4.3. R2 MF Signal Meanings

There are two groups of meanings associated with each set of signals. Group I meanings and Group II meanings are associated with the 15 forward signals. Group A meanings and Group B meanings are associated with the 15 backward signals, as shown in Figure 14.

Figure 14. Multiple Meanings for R2 MF Signals

In general, Group I forward signals and Group A backward signals are used to control the call setup and to transfer address information between the outgoing register (CO) and the incoming register (CPE). The incoming register can then signal to the outgoing register to change over to the Group II and Group B meanings.

Group II forward signals provide the calling party's category, and Group B backward signals provide the condition of the called subscriber's line. For further information, see Table 8 describing the purpose of the signal groups and the changeover in meanings.

Signaling must always begin with a Group I forward signal followed by a Group A backward signal that serves to acknowledge the signal just received and also has its own meaning. Each signal then 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.

Backward signals serve to indicate certain conditions encountered during call setup or to announce switch-over to changed meanings of subsequent backward signals. Changeover to Group II and Group B meanings allows information about the state of the called subscriber's line to be transferred.

Table 8. Purpose of Signal Groups and Changeover in Meaning

Signal	Purpose
Group I	Group I signals control the call set-up and provide address information.
Group A	Group A signals acknowledge Group I signals (see exception under signal A-5 below) for call set-up, and can also request address and other information. Group A signals also control the changeover to Group II and Group B meanings through the following signals:
	A-3	Address Complete - Changeover to Reception of Group B Signals: Indicates the address is complete and signals a changeover to Group II/B meanings; after signal A-3 is sent, signaling cannot change back to Group I/A meanings.
	A-5	Send Calling Party's Category: Requests transmission of a single Group II signal providing the calling party's category. Signal A-5 requests a Group II signal but does not indicate changeover to Group B signals. When the Group II signal requested by A-5 is received, it is acknowledged by a Group A signal; this is an exception to the rule that Group A signals acknowledge Group I signals.
Group II	Group II signals acknowledge signal A-3 or A-5 and provide the calling party category (national or international call, operator or subscriber, data transmission, maintenance or test call).
Group B	Group B signals acknowledge Group II signals and provide the condition of the called subscriber's line. Before Group B signals can be transmitted, the preceding backward signal must have been A-3. Signals cannot change back to Group I/A.

The Incoming Register Backward Signals Can Request:

• Transmission of address
  • Send next digit
  • Send digit previous to last digit sent
  • Send second digit previous to last digit sent
  • Send third digit previous to last digit sent
• Category of the call (the nature and origin)
  • National or international call
  • Operator or subscriber
  • Data transmission
  • Maintenance or test call
• Whether or not the circuit includes a satellite link
• Country code and language for international calls
• Information on use of an echo suppressor

The Incoming Register Backward Signals Can Indicate:

• Address complete - send category of call
• Address complete - put call through
• International, national, or local congestion
• Condition of subscriber's line
  • Send SIT to indicate long-term unavailability
  • Line busy
  • Unallocated number
  • Line free - charge on answer
  • Line free - no charge on answer (only for special destinations)
  • Line out of order

NOTE:

The meaning of certain forward multifrequency combinations may also vary depending upon their position in the signaling sequence. For example, with terminal calls the first forward signal transmitted in international working is a language or discriminating digit (signals I-1 through I-10). When the same signal is sent as other than the first signal, it usually means a numerical digit.

See Table 9 through Table 12 for the signal meanings:

• Table 9: Meanings for R2 MF Group I Forward Signals
• Table 10: Meanings for R2 MF Group II Forward Signals
• Table 11: Meanings for R2 MF Group A Backward Signals
• Table 12: Meanings for R2 MF Group B Backward Signals

Table 9. Meanings for R2 MF Group I Forward Signals

Tone Number	Dialogic Define	(A) Primary Meaning (B) Secondary Meaning
1	SIGI_1	(A) Digit 1  (B) Language digit-French
2	SIGI_2	(A) Digit 2  (B) Language digit-English
3	SIGI_3	(A) Digit 3  (B) Language digit-German
4	SIGI_4	(A) Digit 4  (B) Language digit-Russian
5	SIGI_5	(A) Digit 5  (B) Language digit-Spanish
6	SIGI_6	(A) Digit 6  (B) Spare (language digit)
7	SIGI_7	(A) Digit 7  (B) Spare (language digit)
8	SIGI_8	(A) Digit 8  (B) Spare (language digit)
9	SIGI_9	(A) Digit 9  (B) Spare (discriminating digit)
10	SIGI_0	(A) Digit 0  (B) Discriminating digit
11	SIGI_11	(A) Access to incoming operator (Code 11)  (B) Country code indicator: outgoing half-echo suppressor required
12	SIGI_12	(A) Access to delay operator (code 12); request not accepted  (B) Country code indicator: no echo suppressor required
13	SIGI_13	(A) Access to test equipment (code 13); satellite link not included  (B) Test call indicator
14	SIGI_14	(A) Incoming half-echo suppressor required; satellite link included  (B) Country code indicator: outgoing half-echo suppressor inserted
15	SIGI_15	(A) End of pulsing (code 15); end of identification  (B) Signal not used

Table 10. Meanings for R2 MF Group II Forward Signals

Tone Number	Dialogic Define	Meaning
1	SIGII_1	National: Subscriber without priority
2	SIGII_2	National: Subscriber with priority
3	SIGII_3	National: Maintenance equipment
4	SIGII_4	National: Spare
5	SIGII_5	National: Operator
6	SIGII_6	National: Data transmission
7	SIGII_7	International: Subscriber, operator, or maintenance equipment (without forward transfer)
8	SIGII_8	International: Data transmission
9	SIGII_9	International: Subscriber with priority
10	SIGII_0	International: Operator with forward transfer facility
11	SIGII_11	Spare for national use
12	SIGII_12	Spare for national use
13	SIGII_13	Spare for national use
14	SIGII_14	Spare for national use
15	SIGII_15	Spare for national use

Table 11. Meanings for R2 MF Group A Backward Signals

Tone Number	Dialogic Define	Meaning
1	SIGA_1	Send next digit (n+1)
2	SIGA_2	Send last but one digit (n-1)
3	SIGA_3	Address complete; change to Group B signals; no change back
4	SIGA_4	Congestion in the national network
5	SIGA_5	Send calling party's category; change to Group II; can change back
6	SIGA_6	Address complete; charge; set up speech conditions
7	SIGA_7	Send last but two digit (n-2)
8	SIGA_8	Send last but three digit (n-3)
9	SIGA_9	Spare for national use
10	SIGA_0	Spare for national use
11	SIGA_11	Send country code indicator
12	SIGA_12	Send language or discriminating digit
13	SIGA_13	Send nature of circuit (satellite link only)
14	SIGA_14	Request for information on use of an echo suppressor (Is an incoming half-echo suppressor required?)
15	SIGA_15	Congestion in an international exchange or at its output

Table 12. Meanings for R2 MF Group B Backward Signals

Tone Number	Dialogic 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

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