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doc:appunti:net:adsl

Linea ADSL

La qualità della linea pare abbastanza scarsa: l'allineamento al segnale ADSL richiede diversi minuti.

Questi i valori riportati da un router ZyXEL Prestige 600:

ZyXEL> wan adsl linedata near
relative capacity occupation: 22%
noise margin downstream: 31.5 db
output power upstream: 12.0 dbm
attenuation downstream: 29.5 db

Questo invece i valori riportati da un router DrayTek Vigor 2500:

Mode		G.DMT
State		SHOWTIME
Up Speed	320000
Down Speed	1504000
SNR Margin	31.7
Loop Att.	30.9

Il protocollo utilizzato è RFC2684, LLC.

Apparati ADSL

Brand and model Power supply requirements
Alcatel Speed Touch Home 9V DC, 1000 mA
ZyXEL Prestige 642R-11 16V AC, 1000 mA
DrayTek Vigor 2500 9V AC, 1500 mA

Qualità del segnale

Due sono i parametri fondamentali:

  1. SNR Margin in Downstream (oppure Signal to Noise in DownStream o DS Margin in Downstream, a seconda dell'apparecchio). Se il valore di questa voce è superiore a 12 dB, la qualità della portante è buona o quantomeno sufficientemente stabile.
  2. Line Attenuation in Downstream: per una buona connessione il valore deve essere inferiore ai 42dB.

Ecco una spiegazione più dettagliata presa da http://www.dslreports.com/faq/6728:

Relative Capacity Occupation Percentage of your overall available bandwidth used to obtain your service ATM rate. For example; if your max line synch rate was 5888Kbps and you were provisioned on a 1472Kbps service you would be using 25% capacity. 1472/5888=25% capacity. The lower the relative capacity the better, but you can still get maximum speeds (although a less stable connection) even with a very high relative capacity. In other words you could be synching at 1472Kbps with 98% relative capacity and achieve maximum speeds, but you may experience more disconnects.
Noise Margin (AKA Signal to Noise Ratio) Relative strength of the DSL signal to Noise ratio. 6dB is the lowest dB manufactures specify for modem to be able to synch. In some instances interleaving can help raise the noise margin to an acceptable level. The higher the number the better for this measurement.
Output Power How much power modem (upstream) or DSLAM (downstream) is using. Maximum recommended is about 15dB. The lower the power the better for this measurement.
Line Attenuation Measure of how much the signal has degraded between the DSLAM and the modem. Maximum signal loss recommendation is usually about 60dB. The lower the dB the better for this measurement.
doc/appunti/net/adsl.txt · Last modified: 2012/05/25 12:12 by niccolo