Single ended line probing in DSL system

A Central Office (CO) digital subscriber line (DSL) modem configured to determine if a telephone line qualifies for DSL service, the modem comprising:

• means for transmitting from the CO DSL modem low frequency signals over the telephone line, wherein the low frequency signals are transmitted through circuitry in the CO DSL modem;
• means for receiving reflected versions of the low frequency signals from the telephone line;
• means for measuring at the CO DSL modem a transfer function based on the transmitted low frequency signals and received reflected versions of the low frequency signals, wherein the transfer function models characteristics of the telephone line and the circuitry in the CO DSL modem;
• and
• means for qualifying the telephone line based on the transfer function.

A method for determining if a telephone line qualifies for digital subscriber line (DSL) service, the method comprising:

• transmitting from a Central Office (CO) DSL modem low frequency signals over the telephone line, wherein the low frequency signals are transmitted through circuitry in the CO DSL modem;
• receiving reflected versions of the low frequency signals from the telephone line;
• measuring at the CO DSL modem a transfer function based on the transmitted low frequency signals and received reflected versions of the low frequency signals, wherein the transfer function models characteristics of the telephone line and the circuitry in the CO DSL modem;
• in response to determining that a peak amplitude of the transfer function is less than a predetermined threshold, determining that the telephone line is short circuited;
• in response to the transfer function having more than one peak, determining that at least one load coil is attached to the telephone line;
• in response to no short circuits or load coils being associated with the telephone line:
• comparing a peak frequency of the transfer function to a number of peak frequency values, each peak frequency value associated with a length value;
• and
• estimating the length of the telephone line based on one or more of the peak frequency values and their associated length values.

A computer-readable medium including instructions which, when executed by a processor in a Central Office (CO) digital subscriber line (DSL) modem, cause the modem to perform the operations of:

• transmitting from the CO DSL modem low frequency signals over the telephone line;
• receiving reflected versions of the low frequency signals from the telephone line, wherein the low frequency signals are transmitted through circuitry in the CO DSL modem;
• measuring a transfer function based on the transmitted low frequency signals and received reflected versions of the low frequency signals, wherein the transfer function models characteristics of the telephone line and the circuitry in the CO DSL modem;
• in response to determining that a peak amplitude of the transfer function is less than a predetermined threshold, determining that the telephone line is short circuited;
• in response to the transfer function having more than one peak, determining that at least one load coil is attached to the telephone line;
• in response to no short circuits or load coils being associated with the telephone line:
• comparing a peak frequency of the transfer function to a number of peak frequency values stored in a lookup table, each peak frequency value in the lookup table associated with a length value included in the lookup table;
• and
• estimating the length of the telephone line based on one or more of the peak frequency values and their associated length values.

A computer-readable medium having instructions contained thereon, which, when executed by a processor in a Central Office (CO) digital subscriber line (DSL) modem, cause the processor to perform the operations of:

• transmitting from the CO DSL modem low frequency signals over the telephone line, wherein the low frequency signals are transmitted through circuitry in the CO DSL modem;
• receiving reflected versions of the low frequency signals from the telephone line;
• measuring at the DSL modem a transfer function based on the transmitted low frequency signals and received reflected versions of the low frequency signals, wherein the transfer function models characteristics of the telephone line and the circuitry in the CO DSL modem;
• and
• qualifying the telephone line based on the transfer function.

A Central Office (CO) digital subscriber line (DSL) modem for qualifying a telephone line for DSL services, comprising:

• a processor;
• a memory containing instructions, which, when executed by the processor, cause the processor to perform the operations of:
• transmitting from the CO DSL modem signals over the telephone line, wherein the low frequency signals are transmitted through circuitry in the CO DSL modem;
• receiving reflected versions of the signals from the telephone line;
• measuring at the CO DSL modem a transfer function based on the transmitted and received reflected versions of the signals, wherein the transfer function models characteristics of the telephone line and the circuitry in the CO DSL modem;
• and
• qualifying the telephone line based on the transfer function.