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User Manual

ADSL line parameters

In the web interface, on the System dashboard page in the 'Internet' information panel, you can see the ADSL connection status, its current parameters, and perform the initial diagnostics. To display additional connection information, click 'More details'.

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The main technical characteristics of the established ADSL connection are presented in the parameters 'Standard', 'Speed', 'Noise margin', 'Signal power level' and 'Signal attenuation'. Below are descriptions of the specified parameters and characteristics of the physical communication channel (leased line) of the ADSL technology.

Standard — ADSL standard, with the help of which the connection to the DSLAM (DSL switch) is established. It supports the following ITU-T ADSL standards:

  • G.992.1 ADSL (G.dmt);

  • G.992.2 ADSL Lite (G.lite);

  • G.992.3/4 ADSL2;

  • G.992.5 ADSL2+ (including support of the Annex M mode).

Speed — channel rate of connection to DSLAM. There are two speeds displayed: the first number is the speed per reception, i.e. to the customer (download), and the second number is the speed per transmission, i.e. from the customer (upload).

Maximum theoretically achievable channel speed according to the standard (to the customer / from the customer, in Mbit/s):

  • G.dmt: 8 / 1;

  • G.lite: 1.5 / 0.5;

  • ADSL2: 12 / 1;

  • ADSL2+: 24 / 1; Annex M mode allows increasing the data transmission speed from the customer from 1 to 3.5 Mbit/s.

More information can be found in the ADSL speed article.

Noise margin (also known as Signal-to-noise ratio margin, SNR) — is used to measure line quality and defines a minimum limit at which the signal level is above the noise level. The limit value of noise resistance for data transmission is 6 dB, a value below which the ADSL connection is not guaranteed at all. If the noise resistance is lower than 6 dB, the communication may be interrupted frequently.

If the noise resistance is higher than 10 dB, the line has good parameters for data transmission. The higher the value, the better the line quality. The 'Noise margin' value should be 6 dB and higher. It can reach values up to 30 dB if a short wire is used.

The field 'Noise margin' displays two values — the first number for the direction to the subscriber (downstream), and the second number for the direction from the subscriber (upstream).

'Noise margin' parameter value [dB]:

  • up to 6 dB is a bad line, and there are synchronization problems;

  • 7 dB to 10 dB failures are possible;

  • 11 dB to 20 dB is a good line, no problems with synchronization;

  • 21 dB to 28 dB is a very good line;

  • 29 dB and above is a perfect line.

When connecting the ADSL modem to the DSLAM, the relationship between the parameters of noise margin, connection speed and line length is as follows:

  • if the noise margin is fixed, the connection speed decreases as the line length increases, and vice versa;

  • if the line length is fixed, the noise margin decreases with increasing speed, and vice versa;

  • in the case of a fixed connection speed, the line length should be shorter to increase the noise margin.

Signal power level (also known as Output Power) — shows the output power of the signal at the moment of modem synchronization with DSLAM. Usually, the output power is about 10 dBm when sending data. This value may be lower due to signal losses in power.

Signal attenuation — shows the signal attenuation in the line at the moment of modem synchronization with the DSLAM (this parameter should be less than 45 dB). The attenuation depends on the cable length between the ADSL modem and the DSLAM. The higher the value of this parameter, the lower the line quality and, therefore, the lower the data transfer/receipt speed.

Optimal values should be between 5 and 30 dB (excellent or good line). An attenuation value of 45 dB or higher means that the line is not suitable for ADSL.

The field 'Signal attenuation' displays two values — the first number for the direction to the subscriber (downstream) and the second number for the direction from the subscriber (upstream).

'Signal attenuation' parameter value [dB]:

  • up to 20 dB is a perfect line;

  • 20 dB to 40 dB — stable line;

  • 40 dB to 50 dB — possible failures;

  • 50 dB to 60 dB — the synchronization is periodically lost;

  • 60 dB and above — the equipment will not work.

If the ADSL connection is poor, contact your ISP to solve the physical link problem.

More information about the ADSL line features can be found on the Wiki.

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