Sagem 4450E - Manual (Page 161)

SAGEM 3P@C
3P@C Installation Manual
Page 12-4 Reproduction and communication in any form prohibited without the written permission of
SAGEM SA
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
Twisted pair Adding 30m house parallel Line
attenuation
Length of
lines Downstream
attenuation
(dB) Upstream
attenuation
(dB) Downstream
attenuation
(dB) Upstream
attenuation
(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)
Core diameter
attenuation
(dB)
40 60 80 120 150 300 1,024
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.