CCITT Rec. U.1 (11/1988) – SIGNALLING CONDITIONS TO BE APPLIED IN THE INTERNATIONAL TELEX SERVICE
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