Real time switch overs from one set of timing signals to a redundant set of timing signals in an ATM system, as required by periodic maintenance checks, are accomplished without incurring data errors by this apparatus and method. Each switch over apparatus has a phase locked loop with a ...http://www.google.com.au/patents/US5740211?utm_source=gb-gplus-sharePatent US5740211 - Method and apparatus for a hitless switch-over between redundant signals
