4.5.28	Signal
The purpose of the Signal information element is to allow the network to optionally convey information to a user regarding tones and alerting signals. (See 7).
The Signal information element is coded as shown in Figure 4-34 and Table 4-24.
The length of this information element is three octets.
The Signal information element may be repeated in a message.

               8  7  6  5  4  3  2  1
        1      0  0  1  1  0  1  0  0
       1
Information element identifier
0
0
0
0
0
0
0
1
       2
Length of signal contents
Signal value
       3
FIGURE  4-34/Q.931
Signal information element
TABLE  4-24/Q.931
Signal information element
Signal value (octet 3)
	Bits
	8  7  6  5   4  3  2  1
	0  0  0  0   0  0  0  0	Dial tone on
	0  0  0  0   0  0  0  1	Ring back tone on
	0  0  0  0   0  0  1  0	Intercept tone on
	0  0  0  0   0  0  1  1	Network congestion tone on
	0  0  0  0   0  1  0  0	Busy tone on
	0  0  0  0   0  1  0  1	Confirm tone on
	0  0  0  0   0  1  1  0	Answer tone on
	0  0  0  0   0  1  1  1	Call waiting tone
	0  0  0  0   1  0  0  0	Off-hook warning tone
	0  0  0  0   1  0  0  1	Preemption tone on
	0  0  1  1   1  1  1  1	Tones off
	0  1  0  0   0  0  0  0	Alerting on – pattern 0 (Note 1)
	0  1  0  0   0  0  0  1	Alerting on – pattern 1 (Note 1)
	0  1  0  0   0  0  1  0	Alerting on – pattern 2 (Note 2)
	0  1  0  0   0  0  1  1	Alerting on – pattern 3 (Note 1)
	0  1  0  0   0  1  0  0	Alerting on – pattern 4 (Note 1)
	0  1  0  0   0  1  0  1	Alerting on – pattern 5 (Note 1)
	0  1  0  0   0  1  1  0	Alerting on – pattern 6 (Note 1)
	0  1  0  0   0  1  1  1	Alerting on – pattern 7 (Note 1)
	0  1  0  0   1  1  1  1	Alerting off
	All other values are reserved.
	NOTES
	1     The use of these patterns is network dependent.
	2     Used for special/priority alerting.