MELCAS signaling

The MEL TCP implements the Mercury exchange line (MEL) channel associated signaling (CAS) protocol. The protocol can be run on a PCM30 E1 trunk, or on a T1 trunk in ESF mode.

The following table describes the signaling states of a typical inbound call originating from the PBX. ABCD signaling bits are shown:

State

Network

Direction

Terminal

Idle

1101

1101

Ring on

1011

1101

Ring off

1001

1101

 

Optional FSK caller ID

 

At this point an incoming call is presented to the application. The application can answer or reject it.

If the application rejects the call, the inbound terminal does not respond to the ring signal. The calling party abandons the call with the signaling bits for the outbound side returning to the idle state.

Idle

1101

1101

If the application answers the call, the line code changes to the call established state line code.

Answer

1001

0101

Call established

0101

0101


The following table describes the signaling states of a typical outbound call originating from the terminal (application):

State

Network

Direction

Terminal

Idle

1101

1101

Seizure

1101

 

Dial tone

 

Call progress tone

 


 

0101

 

DTMF address digits

Answer

0101

0101


The following table describes the disconnect of established calls, regardless of which side originated the call.

State

Network

Direction

Terminal

The application disconnects the established call first:

Call established

0101

0101

Clear back

0101

1101

Disconnect clear

0001

1101

1101

Idle

1101

1101

The network disconnects the established call first:

Call established

0101

0101

Disconnect clear

0001

1101

0101

Clear back

1101

1101

Idle

1101

1101

Out of service blocking is also supported.

Network blocked

1111

1101

Terminal blocked

1101

1111