>NMS CAS for the ADI Service Developer’s Reference Manual (6527-22): NEC signaling: “Show Navigation Component Next Topic
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″