS/FXO Ground-Start Signaling

Unlike loop-start interfaces, in which the FXO and FXS each separately control a single

signaling bit, with ground-start signaling each side controls both the A and B bits. We

must consider each interface when the call is initiated by either interface. (See

Table 6 on page 23, Table 7 on page 23, Table 8 on page 24, and Table 9 on page 24). In

all cases, when the FXO/FXS interface is idle, the FXO interface generates A = B = 1

signaling bits and the FXS A = 0, B = 1. When a call is in progress, either side initiates a

call termination if it receives these signaling bits. For example, an FXS goes on-hook if it

receives A=B=1 signaling bits.

Table 6: Ground-Start Signaling at FXO Interface for Call Initiated by the

FXO Interface

Signaling Bits from FXOSignaling Bits to FXO

11 (A=1, B=1)01 (A=0, B=1)Idle (before call starts)

1100FXO grounds ring

0100FXS goes off-hook (grounds

tip)

0111FXO goes off-hook (closes

loop)

0111Duration of call

Table 7: Ground-Start Signaling at FXO Interface for Call Initiated by the

FXS Interface

Signaling Bits from FXOSignaling Bits to FXO

11 (A=1, B=1)01 (A=0, B=1)Idle (before call starts)

00/01 (B-bit toggles)01FXS goes off-hook (grounds

tip and sends AC ring signal)

Chapter 2: CTP2000 Series Interface Modules

Juniper CTP2024 User Manual

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