# EUC signaling for the Netherlands (ALS70D)

ALS70D, the Dutch National CAS protocol, is asymmetrical, meaning that the terminal equipment sends and receives different signals to perform call setup with respect to the near-end switch. Thus, two signaling tables are necessary to specify the protocol, one for the TCP placing calls (outbound), and one for the TCP receiving calls (inbound).

This topic describes how signaling is carried out by the:

- Outbound TCP

- Inbound TCP

## Signaling carried out by the outbound TCP

The following table shows signaling states associated with the outbound TCP when using the EUC TCP for the Netherlands:

State | Outbound AfBf (TCP) | Direction | Inbound AbBb (Network)
--- | --- | --- | ---
Idle | 10 |  | 10
Seizure | 00 |  | 10
The normal behavior after the outbound TCP signals seizure is the detection of a seizure acknowledged. However, call collision can occur, and the TCP can receive a seizure from the network as well. If the seizure from the network comes 200 ms from the original seizure, then the outbound TCP must send seizure acknowledged and receive a call. It then behaves as shown by the table, describing the inbound TCP behavior.
Seizure acknowledged | 00 |  | 11
The inbound network side starts playing a dial tone on the voice channel, meaning that in-band (DTMF detector) resources are available to receive the address information. Once it has detected the dial tone, the outbound side starts to send the address information using DTMF tones or pulse dial. If the method is pulse dial, the Bf bit is switched on (pulse on) and off (pulse off) repeatedly to signal each digit.
Register signaling: digit spill | DTMF |  | 11
Register signaling: pulse dial | 01 pulse on |  | 11
| 00 pulse off |  | 11
If the call is accepted, the inbound side plays a ring tone on the line and then flips the Ab bit to signal 01. Otherwise, it flips the Bb bit to signal 10 (idle).
Ringing | 00 |  | 11
Answer - conversation state | 00 |  | 01
The outbound protocol can receive billing pulses to signal that a unit of cost was billed to the call. In this case, the answer pattern (AB = 01) from inbound temporarily changes to AB = 00.
Answer - conversation state | 00 |  | 01
Billing pulses | 00 |  | 00
Answer - conversation state | 00 |  | 01
Depending on which side hangs up the call first, a clear forward signal or a clear back signal is generated, followed by a clear forward. Idle follows.
Clear back | 00 |  | 11
Clear forward | 10 |  | 01 (or 11)
Idle | 10 |  | 10

## Signaling carried out by the inbound TCP

The following table shows signaling states associated with the inbound TCP when using the EUC TCP for the Netherlands:

State | Outbound AfBf (Network) | Direction | Inbound AbBb (TCP)
--- | --- | --- | ---
Idle | 10 |  | 10
Seizure | 00 |  | 10
Seizure acknowledged | 00 |  | 11
The seizure acknowledged line state for the inbound TCP lasts for a certain time period. This time period is set to 100 ms in the TCP. After that, a ready to receive bit transition is sent to signal the network that the TCP is ready to receive the address information. This signal means that the resource dedicated to detect DTMF tones has been allocated.
Ready to receive | 00 |  | 01
Once it detects the ready to receive signal, the outbound side starts to send the address information using DTMF tones or pulse dial. If the method is pulse dial, the Bf bit is switched on (pulse on) and off (pulse off) repeatedly to signal each digit.
Register signaling: digit spill | DTMF |  | 01
Register signaling: pulse dial | 01 pulse on |  | 01
| 00 pulse off |  | 01
When all the digits have been received, the inbound side flips the Ab bit to signal that it has enough information. This state is maintained for at least 300 ms.
Number received | 00 |  | 11
If the call is accepted, the inbound side plays a ring tone on the line and then flips the Ab bit to signal AB = 01. Otherwise, it plays busy and flips the Bb bit to signal AB = 10 (idle).
Ringing | 00 |  | 11
Answer - conversation state | 00 |  | 01
Depending on which side hangs up the call first, a clear forward signal or a clear back signal is generated, followed by a clear forward. Idle follows.
Clear back | 00 |  | 11
Clear forward | 10 |  | 01 (or 11)
Idle | 10 |  | 10