Qualifying telephone lines for data transmission

1. A method of marketing customer telephone lines for a selected data transmission service, each line having associated tip and ring wires, comprising:

automatically performing single-ended electrical measurements on a selected plurality of customer telephone lines while the associated tip and ring wires are connected together in a common mode configuration;

determining which of the customer lines qualify for the selected data service from the measurements;

sorting the lines based on final distribution points and qualification for the data service; and

offering the selected data service to a portion of the customers in response to said portion having qualified lines available.

2. The method of claim 1 , further comprising:

billing customers for usage of the lines at rates depending on whether the lines qualified for the selected data transmission service.

3. The method of claim 1 , wherein the act of determining includes finding a signal attenuation of the lines and qualifying lines having signal attenuations below a preselected threshold.

4. The method of claim 3 , further comprising:

monitoring a second portion of the customer lines after being placed in service by repeatedly performing one-ended common-modes electrical measurements on the second portion; and

determining which of the lines of the second portion are qualified for the selected data transmission service from the repeated measurements.

5. The method of claim 1 , further comprising:

providing the data transmission service for a second portion of the lines qualified for the selected data transmission service in response to receiving requests from the associated customers for the service.

6. A method of marketing data transmission services to customers over telephone lines having associated tip and ring wires, comprising:

performing single-ended electrical tests on a plurality of telephone lines connected to a final distribution point near where a customer is located, the tests driving tip and ring wires of the lines under test in a common mode configuration;

determining whether the tested lines qualify for a selected data service; and

offering the data service to the customer over one of the tested lines in response to the one of the tested lines being qualified.

7. The method of claim 6 , further comprising: swapping the one of the tested lines with a line originally used by the customer in response to the line originally used by the customer being disqualified for the data service.

8. The method of claim 7 , wherein the act of determining includes finding a signal attenuation of the tested lines and qualifying the tested lines having signal attenuations below a preselected threshold.

9. The method of claim 6 , wherein the act of performing tests is responsive to receiving a request from the customer for the selected data service.

10. A method of marketing data transmission services to customers over telephone lines connected to a switch having a test access, comprising:

connecting a measurement unit to the test access;

using the measurement unit to make single-ended electrical measurements at a first frequency on a telephone line connected to the switch;

determining whether the telephone line is qualified to provide a selected data service based at least in part on a prediction of attenuation at a second frequency, higher than the first frequency, made from the single-ended measurements; and

providing the selected data service to a customer over the telephone line in response to determining that the telephone line is qualified.

11. The method of claim 10 , wherein the act of using the measurement unit to make single ended electrical measurements comprises disconnecting the telephone line from a line card and rerouting it through the test access.

12. The method of claim 10 , wherein the act of determining whether the telephone line is qualified is based at least in part on a prediction of whether the line contains a metallic fault.

13. The method of claim 12 , wherein the act of determining whether the telephone line is qualified is based at least in part on a prediction of whether the line contains a speed inhibiting fault.

14. The method of claim 10 , additionally comprising measuring the capacitance of the telephone line and selecting the first frequency based on the capacitance.

15. The method of claim 10 , wherein the act of determining whether the telephone line is qualified comprises determining whether the predicted attenuation at the second frequency is above a threshold.

16. The method of claim 10 , wherein the second frequency is between about 40 KHz and 300 KHz.

17. The method of claim 10 wherein the first frequency is between about 300Hz and 400 KHz.

18. The method of claim 10 , wherein the first frequency is between about 300KHz and 20 KHz.

19. The method of claim 10 , wherein the act of determining whether the telephone line is qualified is based at least in part on a prediction of attenuation computed from measured impedance and capacitance of the line at the first frequency.

20. The method of claim 9 , wherein the computed attenuation is inversely. proportional to the square route of the sum of the impedance squared added to the reciprocal of the square of the product 2 π times the second frequency and the measured capacitance at the first frequency.