Appendix A: About the Technology

The values in the table below show the minimum xDSL transmission time in milliseconds (ms).

Frame Size

 

 

 

xDSL Data Rate

 

 

 

(da:sa:lt:data:crc)

 

 

 

 

 

 

 

 

7040

6400

3200

1536

 

 

 

 

[bytes]

896 kbps

768 kbps

384 kbps

64 kbps

kbps

kbps

kbps

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

 

 

 

 

 

 

 

 

 

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, 10-7BER means that on average one error occurs per 107 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 10-7BER. A margin of 6 dB, for example, would mean that the SNR can degrade by 6 dB and still provide a performance of 10-7BER. 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 10-7at the given data rate.

Megabit Modem 310F and 320F User Manual

47