ADC 320F Network Card User Manual


 
Appendix A: About the Technology
Megabit Modem 310F and 320F User Manual 47
The values in the table below show the minimum xDSL transmission time in milliseconds (ms).
RATE ADAPTIVE TRANSMISSION
The following definitions are useful for understanding the operation of the Megabit Modem:
Bit Error Rate (BER) is the ratio of received bits that are in error relative to the total number
of bits received, measured over time. For example, 10
-7
BER means that on average one
error occurs per 10
7
bits received.
Signal to Noise Ratio (SNR) is the ratio (typically expressed in dB) of the received signal
power to the received noise power. It is a measure of the quality of the transmission.
Margin (SNR margin) is the amount of degradation in SNR that the system can tolerate
under the current conditions and still achieve a 10
-7
BER. A margin of 6 dB, for example,
would mean that the SNR can degrade by 6 dB and still provide a performance of 10
-7
BER.
The Megabit Modem 310F and 320F have a margin configuration option that defaults to 4
dB, but may be set anywhere between 0 to 15 dB.
Reach is the longest loop length that the system can support with a given margin and a BER
of less than 10
-7
at the given data rate.
Frame Size
(da:sa:lt:data:crc)
[bytes]
xDSL Data Rate
7040
kbps
6400
kbps
3200
kbps
1536
kbps
896 kbps 768 kbps 384 kbps 64 kbps
64 0.088 0.097 0.194 0.405 0.694 0.810 1.620 9.719
128 0.176 0.193 0.386 0.805 1.379 1.609 3.219 19.313
512 0.699 0.769 1.538 3.205 5.494 6.410 12.820 76.922
1024 1.397 1.537 3.074 6.405 10.980 12.810 25.620 153.719
1518 2.071 2.278 4.556 9.492 16.272 18.984 37.969 227.813