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).
R
ATE
A
DAPTIVE
T
RANSMISSION
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
