System information

FCD 901 48
Issue R2A, 07.2009
XMP1 Release 5.5 System Description
SHDSL
Page 5-6 Proprietary Information Aastra
A transmission link with repeaters synchronizes itself section by section
starting from the LT. During the standardized startup procedure, the units
adapt themselves to the individual line parameters (e.g. attenuation,
interference effects) and set up the EOC channel. The values determined in
the course of this "line probing" can be called up by means of an equipment
status request.
An important system parameter is the noise margin, i.e. the system margin
of a link section. In compliance with the relevant ETSI standard, a link with
a system margin of 0 dB can have a bit error ratio of BER 1.E-7. For a
secure and stable operation, a value of at least 6 dB is recommended. In
individual cases, other values can be used after an appropriate BER
measurement.
In case of a failure of a repeater section, all SDSL sections between the
place the error occurred and the NT will be deactivated. A LINK LOSW and
LINK Rep alarm will then be generated in the terminals.
Using the CRC6 check sum generated in the SDSL frame, a performance
data evaluation in compliance with ITU-T G.826 can be carried out at any
time without disturbing normal operation.
Power backoff function
The power backoff represents a Tx power reduction. The backoff factor is
indicated in dB. A value of 0 dB means that the maximum transmit level will
not be reduced.
The line attenuation is determined during SDSL link setup. Using these line
attenuation values, the Tx level can be reduced on short links not requiring
the maximum Tx power. Thus, interference affecting adjacent transmission
links implemented via the same cable can be kept low.
The power backoff mode is possible both in automatic and manual
operation. The corresponding setting is made via the user interface. Using
the online functions made available by the operator software, the S/N and
power backoff values adjusted during link setup can be requested via the
"Link Measured Values" option.
Transmission range
The transmission range depends on the line attenuation and noise or
interference level on the line. This interference level is determined by the
following factors:
• near-end cross-talk attenuation between the wire pairs (NEXT)
• number of "interfering" systems connected to the cable.
Systems offering xDSL services and operating in the same transmission
frequency band represent interferers primarily affecting the noise balance.
For a realistic assessment of the achievable coverage range, both the
required system margin and the factors mentioned above must be taken
into account.