There are four properties that determine effective speed of an ADSL line:


Line attenuation is in relation to the "loop loss" on your line from the DSLAM at the Exchange all the way to your router - the lower the figure the better. The further you are away from the exchange the higher your attenuation figure will be as the signal loss increases.\

It is logarithmic and each 3dB of attenuation halves the strength of the signal power received - a line with 30dB of attenuation only receives 1/1,000th of the power.

True line attenuation is measured at the DSLAM at the exchange and this figure should remain fairly static. Our routers can give us an indication of how much the signal is attenuated as an average against all the frequencies that it uses.

SNR / SNR Margin

Signal to Noise ratio is the measurement of the different between the noise level and the TX (transmit) level of the signal in your line as a ratio of each other. On a radio station the SNR is the different between the background 'hiss' heard between the radio station and the signal of a radio station itself. Background noise is electronmagnetic-radiation from a number of sources ranging from electronic equipment to the big-bang. The SNR is best dueing the day time when less electrical appliances are in-use.

SNR Margin is effectively the same for thing for any kind of domestic use. SNR margin is the difference between the background and TC (transnmit) values. Customer router always show this value irrigardless of whether the term 'margin' is seen.

Sync speed

This is the speed that is negotiated by your router with the line and is dependant on the two factors above.

Check line stats


The DSL interface is normally atm0, for can check this with sh ip int brief. US refers to upsteam and DS refers to downstream.

cisco>show dsl interface atm0
Alcatel 20190 chipset information
         ATU-R (DS)            ATU-C (US)
Modem Status:     Showtime (DMTDSL_SHOWTIME)
DSL Mode:     ITU G.992.1 (G.DMT) Annex A
ITU STD NUM:      0x03                 0x2 
Vendor ID:     'STMI'                 'P   '
Vendor Specific: 0x0000                 0x0000
Vendor Country:     0x0F                 0xB5
Capacity Used:     83%                 82%
Noise Margin:      9.5 dB             12.0 dB
Output Power:     15.5 dBm             13.0 dBm
Attenuation:     16.0 dB              6.5 dB
Defect Status:     None                            None                        
Last Fail Code:     None
Watchdog Counter: 0x90
Watchdog Resets: 0
Selftest Result: 0x00
Subfunction:     0x00 
Interrupts:     7658 (0 spurious)
PHY Access Err:     0
Activations:     1
LED Status:     ON
LED On Time:     100
LED Off Time:     100
Init FW:     embedded
Operation FW:     embedded
FW Version:     2.5.42

          Interleave        Fast    Interleave        Fast
Speed (kbps):           8128               0           832               0
Cells:            7111309               0     308774250               0
Reed-Solomon EC:          0               0            22               0
CRC Errors:             18               0             3               0
Header Errors:             14               0             1               0
Total BER:          1367E-12         0E-0Leakage Avarage BER:      2195E-13         0E-0
LOM Monitoring : Disabled
BT Home Hub (UK)
  • Broadband Connection
  • DSL Connection
  • Details

Direct link: http:///cgi/b/dsl/dt/?ce=1&be=0&l0=1&l1=0

If gthese menu options are not available try:

  • Advanced
  • Status
  • ADSL Line

See Also

Improve SNR