MFC (Multi frequency compelled / Multi-frequency Code) signaling is an in-band address signaling system. The signals consist of a combination of two of a set of six frequencies between 300 and 3400 Hz. This implies that fifteen different combinations can be made. Since more than fifteen signals are needed, signal groups are implemented. There are two forward groups, I and II, and two backward groups called A and B.
| FORWARD SIGNALS | ||
|---|---|---|
| Signal number | Group I (A) | Group II (B) |
| 1 | digit 1 | Ordinary subscriber |
| 2 | digit 2 | Priority subscriber |
| 3 | digit 3 | Maintenance equipment |
| 4 | digit 4 | Hotel subscriber |
| 5 | digit 5 | Operator call (break in allowed) |
| 6 | digit 6 | Data transmission |
| 7 | digit 7 | Int. subscriber (no priority) |
| 8 | digit 8 | Int. subscriber (data transmission) |
| 9 | digit 9 | Int. subscriber (priority) |
| 10 | digit 0 | Int. operator (break in allowed) |
| 11 | Acces code interc. service | National coin box |
| 12 | Request not accepted | Local subscriber |
| 13 | Acces code to maintenance equipment | Maintenance equipment |
| 14 | Spare | Operator call (break in allowed) |
| 15 | End of number | Originating subscriber free of charge |
| BACKWARD SIGNALS | ||
| Signal number | Group A (I) | Group B (II) |
| 1 | Send next digit (n+1) | Subscriber free, last party release |
| 2 | Send last but one digit (n-1) | Subscriber number is changed |
| 3 | Address complete, change to group B | Subscriber line busy |
| 4 | Congestion | Congestion |
| 5 | Send calling party number | Vacant number |
| 6 | Address complete, charge, setup speech path | Subscriber free, charge |
| 7 | Send last but two number (n-2) | Subscriber free, no charge |
| 8 | Send last but three number (n-3) | Subscriber line out of order |
| 9 | Spare | Subscriber marked for absent service |
| 10 | Spare | Spare |
| 11 | Spare | Spare |
| 12 | Spare | Spare |
| 13 | Spare | Spare |
| 14 | Spare | Spare |
| 15 | Spare | Spare |
Веда, Ведические науки, знания и традиции
