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• ITU-T Rec. Q.141 (1988) – Signal code for line signalling
• 2.1 SIGNAL CODE FOR LINE SIGNALLING
  • 2.1.1 General
  • 2.1.2 Transit working
  • 2.1.3 Sending duration of line signalling
  • 2.1.4 Recognition times of line signals
  • 2.1.5 Line signal code of System No. 5
  • 2.1.6 Further specification clauses relative to the signalling code
  • 2.1.7 Backward signals on multilink connections