SYNCHRONIZING DIGITAL NETWORKS

It appears that stable synchronization of large digital transmission networks should be easy, granted accurate clocks, buffers which accept pulses at the incoming rate and deliver them at the local clock rate, and adequate delay for making frames coincide. An electric network analog of a simple linear system in which the clock frequency depends on the fullness of buffers and the departure of frequency setting from midsetting makes it obvious that the system is stable. System frequency should be made to depend strongly on accurate or master clocks; criteria are given for choosing parameters to achieve this. Strategies are given for periodic infrequent adjustments to compensate for changes in transmission time, and for adding new clocks to the network. The practical realization of a synchronized network calls for more information concerning variations of transmission time and for adequate components, particularly, buffers and adjustable delay devices. © 1969 The Bell System Technical Journal