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5.6 Line Interface Signaling

This section describes how to interpret signaling from a line interface, and how to control an interface by sending signaling bits to it.

5.6.1 Overview

There are two signaling directions (shown in Figure 6): Transmit signaling. This is the signaling that the board sends out onto the phone line via the line interface. The transmit signal is used to control the line or phone. Receive signaling. This signaling comes from the phone line through the line interface to the board. An application can monitor this signal to detect loop current (i.e. whether the phone is on-hook or off-hook) or ringing.
The line interfaces on the board convert the signaling into the line condition appropriate for the line type (e.g. loop start, etc.). They also convert incoming information into digital signals recognizable by AG applications. Figure 6. Transmit and Receive Signaling
On the AG Connect board, stream 17 is used for line interface signaling. Figure 7 shows the signaling in the context of the MVIP switch model: Figure 7. Transmit and Receive Signaling In MVIP Switch Model
To monitor receive signals, or to set transmit signals for a line interface, your application can examine or change the data in stream 17 (the line interface signaling stream), in the timeslot associated with the interface.
Note that line interfaces are numbered from 1 upward; timeslots from 0 upward. For example, to direct the phone connected to line interface 5, send the signal byte to Stream:Timeslot 17:4.
Figure 8 illustrates a signaling stream byte. The A bit is used to control or monitor the line. Bits B, C, and D are undefined. Figure 8. Bits in Signaling Byte
The A-bit in the timeslot for a line interface is used differently, depending upon whether the line interface is a loop start or OWS interface. The following sections describe the purpose of the A-bit in each case.

5.6.2 Loop Start Transmit Signaling

With loop-start interfaces, the A-bit transmitted in the signaling timeslot for a loop-start interface 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 are reserved, and should be set to 0: Figure 9. Loop Start Transmit Signaling
Note that if you issue a ResetSwitch command, all bits are set to 0.

5.6.3 Loop Start Receive Signaling

Depending on whether the line has been placed on-hook or off-hook (by setting the A bit), the A-bit received acts either as a ring or loop current indicator. When the line is on-hook, monitoring the A bit will tell you if the line is ringing or not. When the line is off-hook, monitoring the A bit will indicate whether there is loop current flowing or not:

A-bit Setting

Means the following:

(line on-hook)

(line off-hook)

0

Line is not ringing

No loop current

1

Line is ringing

Current is flowing
Bits B, C and D are reserved, and should be ignored. Figure 10. Loop Start Receive Signaling

A-bit Setting	Means the following:
	(line on-hook)	(line off-hook)
0	Line is not ringing	No loop current
1	Line is ringing	Current is flowing

5.6.4 Operator Work Station (OWS) Transmit Signaling

The A-bit transmitted in the signaling timeslot for an OWS interface enables or disables the talk battery feed (the power) to the phone attached to that interface. If the A-bit is 0, talk battery feed is disabled. If the A-bit is 1, talk battery feed is enabled. Bits B, C and D are reserved, and should be set to 0: Figure 11. OWS Transmit Signaling
Note that if you issue a ResetSwitch command, all bits are set to 0.

5.6.5 OWS Receive Signaling

If talk battery feed is enabled, the A-bit received in the signaling timeslot for an OWS interface indicates whether loop current is flowing or not (that is, whether the phone is off-hook or not). 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 12. OWS Receive Signaling
Note that the A-bit in this case is meaningless unless talk battery feed is enabled.

5.6.6 Monitoring the Receive Signals

You can use the SwitchPath CxSampleInput() function to sample the receive signal for a line or phone programmatically. Alternatively, you can use the SW Utility's SampleInput command.
For example, the following SW Utility command samples the receive signal of the phone connected to the first line interface of device "cx0": SampleInput cx0 17:0
If the phone was on-hook, SW Utility would return the following message, indicating that bit A of Stream:Timeslot 17:0 is 0: 17:00=00
If the phone was off-hook, SW Utility would return this message, indicating that bit A of Stream:Timeslot 17:0 is set: 17:00=0f

5.6.7 Controlling the Transmit Signals

You can control the A-bit in either of the following ways:

You can use the SwitchPath CxSendPattern() function or the SW Utility's SendPattern command.

These commands cause a specified byte to be broadcast in one or more Stream:Timeslots in pattern mode: the byte will continue to be passed in the Stream:Timeslot until you disable output on the appropriate switch block output.
For example, to take the loop start line connected to the fourth line interface off-hook, you can use the following SW Utility command to send 0x08 to Stream:Timeslot 17:3 of device "cx0":
SendPattern cx0 0x08 to 17:3

You can assert a pattern in the Stream:Timeslot by connecting it to a Stream:Timeslot broadcasting the pattern you wish to transmit.

The pattern must be generated by a DSP on an AG resource board. When you make a switch connection, the pattern is copied from the MVIP bus to the signaling stream, as shown in Figure 13:

Figure 13. Controlling the Signal by Making a Connection

Note: You should always control signaling to the line interfaces in order to prevent random changes in the line state.

(Page 7 of 11 in this chapter)

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