STA signaling

The operator workstation protocol implements the PBX side of a loop start connection. The protocol talks with analog phones over a local loop link. It is implemented by the STA0 TCP.

This protocol requires an analog board to operate. The board must be capable of providing loop current and ring voltage to a passive terminal. AG 2000 boards have configurations that support this capability.

For information about transmitting an FSK caller ID sequence between the ring cycle while running the STA protocol, see Caller ID generation with the STA protocol.

The following tables describe operator workstation signaling. Two tables are necessary because the protocol changes depending on the side that starts the call.

AG 2000 presents the call to the terminal equipment

The following table describes the case where the AG 2000 (for instance using the STA0 TCP) presents the call to the terminal equipment:

State

Outbound AG 2000

Line/Direction

Inbound terminal

Idle

N/A

No loop current

 

Ringing

Apply ringing voltage

Ringing voltage

(Telephone rings)

At this point, the call can be answered. If it is answered, the phone is picked up, and loop current flows in the circuit. If the call is not answered after a certain number of rings, the STA0 TCP abandons the call.

The protocol does not support connect on proceeding because the outbound protocol must apply a ring signal to the inbound side. Connecting on proceeding would bypass this state and, therefore, the inbound side would not ring.

Answer - conversation state

 

Loop current, voice

Off-hook

AG 2000 clears first (optional)

 

Loop current interruption, or cleardown tone

 

Clear

 


Loop current interruption

On-hook

Idle

 

No loop current

 


Terminal equipment places a call to the AG 2000

The following table describes the case where the terminal equipment places a call to the AG 2000:

State

Outbound terminal

Line/Direction

Inbound AG 2000

Idle

 

No loop current

 

Seizure

Off-hook

Loop current

 

Seizure acknowledge

 


Dial tone

 

The outbound side starts to send the address information using DTMF tones or decadic pulses. If the method is decadic pulses, the loop current goes on (pulse on) and off (pulse off) repeatedly to signal the digits. When the address information has been completely received, the STA0 TCP presents the call to the application. The application must then decide if the call is to be accepted or rejected. If the call is accepted, the STA0 TCP plays a ring tone on the line.

Call progress tones

 


Ring tone

 

If the call is rejected, the STA0 TCP plays a busy tone on the line. The terminal is expected to abandon the call and turn off loop current.

Answer - conversation state

 


Voice

 

AG 2000 clears first (optional)

 


Loop current interruption, or cleardown tone

 

Clear

On-hook


Loop current interruption

 

Idle

 

No loop current

 


Loop start protocol on digital CAS trunks

The STA0 protocol can also be used to implement the network side of loop start protocol on digital CAS trunks. These can be provisioned on boards such as the AG 4040 and CG 6000 series boards.

For an example that shows the signaling bits for the loop start protocol on digital CAS trunks, refer to OPS signaling.

To use the STA0 protocol on a digital trunk, you must set the linetype and CDsignalbits parameters appropriately.