|Publication number||USRE42789 E1|
|Application number||US 10/879,891|
|Publication date||Oct 4, 2011|
|Priority date||Mar 29, 2000|
|Also published as||CA2403657A1, EP1269642A1, EP1269642A4, US6418160, WO2001073961A1|
|Publication number||10879891, 879891, US RE42789 E1, US RE42789E1, US-E1-RE42789, USRE42789 E1, USRE42789E1|
|Inventors||William Lee Miller|
|Original Assignee||At&T Intellectual Property I, L.P.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (25), Non-Patent Citations (6), Classifications (15), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present application is an application for reissue of U.S. Pat. No. 6,418,160 B1, entitled “Method for Testing a Communication Channel”, which has original U.S. application Ser. No. 09/537,830.
The present invention relates generally to a method for testing a communication channel and, more particularly, concerns a communication system that uses modern line probing data in an evaluation method to determine the circuit characteristics of a customer subscriber loop.
Numerous personal computers are connected to other computer systems or to computer networks such as the Internet through the public switched telephone network (PSTN). A common way of connecting a computer to the PSTN for communication with other computers or computer networks is through the use of a modem. Most modems are capable of operating at different transmission rates at different times, and have a typical maximum communication rate of 56 kbps.
Generally, both the transmitting modem and the receiving modem must evaluate the communication channel first in order to optimize the performance. One way of achieving this is, during “handshaking,” to have the transmitting modem transmit, as part of its set-up sequence to the receiving modem, a composite signal which will be recognized by the receiving modem. This allows the receiving modem to evaluate the communication channel and condition itself to have an optimized data rate for this connection. Modems operating under the V.34 and V.90 standards perform such line probing to maximize the data communication rate.
The maximum communication rate that a modem can achieve is related to the hardware or circuit characteristics associated with a particular customer subscriber loop. The subscriber loop is the twisted copper pairs of wires running to a home or a business from the telephone Central Office switching system. The physical characteristics of a particular subscriber loop may effectively limit the transmission rate for a particular customer. There are numerous other problems, however, unrelated to the physical characteristics of the customer subscriber loop, which can degrade communication performance resulting in lower modem transmission rates. Therefore, for customers experiencing degraded modem performance, there is a need for determining whether the characteristics of the customer subscriber loop is responsible for the degraded modem performance.
Presently, a telephone company technician must be dispatched to the particular customer location with special testing equipment to determine the characteristics of the customer subscriber loop. Troubleshooting customer modem transmission problems by dispatching technicians is expensive and time consuming. Accordingly, what is needed is an inexpensive and remotely located system and method for testing subscriber loop characteristics for a particular customer.
For a more complete understanding of this invention, reference should now be had to the embodiments illustrated in greater detail in the accompanying drawings described below by way of examples of the invention. In the drawings:
In this example, the customer modem 12 is connected to modem 22 of the network service provider 20 for subscriber line evaluation. The network service provider 20 represents, for example, the customer's local phone company. Alternatively, the network service provider 20 could be an ISP providing access to the Internet. The modem 22 associated with the network service provider 20 is also, preferably, a conventional modem operating at frequencies below 4000 Hz, such as a V.34 or V.90 type modem. Alternatively, the modem 22 can be a modem having an all-digital interface.
Because the subscriber loop represents the physical connection between a customer premises and another computer system or network, it will likely be different for each customer. Each subscriber loop may have any of several characteristics or circuit elements that can effectively limit the modem communication rates available for that customer. In particular, the physical distance the communication signals must travel along the twisted pair of wires directly affects signal strength. Due to capacitive reactance in the line, signal strength becomes attenuated as the distance increases. To counteract these losses, the lines must be “loaded” with an inductive reactance. The loaded line, however, has the characteristics of a low pass filter with significant signal attenuation above 3000 Hz.
In addition to the loaded or unloaded condition of a particular subscriber loop, the subscriber loop may include one or more analog-to-digital (A/D) conversions. Portions of the subscriber loop may be connected through a digital network such as a digital loop carrier network. Data transmissions across such a digital network require A/D conversions to convert the analog modem signals to digital data for transmission across the digital network and vice-versa. Most of the switching equipment associated with the PSTN digitizes analog signals on subscriber loops by sampling the analog signals at a frequency of 8 kHz. Because of the Nyquist limit, this sampling rate imposes a maximum frequency of 4 kHz that can be sampled and passed from a subscriber loop through a PSTN. Accordingly, there is signal attenuation associated with frequencies above approximately 3400 Hz to account for the effects of A/D conversions along a subscriber loop.
The customer subscriber loop may also connect between two load points or contain a loaded bridge tap. In either case, the subscriber loop will have the characteristics of a notch filter. This would significantly degrade the customer modem performance and require modifications to the subscriber loop by telephone company service personnel to improve performance.
These subscriber loop characteristics—short loop/long loop, loaded/non-loaded, number of A/D conversions, notch filter—all affect the maximum possible transmission rate associated with a customer's modem such as modem 12. The method of the present invention tests for these subscriber loop characteristics and provides an output of the expected transmission rates for a particular customer subscriber loop.
In step 32, the gain slope of the subscriber loop is evaluated and stored. This is accomplished by subtracting the level of the signal strength at 1050 Hz from the level of signal strength detected at 3000 Hz. This value is stored as the gain slope (GS) value. The loaded slope evaluator is then executed in step 34. This is accomplished by analyzing the line probing data and subtracting the signal level at 2850 Hz from the signal level at 3300 Hz. This value is stored as the loaded slope (LS) value. The A/D filter test is performed in step 36. The A/D value (A/D) is stored as the difference between the signal level at 2850 Hz and the signal level at 3750 Hz.
In step 37, the subscriber loop evaluation routine calculates the loss associated with the network. This is accomplished by subtracting 10 dB from the signal level measured at 1050 Hz.
Once the line probing data has been entered and the initial values determined, steps 38-54 perform a series of tests to determine the subscriber loop characteristics which may affect the customer modem transmission rates. In step 38, the subscriber loop is analyzed to determine whether the loop has loaded bridge taps or is working between loads. This is accomplished by determining whether there is signal attenuation greater than 4 dB at any data point between 1250 Hz and 2850 Hz. If a valley of 4 dB or more is detected at any of these frequencies, the routine sets an error flag at step 39 and generates a system message at step 41 indicating that the subscriber loop has a loaded bridge tap or is operating between two loads (MSG A).
In step 40, the routine analyzes whether the gain slope as determined in step 32 is greater than or equal to 7. If so, the error flag is set in step 42, and a system message is generated in step 44 indicating that this particular subscriber loop needs to be loaded (MSG B). In other words, if GS is greater than or equal to 7, the customer subscriber loop is a long loop requiring an inductive load to balance the capacitive losses associated with the long loop. If the error flag is set in either step 39 or 42, it indicates that the customer is likely to experience significantly degraded modem performance. In such cases, modification to the subscriber loop will be required to improve performance.
In step 46, the routine determines whether the loaded slope is less than four and the A/D value is greater than or equal to 17. If these conditions are satisfied, the system generates a message (MSG C) in step 48 indicating that there are two or more A/D conversions in the subscriber loop. Given this condition, the expected modem communication rate is between 19.2 kbps to 26.4 kbps.
In step 50, if the loaded slope value is greater than or equal to 4 and the A/D value is greater than or equal to 16, the system generates a message (MSG D) in step 52 indicating that the subscriber loop is loaded, and that the expected modem communication rate is between 19.2 kbps to 24 kbps. Otherwise, the routine continues to step 54.
In step 54, if the loaded slope value is less than 4 and the A/D value is less than or equal to 16, the system generates a message (MSG E) in step 56 indicating that the subscriber loop is non-loaded and that the expected modem communication rate is between 40 kbps to 53 kbps. Otherwise, the routine continues to step 58.
In step 58, it is determined whether the gain slope value is less than or equal to 7 and no error flag has been set. If this condition is met, the system generates a message (MSG F) in step 60 indicating that all loaded and non-loaded requirements have been met and the expected modem communication rate is the maximum possible modem rate for that loaded or non-loaded condition.
With the subscriber loop evaluation method of
With the evaluator method as described in
The evaluation method is advantageous in that it allows customers with perceived modem connection problems to analyze their unique subscriber loop and determine whether the loop characteristics are responsible for degrading modem performance. In this case, only if an error flag is set would it be necessary to dispatch telephone company personnel to modify the subscriber loop characteristics to alleviate the performance problem. In all other cases, the actual modem performance should be within the range of the expected communication rate as indicated by the evaluation method. If the actual communication rate is different than the expected communication rate, than it can be concluded that the problem is something other than the subscriber loop configuration. For example, the modem software may be set up incorrectly or the customer's ISP may not support higher modem communication rates.
Referring again to
Beginning at step 80, the technician communicates with the customer and instructs the customer of the steps necessary to establish a Hyperterminal session and set up the customer modem to auto-answer. In step 82, the technician, through his personal computer by way of the Hyperterminal session, calls the customer's modem line and establishes a communications link. At this point, the customer's computer system is set up as a Hyperterminal session and auto-answers the incoming call from the technician's modem. Once a communications link has been established, the technician enters the command level of his modem in step 84. This can be accomplished in modems manufactured by U.S. Robotics by typing “+++”. The modem responds with “OK” to verify that communications are at the command level. At this prompt, the technician enters “ATY11” to display the line probing data for the present modem connection. This is shown in step 86. In step 88, the line probing data can be copied such as by, for example, using the cut or copy functions of the Microsoft Windows Operating System. The modem connection can then be terminated and the line evaluator routine can then be executed, with the line probing data entered in step 30 as described above with reference to
In another embodiment, it is contemplated that the modem line evaluation method such as shown in
In another embodiment, it is contemplated that the subscriber loop evaluation routine is contained within portable devices used by telephone company personnel remotely from the Central Office location. In this way, technicians in the field could readily analyze subscriber loop characteristics of a particular customer's line from any location including the customer premises.
From the foregoing, it can be seen that there has been brought to the art a new and improved method for testing a communication channel. The present method has the advantage of eliminating the time and expense associated with dispatching telephone company personnel to a customer location to evaluate the subscriber loop characteristics for a particular customer. While the invention has been described in connection with one or more embodiments, it should be understood that the invention is not limited to those embodiments. On the contrary, the invention covers all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the appended claims.
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|U.S. Classification||375/222, 379/27.01, 370/285|
|International Classification||H04L12/26, H04B1/38, H04B3/30, H04M3/30, H04M1/24|
|Cooperative Classification||H04L43/50, H04L12/2697, H04M3/2209, H04M3/30|
|European Classification||H04L12/26T, H04M3/30, H04L43/50|
|Feb 14, 2014||REMI||Maintenance fee reminder mailed|
|Jul 9, 2014||LAPS||Lapse for failure to pay maintenance fees|