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Appendix B

Line Interface Signaling

Introduction

This appendix describes how to interpret signaling from a line interface, and how to control an interface by sending signaling bits to it.
There are two signaling directions (shown in Figure 18): 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 CTA applications. Figure 18. Transmit and Receive Signaling
On the AG Connect board, the following stream is used for line interface signaling: MVIP-90: stream 17 MVIP-95: local streams 2 and 3
Figure 19 and Figure 20 show the signaling in the context of the MVIP switch model: Figure 19. Signaling In MVIP-90 Switch Model Figure 20. Signaling In MVIP-95 Switch Model
To monitor receive signals, or to set transmit signals for a line interface, your application can examine or change the data in the line interface signaling stream, in the timeslot associated with the interface.

Loop Start Line Interface Signaling

Figure 21 illustrates a signaling stream byte. The A bit is used to control or monitor the line. Bits B, C, and D are reserved. Figure 21. Bits in Loop Start Line Interface Signaling Byte

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 22. Loop Start Transmit Signaling Note: If you reset the switch, all bits are set to 0.

Loop Start Receive Signaling

Depending on whether the line has been placed on-hook or off-hook (by setting the A bit in the transmit signaling), the A-bit received acts either as a ring indicator 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 23. 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

Operator Work Station (OWS) Interface Signaling

OWS interface transmit signaling bits are used differently, depending upon whether your AG Connect board supports the Ringing option or not. The following sections describe both cases:

OWS Transmit Signaling (Boards Without Ringing)

With OWS interfaces on boards that do not support the Ringing option, transmit signaling works as illustrated in this diagram: Figure 24. OWS Transmit Signaling (Boards Without Ringing)
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:
Note that if you reset the switch, all bits are set to 0.

OWS Transmit Signaling (Boards With Ringing)

With OWS interfaces on boards that support the Ringing option, transmit signaling works as illustrated in this diagram: Figure 25. OWS Transmit Signaling
The signaling bits are used as follows: 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. Bit B controls ringing. If bit B is 1 and the phone is on-hook, the phone rings in the cadence specified by bit C (see below). The phone will continue to ring until it is taken off-hook or bit B is reset. If bit B is not reset when the phone is off-hook, the phone will resume ringing when it is placed on- hook. You can determine the phone's status by monitoring incoming signaling. The OWS phone receives power whenever bit B is set and the phone is actually ringing, regardless of the setting of bit A. Bit C controls the 6-second cadence of the ring: - If bit C is 0 and bit B is 1, the phone will ring two seconds, stop for four seconds, and then cycle again: "ring...........ring...........ring..........." - If bit C is 1 and bit B is 1, the phone will ring for 3/4 second, stop for 1/2 second, ring for 3/4 second, stop for four seconds, and then cycle again: "ring ring..........ring ring..........ring ring.........." Bit D is reserved, and should be set to 0.
Note that if you reset the switch, all bits are set to 0.
Phone ringing is phased; that is, only one phone can begin ringing each 1/4 second. For example, if you direct two phones to ring, the first phone rings 1/4 second after you give the command; the second rings 1/2 second after the command.
Also, the AG Connect With Ringing board can only apply ringing voltage to 8 phones at any given time. If more than 8 phones are set to ring, the board delays the ringing of each extra phone until one of the first eight phones is not actually ringing (e.g. the phone is in the four-second "quiet" phase of its ring). If 24 phones are set to ring, some phones' rings may be delayed up to 6 seconds after the B bit is set for the phones.

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 26. OWS Receive Signaling
Note that the A-bit in this case is meaningless unless talk battery feed is enabled.

Monitoring and Controlling Signals

Monitoring the Receive Signals

You can use the CT Access swiSampleInput function to sample the receive signal for a line or phone programmatically. Alternatively, you can use the swish swi.SampleInput command.
For example, the following swish command samples the receive signal of the phone connected to the first line interface of device cx0: swi.SampleInput cx0 17:0
If the phone was on-hook, swish 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, swish would return this message, indicating that bit A of Stream:Timeslot 17:0 is set: 17:00=0f

Controlling the Transmit Signals

You can control the transmit bits in any of the following ways:

You can use the CT Access swi.SendPattern function or the swish swi.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 swish command to send 0x08 to Stream:Timeslot 17:3 of device cx0:

swi.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 27:

Figure 27. 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.

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