1 Signalling types
2
Free line condition
3
Call
4
Call-confirmation signal
5
Signals preceding selection
5.1 Proceed-to-select signal
5.2 Proceed-to-transmit signal
6
Selection signals
7
Call-connected signal
8
Idle circuit condition
9
Clearing
9.1 Clearing signal
9.2 Clear-confirmation signal
9.3 Guard delay
10 Service signals
10.1 Signals for ineffective calls
10.2 Waiting signals
10.3 Service-connected signal
10.4 Backward busying signal
10.5 Retest signal
11 Setting-up time
12 Both-way working
13 Transit working
References