Patent ID: 8798946

Claim:
A method for estimating a transfer function at a central office (CO) to be used for performing loop qualification of a digital subscriber line between the CO, and a customer premises (CP) regardless of the topology of the loop to be qualified, the method comprising the steps of: retrieving at the CO a value Z in1 0 of the impedance at the CO side when the end of the line at the CP is short circuited, retrieving at the CO a value Z in1 0 of the impedance at the CO when the end of the line at the CP is open and estimating, using a calculator, the transfer function based on a transmission matrix T expressed by the following equation: T = [ Z in ⁢ ⁢ 1 ∞ ⁢ f s 2 Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 Z in ⁢ ⁢ 1 ∞ ⁢ Z in ⁢ ⁢ 1 0 2 ( Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 ) ⁢ f s 2 f s 2 Z in ⁢ ⁢ 1 ∞ ⁡ ( Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 ) Z in ⁢ ⁢ 1 ∞ ( Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 ) ⁢ f s 2 ] wherein f S is set to 1 under the assumption that an impedance of the ports of the loop are equal to each other such that the loop to be qualified is assumed to be symmetric independently of the symmetric characteristics of the loop to be qualified.