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Appendix B

Line Interface Signaling

Introduction

This appendix describes how to interpret signaling to and from the AG-8 and AG-8/80 line interfaces. Note: The telephony protocol, embodied by a TCP (Trunk Control Program) running on the AG-8 and AG-8/80 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 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 (for example, loop start). They also convert incoming information into digital signals recognizable by AG-based applications.
To monitor receive signaling, or to set transmit signaling for a line interface, an application can examine or change the data in stream 17 (the line interface signaling stream in MVIP-90 terms), in the timeslot associated with the specific 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, using the MVIP-90 switch model, send the signal byte to stream:timeslot 17:4.

LS and ELS Line Interfaces

For loop start and enhanced loop start line interfaces, the transmit signaling determines how to interpret receive signaling. Transmit signaling determines whether the line is off-hook or on-hook. The hybrid ID is 0x40 for a loop start line interface, and 0x78 for an enhanced loop start line interface.

Loop Start Transmit Signaling

With loop-start interfaces, the transmitted signaling A bit in the signaling timeslot causes the interface to seize the line (go off-hook) or release the line (go on-hook). If the A bit is set to 1, the line goes off-hook. If the A bit is set to 0, the line goes on-hook. Bits B, C and D are reserved, and should be set to 0.
Figure 19 shows transmit signaling for LS line interfaces: Figure 19. Loop Start Transmit Signaling
The following table summarizes the transmit signaling for loop start line interfaces: Bit Hex Bitmask To take line off-hook To put line on-hook A bit 0x08 0x08 0 B bit 0 Reserved. Reserved. C bit 0 Reserved. Reserved. D bit 0 Reserved. Reserved. Note: If you reset the switch, all bits are set to 0.

Bit	Hex Bitmask	To take line off-hook	To put line on-hook
A bit	`0x08`	`0x08`	`0`
B bit	0	Reserved.	Reserved.
C bit	0	Reserved.	Reserved.
D bit	0	Reserved.	Reserved.

Loop Start Receive Signaling

Depending on how the transmitted signaling A bit is set, the line has been placed on-hook or off-hook. The received signaling A bit acts either as a ring signal detector or a loop current indicator. When the line is on-hook, monitoring the A bit will tell you if the line is ringing. When the line is off-hook, monitoring the A bit will indicate whether there is loop current flowing. The B bit is the same as the A bit. Bits C and D are reserved, and should be ignored.
Figure 20 shows receive signaling for LS line interfaces: Figure 20. Loop Start Receive Signaling
The following table summarizes the receive signaling for loop start line interfaces: Bit Hex Bitmask If line is off-hook If line is on-hook A bit 0x08 Detects loop current: Value Description 0 No loop current 0x08 Current is flowing Detects ring signal: Value Description 0 Not ringing 0x08 Ringing B bit 0x04 Same as A bit. Same as A bit. C bit N/A Reserved. Reserved. D bit N/A Reserved. Reserved.

Bit	Hex Bitmask	If line is off-hook	If line is on-hook
A bit	`0x08`	Detects loop current: Value Description `0` No loop current `0x08` Current is flowing	Detects ring signal: Value Description `0` Not ringing `0x08` Ringing
B bit	`0x04`	Same as A bit.	Same as A bit.
C bit	N/A	Reserved.	Reserved.
D bit	N/A	Reserved.	Reserved.

Enhanced Loop Start (ELS)Signaling

Figure 21 shows transmit signaling for ELS line interfaces: Figure 21. ELS Transmit Signaling
The following table summarizes the transmit signaling for ELS line interfaces: Bit Hex Bitmask To take line off-hook To put line on-hook A bit 0x08 0x08 0 B bit 0 Reserved. Reserved. C bit 0 Reserved. Reserved. D bit 0 Reserved. Reserved.
Figure 22 shows receive signaling for ELS line interfaces: Figure 22. ELS Receive Signaling
The following table summarizes the receive signaling for ELS line interfaces: Bit Hex Bitmask If line is off-hook If line is on-hook A bit 0x08 Detects loop current: Value Description 0 No loop current 0x08 Current is flowing Detects ring signal: Value Description 0 Not ringing 0x08 Ringing B bit 0x04 Polarity detector for loop current (only when current is detected): Value Description 0 Tip is negative, ring is positive 0x08 Tip is positive, ring is negative C bit N/A Reserved. Reserved. D bit N/A Reserved. Reserved.
You can change the receive gain from the default value of 0 dB to 6 dB for ELS line interfaces on the AG board by adding the HybridConfig statement to the AG configuration file, ag.cfg. The syntax for the HYBRIDCONFIG statement is:
HybridConfig = config slot 0[,config_slot_1,...,config_slot_n]
config_slot_n is a hexadecimal number, 0xXY, that changes the receive gain for the corresponding ELS hybrid. X determines if the hybrid is receiving A-law or mu-law. Y sets the receive gain.
For example: To set all eight ELS hybrids to use 6 dB gain in an A-law environment: HybridConfig = 0x24, 0x24, 0x24, 0x24, 0x24, 0x24, 0x24, 0x24 To set all eight ELS hybrids to use 6 dB gain in a mu-law environment: HybridConfig = 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04
If you specify fewer config_slot_n arguments than there are ELS hybrids on the designated AG board, agmon assigns the value of the last config_slot argument to any subsequent ELS hybrids. For example, if you specify five config_slot assignments for a board with 8 ELS hybrids, the fifth value is assigned to the sixth, seventh, and eighth hybrids.

Bit	Hex Bitmask	To take line off-hook	To put line on-hook
A bit	`0x08`	`0x08`	`0`
B bit	0	Reserved.	Reserved.
C bit	0	Reserved.	Reserved.
D bit	0	Reserved.	Reserved.

Bit	Hex Bitmask	If line is off-hook	If line is on-hook
A bit	`0x08`	Detects loop current: Value Description `0` No loop current `0x08` Current is flowing	Detects ring signal: Value Description `0` Not ringing `0x08` Ringing
B bit	`0x04`	Polarity detector for loop current (only when current is detected): Value Description `0` Tip is negative, ring is positive `0x08` Tip is positive, ring is negative
C bit	N/A	Reserved.	Reserved.
D bit	N/A	Reserved.	Reserved.

DID Line Interface Signaling

There are no dependencies between DID transmit signaling and DID receive signaling.
Figure 23 and the following table describe DID transmit signaling: Figure 23. DID Transmit Signaling Bit Hex Bitmask Description A bit 0x08 Reverse battery polarity Value Description 0 Normal polarity 0x08 Reverse polarity B bit 0x04 Must be 0. C bit N/A Reserved. D bit N/A Reserved.
Figure 24 and the following table describe DID receive signaling: Figure 24. DID Receive Signaling Bit Hex Bitmask Description A bit 0x08 Loop current detector Value Description 0 No current detected 0x08 Current detected B bit 0x04 Same as A bit. C bit N/A Reserved. D bit N/A Reserved.

Bit	Hex Bitmask	Description
A bit	`0x08`	Reverse battery polarity Value Description `0` Normal polarity `0x08` Reverse polarity
B bit	`0x04`	Must be 0.
C bit	N/A	Reserved.
D bit	N/A	Reserved.

Bit	Hex Bitmask	Description
A bit	`0x08`	Loop current detector Value Description `0` No current detected `0x08` Current detected
B bit	`0x04`	Same as A bit.
C bit	N/A	Reserved.
D bit	N/A	Reserved.

E&M Line Interface Signaling

There are no dependencies between E&M transmit signaling and E&M receive signaling.
Figure 25 and the following table describe E&M transmit signaling: Figure 25. E&M Transmit Signaling Bit Hex Bitmask Description A bit 0x08 M-lead relay Value Description 0 On-hook 0x08 Off-hook B bit 0x04 Enable battery Value Description 0 No talk battery on tip and ring 0x04 Talk battery on tip and ring C bit N/A Reserved. D bit N/A Reserved.
Figure 26 and the following table describe E&M receive signaling:

Figure 26. E&M Receive Signaling

Bit

Hex Bitmask

Description

A bit

0x08

E-lead relay
Value Description
0 Detect on-hook
0x08 Detect off-hook

B bit

0x04

Same as A bit.

C bit

N/A

Reserved.

D bit

N/A

Reserved.

Bit	Hex Bitmask	Description
A bit	`0x08`	M-lead relay Value Description `0` On-hook `0x08` Off-hook
B bit	`0x04`	Enable battery Value Description `0` No talk battery on tip and ring `0x04` Talk battery on tip and ring
C bit	N/A	Reserved.
D bit	N/A	Reserved.

Bit	Hex Bitmask	Description
A bit	`0x08`	E-lead relay Value Description `0` Detect on-hook `0x08` Detect off-hook
B bit	`0x04`	Same as A bit.
C bit	N/A	Reserved.
D bit	N/A	Reserved.

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