ALL-MC115VDSL2 Mini Modem Master/Slave Manual
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5. Problem:
What is SNR(Signal-to-Noise)
Answer:
Signal-to-noise ratio (often abbreviated SNR or S/N) is a measure used in science and engineering
that compares the level of a desired signal to the level of background noise. It is defined as the ratio
of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise. While
SNR is commonly quoted for electrical signals, it can be applied to any form of signal (such as
isotope levels in an ice core or biochemical signaling between cells). The ratio is usually measured
in decibels(dB)
The signal-to-noise ratio, the bandwidth, and the channel capacity of a communication channel are
connected by the Shannon–Hartley theorem.
In digital communications, the SNR will probably cause a reduction in data speed because of
frequent errors that require the source (transmitting) computer or terminal to resend some packets of
data. SNR measures the quality of a transmission channel over a network channel. The greater the
ratio, the easier it is to identify and subsequently isolate and eliminate the source of noise.
6. Problem:
Connected the Co and CPE within 300 meters RJ-11 phone cable got only less than 10 Mbit/s
Cause:
1. Some testing program which is base on TCP/IP protocol such as FTP, Iperf, NetIQ, the
bandwidth of testing outcome will be limited by TCP window size.
2. Some operating system limited the maximum bandwidth, such as windows series OS.
Solution:
We recommend to test VDSL2 bandwidth best by Smartbit equipment(Packet generator), if you
don't have Smartbit, we recommend test that by IPERF program, and TCP window size must be
setted max. 64k, the parameter as iperf –c server IP address –i 1 –t 50 –w
65535
for client side.
