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VoIP exchange lines do not provide a clock pulse as ISDN does, so it is important that the VoIP gateway itself generates a clock pulse in order to synchronize any ISDN equipment used. The gateway generates the clock pulse with an oscillating circuit consisting of a quartz crystal and capacitors.

The clock accuracy is specified in ppm (parts per million). The lower the ppm value, the more accurate the frequency.

Clock accuracies of 50ppm or less are generally considered to be uncritical with regard to quality issues.

LANCOM VoIP routers have the following clock accuracies:

  • LANCOM 883 VoIP: 25ppm
  • LANCOM 884 VoIP: 5ppm
  • LANCOM R883+: 5 ppm
  • LANCOM 1781x: 25ppm
  • LANCOM 1783x: 25ppm
  • LANCOM 1784: 5ppm
  • LANCOM 1793x: 5 ppm
  • LANCOM 1906VA: 5ppm
  • LANCOM 1906VA-4G: 5ppm