# EUC signaling for Sweden (P7/P8)

P7/P8, the Swedish 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.

Two variations of incoming calls can be received: using the P7 or using the P8 protocol. The P7 protocol is two-way: it can be used both to place and to receive calls. The inbound (call reception) capability does not support the transfer of DID digit, but acts essentially as a subscriber's telephone on a E1 timeslot. The P8 protocol is inbound only, and supports DID transmission.

Three signaling tables are necessary to specify the protocol:

- Placing calls with P7

- Receiving calls with P7

- Receiving calls with P8

## Placing calls with P7

The following table shows signaling states associated with placing calls with P7 when using the EUC TCP for Sweden:

State | Outbound AfBf (TCP) | Direction | Inbound AbBb (Network)
--- | --- | --- | ---
Idle | 10 |  | 10
Seizure | 00 |  | 10
The inbound network side starts playing a dial tone on the voice channel, indicating that in-band (DTMF detectors) resources are available to receive the address information.
Dial tone | 00 |  | 10
Once it has detected the dial tone, the outbound side starts to send the address information using DTMF tones.
Register signaling: digit spill | DTMF |  | 10
If the call is accepted, the inbound side plays a ring tone on the line and then flips the Ab bit to signal 00. Otherwise, it plays busy on the line.
Ringing | 00 |  | 10
Answer - conversation state | 00 |  | 00
The outbound protocol can receive billing pulses to signal that a unit of cost has been billed to the call. In this case, the answer pattern (AB = 00) from inbound temporarily changes to AB = 01.
Answer - conversation state | 00 |  | 00
Billing pulses | 00 |  | 01
Answer - conversation state | 00 |  | 00
Depending on which side hangs up the call first, a clear forward signal or a clear back signal followed by a clear forward signal, is generated. Idle follows.
Clear back | 00 |  | 10
Clear forward | 10 |  | 00 or 10
Idle | 10 |  | 10

## Receiving calls with P7

The following table shows signaling states associated with receiving calls with P7 when using the EUC TCP for Sweden:

State | Outbound AfBf (Network) | Direction | Inbound AbBb (TCP)
--- | --- | --- | ---
Idle | 10 |  | 10
Seizure | 01 |  | 10
Immediately when seized, the CPE (the TCP) plays a ring tone on the line if the connected telephone is on-hook; a busy tone if it is off-hook. If the tone is busy, the network abandons the call. When the connected telephone is picked up, the TCP flips the A-bit to signal answer. The network then flips its Bf bit to signal that the call is through-connected to the remote caller.
Ringing | 01 |  | 10
Answer | 01 |  | 00
Through connection | 00 |  | 00
Depending on which side hangs up the call first, a clear forward signal or a clear back signal followed by a clear forward signal, is generated. Idle follows.
Clear back | 00 |  | 10
Clear forward | 10 |  | 00 or 10
Idle | 10 |  | 10
If there is a clear back (for example, if the CPE clears the call first and the network has a call waiting for that timeslot), the line can be seized immediately. In this case, the sequence restarts from the seizure (second row of this table).
Clear back | 00 |  | 10
Seizure | 01 |  | 10

## Receiving calls with P8

The following table shows signaling states associated with receiving calls with P8 when using the EUC TCP for Sweden:

State | Outbound AfBf (Network) | Direction | Inbound AbBb (TCP)
--- | --- | --- | ---
Idle | 10 |  | 10
Seizure | 00 |  | 10
Proceed to send (seizure acknowledged) | 00 |  | 00
Once it has detected the proceed to send signal, the outbound side starts to send the address information using DTMF tones.
Register signaling: digit spill | DTMF |  | 00
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, and during ringing.
Number received | 00 |  | 10
If the call is accepted, the inbound side plays a ring tone on the line and then flips the Ab bit to signal AB = 00. Otherwise, it plays a busy tone and the network abandons the call.
Ringing | 00 |  | 10
Answer - conversation state | 00 |  | 00
Depending on which side hangs up the call first, a clear forward signal or a clear back signal followed by a clear forward signal, is generated. Idle follows. If the network clears the call first, the CPE must stay in connected (AB=00) for at least 150 ms but less than 250 ms.
Clear back | 00 |  | 10
Clear forward | 10 |  | 00 or 10
Idle | 10 |  | 10