BRX-XLR User Guide
40
180-0145-001-R05
Changing the value of INP and/or Delay influences the error correction capability of the Reed-
Solomon code. The ability to improve the line protection against impulsive noise has to be traded-off
against increased FEC parity ratio and hence lower achievable net data rate. More specifically the INP
(expressed in symbols) and Delay (in msec) are related to the FEC parity ratio by the following
equation:
FEC parity ratio = ½ * (INP/Delay)
The FEC parity ratio is a component of the total overhead that will exist on the line. The tables below,
from ITU-T G.992.5 Annex K, illustrate how the net data rate is affected as the INP Min and Max-delay
are varied. The bitrates in these tables represent theoretical maximums which are not necessarily
achievable with real DSL equipment but rather provide guidance to theoretical ceilings in bitrates for
the corresponding parameters. Service Providers are encouraged to undertake testing on the actual
ADSL2plus equipment that they plan to use in order to determine more realistic achievable net data
rates.
Table 12: Maximum Downstream Attainable Rate, no Extended Framing Parameters
Table 13: Maximum Downstream Attainable Rate with 16K Interleaving and
