External Clock Failure Detection in Failed Communication Networks
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
In communication networks wherein a host and Data Terminal Equipment (DTE) are interconnected through modems, the operations have to be perfectly synchronized. For this, a modem is provided with a phase- locked oscillator (PLO) belonging to a so-called Internal Clock. The host and each DTE are also provided with a clock, the so- called External Clock, which operates at the corresponding host or DTE rate, and can be used to control the PLO of the associated modem. In a communication network involving a secondary link, as shown in the figure, DTE 4 could provide the External Clock to Modem 4. External clock out of range from DTE 4 or impairments on the telephone line of the secondary link result in a degradation of the External Clock that Modem 3 drives to Modem 2.