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. |
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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. |
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Network blocked |
1111 |
|
1101 |
Terminal blocked |
1101 |
|
1111 |