NMS CAS for the ADI Service Developer’s Reference Manual (6527-22): NEC signaling

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NEC signaling

The NEC PBX protocol implements the specifications of the 30 DLI (digital line interface) using PA-30DTS package, as specified in Annex 303-15-B 2/2 from NEC, NEC Australia PTY, LTD.

The NEC PBX protocol is generally a single B bit signaling protocol. The exception to this is the blocking signal, which uses both the A and B bits. The protocol is asymmetric between the TE side (user or application side) and the NT side (network or PBX side). The signaling channels supporting the line signaling of these protocols are referred to as Af and Bf in the forward direction, and Ab and Bb 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). The C and D bits are never used. Their value is fixed at 0 and 1 respectively.

This topic describes NEC line signaling in the following cases:

*

Calls originating from the PBX
*

Calls placed to the PBX

Calls originating from the PBX

The following table illustrates the signaling states of a typical inbound call originating from the PBX:

State

Outbound PBX AfBf

Direction

Inbound terminal
AbBb

Idle

00

00

Ring on

01

00

Ring off

00

00

An incoming call is presented to the application. The application can answer or reject it. If the application answers the call, the line code changes to the conversation state line code after the outbound side re-asserts ring on B signaling bit.

Ring on

01

00

Answer – conversation state

01

01

If the application rejects the call, the protocol does not respond to the ring signal. The calling party eventually abandons the call with the signaling bits for the outbound side remaining in the idle state.

The application disconnects the call, as shown:

Clear back

01

00

Idle

00

00

Calls placed to the PBX

The following table illustrates the signaling states of a typical outbound call placed to the connecting PBX:

State

Outbound terminal
AfBf

Direction

Inbound PBX
AbBb

Idle

00

00

Seizure

01

00

Seizure acknowledge

01

Dial tone

00

Dialing

01

DTMF digits dialed

00

The remote switch either answers or rejects the call. If the call is answered, the answer signal, AB = 01 is asserted. The switch can provide ring tone before answering the call. The outbound TCP performs call progress detection at this phase.

Answer – conversation state

01

01

The application disconnects the call, as shown:

Clear forward

00

01

Idle

00

00″

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