Sagem 4450E - Manual (Page 162)

SAGEM 3P@C
3P@C Installation Manual
Page 12-5 Reproduction and communication in any form prohibited without the written permission of
SAGEM SA
To reduce the crosstalk interference, the subscribers with the approximate length of subscriber line should be
placed on the same subscriber board or in the same pair cables; the ADSL subscriber line should be kept far
from the ISDN subscriber line as much as possible.
„ Noise
The noise are mostly background noises from lines, radio-frequency interference from the electrical equipment
near the lines and such radio interferences as narrowband peak noise signals of AM broadcast, the affect of
these interferences on lines is of long-term, and its impact on the transmission rate is reflected on the
deterioration of SNR index of each sub-channel.
„ Pulse noise
The pulse noise refers to the outburst discrete pulse interference, it has a large amplitude and the duration is far
shorter than the time interval. The possible sources are the ringing signals from telephones, human-made
electric sparks (auto ignition, power line), and large power transfer. The spectrum of the pulse noise is very wide,
which can affect many sub-channels, but the amplitude at the frequency points is lowered accordingly, and its
affect on the specific sub-channel is slighter than the noise of narrow frequency band. The pulse noise is hard to
be tested because it occurs randomly, and at present, no specific index requirement is available. The test value
within a period of time does not exceed this test pulse according to the test pulse noise model in the
transmission loss of the ADSL standard.
„ Telephone interference:
In addition to the interferences in ringing, off-hook and on-hook, the non-linearity of the telephone during
conversation will also affect the data service. The test abroad shows that the non-linearity phenomenon does not
occur when the power of the upstream signals sent by each telephone set should be lowered by 12db in
average, and to some telephone sets, 24 db should be lowered. This means that the difference in the
performance of the phone set will affect the quality of data transmission.
„ Reflection interference
The bridged tap is a short line reaching somewhere, and the non-termination tap can emit energy, lower the
strength of signals and become a noise source. There are at least 3 connectors (bridge point) from the Central
office terminal to subscribers, the core diameter of each connector will change accordingly, and the cable loss
leads to the abrupt resistance change, thus causing the loss of power reflection wave. It takes the form of
echoes in the voice communication while in ADSL, the complex modulation mode is very easy to be affected by
the reflection signals. Currently, there is no such equipment as testing the reflection source in the subscriber
allocation cables in the frequency of 300KHz or above. At present, the echo cancellation technology is mostly
used and it is excellent in the cancellation of echo effect from a certain source. When the signals, however, are
reflected in many places, the echo cancellation is hardly effective.
12.1.2. ADSL Line Commissioning
1.1.1.60 Connection, Configuration and Test of Central office terminal
1) Connecting the ADSL equipment
Subscribers need to remove the original jumpers at the distribution frame upon applying for the commissioning of
ADSL service, and connect the distribution lines and jumpers again basing on the situation of the ADSL
equipment, to separate the traditional PSTN service from the data service, as shown in Figure 12-4.