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Appendix D

Line Interface Signaling

This appendix describes how to interpret signaling from the QX 2000 board's line interfaces and how to control the line interfaces by sending signaling bits to it. Note: The trunk control DLL running on the QX 2000 board automatically controls and monitors the line signaling bits. This information is provided for reference only. Controlling the signaling bits manually may violate local telecommunications regulations.
There are two signaling directions: Transmit signaling. This is the signaling that the QX 2000 board sends to the telephone line. The transmit signaling is used to control the line or phone. Receive signaling. This signaling comes from the phone line to the QX 2000 board. An application can monitor the receive signaling to detect loop current to determine if a phone is on-hook or off-hook. Figure 24. Transmit and Receive Signaling
To monitor receive signals or to set transmit signals, you examine or change the data in the signaling streams. For example, to monitor the signaling for the first analog interface on the QX 2000 board, examine Local Bus: stream 0: timeslot 0 (or stream 16: timeslot 0 in the MVIP-90 switch model).
Figure 25 illustrates a signaling stream byte. The A bit is used. Bits B, C, and D are undefined. Figure 25. Bits in Signaling Byte

With loop start interfaces, the A bit transmitted in the signaling timeslot causes the interface to seize the line (go off-hook) or release the line (go on-hook). If bit A is set to 1, the line goes off-hook. If bit A is set to 0, the line goes on-hook. Bits B, C, and D should be set to 0. Figure 26. Loop Start Transmit Signaling

Depending on whether the line has been placed on-hook or off-hook (by setting the A bit in the signaling output stream), the A bit received acts either as a ring detector or a loop current detector. When the line is on-hook, monitoring the A bit tells you if the line is ringing. When the line is off-hook, monitoring the A bit and B bit indicates whether there is loop current flowing. Figure 27. QX 2000/100-4L Loop Start Receive Signaling

Depending on whether the line has been placed on-hook or off-hook (by setting the A bit in the signaling output stream), the B bit received acts either as a ring detector or a reversal current detector. When the line is on-hook, monitoring the B bit tells you if the line is ringing. When the line is off-hook, monitoring the A bit and B bit indicates whether there is loop current flowing. Figure 28. QX 2000/80-4L Loop Start Receive Signaling

If talk battery feed is enabled, the A bit received in signaling stream for the local phone (an Operator Work Station interface) indicates whether loop current is flowing. If the A bit is 0, no loop current is flowing. If the A bit is 1, current is flowing. Bits B, C, and D are reserved and should be ignored. Figure 29. Local Phone Receive Signaling

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