Results of some studies of p.c.m. network synchronisation systems

For synchronised operation of p.c.m. telephone exchanges it is desired to ensure equality of oscillator frequency at every exchange. A multivariable control system using a phase-locked technique can be devised to produce long-term synchronisation. Many authors have been active in this field, and this paper indicates some of the results of analysis of the stability and operating frequency, with particular reference to work of the present authors. An important system, known as the ''double-ended system'', has not been treated by most previous authors, although this is likely to form the basis of a practical system. This is described here and details of its performance are given. The performance criterion for the system is that no two connected exchanges shall have a phase difference greater than a certain fixed amount. Certain operation modes of the system violate this condition and they are investigated. Means for eliminating them are suggested. The transient motion may be examined by use of Liapunov functions.