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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 13): 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 CT Access applications. Figure 13. 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 14 and Figure 15 show the signaling in the context of the MVIP-90 and MVIP-95 switch model: Figure 14. Signaling In MVIP-90 Switch Model Figure 15. 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.

Operator Work Station (OWS) Interface Signaling

Figure 16 illustrates a signaling stream byte: . Figure 16. Bits in Signaling Byte

OWS Transmit Signaling

With OWS interfaces on boards that support the Ringing option, transmit signaling works as illustrated in this diagram: Figure 17. 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 (see below). 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.
In addition, the S 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 18. OWS Receive Signaling Note: 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
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 19:

Figure 19. 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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