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• ITU-T Rec. Q.553 (1988)
• 1 General
• 2 Characteristics of interfaces
  • 2.1 Characteristics common to all 4-wire analogue interfaces
  • 2.2 Characteristics of interface C11
  • 2.3 Characteristics of interface C12
  • 2.4 Characteristics of interface C13
• 3 Characteristics of half connections
  • 3.1 Characteristics common to all 4-wire analogue interfaces
  • 3.2 Characteristics for interface C11
  • 3.3 Characteristics for interface C12
  • 3.4 Characteristics for interface C13