【 Weak current College 】 ADSL subscriber line maintenance fault analysis

ADSL access technology dramatically improves the user's Internet access speed, solve the past presence of network bottlenecks. But as the rapid increase in ADSL user, user fault complaint also has significantly increased, in these user fails the complaint line fault accounted for a considerable proportion. This phenomenon is due mainly to the direct use of the existing ADSL PSTN users access network business broadband access, the original lines were not suitable for high frequency signal transmission problems causing the ADSL subscriber line failures occur frequently, haunt the majority of Internet users and track maintenance personnel.


Causes the line ADSL user failure reasons mainly can be divided into two broad categories: the first is attenuation class line failure; the second category is interference class line fault. Attenuation class line fault main findings are: subscriber line is too long, the line material transmission performance difference, circuit breaker, short circuit and oxidation, bad connector, bridged taps, lines exist with Induction coil, etc. Disturbance class line fault main findings are: Central Office or client device background noise is high, radio interference, cables in different lines on the signal crosstalk, household appliances, electromagnetic interference, motor or electric locomotive caused by electromagnetic interference, weather causes interference (such as lightning), etc. While the user failures are often some of the above factors together. The following routine maintenance for some ADSL failsafe for further analysis.

Failsafe: bad, connector oxidation

S a weather phenomenon ADSL users call normal, but no Internet access, Modem activation indicator has been in Flash, users will call on the off-hook State to make the Modem activates lights correctly.

«Test section of the measuring Chamber in Central Office will subscriber line mixed line (that is, user A, B cable shorted), in the user-side measurement lines loop resistance Ω for 4653, in user floor outside junction Office measurement lines loop resistance Ω for 673.

«Analysis section of the call from user can properly concluded that the user does not exist outside line, short circuit breaker. At the junction of ring resistance test results to normal, but in the user-end test to ring resistivity index not working properly after the inspection found that the user is determined by three under huxian paragraph lines threaded together, joint replacement, the oxidation of serious users after fault disappears under huxian, phone and Internet users are normal, and no drop off.

«Summary section of the user drag test is maintaining Central ADSL lines, an important test, suitable for the opening of the line ADSL business ring resistivity index should be less than 900 Ω, depending on the test to the subscriber line loop resistance derived from the line length (with loop resistance per unit length divided by the number of lines on the DC resistance) and the user's actual line length deviation of the larger the circuit on a bad, connectors, such as oxidation. faults It should be noted that the use of 112 measurement automatic test users outside loop resistance, since its test online imposed DC current will breakdown some of the not very serious oxidation film of oxide film to get good results, this is also why the user will in this case placed off-hook State telephone Modem can activate reason (PSTN users pick up after the current line).

Failsafe 2: user inlet attenuation is too large

S a weather phenomenon ADSL user application Mbit/s downlink bandwidth, but unlike other 2Mbit/s bandwidth of a user compare slower.

«Test section of used instrument in the user-end test, the test results display the user maximum downlink direction can be opened at 1.3Mbit/s, loop resistance number 820 Ω; in user outdoor luminaires, test the user port downlink direction maximum opening speed 2.9Mbit/s, loop resistance 795 Ω, under users, no long 100m huxian.

«Eclipse from test results analysis, user opened rate lower mainly due to the user's next huxian signal attenuation is too large, will be replaced by the following huxian copper twisted pairs of the user-side measurement to downlink maximum opening speed 2.6Mbit/s, users go online rate gains.

«Summary section of the current user inlet (commonly known as "the next huxian") most of the parallel single-ply yarn, material for the ferro-alloy material, its transmission performance of high-frequency signal and anti-interference performance well below the twisted-pair copper material, it can cause line attenuation is too large to open rates low by user or activate the difficulties. Recommend copper material twisted pair, and the length should not exceed 100m.

Failsafe III: huxian wiring unreasonable cause signal interference serious

S a weather phenomenon ADSL users reflect the Internet slow download speed only 7kbit/s, and frequently dropped.

«Test section of used instrument to test the user side, the downlink direction maximum opening speed 232kbit/s, the actual opening rate only 96kbit/s. The user's next huxian length 150m, is parallel to, and to fixed-line, outdoor wire rod, indoor heating pipe, and many other places. Replace a user with a twisted pair huxian and to minimize the length to 100m, while not in other parts of the winding, user fault disappears down maximum opening rate reached 2.6Mbit/s, the actual opening of downlink speed for 512kbit/s download speed also increases, to 60kbit/s.

«Analysis section of the appropriate opening of ADSL business subscriber line ADSL band (10kHz-1.1MHz) background noise power spectral density should be less than-94dBm/Hz. In the user-end test to the background noise is too high, but in the sense of the next junction at huxian post test results to determine the normal user failure is largely due to excessively long and cabling under huxian, introduces too much interference signal,Causing the user to open rates low and often dropped.

«Summary section of the excessively long and under huxian excessive winding will lead to the introduction of its like antenna that external electromagnetic interference signal and the parallel lines of anti-interference ability, further exacerbated the problem.

Failure case study 4: device port high background noise

] [A type respondent access phenomenon ADSL Central Office equipment users generally open rate is low, line ring resistance of more than 500 Ω users is very difficult to activate.

«Test section from the failure of performance, you can determine the problem may be with the Central Office equipment, in the measurement units to disconnect a user outside line directly test the DSLAM ports found in this location on the direction to the downward direction on the maximum rate at which can be opened only 3.4Mbit/s, further testing background noise power spectral density and ADSL broadband noise band.

Analysis of the probabilities in measuring s test to user port downlink maximum opening rate only reached 3.4Mbit/s, and test point unit port is very near distance, line attenuation can be ignored, so the cause of this failure phenomenon is mainly due to signal interference. Select the measurement units to disconnect a user outside line for testing can be queued outside interference, which is used to verify the DSLAM port noise leakage. Suitable for the opening of the subscriber line ADSL business ADSL broadband noise band index reference values are: uplink direction is less than-50.23dBm; downlink direction is less than-40.23dBm. In this case the background noise of port power spectral density while there is no more than the given point of reference values-94dBm/Hz, but the entire ADSL band especially downward direction of noise power is high, resulting in a downward direction of broadband noise indicators are not eligible.

«Summary section of the work of taken G.DMT ADSL subscriber line in the measurement units to disconnect a user outside line test after being down maximum opening rates should be greater than 7Mbit/s, when the test data is less than this value describes the DSLAM user port higher noise floor or on-line distribution cable attenuation. So on ADSL faults user maintenance should first ensure that the test in the measurement of indicators is normal, thereby avoiding blind outside line test.

To sum up, in order to ensure the normal use of ADSL users, reducing the failure rate of complaint, the user should pay attention to the user to install cabling, avoid some can cause users to fail the wiring in the future.

On the other hand, as the ADSL business of large-scale, past PSTN line maintenance tools and test methods have been insufficient to find the cause of the failure of broadband users, the need to introduce some new test method, for example, the background noise power spectral density test, broadband noise testing, performance testing of longitudinal balance line, cable crosstalk specifications testing, etc. Only through extensive testing to find the real obstacles to ADSL users.