Method and apparatus of determining properties of a signal transmission channel

A subscriber terminal connected to a subscriber end point of a telephone network having a plurality of subscribers, said subscriber terminal comprising:

• a connection between said subscriber terminal and a subscriber end point, said subscriber end point being connected to the telephone network by a digital channel portion, and
• a probing signal transmitter for sending, to a second subscriber terminal to which a signal transmission channel has been established, a 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 the value of the sign bit changes with every adjacent frame portion.

A telephone network comprising:

• a connection between a subscriber end point of said telephone network and a first subscriber terminal, said subscriber end point being connected to the telephone network by a digital channel portion, and
• a probing signal transmitter for sending, to a second subscriber terminal to which a signal transmission channel has been established, a digital probing signal having a sequence of frames, each frame having a sequence of digital symbols, the sequence including the same preset number of digital symbols, each symbol having one sign bit and one data bit, wherein digital values of all symbols over all frames are equal except for one bit position of each symbol, the value of which changes with every other frame.

A telephone network comprising:

• a connection between a subscriber end point of said telephone network and a first subscriber terminal, said subscriber end point being connected to the telephone network by a digital channel portion,
• a probing signal transmitter for sending, to said second subscriber terminal, a digital probing signal having a sequence of frames, each frame having a sequence of digital symbols, the sequence including the same preset number of digital symbols, each symbol having a one sign bit and one data bit, wherein digital values of all symbols are equal except for at least one symbol of each frame having a different digital value compared to the remaining equal values.