Patent ID: 7010000

Claim:
In a telephone network connecting a first subscriber end point to a second subscriber end point by a signal transmission channel having a digital channel portion, a method of determining properties of said signal transmission channel, said method comprising: sending a digital probing signal from a first subscriber terminal connected to said first subscriber end point to a second subscriber terminal, connected to said second subscriber end point, said digital probing signal having a sequence of probing frames, each probing frame having at least two frame portions, each frame portion having the same preset number of digital symbols, each digital symbol having one sign bit and one data bit, wherein absolute digital values of all symbols in the frame portions are equal, and wherein a value of the sign bit changes with every adjacent frame portion, receiving, at said second subscriber terminal, a received signal resulting from having transmitted said digital probing signal through said signal transmission channel; comparing said received signal with said digital probing signal to distinguish between possible channel configurations of said signal transmission channel; and transmitting a response signal from said second subscriber terminal to said first subscriber terminal, said response signal carrying information indicative of a result of comparing said received signal with said digital probing signal.