• ITU-T Rec. Q.521 (1988)
  • 1 General
  • 2 Exchange functions - Introduction and framework
    • 2.1 General
    • 2.2 Exchange model
  • 3 Utilization of exchange functions for services
    • 3.1 General
  • 4 General functions required for operation of an exchange in the IDN, ISDN or mixed analogue/digital environment
    • 4.1 Timing and synchronization
    • 4.2 Signalling