Non-interfering method for measuring propagation delay of telecommunications network and apparatus for accomplishing same

DETAILED DESCRIPTION It is therefore an object of the invention to provide a method for determining the propagation delay between devices communicating over a transmission line without interrupting the communication.
In accord with the object of the invention, a method for measuring the propagation delay of an unconditioned data communication line is provided and generally comprises: (a) transmitting a known signal at a non-interrupting frequency over the data communication line from a first communicating means to a second communicating means; (b) looping the known signal back from the second communicating means to the first communicating means over the secondary channel, and detecting receipt of the known signal; (c) determining a loop time between the transmitting and receipt at the first communicating means of the known signal; (d) determining a delay distortion time as a function of the frequency of the known signal and an approximate distance between the first and second communicating means; and (e) determining propagation delay from said determined loop time, delay distortion time, and known fixed delays of the communicating means.
The propagation delay for a particular secondary channel frequency is preferably determined by subtracting a correction factor from the round trip delay (loop time minus known fixed delays).
Alternatively, for any given secondary channel frequency, round trip or one way delay distortion may be determined from a look-up table which relates distance ranges to distortion delay relative to a middle frequency.
An approximate distance between the communicating means from which a distance range is chosen is obtained from the difference of the measured loop time and the known fixed delays of the communicating means.
The propagation delay is then determined by subtracting the known fixed delays and the round trip delay distortion time from the determined loop time, and dividing by two.
A better understanding of the invention, and additional advantages and objects of the invention will become apparent to those skilled in the art upon reference to the detailed description and the accompanying drawings