SAGEM 3P@C

Factors Affecting the ADSL transmission quality

„Subscriber line attenuation

The attenuation of the ADSL subscriber line is an important factor to affect the ADSL commissioning, relevant to the length of lines. In the condition of the 0.4mm twisted pairs, the test data for the subscriber line attenuation is shown in the table below:

Table 12-2 ADSL subscriber line length attenuation table

Line

 

Twisted pair

 

Adding 30m house parallel

attenuation

 

Downstream

Upstream

Downstream

Upstream

Length

of

attenuation

attenuation

attenuation

attenuation

lines

 

(dB)

(dB)

(dB)

(dB)

1km

 

22.0

16.0

24.0

16.5

2km

 

40.0

28.5

44.5

30.0

3km

 

56.5

40.0

58.5

41.5

4km

 

63.5

51.0

65.5

51.5

The greater the degree of attenuation of the subscriber line is, the lower the connection rate of subscriber line becomes. The subscriber line will exceed the limit for commissioning the ADSL service when it exceeds a certain length and its attenuation becomes extremely high.

The above is the attenuation pair standard determined by the line length. In the same way, the Ministry of Posts and Telecommunications definitely provides the requirements on line attenuation (per kilometer) within different frequency bands, and different core diameters lead to different degrees of attenuation, for details, see the table below:

Table 12-3 ADSL line attenuation per kilometer within different frequency bands

f0

 

 

 

 

 

 

 

(kHz)

40

60

80

120

150

300

1,024

Core diameter

attenuation

 

 

 

 

 

 

 

(dB)

 

 

 

 

 

 

 

0.32mm

11.40

13.01

14.38

15.12

16.80

18.13

33.50

0.4mm

8.29

9.34

10.05

10.87

12.10

14.78

27.30

0.5mm

5.99

6.85

7.06

7.77

9.00

12.18

22.50

„Crosstalk interference

When there are multiple ADSL subscribers in the same cable, or there are HDSL subscribers, ISDN subscribers or the data transmission subscribers in other modes, the crosstalk interface would occur, and the characteristics of the channel will vary along with the number of such subscribers, enabling/disabling status and the changes of transmission rate. Based on the analysis on ADSL, HDSL and ISDN by means of transmission spectrum, the ISDN service can basically ignore the crosstalk interference from the ADSL service due to its low frequency band, and the ADSL equipment using the FDM technology can minimize the affects of crosstalk only against the ADSL line due to its separation of upstream/downstream frequency bands. The cross-talk interference mainly comes from the NEXT-NearEndCrosstalk (The cross-talk interference of the interference source on the receiver of the interference line pair in the case that the interference source and the receiver of the interfered line pairs are at the same end) of HDSL and the comprehensive FEXT-FarEndCrosstalk (The cross-talk interference of the interference source on the receiver of the interference line pair in the case that the interference source and the receiver of the interfered line pairs are far from each other) of many other ADSL line pairs.

The non-symmetric design of the ADSL rate allows a low rate of the upstream signal and low frequency band occupied, the crosstalk is less at the user end accordingly and the office end is easy to be controlled both in line connection and pair arrangement, which is favorable to control crosstalks. Crosstalk generally occurs to the connector of lines and the fault point of lines, and at the user end, generally the house line uses the parallel cable, to which the crosstalk is easy to occur.

3P@C Installation Manual

Page 12-4

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