Voice API Programming Guide — June 2005 183
R2/MF Signaling
15.5 R2/MF Compelled Signaling
R2/MF interregister signaling uses forward and backward compelled signaling. Simply put, with
compelled signaling each signal is sent until it is responded to by a return signal, which in turn is
sent until responded to by the other party. Each signal stays on until the other party responds, thus
compelling a response from the other party.
Reliability and speed requirements for signaling systems are often in conflict: the faster the
signaling, the more unreliable it is likely to be. Compelled signaling provides a balance between
speed and reliability because it adapts its signaling speed to the working conditions with a
minimum loss of reliability.
The R2/MF signal is composed of two significant events: tone-on and tone-off. Each tone event
requires a response from the other party. Each response becomes an acknowledgment of the event
and an event for the other party to respond to.
Compelled signaling must always begin with a Group I forward signal.
•The CO starts to send the first forward signal.
•As soon as the CPE recognizes the signal, it starts to send a backward signal that serves as an
acknowledgment and at the same time has its own meaning.
Table27. Meanings for R2/MF Group B Backward Signals
Tone
Number Intel Define Meaning
1 SIGB_1 Spare for national use
2 SIGB_2 Send special information tone to indicate long-term unavailability
3 SIGB_3 Subscriber line busy
4 SIGB_4 Congestion encountered after change to Group B
5 SIGB_5 Unallocated number
6 SIGB_6 Subscriber line free; charge on answer
7 SIGB_7 Subscriber line free; no charge (only for calls to special destinations)
8 SIGB_8 Subscriber line out of order
9 SIGB_9 Spare for national use
10 SIGB_0 Spare for national use
11 SIGB_11 Spare for national use
12 SIGB_12 Spare for national use
13 SIGB_13 Spare for national use
14 SIGB_14 Spare for national use
15 SIGB_15 Spare for national use