# WNK signaling

The wink start protocol (WNK) family includes protocols used on T1 in the USA, Hong Kong, and Taiwan, and protocols used on E1 elsewhere. The protocol uses one-bit signaling (or presence or absence of current in the analog case), and owes its name to the wink (brief presence of current or variation of the signaling bit) that the inbound side uses to indicate readiness to receive address signaling. Register signaling is performed by in-band DTMF or MF tones, or by out-of-band decadic pulses.

The international wink start (IWK), DID, and OGT protocols are incorporated into the wink start protocol.

The wink start protocol is symmetrical (same implementation from the network or from customer premises equipment).

The signaling channel supporting the WNK line signaling protocol is referred to as Af in the forward direction, and Ab in the backward direction. The forward channel indicates the condition of the outbound switch equipment and reflects the condition of the calling party's line. The backward channel indicates the condition of the called party's line (the inbound equipment).

On T1 trunks, the other bits in either direction usually follow the state of the A bit. On E1 trunks, the value of the B, C, and D bits is usually 1, 0, 1 respectively.

In the U.S. and Taiwan, the idle code is A=0.

In Hong Kong, two variations are possible in the Hong Kong Telecom network:

- Pulse on busy (idle code is A=0)

- Pulse on idle (idle code is A=1)

The two variations execute call setup in exactly the same way, except that all bit changes are opposite. The WNK TCP parameter optionflags, bit 1, specifies which variation to use.

The line signaling for a typical call is described in the following table. The table represents the pulse on busy variation:

State | Outbound Af | Direction | Inbound Ab
--- | --- | --- | ---
Idle | 0 |  | 0
Seizure | 1 |  | 0
Seizure acknowledge | 1 |  | 0-1-0 (wink)
The outbound side starts to send the address information using DTMF tones, MF tones, or decadic pulses. If the method is decadic pulses, the Af bit is switched off (pulse on) and on (pulse off) repeatedly to signal the digits.
Register signaling: digit spill | DTMF or MF |  | 0
Register signaling: pulse dial | 0 pulse on |  | 0
| 1 pulse off |  | 0
All the address information has been transferred. The inbound side accepts or rejects the call by playing the ring or the busy tone on the voice path. If the call is rejected, the outbound side switches back to signaling A = 0 (idle), thus clearing the line.
Clear forward and idle | 0 |  | 0
If the call is accepted, the inbound side answers the call by flipping both backward bits to 1.
Answer - conversation state | 1 |  | 1
Depending on which side hangs up the call first, a clear back signal or a clear forward signal is generated. Idle follows.
Inbound hangs up first: Clear back | 1 |  | 0
Outbound hangs up first: Clear forward | 0 |  | 0 or 1
Idle | 0 |  | 0

In analog variations the digital bit signaling is translated into E & M or DID analog signaling by the line interface circuitry on the board.

In U.S. implementations, the wink start protocol can transfer ANI (caller ID) information in addition to DID digits (direct inward dialing - the called address). A separator tone is used to distinguish between DID and ANI digits in the DTMF digit spill. Usually the separator tone is an * (asterisk) (941+1209 Hz). The parameter NCC.X.ADI_WNK.anididtone (see following table) determines the TCP's behavior with respect to ANI digits.

Taiwan and Hong Kong do not use ANI digits.