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Message: <blockquote data-quote="dileeshakr" data-source="post: 18676050" data-attributes="member: 160527">මාත් ඕක ලඟදි දන්නේ.Noise (dBm) in communications is a combination of unwanted interfering signal sources, such as crosstalk, radio frequency interference, distortion, etc.Signal-to-noise ratio (SNR) is defined as the power ratio between a signal (meaningful information) and the background noise (unwanted signal):SNR = signal / noiseThe more commonly used SNR margin, as described below is sometimes abbreviated as simply SNR as well.SNR margin (dB, a.k.a. noise margin) is the ratio by which the signal exceeds the minimum acceptable amount (minimum SNR) to sustain a certain speed. It is normally measured in decibels. SNR margin is often confused and used interchangeably with SNR. Some NAT wireless routers, for example (notably dd-wrt open source router firmware) use SNR margin, only denoted as "SNR". SNR margin is simply calculating the difference between signal (RSSI) and noise to get the SNR margin as a positive number expressed in db.SNR margin = signal(dBm) - noise(dBm)For example, if singal (RSSI) = -55db, and noise = -80db, then:(-55db signal) - (-80db noise) = 25 SNR marginHigher SNR/SNR margin numbers repesent cleaner/stronger signals, with less background noise. The higher the SNR margin the more stable the connection. In some instances interleaving can help raise the noise margin to an acceptable level.6dB or below noise margin is bad, it will experience no synch or intermittent synch problems7dB-10dB is fair but does not leave much room for variances in conditions11dB-20dB is good with little or no synch problems (if no large variation)20dB-28dB is excellent29dB or above is outstandingNote that there may be short term bursts of noise that may drop the margin, but due to the sampling time of the management utility in your modem, will not necessarily show up in its interface.Some DSL routers display both the actual SNR, and the signal-to-noise margin (SNR margin) as a separate value, which (again) is the difference between the actual SNR and the SNR required to sync at a specific speed. For example:actual SNR = 44dBSNR to sync at 8Mbit/s = 35dBSNR margin = 44-35= 9dBAs with actual SNR, the higher that SNR margin number, the better (stronger signal over background noise), and above 6dB is acceptable.</blockquote>

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