External Clock Failure Detection in Communication Networks
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
In present communication networks wherein DTE (data terminal equipment) units are being interconnected through modems the operations have to be perfectly synchronized. For that purpose, the modem is provided with a phase locked oscillator (PLO) belonging to a so-called internal clock. On the other hand each DTE is also provided with a clock (so-called external clock) operating at the corresponding DTE rate. In most systems, one of the external clocks is used to control the internal clock PLO. The remaining DTE clock signals are derived from the PLO-controlled output and provided to the remaining DTEs. In most known systems there is no checking against the effective presence of the external clock signal at the PLO input.